ALBERT

Description: The dynamics of the magnetic relaxation process during the sustainment of spheromak configurations at different helicity injection rates is studied. The three-dimensional activity is recovered using time-dependent resistive magnetohydrodynamic simulations. A cylindrical flux conserver with concentric electrodes is used to model configurations driven by a magnetized coaxial gun. Magnetic helicity is injected by tangential boundary flows. Different regimes of sustainment are identified and characterized in terms of the safety factor profile. The spatial and temporal behavior of fluctuations is described. The dynamo action is shown to be in close agreement with existing experimental data. These results are relevant to the design and operation of helicity injected devices, as well as to basic understanding of the plasma relaxation mechanism in quasi-steady state.

Description: The present experiments were performed on the PF-1000 plasma focus device at a current of 2 MA with the deuterium injected from the gas-puff placed in the axis of the anode face. The XUV frames showed, in contrast with the interferograms, the fine structure: filaments and spots up to 1 mm diameter. In the deuterium filling, the short filaments are registered mainly in the region of the internal plasmoidal structures and their number correlates with the intensity of neutron production. The longer filamentary structure was recorded close to the anode after the constriction decay. The long curve-like filaments with spots were registered in the big bubble formed after the pinch phase in the head of the umbrella shape of the plasma sheath. Filaments can indicate the filamentary structure of the current in the pinch. Together with the filaments, small compact balls a few mm in diameter were registered by both interferometry and XUV frame pictures. They emerge out of the dense column and their life-time can be greater than hundreds of ns.

Description: The radiation pressure acceleration of protons in the interaction of Gaussian laser pulses and surface modulated targets is examined by multi-dimensional particle-in-cell simulations. It is shown that strong longitudinal quasi-static magnetic field is generated on the modulated surface of the target, which significantly enhances the transverse diffusion of electrons. This is beneficial for suppressing the transverse Rayleigh-Taylor instability. Finally, the surface of the accelerated proton beams becomes smoother than that in the case of the planar target, and a final mono-energetic proton beam is obtained by using the surface modulated target.

Description: The dependence of divertor asymmetry and scrape-off layer (SOL) flow on heating power has been investigated in the Experimental Advanced Superconducting Tokamak (EAST). Divertor plasma exhibits an outboard-enhanced in-out asymmetry in heat flux in lower single null configuration for in reversed (ion ∇ B drift direction toward the upper X-point) field directions. Upper single null exhibits an inboard-favored asymmetry in low heating power condition, while exhibits an outboard-favored asymmetry when increasing the heating power. Double null has the strongest in-out asymmetry in heat flux, favoring the outer divertor. The in-out asymmetry ratios of q t , out / q t , in and P out / P total increase with the power across the separatrix P loss , which is probably induced by the enhanced radial particle transport due to a large pressure gradient. The characteristics of the measured SOL parallel flow under various discharge conditions are consistent with the Pfirsch-Schlüter (PS) flow with the parallel Mach number M ∥ decreasing with the line averaged density but increasing with P loss , in the same direction as the PS flow. The contributions of both poloidal E × B drift and parallel flow on poloidal particle transport in SOL on EAST are also assessed.

Description: Magnetic islands have been implemented in the gyrokinetic toroidal code to study the effects of the islands on microturbulence. The pressure profile flattening is verified in the simulation with the islands. Simulations of ion temperature gradient instability find that different toroidal modes are linearly coupled together and that toroidal spectra become broader when the island width increases. The real frequencies and growth rates of different toroidal modes approach each other with the averaged value independent of the island width. The linear mode structures are enhanced at the island separatrices and weakened at the island centers, consistent with the flattening of the pressure profile inside the islands.

Description: A study is presented for the oblique propagation of ion acoustic cnoidal waves in a magnetized plasma consisting of cold ions and two temperature superthermal electrons modelled by kappa-type distributions. Using the reductive perturbation method, the nonlinear Korteweg de-Vries equation is derived, which further gives the solutions with a special type of cnoidal elliptical functions. Both compressive and rarefactive structures are found for these cnoidal waves. Nonlinear periodic cnoidal waves are explained in terms of plasma parameters depicting the Sagdeev potential and the phase curves. It is found that the density ratio of hot electrons to ions μ significantly modifies compressive/refractive wave structures. Furthermore, the combined effects of superthermality of cold and hot electrons κ c , κ h , cold to hot electron temperature ratio σ , angle of propagation and ion cyclotron frequency ω ci have been studied in detail to analyze the height and width of compressive/refractive cnoidal waves. The findings in the present study could have important implications in understanding the physics of electrostatic wave structures in the Saturn's magnetosphere where two temperature superthermal electrons are present.

Description: A smart monitoring system for superconducting cable test is proposed with an adaptive current control of a superconducting transformer secondary. The design, based on Fuzzy Gain Scheduling, allows the controller parameters to adapt continuously, and finely, to the working variations arising from transformer nonlinear dynamics. The control system is integrated in a fully digital control loop, with all the related benefits, i.e., high noise rejection, ease of implementation/modification, and so on. In particular, an accurate model of the system, controlled by a Fuzzy Gain Scheduler of the superconducting transformer, was achieved by an experimental campaign through the working domain at several current ramp rates. The model performance was characterized by simulation, under all the main operating conditions, in order to guide the controller design. Finally, the proposed monitoring system was experimentally validated at European Organization for Nuclear Research (CERN) in comparison to the state-of-the-art control system [P. Arpaia, L. Bottura, G. Montenero, and S. Le Naour, “Performance improvement of a measurement station for superconducting cable test,” Rev. Sci. Instrum.83, 095111 (2012)] of the Facility for the Research on Superconducting Cables, achieving a significant performance improvement: a reduction in the system overshoot by 50%, with a related attenuation of the corresponding dynamic residual error (both absolute and RMS) up to 52%.

Description: This paper presents a method which uses the characteristics of the etch pits induced in a polyallyl-diglycol-carbonate (PADC) detector of the CR-39/PM-355 type to estimate particle energy. This method is based on the data provided by a semiautomatic system that selects tracks according to two parameters, crater diameters, and mean gray level values. In this paper we used the results of the calibration measurements that were obtained in our laboratory in the period 2000–2014. Combining the information on the two parameters it is possible to determine unambiguously the incident projectile energy values. The paper presents the results of an attempt to estimate the energy resolution of the method when analyzing the tracks produced in the CR-39/PM-355 detector by energetic ions such as alpha particles, protons, and deuterons. We discuss the energy resolution of the measurement of light charged particle energy which is based on the parameters (crater diameter and mean gray level value) of tracks induced in solid state nuclear track detectors of the PADC type.

Description: In this work, an automated apparatus for driving single electrostatic probes and acquiring the plasma-related data has been designed and fabricated. The voltage range of the present system is ±110 V with an adjustable voltage step as low as 3 mV. Voltage and current measurements are carried out with high resolution and high accuracy circuits, both based on 16 bit analog-to-digital converters. The code embedded in a micro-controller, schedules the operation of the device and transfers the experimental data to a personal computer. The modular design of the system makes possible its modification and thus increases its adaptability to different plasma setups. Finally, the reliable operation of the entire device is confirmed by tests in Electron Cyclotron Resonance plasma.

Description: We report on the production of metal ions of magnesium and zinc in the beam plasma formed by a forevacuum-pressure electron source. Magnesium and zinc vapor were generated by electron beam evaporation from a crucible and subsequently ionized by electron impact from the e-beam itself. Both gaseous and metallic plasmas were separately produced and characterized using a modified RGA-100 quadrupole mass-spectrometer. The fractional composition of metal isotopes in the plasma corresponds to their fractional natural abundance.

Description: To better understand the role of residual electrons in the repeatability of an atmospheric pressure plasma plume, the characteristics of a helium plasma jet from the 1st, 2nd,… until the repeatable discharge pulse are investigated for the first time. It's found that the longest plasma plume is achieved in the 1st discharge pulse. The length of the plasma plume becomes shorter and shorter and reaches a constant value in the 3rd discharge pulse and keeps the same for the following pulses. The dynamics of the 1st discharge pulse show that the plasma bullet appears random in nature. Two photomultiplier tubes are used to distinguish the two potential factors that could result in the stochastic dynamics of the plasma bullet, i.e., stochastic ignition of the plasma and the stochastic propagation velocity. The results show that the stochastic propagation velocity occurs only in the 1st and the 2nd discharge pulses, while the stochastic ignition of the plasma presents until the 100th pulse. The dynamics of the plasma propagation become repeatable after about 100 pulses. Detail analysis shows that the repeatability of plasma bullet is due to the residual electrons density. The residual electron density of 10 9  cm −3 or higher is needed for repeatable discharges mode.

