ALBERT

Notes: A simple technique is demonstrated for measuring strains in an electromagnetically noisy environment using electrical strain gauges. For applications in which strains are produced electromagnetically in current-carrying structures, the noise signal can be much larger than the strain signal. Furthermore, the noise signal is at precisely the same frequency as the strain signal, making standard methods of synchronous signal detection difficult. This problem has been surmounted by modulating the detection circuit sensitivity. Bridge circuit modulation has been shown to effectively decouple the strain signal from the noise, even at very low strain levels of ∼10−8 m/m.

Notes: We have completed a finite difference computer simulation of two diverging electrostatic analyzers. In both analyzers, the deflecting plates are cylindrical surfaces which flare out from each other like two arms of a hyperbola. The analyzers are the soft particle spectrometer (SPS) and the spectrographic particle imager (SPI), which correspond, respectively, to an energy spectrometer and an energy spectrograph. The simulation consists of two steps: (1) a finite difference computation of the electrostatic potential field inside the instrument; and (2) a ray-tracing computation in which many particles are ray traced through the instrument and statistics are gathered on the particles that make it to the collecting region. In both cases, the simulation is two-dimensional, restricted to the central plane of the instrument. This limitation turns out to be unimportant because the statistics acquired during simulation agree well with experimentally acquired statistics for each instrument. In the case of SPI, the computer simulation has been used to provide information on how variation of geometric parameters affects the quantities that describe a good spectrograph.

Notes: A compact, dual-beam laser deflection system was built, mainly from commercially available parts. While the detector and electronics yielded noise levels at the theoretical level for the detector, pointing instability of the laser led to an increase in noise by a factor of about 103. The dual-beam arrangement gave only a factor of about 4 improvement over the single-beam mode due to alignment and drift problems. Further improvement requires a feedback system to minimize signal arising from common-mode beam displacements.

Notes: The time-resolution capabilities of two 28-mm-diam side-on photomultiplier tubes, Hamamatsu R928 and RCA 931-A, were studied by point illumination of the photocathode surface with the attenuated beam of a synchronously pumped dye laser (10-ps pulse width). Using the time-correlated single photon counting technique, an apparatus response of 112 ps FWHM was obtained. Contour maps giving the time shift and the width of the response were constructed as a function of the point of illumination of the photocathode surface. These data permit selection of the optimized photocathode region to be illuminated during fluorescence decay measurements.

Notes: The principle of the change in the "decay time'' of the fluorescence of a small sample of neodymium in a glass matrix, excited by infrared radiation from a high-power light emitting diode has been used in the construction of a fiber-optic temperature sensor. Such a device is an inexpensive transducer and has demonstrated a fiber-optic sensor not requiring referencing to the intensity of the exciting radiation.

Notes: A new fully automated apparatus for measuring the thermal conductivity of liquids is described. This apparatus has been developed to meet the needs of industrial applications. The principle of the measurement is based on the absolute transient hot-wire method. All data acquisition and instrument control can be performed using a microcomputer. After filling with a sample liquid in a cell the apparatus can automatically measure the thermal conductivity at the desired temperature without any manual procedures. The automated procedures include an algorithm to determine onset time of natural convection. The applicability of the apparatus has been tested to measure the thermal conductivity of toluene at room temperature and the results have an estimated accuracy of ±1.0 to ±1.5% depending on a sample to be measured.

Notes: Overvoltage protection circuits have been developed to protect oscilloscope inputs or other 50-Ω recording systems from fast (τr∼1 ns) rise-time pulses. These circuits are voltage dividers with linear output up to a specified level, typically 1.4 V, beyond which fast switching diodes limit the output to (approximately-less-than)5 V for inputs as high as 5 kV. The clipping circuits are frequency compensated for flat response to several hundred megahertz.

Notes: Flows with coherent structures allow see-free measurements of local velocity and velocity fluctuations. Continuous turbulent velocity histories in ionizing shock waves are obtained at a 10-MHz sampling rate. From this, correlation profiles and frequency spectra are determined which reveal the presence of prominent high-frequency components.