Description: We present a full two-fluid magnetohydrodynamic (MHD) description for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure, and electron inertia. According to this description, each plasma species introduces a new spatial scale: the ion inertial length λ i and the electron inertial length λ e , which are not present in the traditional MHD description. In the present paper, we seek for possible changes in the energy power spectrum in fully developed turbulent regimes, using numerical simulations of the two-fluid equations in two-and-a-half dimensions. We have been able to reproduce different scaling laws in different spectral ranges, as it has been observed in the solar wind for the magnetic energy spectrum. At the smallest wavenumbers where plain MHD is valid, we obtain an inertial range following a Kolmogorov k −5∕3 law. For intermediate wavenumbers such that λ i − 1 ≪ k ≪ λ e − 1 , the spectrum is modified to a k −7∕3 power-law, as has also been obtained for Hall-MHD neglecting electron inertia terms. When electron inertia is retained, a new spectral region given by k 〉 λ e − 1 arises. The power spectrum for magnetic energy in this region is given by a k −11∕3 power law. Finally, when the terms of electron inertia are retained, we study the self-consistent electric field. Our results are discussed and compared with those obtained in the solar wind observations and previous simulations.

Description: A novel mechanism of collisionless heating in large planar arrays of small inductive coils operated at radio frequencies is presented. In contrast to the well-known case of non-local heating related to the transversal conductivity, when the electrons move perpendicular to the planar coil, we investigate the problem of electrons moving in a plane parallel to the coils. Two types of periodic structures are studied. Resonance velocities where heating is efficient are calculated analytically by solving the Vlasov equation. Certain scaling parameters are identified. The concept is further investigated by a single particle simulation based on the ergodic principle and combined with a Monte Carlo code allowing for collisions with Argon atoms. Resonances, energy exchange, and distribution functions are obtained. The analytical results are confirmed by the numerical simulation. Pressure and electric field dependences are studied. Stochastic heating is found to be most efficient when the electron mean free path exceeds the size of a single coil cell. Then the mean energy increases approximately exponentially with the electric field amplitude.

Description: A pulsed slow-positron beam generated by an electron linear accelerator was directly used for positron annihilation lifetime spectroscopy without any positron storage devices. A waveform digitizer was introduced to simultaneously capture multiple gamma-ray signals originating from positron annihilation events during a single accelerator pulse. The positron pulse was chopped and bunched with the chopper signals also sent to the waveform digitizer. Time differences between the annihilation gamma-ray and chopper peaks were calculated and accumulated as lifetime spectra in a computer. The developed technique indicated that positron annihilation lifetime spectroscopy can be performed in a 20 μ s time window at a pulse repetition rate synchronous with the linear accelerator. Lifetime spectra of a Kapton sheet and a thermally grown SiO 2 layer on Si were successfully measured. Synchronization of positron lifetime measurements with pulsed ion irradiation was demonstrated by this technique.

Description: The collision-less transfer of momentum and energy from explosive debris plasma to magnetized background plasma is a salient feature of various astrophysical and space environments. While much theoretical and computational work has investigated collision-less coupling mechanisms and relevant parameters, an experimental validation of the results demands the measurement of the complex, collective electric fields associated with debris-background plasma interaction. Emission spectroscopy offers a non-interfering diagnostic of electric fields via the Stark effect. A unique experiment at the University of California, Los Angeles, that combines the Large Plasma Device (LAPD) and the Phoenix laser facility has investigated the marginally super-Alfvénic, quasi-perpendicular expansion of a laser-produced carbon (C) debris plasma through a preformed, magnetized helium (He) background plasma via emission spectroscopy. Spectral profiles of the He II 468.6 nm line measured at the maximum extent of the diamagnetic cavity are observed to intensify, broaden, and develop equally spaced modulations in response to the explosive C debris, indicative of an energetic electron population and strong oscillatory electric fields. The profiles are analyzed via time-dependent Stark effect models corresponding to single-mode and multi-mode monochromatic (single frequency) electric fields, yielding temporally resolved magnitudes and frequencies. The proximity of the measured frequencies to the expected electron plasma frequency suggests the development of the electron beam-plasma instability, and a simple saturation model demonstrates that the measured magnitudes are feasible provided that a sufficiently fast electron population is generated during C debris–He background interaction. Potential sources of the fast electrons, which likely correspond to collision-less coupling mechanisms, are briefly considered.

Description: It is shown that co-linear injection of electrons or positrons into the wakefield of the self-modulating particle beam is possible and ensures high energy gain. The witness beam must co-propagate with the tail part of the driver, since the plasma wave phase velocity there can exceed the light velocity, which is necessary for efficient acceleration. If the witness beam is many wakefield periods long, then the trapped charge is limited by beam loading effects. The initial trapping is better for positrons, but at the acceleration stage a considerable fraction of positrons is lost from the wave. For efficient trapping of electrons, the plasma boundary must be sharp, with the density transition region shorter than several centimeters. Positrons are not susceptible to the initial plasma density gradient.

Description: The foundational theory for dusty plasmas is the dust charging theory that provides the dust potential and charge arising from the dust interaction with a plasma. The most widely used dust charging theory for negatively charged dust particles is the so-called orbital motion limited (OML) theory, which predicts the dust potential and heat collection accurately for a variety of applications, but was previously found to be incapable of evaluating the dust charge and plasma response in any situation. Here, we report a revised OML formulation that is able to predict the plasma response and hence the dust charge. Numerical solutions of the new OML model show that the widely used Whipple approximation of dust charge-potential relationship agrees with OML theory in the limit of small dust radius compared with plasma Debye length, but incurs large (order-unity) deviation from the OML prediction when the dust size becomes comparable with or larger than plasma Debye length. This latter case is expected for the important application of dust particles in a tokamak plasma.

Description: Using the ideal magnetohydrodynamic model, we calculate the temporal evolution of initial ripples on the boundaries of a planar plasma slab that is subjected to the magneto-Rayleigh-Taylor instability. The plasma slab consists of three regions. We assume that in each region the plasma density is constant with an arbitrary value and the magnetic field is also constant with an arbitrary magnitude and an arbitrary direction parallel to the interfaces. Thus, the instability may be driven by a combination of magnetic pressure and kinetic pressure. The general dispersion relation is derived, together with the feedthrough factor between the two interfaces. The temporal evolution is constructed from the superposition of the eigenmodes. Previously established results are recovered in the various limits. Numerical examples are given on the temporal evolution of ripples on the interfaces of the finite plasma slab.

Description: A major goal of nanotechnology is to develop the capability to arrange matter at will by placing individual atoms at desired locations in a predetermined configuration to build a nanostructure with specific properties or function. The scanning tunneling microscope has demonstrated the ability to arrange the basic building blocks of matter, single atoms, in two-dimensional configurations. An array of various nanostructures has been assembled, which display the quantum mechanics of quantum confined geometries. The level of human interaction needed to physically locate the atom and bring it to the desired location limits this atom assembly technology. Here we report the use of autonomous atom assembly via path planning technology; this allows atomically perfect nanostructures to be assembled without the need for human intervention, resulting in precise constructions in shorter times. We demonstrate autonomous assembly by assembling various quantum confinement geometries using atoms and molecules and describe the benefits of this approach.

Description: We developed a silicon avalanche photodiode (Si-APD) linear-array detector for use in nuclear resonant scattering experiments using synchrotron X-rays. The Si-APD linear array consists of 64 pixels (pixel size: 100 × 200 μm 2 ) with a pixel pitch of 150 μm and depletion depth of 10 μm. An ultrafast frontend circuit allows the X-ray detector to obtain a high output rate of 〉10 7 cps per pixel. High-performance integrated circuits achieve multichannel scaling over 1024 continuous time bins with a 1 ns resolution for each pixel without dead time. The multichannel scaling method enabled us to record a time spectrum of the 14.4 keV nuclear radiation at each pixel with a time resolution of 1.4 ns (FWHM). This method was successfully applied to nuclear forward scattering and nuclear small-angle scattering on 57 Fe.

Description: We describe a nanosecond time-resolved fluorescence spectrometer that acquires fluorescence decay waveforms from each well of a 384-well microplate in 3 min with signal-to-noise exceeding 400 using direct waveform recording. The instrument combines high-energy pulsed laser sources (5–10 kHz repetition rate) with a photomultiplier and high-speed digitizer (1 GHz) to record a fluorescence decay waveform after each pulse. Waveforms acquired from rhodamine or 5-((2-aminoethyl)amino) naphthalene-1-sulfonic acid dyes in a 384-well plate gave lifetime measurements 5- to 25-fold more precise than the simultaneous intensity measurements. Lifetimes as short as 0.04 ns were acquired by interleaving with an effective sample rate of 5 GHz. Lifetime measurements resolved mixtures of single-exponential dyes with better than 1% accuracy. The fluorescence lifetime plate reader enables multiple-well fluorescence lifetime measurements with an acquisition time of 0.5 s per well, suitable for high-throughput fluorescence lifetime screening applications.