Notes: An electrostatic quadrupole device capable of deflecting an ion beam at right angles is described. It is useful for overlapping an ion beam and a laser beam. Its aberrations are negligible in many applications where fine focusing is not required. The construction is simpler and less expensive than other similar devices.

Notes: A novel design for a low-temperature valve is presented. Designed to be used on fill-line capillaries and flow lines in low-temperature apparatus, the valve has nearly zero dead volume as well as a very small total volume. It employs no metallic bellows as in standard valve designs. Instead, a Kapton membrane is epoxied into a cylindrical form to provide a flexible diaphragm, which is activated by pressurized helium. The valve is simple to construct, having only one machining operation, and uses materials readily available. It has been tested in liquid helium to be leaktight above Tλ with a 1-bar pressure differential across the capillary containing the valve.

Notes: A compact magnetic energy analyzer designed for the measurement of electron energies in the range from 20 keV through 1.5 MeV is described. The simple device, based on the semicircular focusing principle, is constructed from a high induction permanent magnet enclosed in a soft iron case. The design and operation of the analyzer in pulsed electron beam devices are discussed.

Notes: A Bragg crystal spectrometer, utilizing a microchannel plate coupled to optical film as the detection medium, has been constructed for use in soft x-ray spectroscopy. The sensitivity of this intensified gated camera to x-rays has been compared directly with standard x-ray film using a calibrated x-ray source. In addition, this high gain, intensified crystal spectrograph (ICS) has been used in an experiment to precisely measure spectral coincidences between x-ray lines in laser-generated plasmas, thus identifying candidates for photoresonant x-ray lasing schemes in the 10–21-A(ring) region. At long wavelengths the ICS was able to obtain useful data on faint lines in a single laser shot, rather than the multiple shots required by an adjacent spectrograph using x-ray film. It also allowed line coincidences to be verified by a new technique utilizing split disk targets. The design and construction of the ICS and results obtained with it are compared with those obtained with standard x-ray film.

Notes: We have constructed a scanning tunneling microscope for operation under UHV conditions (10−8 Pa). With this instrument topographic measurements can be made on metal and semiconductor surfaces by means of a scanning tip electrode, driven by piezoelectric ceramic elements. The maximum area covered ranges up to 4000×4000 A(ring)2 with a resolution better than 10 A(ring) laterally and 0.15 A(ring) rms perpendicular to the plane. Because of its compact design, the scan unit is very insensitive to vibrations and has a response time down to 0.3 ms. This allows a high scan rate to be used. In order to minimize temperature effects, special attention is paid to the geometry of the construction and the materials used, resulting in a drift ≤4 A(ring)/min along the surface and 0.5 A(ring)/min perpendicular.

Notes: An infrared cell is described that allows catalytic materials to be investigated by conventional transmission measurements at temperatures ranging from −196 to 600 °C over the spectral region from 10 to 6000 cm−1 using silicon windows and over any desirable spectral range using easily replaceable windows of choice. The sample environment can span vacuum to supra-atmospheric pressure. The thermal response of the cell is rapid, allowing it to be used for temperature programmed desorption studies along with the spectral examination of the catalyst. The sample can be in the form of a self-supporting wafer located at the center of the cell body and requiring the gas stream to pass through it. This configuration allows the cell to be used as a differential microreactor. The gas path length is short and the volume is small in order to minimize the spectral background from the ambient gas environment and to allow easy and rapid change of its composition.

Notes: Modification of a commerical motor to drive a chopper blade in UHV is described. The motor has performed satisfactorally at a frequency of 200 Hz over prolonged periods. The observed pressure rise which is due primarily to outgassing of the bearings is less than 1×10−9 Torr.

Notes: A simplified model is presented to explain the gain characteristics of a microchannel plate (MCP) operated in the reflection mode for detecting low-energy positive ions. Analysis, taking into account an automatic preacceleration effect of the potential applied across a MCP on incident ions penetrating into the microchannels, can lead to high gain performance in this operation mode. The resultant calculated gain-applied potential and gain-incident ion energy curves fit well to the data reported previously. It is also shown that the gain is almost entirely determined by the transmissibility of incident ions through the microchannels toward the backplate.

Notes: A new apparatus for production of artificial compositionally modulated materials is presented. It consists of an ion gun that sputters from alternating targets on a rotating assembly, the position of which is controlled by a thickness monitoring crystal. The apparatus is simple, relatively inexpensive, and flexible, in that it allows deposition of metals, semiconductors, and insulators under the same conditions.

Notes: Thermistor mounts are widely used for microwave power measurement, but suffer from drift caused by ambient temperature fluctuations. A Peltier oven has been developed which can be easily fitted to a thermistor mount to stabilize the mount temperature near the ambient temperature, thereby reducing the drift substantially.

Notes: A microcomputer-based system was designed to measure water transport in trees by the heat pulse method. The system comprises a heater probe as a heat source and a thermistor, incorporated into a bridge which is automatically balanced by the microcomputer. The overall dynamic range of the system for temperature is 22 bits and the resolution for temperature determination is about 1.45×10−4 °C. The elapsed time between the heat pulse injection and the thermal peak at the thermistor is calculated by the microcomputer. The computation program includes algorithms for base-line slope correction and a noise immune derivative evaluating routine for peak recognition. The system was tested in the laboratory and in the field on a citrus tree.

Notes: An improved double Michelson laser interferometer dilatometer is described. The unit is suitable for the study of materials of arbitrary size or shape with time-dependent and near zero coefficients of thermal expansion (CTE) over the range 100 to 〉450 K. Direct recording of four amplified photodetector signals gives a ΔL/L resolution of 5×10−8 and an average CTE error in the 10−10–10−9 K−1 range. An inexpensive automatic digital counter–microprocessor combination permits recording of instantaneous ΔL/L and CTE values at 〉30-s intervals. The resolution of ΔL/L in this case is 〈8×10−7 while the instantaneous CTE (4 K interval) has an uncertainty of 〈2×10−7 K−1. The latter values are based on a counting unit of λ/2 and interpolating. Smaller counting units reduce errors proportionately to the system noise level and the limitations of the temperature measurement.

Notes: A microchannel-plate photomultiplier (MCP-PMT) has been applied to the time-correlated single-photon counting technique. Electrical and timing characteristics were investigated for the two types of MCP-PMT's, nonproximity type (Hamamatsu R1264) and proximity type (R1564), which are different in distance between the photocathode and MCP. In the proximity type, the transit-time spread was found to be 60 ps, i.e., a factor of 4 shorter than that in conventional photomultipliers with a dynode string. It was concluded that both types of MCP-PMT's are fully applicable to the single-photon counting method and that the proximity type MCP-PMT in particular leads to further improvements in the cathode transit-time difference and the wavelength effect of the timing properties. Some examples of experimental results are shown for fluorescence decay curves and picosecond time-resolved spectra.

Notes: A sample positioner and an electron energy analyzer for studies of photofield emission have been designed and constructed. The sample positioner allows photofield emission from every facet of a field emitter to be measured under illumination at arbitrary angles of light incidence and polarization. The electrons emitted from a selected facet are decelerated to a kinetic energy E0 by a series of cylindrical lenses and introduced into either one of two energy analyzers. The deflection energy analyzer, formed from two identical 127° cylindrical analyzers, is used when high-energy resolution is required. The full width at half-maximum height of the resolution function of this analyzer is proportional to E0 down to a minimum kinetic energy which is less than 0.5 eV, and is given by ΔEFWHM=(0.0390±0.0006)E0. The throughput depends on E0 due to a combination of resolution and aperturing effects, and varies as E3/20. The signal-to-noise ratio of the analyzer is limited to 2×104 by inelastic scattering of electrons. The retardation energy analyzer is used for aligning the system and for measuring the energy-integrated current.