Description: Diagnostic for investigating and distinguishing different laser ion acceleration mechanisms has been developed and successfully tested. An ion separation wide angle spectrometer can simultaneously investigate three important aspects of the laser plasma interaction: (1) acquire angularly resolved energy spectra for two ion species, (2) obtain ion energy spectra for multiple species, separated according to their charge to mass ratio, along selected axes, and (3) collect laser radiation reflected from and transmitted through the target and propagating in the same direction as the ion beam. Thus, the presented diagnostic constitutes a highly adaptable tool for accurately studying novel acceleration mechanisms in terms of their angular energy distribution, conversion efficiency, and plasma density evolution.

Description: μLaue diffraction with a polychromatic X-ray beam can be used to measure strain fields and crystal orientations of micro crystals. The hydrostatic strain tensor can be obtained once the energy profile of the reflections is measured. However, this remains a challenge both on the time scale and reproducibility of the beam position on the sample. In this review, we present a new approach to obtain the spatial and energy profiles of Laue spots by using a pn-junction charge-coupled device, an energy-dispersive area detector providing 3D resolution of incident X-rays. The morphology and energetic structure of various Bragg peaks from a single crystalline Cu micro-cantilever used as a test system were simultaneously acquired. The method facilitates the determination of the Laue spots’ energy spectra without filtering the white X-ray beam. The synchrotron experiment was performed at the BM32 beamline of ESRF using polychromatic X-rays in the energy range between 5 and 25 keV and a beam size of 0.5 μ m × 0.5 μ m. The feasibility test on the well known system demonstrates the capabilities of the approach and introduces the “3D detector method” as a promising tool for material investigations to separate bending and strain for technical materials.

Description: A short prototype (847-mm-long) of an Insertion Device (ID) with the dynamic compensation of ID magnetic forces has been designed, built, and tested at the Advanced Photon Source (APS) of the Argonne National Laboratory. The ID magnetic forces were compensated by the set of conical springs placed along the ID strongback. Well-controlled exponential characteristics of conical springs permitted a very close fit to the ID magnetic forces. Several effects related to the imperfections of actual springs, their mounting and tuning, and how these factors affect the prototype performance has been studied. Finally, series of tests to determine the accuracy and reproducibility of the ID magnetic gap settings have been carried out. Based on the magnetic measurements of the ID B eff , it has been demonstrated that the magnetic gaps within an operating range were controlled accurately and reproducibly within ±1 μ m. Successful tests of this ID prototype led to the design of a 3-m long device based on the same concept. The 3-m long prototype is currently under construction. It represents R&D efforts by the APS toward APS Upgrade Project goals as well as the future generation of IDs for the Linac Coherent Light Source (LCLS).

Description: A description is given of an ultra-high vacuum surface-analysis chamber that incorporates an internal cell for performing atomic layer deposition at a pressure of up to ∼1 Torr. The apparatus permits the growth process to be interrupted in stages during which data can be obtained using infrared and x-ray photoemission spectroscopies together with other electron-based techniques. Demonstration results are given for the adsorption of H 2 O on Si (100) at a pressure of ∼0.3 Torr. The system described is generally applicable in the study of any surface reaction under non-high-vacuum conditions in which there is a need for both infrared and electron spectroscopies.

Description: We recently reported the development of a high pressure electrical conductivity probe (HP-ECP) for experimental studies of formation of gas hydrates from electrolytes. The onset of the formation of methane-propane mixed gas hydrate from salt solutions was marked by a temporary upward spike in the electrical conductivity. To further understand hydrate formation a second generation of window-less HP-ECP (MkII), which has a much smaller heat capacity than the earlier version and allows access to faster cooling rates, has been constructed. Using the HP-ECP (MkII) the electrical conductivity signal responses of NaCl solutions upon the formation of ice, tetrahydrofuran hydrates, and methane–propane mixed gas hydrate has been measured. The concentration range of the NaCl solutions was from 1 mM to 3M and the driving AC frequency range was from 25 Hz to 5 kHz. This data has been used to construct an “electrical conductivity response phase diagrams” that summarize the electrical conductivity response signal upon solid formation in these systems. The general trend is that gas hydrate formation is marked by an upward spike in the conductivity at high concentrations and by a drop at low concentrations. This work shows that HP-ECP can be applied in automated measurements of hydrate formation probability distributions of optically opaque samples using the conductivity response signals as a trigger.

Description: In thermomechanical testing of hypersonic materials and structures, direct observation and quantitative strain measurement of the front surface of a test specimen directly exposed to severe aerodynamic heating has been considered as a very challenging task. In this work, a novel quartz infrared heating device with an observation window is designed to reproduce the transient thermal environment experienced by hypersonic vehicles. The specially designed experimental system allows the capture of test article's surface images at various temperatures using an optical system outfitted with a bandpass filter. The captured images are post-processed by digital image correlation to extract full-field thermal deformation. To verify the viability and accuracy of the established system, thermal strains of a chromiumnickel austenite stainless steel sample heated from room temperature up to 600 °C were determined. The preliminary results indicate that the air disturbance between the camera and the specimen due to heat haze induces apparent distortions in the recorded images and large errors in the measured strains, but the average values of the measured strains are accurate enough. Limitations and further improvements of the proposed technique are discussed.

Description: Gas-puff Z-pinch experiments were conducted on the 1 MA, 200 ns pulse duration Cornell Beam Research Accelerator (COBRA) pulsed power generator in order to achieve an understanding of the dynamics and instability development in the imploding and stagnating plasma. The triple-nozzle gas-puff valve, pre-ionizer, and load hardware are described. Specific diagnostics for the gas-puff experiments, including a Planar Laser Induced Fluorescence system for measuring the radial neutral density profiles along with a Laser Shearing Interferometer and Laser Wavefront Analyzer for electron density measurements, are also described. The results of a series of experiments using two annular argon (Ar) and/or neon (Ne) gas shells (puff-on-puff) with or without an on- (or near-) axis wire are presented. For all of these experiments, plenum pressures were adjusted to hold the radial mass density profile as similar as possible. Initial implosion stability studies were performed using various combinations of the heavier (Ar) and lighter (Ne) gasses. Implosions with Ne in the outer shell and Ar in the inner were more stable than the opposite arrangement. Current waveforms can be adjusted on COBRA and it was found that the particular shape of the 200 ns current pulse affected on the duration and diameter of the stagnated pinched column and the x-ray yield.

Description: During July 2012, 150 almost identical H-mode plasmas were consecutively created in the Joint European Torus, providing a combined total of approximately 8 minutes of steady-state plasma with 15 000 Edge Localised Modes (ELMs). In principle, each of those 15 000 ELMs are statistically equivalent. Here, the changes in edge density and plasma energy associated with those ELMs are explored, using the spikes in Beryllium II (527 nm) radiation as an indicator for the onset of an ELM. Clearly different timescales are observed during the ELM process. Edge temperature falls over a 2 ms timescale, edge density and pressure fall over a 5 ms timescale, and there is an additional 10 ms timescale that is consistent with a resistive relaxation of the plasma's edge. The statistical properties of the energy and density losses due to the ELMs are explored. For these plasmas the ELM energy (δ E ) is found to be approximately independent of the time between ELMs, despite the average ELM energy ( 〈 δ E 〉 ) and average ELM frequency ( f ) being consistent with the scaling of 〈 δ E 〉 ∝ 1 / f . Instead, beyond the first 0.02 s of waiting time between ELMs, the energy losses due to individual ELMs are found to be statistically the same. Surprisingly no correlation is found between the energies of consecutive ELMs either. A weak link is found between the density drop and the ELM waiting time. Consequences of these results for ELM control and modelling are discussed.

Description: The compression of a relativistic Gaussian laser pulse in a magnetized plasma is investigated. By considering relativistic nonlinearity and using non-linear Schrödinger equation with paraxial approximation, a second-order differential equation is obtained for the pulse width parameter (in time) to demonstrate the longitudinal pulse compression. The compression of laser pulse in a magnetized plasma can be observed by the numerical solution of the equation for the pulse width parameter. The effects of magnetic field and chirping are investigated. It is shown that in the presence of magnetic field and negative initial chirp, compression of pulse is significantly enhanced.

Description: Nonlinear saturation amplitudes (NSAs) of the first two harmonics in classical Rayleigh-Taylor instability (RTI) in cylindrical geometry for arbitrary Atwood numbers have been analytically investigated considering nonlinear corrections up to the fourth-order. The NSA of the fundamental mode is defined as the linear (purely exponential) growth amplitude of the fundamental mode at the saturation time when the growth of the fundamental mode (first harmonic) is reduced by 10% in comparison to its corresponding linear growth, and the NSA of the second harmonic can be obtained in the same way. The analytic results indicate that the effects of the initial radius of the interface ( r 0 ) and the Atwood number ( A ) play an important role in the NSAs of the first two harmonics in cylindrical RTI. On the one hand, the NSA of the fundamental mode first increases slightly and then decreases quickly with increasing A . For given A , the smaller the r 0 / λ (with λ perturbation wavelength) is, the larger the NSA of the fundamental mode is. When r 0 / λ is large enough ( r 0 ≫ λ ), the NSA of the fundamental mode is reduced to the prediction of previous literatures within the framework of third-order perturbation theory [J. W. Jacobs and I. Catton, J. Fluid Mech. 187 , 329 (1988); S. W. Haan, Phys. Fluids B 3 , 2349 (1991)]. On the other hand, the NSA of the second harmonic first decreases quickly with increasing A , reaching a minimum, and then increases slowly. Furthermore, the r 0 can reduce the NSA of the second harmonic for arbitrary A at r 0 ≲ 2 λ while increase it for A   ≲   0.6 at r 0 ≳ 2 λ . Thus, it should be included in applications where the NSA has a role, such as inertial confinement fusion ignition target design.

Description: The δ   f particle-in-cell code GEM is used to study the transport “shortfall” problem of gyrokinetic simulations. In local simulations, the GEM results confirm the previously reported simulation results of DIII-D [Holland et al. , Phys. Plasmas 16 , 052301 (2009)] and Alcator C-Mod [Howard et al. , Nucl. Fusion 53 , 123011 (2013)] tokamaks with the continuum code GYRO. Namely, for DIII-D the simulations closely predict the ion heat flux at the core, while substantially underpredict transport towards the edge; while for Alcator C-Mod, the simulations show agreement with the experimental values of ion heat flux, at least within the range of experimental error. Global simulations are carried out for DIII-D L-mode plasmas to study the effect of edge turbulence on the outer core ion heat transport. The edge turbulence enhances the outer core ion heat transport through turbulence spreading. However, this edge turbulence spreading effect is not enough to explain the transport underprediction.

Description: In the present work, we extend results of a previous paper [Peter et al. , Phys. Plasmas 20 , 12 3104 (2013)] and develop a semi-analytical model to account for thermal effects on the nonlinear dynamics of the electron beam in free-electron lasers. We relax the condition of a cold electron beam but still use the concept of compressibility, now associated with a warm beam model, to evaluate the time scale for saturation and the peak laser intensity in high-gain regimes. Although vanishing compressibilites and the associated divergent densities are absent in warm models, a series of discontinuities in the electron density precede the saturation process. We show that full wave-particle simulations agree well with the predictions of the model.

Description: Particle pairing in a complex plasma was experimentally studied with the emphasis on pair spatial extent and stability. Micron-size particles were suspended in the (pre)sheath area above the lower electrode in a capacitively coupled radio-frequency discharge in argon. They formed vertical pairs due to the ion wakes created by the flow of ions past particles. We discuss the confinement mechanism for the lower particle, resulting from a combination of the wake field and the field of non-uniform sheath. A model of particle pairs is proposed, which provides good description for the dependence of pair size and stability on experimental parameters.

Description: Significantly collimated fast electron beam with a divergence angle 10° (FWHM) is observed when an ultra-intense laser pulse ( I  = 10 14  W/cm 2 , 300 fs) irradiates a uniform critical density plasma. The uniform plasma is created through the ionization of an ultra-low density (5 mg/c.c.) plastic foam by X-ray burst from the interaction of intense laser ( I  = 10 14  W/cm 2 , 600 ps) with a thin Cu foil. 2D Particle-In-Cell (PIC) simulation well reproduces the collimated electron beam with a strong magnetic field in the region of the laser pulse propagation. To understand the physical mechanism of the collimation, we calculate energetic electron motion in the magnetic field obtained from the 2D PIC simulation. As the results, the strong magnetic field (300 MG) collimates electrons with energy over a few MeV. This collimation mechanism may attract attention in many applications such as electron acceleration, electron microscope and fast ignition of laser fusion.

Description: In this work, stochastic behavior of atmospheric pressure dielectric barrier discharge (DBD) has been investigated. The experiment is performed in a DBD reactor consisting of a pair of stainless steel parallel plate electrodes powered by a 50 Hz ac high voltage source. Current pulse amplitude distributions for different space gaps and the time separation between consecutive current pulses are studied. A probability distribution function is proposed to predict the experimental distribution function for the current pulse amplitudes and the occurrence of the transition regime of the pulse distribution. Breakdown voltage at different positions on the dielectric surface is suggested to be stochastic in nature. The simulated results based on the proposed distribution function agreed well with the experimental results and able to predict the regime of transition voltage. This model would be useful for the understanding of stochastic behaviors of DBD and the design of DBD device for effective operation and applications.

Description: A simplified method for calibrating atomic force microscope cantilevers was recently proposed by Sader et al. [Rev. Sci. Instrum.83, 103705 (2012); Sec. III D] that relies solely on the resonant frequency and quality factor of the cantilever in fluid (typically air). This method eliminates the need to measure the hydrodynamic function of the cantilever, which can be time consuming given the wide range of cantilevers now available. Using laser Doppler vibrometry, we rigorously assess the accuracy of this method for a series of commercially available cantilevers and explore its performance under non-ideal conditions. This shows that the simplified method is highly accurate and can be easily implemented to perform fast, robust, and non-invasive spring constant calibration.

Description: There exist a number of algorithms to map the phase to amplitude in direct digital synthesis (DDS). For DDS with more than 14 output bits, the Coordinate Rotation Digital Computer (CORDIC) algorithm is well known for its high precision. Also, it is effective in solutions where there is the need of in-phase and quadrature components simultaneously because the algorithm calculates both. In this paper, a Taylor expansion based method was proposed to calculate both in-phase and quadrature at the same time. Numerical simulations for different data format, e.g., double and finite bits, were carried out in Matlab and Quartus, which were followed by the hardware implementation in Field Programmable Gate Array. The results demonstrated that the proposed method possessed higher precision and exhausted less logic elements than the CORDIC algorithm.

Description: We present a Time-to-Digital Converter (TDC) card with a compact form factor, suitable for multichannel timing instruments or for integration into more complex systems. The TDC Card provides 10 ps timing resolution over the whole measurement range, which is selectable from 160 ns up to 10 μ s, reaching 21 ps rms precision, 1.25% LSB rms differential nonlinearity, up to 3 Mconversion/s with 400 mW power consumption. The I/O edge card connector provides timing data readout through either a parallel bus or a 100 MHz serial interface and further measurement information like input signal rate and valid conversion rate (typically useful for time-correlated single-photon counting application) through an independent serial link.

Description: This paper proposes a new pulse-mixing scheme utilizing both pulse-shrinking and pulse-stretching mechanisms to improve the performance of time-to-digital converters (TDCs). The temporal resolution of the conventional pulse-shrinking mechanism is determined by the size ratio between homogeneous and inhomogeneous elements. The proposed scheme which features double-stage operation derives its resolution according to the time difference between pulse-shrinking and pulse-stretching amounts. Thus, it can achieve greater immunity against temperature and ambient variations than that of the single-stage scheme. The circuit area also can be reduced by the proposed pulse-mixing scheme. In addition, this study proposes an improved cyclic delay line to eliminate the undesirable shift in the temporal resolution successfully. Therefore, the effective resolution can be controlled completely by the pulse-mixing unit to improve accuracy. The proposed TDC composed of only one cyclic delay line and one counter is fabricated in a TSMC CMOS 0.35-μm DPQM process. The chip core occupies an extremely small area of 0.02 mm 2 , which is the best among the related works. The experimental result shows that an effective resolution of around 53 ps within ±13% variation over a 0–100 °C temperature range is achieved. The power consumption is 90 μW at a sample rate of 1000 samples/s. In addition to the reduced area, the proposed TDC circuit achieves its resolution with less thermal-sensitivity and better fluctuations caused by process variations.