Notes: A spectrometer for inverse photoemission in the vacuum ultraviolet range is described. A spherical grating with an acceptance of f/4 is used in normal incidence. Two position-sensitive detectors allow the registration of spectra covering the whole range of photon energies from 8 to 28 eV in parallel. The optical resolution is 18 A(ring) for the Lyman-α line of hydrogen. A space-charge-limited electron gun with an energy spread of 0.25 eV is used to excite inverse photoemission spectra. The large acceptance angle of the grating allows one to measure spectra with high efficiency and low background level.

Notes: A new technique to measure gas–liquid densities using the one-dimensional projection method is presented. The measurements were made in an NMR autoclave under high-temperature and high-pressure conditions. Some of the results of densities of cyclopentane determined from the room temperature to the supercritical regions are reported.

Notes: A sensitive diaphragm-type pressure transducer suitable for use at very low temperatures is described. This device was optimized for pressures up to 3.5 MPa, but sensors for other pressure ranges can be readily manufactured. The external pressure deflects two sapphire disks which causes a change in capacitance between the platinum electrodes sputtered on the disks. The transducer can easily resolve changes of 1 Pa at 3.5 MPa, while reproducibility and hysteresis, though not fully tested yet, are better than 10 Pa. The transducer is 610 μm thick and 8 mm diameter.

Notes: The operational error in the heat flux measurements is theoretically investigated when the heat flux from a furnace wall to the environment is measured by a heat flux transducer. Change of the original heat flux, which is caused by placing a transducer on the furnace wall, is clarified by solving a three-dimensional heat transfer problem. The operational error is explicitly given by a simple equation taking into account the thermal properties of the furnace wall and the transducer. Numerical results are also provided for a typical application to industrial furnaces.

Notes: We have designed a device for measuring sound speeds in reactive liquids at high pressure and temperature. It has been tested in experiments on liquid-potassium metal at pressures up to 0.7 GPa and temperatures up to 423 K. The limitations on pressure and temperature were imposed by auxiliary instrumentation rather than the properties of the device, and it seems likely that it would be suitable for more extreme conditions. The data on potassium agree well with precise room-temperature data. The sound velocities measured as a function of pressure at various temperatures can be used to calculate equation-of-state parameters such as the bulk modulus and its pressure derivatives. The experiments on potassium indicate that bulk modulus can be determined to ±1%, its first pressure derivative to about ±5%, and second pressure derivative to about ±50% (the last for a run with a 0.7-GPa pressure range). The device should permit sound velocity measurements in a variety of liquids which are reactive, corrosive, and/or miscible with pressure media.

Notes: An apparatus for the measurement of sound velocity in gases up to pressures of 10 kbar and down to temperatures of 77 K is described. Important features of the experimental setup include a specially designed ultrasonic cell with double reflectors, based on the phase comparison pulse-echo technique, and a vacuum type of cryostat using a cold finger system for temperature control. Detailed measurements on argon down to the melting line show that the method is capable of giving a precision of 0.02% for the sound velocity.

Notes: A UHV sample manipulator with greater than 22 in. of vertical translation and 360° of independent polar and azimuthal sample rotation is described.

Notes: An instrument is presented which collects large samples of ambient fogwater by impaction of droplets on a screen. The collection efficiency of the instrument is determined as a function of droplet size, and it is shown that fog droplets in the range 3–100-μm diameter are efficiently collected. No significant evaporation or condensation occurs at any stage of the collection process. Field testing indicates that samples collected are representative of the ambient fogwater. The instrument may easily be automated, and is suitable for use in routine air quality monitoring programs.

Notes: The spatial distribution of neutral deuterium has been determined in a reversed field pinch by fluorescence scattering. The first series of measurements, with a resolution of 4 cm were made with the laser tuned to the Dα, n=2−3(6561 A(ring)) transition. The second set of measurements, with both 4 and 2 cm resolution were performed with the laser tuned to the Dβn=2−4(4861 A(ring)) wavelength. The improvement in signal to noise obtained was substantial, being increased by a factor of (approximately-equal-to)2.5 in general. This is believed to be the first such measurement at this wavelength. The advantages of using this transition are such that this technique can be extended to measure the electron density near the plasma edge.

Notes: The TFTR Thomson scattering system has been operational since January 1984. The diagnostic uses two ruby lasers and two spectrometer-detector systems to provide profiles at two times in a discharge. The two scattering lines consist of 76 spatial channels which span the 200-cm vacuum vessel along a major radius. The detectors are gated, intensified CCD arrays with single photoelectron sensitivity. Te(R) and Ne(R) profiles are presented.

Notes: The determination of temperature of electron density of reactor-grade fusion plasmas (T〉5 keV, Ne≥1013 cm−3) will require enhanced capability in Thomson scattering diagnostics. While improved detection systems will help, it is clear that the scattered population must be increased because of the excessive thermal broadening. The system described here has a Nd:glass oscillator followed by three stages of amplifier. At present, the system generates a 60 J single pulse with beam divergence less than 0.6 mR. This pulse can be used with a KDP-II frequency doubler to generate 30 J pulses of 1.06 and 0.53 μm.

Notes: A design for an electrode array for use in nonlinear optics experiments is presented. The array applies a spatially periodic transverse electric field (amplitude ∼ 3 kV/mm and period 4 mm) to a gas sample through which a laser beam is focused.

Notes: The 3-MeV protons created by d(d, p)t fusion reactions in a moderately sized tokamak leave the plasma on trajectories determined by the position of their birth and by the poloidal magnetic field. Pitch-angle resolution of the escaping 3-MeV protons can separately resolve the spatial distribution of the d(d, p)t fusion reactions and the poloidal field distribution inside the tokamak. These diagnostic techniques have been demonstrated on PLT with an array of collimated surface barrier detectors.

Notes: The characteristics of a small, water-cooled, 90° magnetic deflection mass spectrometer suitable for analyzing positive and negative hydrogen ion species is described.

Notes: The depth of the rocking mode infrared absorption peak at 450 cm−1 from IR response at 500 cm−1 has been observed to be a linear function of silicon dioxide thickness grown on silicon wafers. At the critical oxide thickness of 100 A°, the depth becomes zero, i.e., the IR response is flat. With further decrease of oxide thickness, the absorption peak changes sign and for oxide-free silicon, the absorption minima is shifted by about 2% from the IR response at 500 cm−1. Such IR response has been successfully used for determining oxide thicknesses in the range of 100–1200 A° with ±50 A° accuracy.

Notes: Thermal imaging cameras sensitive to 3–5 μ radiation are routinely used to measure heat flow to the main limiter, to the vacuum vessel wall behind the main limiter, and to the divertor plate limiters. The cameras are equipped to provide either a standard television image, one frame per ∼16.7 ms, or a surface temperature profile on one line of the image with a time resolution of ∼125 μs. In the former mode, we can determine both the location and the intensity of the heating on the main limiter during multimegawatt neutral-beam injection into plasma; in the latter mode, we can measure heat pulses striking the limiter from plasma processes occurring on fast timescales (e.g., Dα spikes of ∼500 μs duration). Data is stored in both video image and digitized forms. In the latter, a "peak-sample-hold'' circuit electronically records the maximum signal of each line sweep and stores this data in digitized form on magnetic tape. This facilitates later comparisons of infrared camera data with other diagnostic signals using plotting packages on the DEC-10.

Notes: A detector setup with three LN-cooled Si(Li) diodes is used to measure soft x-ray spectra (0.8–20 keV) emitted from the inside walls of the PDX vessel during the plasma discharge. The setup is part of a pulse-height-analysis system, which is used to measure the plasma and wall radiation simultaneously at five different radial positions. The wall and the plasma radiation are measured under different plasma conditions (e.g., OH and neutral beam heating). The wall radiation is very much increased during the neutral beam heating, with an enhancement factor of at least 10 over the OH wall radiation. Since we measure the plasma and the wall radiation at the same time, the measurements allow the conclusion that the wall radiation can be attributed essentially to fluorescence (line radiation, e.g., Ti-Kα) and scattering (continuum part of the wall radiation spectrum). The fluorescence and the scattering are both caused by soft x-ray radiation flux coming from the plasma. There seems to be no need to invoke other, more exotic causes for the wall radiation, for example, charge particle bombardment of the wall.