Description: Real time, in situ , multiframe, diffraction, and imaging measurements on bulk samples under high and ultrahigh strain-rate loading are highly desirable for micro- and mesoscale sciences. We present an experimental demonstration of multiframe transient x-ray diffraction (TXD) along with simultaneous imaging under high strain-rate loading at the Advanced Photon Source beamline 32ID. The feasibility study utilizes high strain-rate Hopkinson bar loading on a Mg alloy. The exposure time in TXD is 2–3 μs, and the frame interval is 26.7–62.5 μs. Various dynamic deformation mechanisms are revealed by TXD, including lattice expansion or compression, crystal plasticity, grain or lattice rotation, and likely grain refinement, as well as considerable anisotropy in deformation. Dynamic strain fields are mapped via x-ray digital image correlation, and are consistent with the diffraction measurements and loading histories.

Description: We report techniques developed to utilize three-dimensional momentum information as feedback in adaptive femtosecond control of molecular dynamics. Velocity map imaging is used to obtain the three-dimensional momentum map of the dissociating ions following interaction with a shaped intense ultrafast laser pulse. In order to recover robust feedback information, however, the two-dimensional momentum projection from the detector must be inverted to reconstruct the full three-dimensional momentum of the photofragments. These methods are typically slow or require manual inputs and are therefore accomplished offline after the images have been obtained. Using an algorithm based upon an “onion-peeling” (also known as “back projection”) method, we are able to invert 1040 × 1054 pixel images in under 1 s. This rapid inversion allows the full photofragment momentum to be used as feedback in a closed-loop adaptive control scheme, in which a genetic algorithm tailors an ultrafast laser pulse to optimize a specific outcome. Examples of three-dimensional velocity map image based control applied to strong-field dissociation of CO and O 2 are presented.

Description: In order to improve the atom spin gyroscope's operational accuracy and compensate the random error caused by the nonlinear and weak-stability characteristic of the random atomic spin gyroscope (ASG) drift, the hybrid random drift error model based on autoregressive (AR) and genetic programming (GP) + genetic algorithm (GA) technique is established. The time series of random ASG drift is taken as the study object. The time series of random ASG drift is acquired by analyzing and preprocessing the measured data of ASG. The linear section model is established based on AR technique. After that, the nonlinear section model is built based on GP technique and GA is used to optimize the coefficients of the mathematic expression acquired by GP in order to obtain a more accurate model. The simulation result indicates that this hybrid model can effectively reflect the characteristics of the ASG's random drift. The square error of the ASG's random drift is reduced by 92.40%. Comparing with the AR technique and the GP + GA technique, the random drift is reduced by 9.34% and 5.06%, respectively. The hybrid modeling method can effectively compensate the ASG's random drift and improve the stability of the system.

Description: This paper describes the design and performance of an extremely low-noise differential transimpedance amplifier, which takes its two inputs from separate photodiodes. The amplifier was planned to serve as the front-end electronics for a highly sensitive shadow-displacement sensing system, aimed at detecting very low-level “Violin-Mode” ( VM ) oscillations in 0.4 mm diameter by 600 mm long fused-silica suspension fibres. Four such highly tensioned fibres support the 40 kg test-masses/mirrors of the Advanced Laser Interferometer Gravitational wave Observatory interferometers. This novel design of amplifier incorporates features which prevent “noise-gain peaking” arising from large area photodiode (and cable) capacitances, and which also usefully separate the DC and AC photocurrents coming from the photodiodes. In consequence, the differential amplifier was able to generate straightforwardly two DC outputs, one per photodiode, as well as a single high-gain output for monitoring the VM oscillations—this output being derived from the difference of the photodiodes’ two, naturally anti-phase, AC photocurrents. Following a displacement calibration, the amplifier's final VM signal output was found to have an AC displacement responsivity at 500 Hz of (9.43 ± 1.20) MV(rms) m −1 (rms), and, therefore, a shot-noise limited sensitivity to such AC shadow- (i.e., fibre-) displacements of (69 ± 13) picometres/√Hz at this frequency, over a measuring span of ±0.1 mm.

Description: We investigate the dispersion relation for low frequency electromagnetic waves propagating parallel to the ambient magnetic field, considering that the velocity distributions of ions and electrons can be either bi-Maxwellian of product bi-kappa distributions. The effect of the anisotropy and non-thermal features associated to the product-bi-kappa distributions on the firehose instability are numerically investigated. The general conclusion to be drawn from the results obtained is that the increase in non-thermal features which is consequence of the decrease of the κ indexes in the ion distribution contributes to increase the instability in magnitude and wave number range, in comparison with bi-Maxwellian distributions with similar temperature anisotropy, and that the increase of non-thermal features in the electron distribution contributes to the quenching of the instability, which is nevertheless driven by the anisotropy in the ion distribution. Significant differences between results obtained either considering product-bi-kappa distributions or bi-kappa distributions are also reported.

Description: The effects of shock dynamics on compressibility of indirect-drive ignition-scale surrogate implosions, CH shells filled with D 3 He gas, have been studied using charged-particle spectroscopy. Spectral measurements of D 3 He protons produced at the shock-bang time probe the shock dynamics and in-flight characteristics of an implosion. The proton shock yield is found to vary by over an order of magnitude. A simple model relates the observed yield to incipient hot-spot adiabat, suggesting that implosions with rapid radiation-power increase during the main drive pulse may have a 2× higher hot-spot adiabat, potentially reducing compressibility. A self-consistent 1-D implosion model was used to infer the areal density ( ρR ) and the shell center-of-mass radius ( R cm ) from the downshift of the shock-produced D 3 He protons. The observed ρR at shock-bang time is substantially higher for implosions, where the laser drive is on until near the compression bang time (“short-coast”), while longer-coasting implosions have lower ρR . This corresponds to a much larger temporal difference between the shock- and compression-bang time in the long-coast implosions (∼800 ps) than in the short-coast (∼400 ps); this will be verified with a future direct bang-time diagnostic. This model-inferred differential bang time contradicts radiation-hydrodynamic simulations, which predict constant 700–800 ps differential independent of coasting time; this result is potentially explained by uncertainties in modeling late-time ablation drive on the capsule. In an ignition experiment, an earlier shock-bang time resulting in an earlier onset of shell deceleration, potentially reducing compression and, thus, fuel ρR .

Description: In this work, the low frequency waves and gravitational (Jeans) instability of a homogeneous gyrotropic, magnetized, quantum plasma is investigated using the quantum magnetohydrodynamic and Chew-Goldberger-Low fluid models. An analytical dispersion relation for the considered system is obtained solving the linearized perturbations equations employing the Fourier transformation. The onset criterion of the “firehose” instability is retained in parallel propagation, which is unaffected due to the presence of quantum corrections. The gravitational mode modified by the quantum corrections is obtained separately along with the “firehose” mode. In perpendicular propagation, the quantum diffraction term is coupled with the Jeans and Alfven modes whereas in parallel propagation, the Alfven mode does not contribute to the dispersion characteristics as it leads to the “firehose” instability criterion in terms of quantum pressure anisotropy. The stabilizing influences of the quantum diffraction parameter and magnetic field on the growth rates of Jeans instability are examined. It is observed that the growth rate stabilizes much faster in transverse mode due to Alfven stabilization as compared to the longitudinal mode of propagation.

Description: We present a novel high-precision two-way optic-fiber time transfer scheme. The Inter-Range Instrumentation Group (IRIG-B) time code is modified by increasing bit rate and defining new fields. The modified time code can be transmitted directly using commercial optical transceivers and is able to efficiently suppress the effect of the Rayleigh backscattering in the optical fiber. A dedicated codec (encoder and decoder) with low delay fluctuation is developed. The synchronization issue is addressed by adopting a mask technique and combinational logic circuit. Its delay fluctuation is less than 27 ps in terms of the standard deviation. The two-way optic-fiber time transfer using the improved codec scheme is verified experimentally over 2 m to100 km fiber links. The results show that the stability over 100 km fiber link is always less than 35 ps with the minimum value of about 2 ps at the averaging time around 1000 s. The uncertainty of time difference induced by the chromatic dispersion over 100 km is less than 22 ps.

Description: Neutrons spectra from most of known sources require being collimated for numerous applications; among them one is the Neutron Activation Analysis. High energy neutrons are collimated through a mechanical procedure as one of the most promising methods. The output energy of the neutron beam depends on the velocity of the rotating Polyethylene disks. The collimated neutrons are then measured by an innovative detection technique with high accuracy.

Description: Despite its affordability, the krypton Hall-effect thruster in applications always had problems in regard to performance. The reason for this degradation is studied from the perspective of the near-wall conductivity of electrons. Using the particle-in-cell method, the sheath oscillation characteristics and its effect on near-wall conduction are compared in the krypton and xenon Hall-effect thrusters both with wall material composed of BNSiO 2 . Comparing these two thrusters, the sheath in the krypton-plasma thruster will oscillate at low electron temperatures. The near-wall conduction current is only produced by collisions between electrons and wall, thereby causing a deficiency in the channel current. The sheath displays spatial oscillations only at high electron temperature; electrons are then reflected to produce the non-oscillation conduction current needed for the krypton-plasma thruster. However, it is accompanied with intensified oscillations.

Description: In toroidally confined plasmas, the Grad-Shafranov equation, in general, a non-linear partial differential equation, describes the hydromagnetic equilibrium of the system. This equation becomes linear when the kinetic pressure is proportional to the poloidal magnetic flux and the squared poloidal current is a quadratic function of it. In this work, the eigenvalue of the associated homogeneous equation is related with the safety factor on the magnetic axis, the plasma beta, and the Shafranov shift; then, the adjustable parameters of the particular solution are bounded through physical constrains. The poloidal magnetic flux becomes a linear superposition of independent solutions and its parameters are adjusted with a non-linear fitting algorithm. This method is used to find hydromagnetic equilibria with normal and reversed magnetic shear and defined values of the elongation, triangularity, aspect-ratio, and X-point(s). The resultant toroidal and poloidal beta, the safety factor at the 95% flux surface, and the plasma current are in agreement with usual experimental values for high beta discharges and the model can be used locally to describe reversed magnetic shear equilibria.

Description: Acceleration in development of additional conventional hydropower requires tools and methods to perform laboratory and in-field validation of turbine performance and fish passage claims. The new-generation Sensor Fish has been developed with more capabilities to accommodate a wider range of users over a broader range of turbine designs and operating environments. It provides in situ measurements of three-dimensional (3D) linear accelerations, 3D rotational velocities, 3D orientation, pressure, and temperature at a sampling frequency of 2048 Hz. It also has an automatic floatation system and built-in radio-frequency transmitter for recovery. The relative errors of the pressure, acceleration, and rotational velocity were within ±2%, ±5%, and ±5%, respectively. The accuracy of orientation was within ±4° and accuracy of temperature was ±2 °C. The new-generation Sensor Fish is becoming a major technology and being deployed for evaluating the conditions for fish passage of turbines or other hydraulic structures in both the United States and several other countries.

Description: Geodesic acoustic mode in anisotropic tokamak plasmas is theoretically analyzed by using double adiabatic model and gyro-kinetic equation. The bi-Maxwellian distribution function for guiding-center ions is assumed to obtain a self-consistent form, yielding pressures satisfying the magnetohydrodynamic (MHD) anisotropic equilibrium condition. The double adiabatic model gives the dispersion relation of geodesic acoustic mode (GAM), which agrees well with the one derived from gyro-kinetic equation. The GAM frequency increases with the ratio of pressures, p ⊥ / p ∥ , and the Landau damping rate is dramatically decreased by p ⊥ / p ∥ . MHD result shows a low-frequency zonal flow existing for all p ⊥ / p ∥ , while according to the kinetic dispersion relation, no low-frequency branch exists for p ⊥ / p ∥ ≳ 2.

Description: Nanoparticles are grown from the sputtering of a tungsten cathode in a direct current argon glow discharge. Laser light scattering of a vertical laser sheet going through the plasma reveals that the dust particle cloud is compressed and pushed towards the anode during the discharge. Scanning electron microscopy images of substrates exposed to the plasma for given durations show that dust particles are continuously falling down on the anode during the discharge. These observations are explained by the fact that the electrostatic force at the negative glow-anode sheath boundary cannot balance the ion drag, gravity, and thermophoresis forces for particles of more than a few tens of nanometres in diameter.

Description: We investigate the generation of intense pulsed focused ion beams at the 6 MeV level using an inductive voltage adder (IVA) pulsed-power generator, which employs a magnetically insulated transmission line (MITL). Such IVA machines typical run at an impedance of few tens of Ohms. Previous successful intense ion beam generation experiments have often featured an “axial” pinch-reflex ion diode (i.e., with an axial anode-cathode gap) and operated on a conventional Marx generator/water line driver with an impedance of a few Ohms and no need for an MITL. The goals of these experiments are to develop a pinch-reflex ion diode geometry that has an impedance to efficiently match to an IVA, produces a reasonably high ion current fraction, captures the vacuum electron current flowing forward in the MITL, and focuses the resulting ion beam to small spot size. A new “radial” pinch-reflex ion diode (i.e., with a radial anode-cathode gap) is found to best demonstrate these properties. Operation in both positive and negative polarities was undertaken, although the negative polarity experiments are emphasized. Particle-in-cell (PIC) simulations are consistent with experimental results indicating that, for diode impedances less than the self-limited impedance of the MITL, almost all of the forward-going IVA vacuum electron flow current is incorporated into the diode current. PIC results also provide understanding of the diode-impedance and ion-focusing properties of the diode. In addition, a substantial high-energy ion population is also identified propagating in the “reverse” direction, i.e., from the back side of the anode foil in the electron beam dump.

Description: Electron bulk heating during magnetic reconnection with symmetric inflow conditions is examined using kinetic particle-in-cell simulations. Inflowing plasma parameters are varied over a wide range of conditions, and the increase in electron temperature is measured in the exhaust well downstream of the x-line. The degree of electron heating is well correlated with the inflowing Alfvén speed c Ar based on the reconnecting magnetic field through the relation Δ T e = 0.033   m i   c A r 2 , where Δ T e is the increase in electron temperature. For the range of simulations performed, the heating shows almost no correlation with inflow total temperature T t o t = T i + T e or plasma β . An out-of-plane (guide) magnetic field of similar magnitude to the reconnecting field does not affect the total heating, but it does quench perpendicular heating, with almost all heating being in the parallel direction. These results are qualitatively consistent with a recent statistical survey of electron heating in the dayside magnetopause (Phan et al ., Geophys. Res. Lett. 40 , 4475, 2013), which also found that Δ T e was proportional to the inflowing Alfvén speed. The net electron heating varies very little with distance downstream of the x-line. The simulations show at most a very weak dependence of electron heating on the ion to electron mass ratio. In the antiparallel reconnection case, the largely parallel heating is eventually isotropized downstream due a scattering mechanism, such as stochastic particle motion or instabilities. The simulation size is large enough to be directly relevant to reconnection in the Earth's magnetosphere, and the present findings may prove to be universal in nature with applications to the solar wind, the solar corona, and other astrophysical plasmas. The study highlights key properties that must be satisfied by an electron heating mechanism: (1) preferential heating in the parallel direction; (2) heating proportional to m i   c A r 2 ; (3) at most a weak dependence on electron mass; and (4) an exhaust electron temperature that varies little with distance from the x-line.

Description: High-speed atomic force microscopy has attracted much attention due to its unique capability of visualizing nanoscale dynamic processes at a solid/liquid interface. However, its usability and resolution have yet to be improved. As one of the solutions for this issue, here we present a design of a high-speed Z -tip scanner with screw holding mechanism. We perform detailed comparison between designs with different actuator size and screw arrangement by finite element analysis. Based on the design giving the best performance, we have developed a Z tip scanner and measured its performance. The measured frequency response of the scanner shows a flat response up to ∼10 kHz. This high frequency response allows us to achieve wideband tip-sample distance regulation. We demonstrate the applicability of the scanner to high-speed atomic-resolution imaging by visualizing atomic-scale calcite crystal dissolution process in water at 2 s/frame.

Description: A suspension system of classical geophone was developed, adopting multiple pairs of leaf springs as a substitute for one pair. The finite element analysis was used as the solving means, and the results indicated that the geophone performance with developed suspension system was more favorable than that with conventional suspension system. First, the operating broadband of the improved geophone was wider than that of the conventional geophone. Second, the distortion of output signal for a geophone was slightly reduced, which was usually enlarged with improving the ratio of spurious resonant frequency to natural frequency.

Description: A liquid membrane electrochemical etching process for preparing nano-tips is proposed by the introduction of buoyant force to the lower tip, in which the lower portion of the anodic wire is immersed into a floating layer. A mathematical model of this method is derived. Both calculation and experimental results demonstrate that the introduction of buoyant force can significantly decrease the tip radius. The lubricating oil and deionized water floating layers were tested for the processing of nano-tips. Further, high-aspect-ratio nano-electrodes were prepared by applying a relative vertical movement to the anodic wire.

Description: Construction and characterization of a multichannel photodiode detector based on commercially available components with high signal to noise of ∼10 6 and a rapid frame rate, suitable for time resolved femtosecond spectroscopy with high repetition femtosecond sources, is presented.