Notes: The characteristics of operating an extended-area, triple-layer microchannel-plate assembly are described in detail. The assembly has an anode array to produce 120 channels of information. When run in the pulse-counting mode, gains of up to 5×108 are obtained with very low levels of dark current. A number of special features and problems have been observed during operation. These include unexpectedly high count rates for each channel and severe gain variation along the length of the plate. A model distribution function for a pulse is derived and it is shown that this gain variation is due to space-charge effects that occur in the interstage gaps. This effect, although previously discounted, can consistently explain the data presented here and earlier by other authors. One assembly was rebuilt and now exhibits much greater uniformity in gain. Its pulse-height spectrum also has the unusually small, full-width at half-maximum: gain ratio of typically 50%.

Notes: Raman measurements on ethanol containing rhodamine 6G have been carried out by a single-photon counting technique with highly repetitive (∼82 MHz), short-duration (∼5 ps) laser pulses using a time gate as narrow as 31 ps. The Raman-to-fluorescence intensity ratio and the signal-to-noise ratio have been improved by factors of 129 and 4.2, respectively. These values are in good agreement with numerical estimations. This method has also been found to be very effective in reducing dark counts and interfering plasma lines from the laser tube. The optimum width and position of the gate to attain the best signal-to-noise ratio for a given fluorescence decay time and a response function of the experimental system are also discussed.

Notes: A high-intensity supersonic nozzle beam source is described, whose beam energy can be varied between 2 and 170 meV (helium). Experimental performance and time-of-flight measurements on cold helium beams are reported. Condensation in the free jet expansions of helium has been studied by mass spectrometric detection of He+2. A correlation between the maximum speed ratio and the onset of clustering is observed.

Notes: A precision liquid-helium temperature proportional thermostat designed for use with a superconducting cavity stabilized oscillator is described, where temperature of the X-band superconducting Nb cavity mounted inside a vacuum can is regulated at the temperature below 2 K. By noticing the fact that the time for establishment of thermal equilibrium is very short at liquid-helium temperature and thermal transfer properties can, therefore, be measured in the frequency domain, the frequency domain technique rather than the conventional time domain technique is used to design and measure feedback loops of a thermostat. The application of a second-order loop to the design of thermostats is discussed in order to obtain better transient and steady-state performance. In the thermostat constructed, temperature is measured with a germanium resistance thermometer in the ac Wheatstone bridge, a commercial lock-in amplifier is used as a null detector, and the second-order loop is used. The loop characteristics were confirmed by measuring the Bode plot of the feedback loop which also contains the frequency response of the thermal interface, and the gain crossover frequency and the phase margin were 26 Hz and 52°, respectively, at the operating temperature near 1.7 K. The thermostat has achieved the long-term temperature drift of less than 3.2 μK, where the drift caused by the instability of the bridge itself is excepted, in the presence of the liquid-helium temperature fluctuation of 35 mK for periods more than 10 h; it has also shown very fast and good transient response. In addition, the Bode plots of the closed loops have shown that the loop is stable to the variation of the gain crossover frequency of more than four octaves. It has been shown that the method of designing a precision thermostat by measuring its thermal properties in the frequency domain can be useful and can give very reliable results at liquid-helium temperature.

Notes: A scattering cell is described that is suitable for use with targets of alkali and alkaline earth vapors in beam-static gas collision experiments. A novel feature of this vapor oven design is that the entire assembly can be rapidly moved into and out of the projectile beam path. When used with fixed beam defining apertures, this arrangement results in greatly simplified total scattering cross-section measurements using an attenuation technique. Examples of cross sections measured in this way are presented for electron capture and loss by D+/D− in a Cs target between 0.1 and 4.0 keV/amu.