Description: The neutron imaging system at the National Ignition Facility (NIF) is an important diagnostic tool for measuring the two-dimensional size and shape of the neutrons produced in the burning deuterium-tritium plasma during the stagnation stage of inertial confinement fusion implosions. Since the neutron source is small (∼100 μ m) and neutrons are deeply penetrating (〉3 cm) in all materials, the apertures used to achieve the desired 10- μ m resolution are 20-cm long, triangular tapers machined in gold foils. These gold foils are stacked to form an array of 20 apertures for pinhole imaging and three apertures for penumbral imaging. These apertures must be precisely aligned to accurately place the field of view of each aperture at the design location, or the location of the field of view for each aperture must be measured. In this paper we present a new technique that has been developed for the measurement and characterization of the precise location of each aperture in the array. We present the detailed algorithms used for this characterization and the results of reconstructed sources from inertial confinement fusion implosion experiments at NIF.

Description: Laser-based time-domain thermoreflectance (TDTR) and frequency-domain thermoreflectance (FDTR) techniques are widely used for investigating thermal transport at micro- and nano-scales. We demonstrate that data obtained in TDTR measurements can be represented in a frequency-domain form equivalent to FDTR, i.e., in the form of a surface temperature amplitude and phase response to time-harmonic heating. Such a representation is made possible by using a large TDTR delay time window covering the entire pulse repetition interval. We demonstrate the extraction of frequency-domain data up to 1 GHz from TDTR measurements on a sapphire sample coated with a thin layer of aluminum, and show that the frequency dependencies of both the amplitude and phase responses agree well with theory. The proposed method not only allows a direct comparison of TDTR and FDTR data, but also enables measurements at high frequencies currently not accessible to FDTR. The frequency-domain representation helps uncover aspects of the measurement physics which remain obscured in a traditional TDTR measurement, such as the importance of modeling the details of the heat transport in the metal transducer film for analyzing high frequency responses.

Description: The ability to synchronize a femtosecond laser to x-ray pulses is crucial for performing ultrafast time-resolved x-ray scattering experiments at synchrotrons. Conventionally, the task has been achieved by locking a harmonic frequency of the laser oscillator to the storage ring master radio-frequency (RF). However, when the frequency mismatch between the two sources cannot be compensated by small adjustments to the laser cavity length, synchronization to a harmonic frequency requires modifying the optical components of the laser system. We demonstrate a novel synchronization scheme, which is a flexible alternative for synchronizing these two sources operating at arbitrarily different frequencies. First, we find the greatest common divisor (GCD) of the two frequencies that is still within the limited tuning range of the laser cavity length. The GCD is generated by dividing down from the storage ring RF, and is separately multiplied up to provide a feedback signal for synchronizing the laser cavity. Unique to our scheme, the GCD also serves as a harmonic RF source for the laser amplifier such that only laser oscillator pulses at fixed integer multiples of the storage ring RF are selected for amplification and delivery to experiments. Our method is implemented at the Photon Test Facility beamline of Pohang Light Source where timing-jitter less than 4 ps (r.m.s.) is measured using a new shot-to-shot method.

Description: A semi-adiabatic isoperibol solution calorimeter has been indigenously developed. The measurement system comprises modules for sensitive temperature measurement probe, signal processing, data collection, and joule calibration. The sensitivity of the temperature measurement module was enhanced by using a sensitive thermistor coupled with a lock-in amplifier based signal processor. A microcontroller coordinates the operation and control of these modules. The latter in turn is controlled through personal computer (PC) based custom made software developed with LabView. An innovative summing amplifier concept was used to cancel out the base resistance of the thermistor. The latter was placed in the dewar. The temperature calibration was carried out with a standard platinum resistance (PT100) sensor coupled with an 8½ digit multimeter. The water equivalent of this calorimeter was determined by using electrical calibration with the joule calibrator. The experimentally measured values of the quantum of heat were validated by measuring heats of dissolution of pure KCl (for endotherm) and tris (hydroxyl methyl) amino-methane (for exotherm). The uncertainity in the measurements was found to be within ±3%.

Description: A biomedical microwave tomography system with 3D-imaging capabilities has been constructed and translated to the clinic. Updates to the hardware and reconfiguration of the electronic-network layouts in a more compartmentalized construct have streamlined system packaging. Upgrades to the data acquisition and microwave components have increased data-acquisition speeds and improved system performance. By incorporating analog-to-digital boards that accommodate the linear amplification and dynamic-range coverage our system requires, a complete set of data (for a fixed array position at a single frequency) is now acquired in 5.8 s. Replacement of key components (e.g., switches and power dividers) by devices with improved operational bandwidths has enhanced system response over a wider frequency range. High-integrity, low-power signals are routinely measured down to −130 dBm for frequencies ranging from 500 to 2300 MHz. Adequate inter-channel isolation has been maintained, and a dynamic range 〉110 dB has been achieved for the full operating frequency range (500–2900 MHz). For our primary band of interest, the associated measurement deviations are less than 0.33% and 0.5° for signal amplitude and phase values, respectively. A modified monopole antenna array (composed of two interwoven eight-element sub-arrays), in conjunction with an updated motion-control system capable of independently moving the sub-arrays to various in-plane and cross-plane positions within the illumination chamber, has been configured in the new design for full volumetric data acquisition. Signal-to-noise ratios (SNRs) are more than adequate for all transmit/receive antenna pairs over the full frequency range and for the variety of in-plane and cross-plane configurations. For proximal receivers, in-plane SNRs greater than 80 dB are observed up to 2900 MHz, while cross-plane SNRs greater than 80 dB are seen for 6 cm sub-array spacing (for frequencies up to 1500 MHz). We demonstrate accurate recovery of 3D dielectric property distributions for breast-like phantoms with tumor inclusions utilizing both the in-plane and new cross-plane data.

Description: In situ x-ray absorption spectroscopy (XAS) provides element-specific characterization of both crystalline and amorphous phases and enables direct correlations between electrochemical performance and structural characteristics of cathode and anode materials. In situ XAS measurements are very demanding to the design of the experimental setup. We have developed a sample chamber that provides electrical connectivity and inert atmosphere for operating electrochemical cells and also accounts for x-ray interactions with the chamber and cell materials. The design of the sample chamber for in situ measurements is presented along with example XAS spectra from anode materials in operating pouch cells at the Zn and Sn K-edges measured in fluorescence and transmission modes, respectively.

Description: The light intensity of 6 Li III line spectrum at λ = 516.7 nm was observed during 6 Li 3+ beam tuning at the Hyper-Electron Cyclotron Resonance (ECR) ion source. Separation of ion species of the same charge to mass ratio with an electromagnetic mass analyzer is known to be an exceptionally complex process. However, 6 Li III line intensity observation conducted in this study gives new insights into its simplification of this process. The light intensity of 6 Li III line spectrum from the ECR plasma was found to have a strong correlation with the extracted 6 Li 3+ beam intensity from the RIKEN Azimuthal Varying Field cyclotron.

Description: The paper describes a time- and angle-resolved photoemission apparatus consisting of a hemispherical analyzer and a pulsed laser source. We demonstrate 1.48-eV pump and 5.92-eV probe measurements at the ⩾10.5-meV and ⩾240-fs resolutions by use of fairly monochromatic 170-fs pulses delivered from a regeneratively amplified Ti:sapphire laser system operating typically at 250 kHz. The apparatus is capable to resolve the optically filled superconducting peak in the unoccupied states of a cuprate superconductor, Bi 2 Sr 2 CaCu 2 O 8 + δ . A dataset recorded on Bi(111) surface is also presented. Technical descriptions include the followings: A simple procedure to fine-tune the spatio-temporal overlap of the pump-and-probe beams and their diameters; achieving a long-term stability of the system that enables a normalization-free dataset acquisition; changing the repetition rate by utilizing acoustic optical modulator and frequency-division circuit.

Description: Previous nonlinear gyrokinetic simulations of specific DIII-D L-mode cases have been found to significantly underpredict the ion heat transport and associated density and temperature fluctuation levels by up to almost one of order of magnitude in the outer-core domain, i.e., roughly in the last third of the minor radius. Since then, this so-called shortfall issue has been subject to various speculations on possible reasons and furthermore motivation for a number of dedicated comparisons for L-mode plasmas in comparable machines. However, only a rather limited number of simulations and gyrokinetic codes has been applied to the original scenario, thus calling for further dedicated investigations in order to broaden the scientific basis. The present work contributes along these lines by employing another well-established gyrokinetic code in a numerically and physically comprehensive manner. Contrary to the previous studies, only a mild underprediction is observed at the outer radial positions which can furthermore be overcome by varying the ion temperature gradient within the error bars associated with the experimental measurement. The significance and reliability of these simulations are demonstrated by benchmarks, numerical convergence tests, and furthermore by extensive validation studies. The latter involve cross-phase and cross-power spectra analyses of various fluctuating quantities and confirm a high degree of realism. The code discrepancies come as a surprise since the involved software packages had been benchmarked repeatedly and very successfully in the past. Further collaborative effort in identifying the underlying difference is hence required.

Description: We examined the plasma flow response to meso- and microscale magnetic dipoles by performing three-dimensional full particle-in-cell simulations. We particularly focused on the formation of a magnetosphere and its dependence on the intensity of the magnetic moment. The size of a magnetic dipole immersed in a plasma flow can be characterized by a distance L from the dipole center to the position where the pressure of the local magnetic field becomes equal to the dynamic pressure of the plasma flow under the magnetohydrodynamics (MHD) approximation. In this study, we are interested in a magnetic dipole whose L is smaller than the Larmor radius of ions r iL calculated with the unperturbed dipole field at the distance L from the center. In the simulation results, we confirmed the clear formation of a magnetosphere consisting of a magnetopause and a tail region in the density profile, although the spatial scale is much smaller than the MHD scale. One of the important findings in this study is that the spatial profiles of the plasma density as well as the current flows are remarkably affected by the finite Larmor radius effect of the plasma flow, which is different from the Earth's magnetosphere. The magnetopause found in the upstream region is located at a position much closer to the dipole center than L . In the equatorial plane, we also found an asymmetric density profile with respect to the plasma flow direction, which is caused by plasma gyration in the dipole field region. The ion current layers are created in the inner region of the dipole field, and the electron current also flows in the region beyond the ion current layer because ions with a large inertia can closely approach the dipole center. Unlike the ring current structure of the Earth's magnetosphere, the current layers in the microscale dipole fields are not circularly closed around the dipole center. Since the major current is caused by the particle gyrations, the current is independently determined to be in the direction of the electron and ion gyrations, which are the same in both the upstream and downstream regions. The present analysis on the formation of a magnetosphere in the regime of a microscale magnetic dipole is significant for understanding the solar wind response to the crustal magnetic anomalies on the Moon surface, such as were recently observed by spacecraft.

Description: Ellipsometry is one of the standard methods for observation of glass transition in thin polymer films. This work proposes that sensitivity of the method to surface morphology can complicate manifestation of the transition in a few nm thick samples. Two possible mechanisms of free surface roughening in the vicinity of glass transition are discussed: roughening due to lateral heterogeneity and roughening associated with thermal capillary waves. Both mechanisms imply an onset of surface roughness in the glass transition temperature range, which affects the experimental data in a way that shifts apparent glass transition temperature. Effective medium approximation models are used to introduce surface roughness into optical calculations. The results of the optical modeling for a 5 nm thick polystyrene film on silicon are presented.

Description: Investigations of emission of harmonics from argon gas jet irradiated by 700 fs, 5 mJ pulses from a KrF laser are presented. Harmonics conversion was optimized by varying the experimental geometry and the nozzle size. For the collection of the harmonic radiation silicon and solar-blind diamond semiconductor detectors equipped with charge preamplifiers were applied. The possibility of using a single-crystal CVD diamond detector for separate measurement of the 3rd harmonic in the presence of a strong pumping radiation was explored. Our experiments show that the earlier suggested 0.7% conversion efficiency can really be obtained, but only in the case when phase matching is optimized with an elongated gas target length corresponding to the length of coherence.

Description: The electrostatic potential profile and the particle densities of a simplified auroral double layer are found using a relaxation method to solve Poisson's equation in one dimension. The electron and ion distribution functions for the ionosphere and magnetosphere are specified at the boundaries, and the particle densities are found from a collisionless kinetic model. The ion distribution function includes the gravitational potential energy; hence, the unperturbed ionospheric plasma has a density gradient. The plasma potential at the upper boundary is given a large negative value to accelerate electrons downward. The solutions for a wide range of dimensionless parameters show that the double layer forms just above a critical altitude that occurs approximately where the ionospheric density has fallen to the magnetospheric density. Below this altitude, the ionospheric ions are gravitationally confined and have the expected scale height for quasineutral plasma in gravity.

Description: The RF properties of an accelerating structure, and the pulse structure and charge per bunch in the electron beam propagating through it are important parameters that determine the impact of beam loading in the structure. The injector linac of the Compact Ultrafast Terahertz Free-Electron Laser (CUTE-FEL) has been operated with two different pulse structures during initial commissioning experiments and the effect of beam loading on the accelerated electron beam parameters has been studied analytically for these two pulse structures. This paper discusses the analytical study of beam loading in a Standing Wave, Plane Wave Transformer linac employed in the CUTE-FEL setup, and a possible technique for its compensation for the electron beam parameters of the CUTE-FEL. A parametric study has been performed to study beam loading for different beam currents and to optimize injection time of the electron beam to compensate beam loading. Results from the parametric study have also been used to explain previously observed results from acceleration experiments in the CUTE-FEL setup.

Description: We report the design, construction, and performances of a microwave (MW) heating device for laboratory experiments with non-contact, homogeneous internal heating. The device generates MW radiation at 2.47 GHz from a commercial magnetron supplied by a pulsed current inverter using proprietary, feedback based command and control hardware and software. Specially designed MW launchers direct the MW radiation into the sample through a MW homogenizer, devised to even the MW power distribution into the sample's volume. An adjustable MW circuit adapts the MW generator to the load (i.e., the sample) placed in the experiment chamber. Dedicated heatsinks maintain the MW circuits at constant temperature throughout the experiment. Openings for laser scanning for image acquisition with a CCD camera and for the cooling circuits are protected by special MW filters. The performances of the device are analyzed in terms of heating uniformity, long term output power stability, and load matching. The device is used for small scale experiments simulating Earth's mantle convection. The 30 × 30 × 5 cm 3 convection tank is filled with a water‑based viscous fluid. A uniform and constant temperature is maintained at the upper boundary by an aluminum heat exchanger and adiabatic conditions apply at the tank base. We characterize the geometry of the convective regime as well as its bulk thermal evolution by measuring the velocity field by Particle Image Velocimetry and the temperature field by using Thermochromic Liquid Crystals.

Description: This paper announces the implementation of a long wavelength infrared camera to obtain high-speed thermal images of an aircraft engine's in-service thermal barrier coated turbine blades. Long wavelength thermal images were captured of first-stage blades. The achieved temporal and spatial resolutions allowed for the identification of cooling-hole locations. The software and synchronization components of the system allowed for the selection of any blade on the turbine wheel, with tuning capability to image from leading edge to trailing edge. Its first application delivered calibrated thermal images as a function of turbine rotational speed at both steady state conditions and during engine transients. In advance of presenting these data for the purpose of understanding engine operation, this paper focuses on the components of the system, verification of high-speed synchronized operation, and the integration of the system with the commercial jet engine test bed.

Description: We present a home built electrochemical scanning tunneling microscope (ECSTM) with very high stability and repeatability. Its coarse approach is driven by a closely stacked piezo motor of GeckoDrive type with four rigid clamping points, which enhances the rigidity, compactness, and stability greatly. It can give high clarity atomic resolution images without sound and vibration isolations. Its drifting rates in XY and Z directions in solution are as low as 84 pm/min and 59 pm/min, respectively. In addition, repeatable coarse approaches in solution within 2 mm travel distance show a lateral deviation less than 50 nm. The gas environment can be well controlled to lower the evaporation rate of the cell, thus reducing the contamination and elongating the measurement time. Atomically resolved SO 4 2− image on Au (111) work electrode is demonstrated to show the performance of the ECSTM.

Description: From rovers on the surface of Mars to Voyager 1 near the edge of the solar system, spacecraft regularly call home to Earth. For five decades, the Deep Space Network has been at the other end of the line.

Description: The newly named Nobelists kept alive work on gallium nitride until their successful innovations paved the way to practical devices.

Description: The discomforts of noise in working and living can be reduced only by a rational approach to acoustics problems when building houses and factories, writes the technical director of the Acoustics Laboratory at the Massachusetts Institute of Technology.

Description: Integrated circuits with nanomaterial components can revolutionize technology, but only if they can be economically fabricated in large numbers.

Description: The belt emerges as a fundamental climatic feature of atmospheric circulation patterns on a rotating and differentially heated planet. But locating its edges and discerning anthropogenic influences remain difficult research problems.

Description: By manipulating fluorescence, the three prizewinners brought the hidden machinery of living cells into view.

Description: Researchers maintain that excellence in science requires a long-term strategy, money, and closer interactions with the commercial sector.

Description: Nonnuclear states’ patience with weapons states’ inaction on disarmament is wearing thin.

Description: The expansion of the Department of Energy’s high-bandwidth linkage is a step toward a global network for the transfer of scientific information.