Notes: An ultrahigh-vacuum system has been constructed and outfitted with molecular beam sources and surface analysis equipment [Auger electron spectroscopy (AES) and reflection high-energy electron diffraction (RHEED)]. The sample insertion system is a low-temperature apparatus. With this equipment, films can be grown in the 10−11–10−9-Torr range with substrate temperatures at 4.2–20 K. A modification of the system will permit growth at elevated temperatures followed by in situ low-temperature measurements. The design of the low-temperature apparatus permits extensive measurements to be taken in an environment in which the temperature can be controlled over a range from 0.3 to 300 K and the magnetic field from 10−7 to 6 T.

Notes: Heterodyne detection will be used to measure the scattered signal from a 100-MW pulsed CO2 laser Thomson scattered from energetic alpha particles. This measurement requires local oscillators displaced from the pump line by 6 to 21 GHz. We are developing cw sequence and regular band N2O and CO2 lasers which provide many lines in the required frequency range. The sequence lines are obtained by using a small in-cavity hot cell. Operating characteristics will be discussed for a variety of experimental arrangements.

Notes: Neutral particle flux parallel and perpendicular to the plasma current and at energies equal to and below the injection energy has been observed with the parallel and perpendicular charge exchange spectrometers on Doublet III. Initial neutral injection is marked by a rapid increase in the high-energy neutral efflux which usually relaxes over tens of milliseconds to a lower equilibrium value. As injected power is increased by the stepped addition of more neutral beams, the measured flux is not linearly additive, often increasing slightly or not at all. For very high values of injected power, in the 5–7-MW range, the neutral particle flux is often observed in bursts correlated with the rapid fall of giant sawteeth on soft x-ray signals. In many of these shots the fishbone instability is present and is observed with the perpendicular spectrometer, however the parallel flux does not correlate with fluctuations observed with magnetic probes unless the instability terminates rapidly, in which case both a soft x-ray drop and a burst of neutrals occurs. Some aspects of these measurements have been modeled by a particle transport code with particular emphasis on changes in the neutral density profile during high-power neutral injection.

Notes: Diagnostic methods and the applications of fusion product measurements in tokamaks are reviewed with emphasis on results from PLT, PDX, and TFTR. Measurements have been made using the 2.5-MeV neutron from the d(d, n)3He reaction, the 3-MeV proton from the d(d, p)t reaction, both the 3.7-MeV alpha and the 14.7-MeV proton from the d(3He, p)α reaction, and the 14-MeV neutron from the d(t, n)α reaction. The common use of these measurements is the determination of the ion temperature from the magnitude of the d-d neutron emission. For tokamak plasmas, these results are usually in good agreement with the charge exchange ion temperature. Recently, the charged fusion products have been used for high-resolution spectroscopic purposes, and emission profile measurements. Pitch angle resolution of the escaping 3-MeV proton emission has been used to determine the poloidal magnetic field inside the tokamak. Major issues in this field include the expected tritium operation on TFTR where the neutron measurements will determine when tritium will be introduced into the TFTR vessel and provide a measurement of the fusion power multiplication value (Q). The TFTR Q∼1 experiments will also provide a chance to measure the confinement of 3.5-MeV alphas in a tokamak.

Notes: There are several nuclear reactions between fast-confined α particles and low-z ions in ignited D–T plasma. Some of them produce unique and highly penetrating neutron or γ radiation. A study has begun to evaluate the feasibility of using these reactions to determine the spatial profile of fast-confined reaction product α particles, and to determine a crude envelope of their speed distribution as they thermalize. Particular attention is paid to the means of detecting these radiations, measuring their spectra, and most important of all, reducing and discriminating against the very much larger background of interfering radiation.

Notes: We report here on the design and implementation of analog circuitry which allows the processing of the components of vector waveforms to obtain polarization information. The waveforms are the voltages derived from orthogonal sensors such as magnetometers or seismometers which provide information on the time variation of vector processes. The circuits take the voltages from the individual sensors and process them to produce estimates of the spectral matrix at a particular frequency. From the components of the spectral matrix one may determine the wave polarization parameters including the signal power, ellipticity, handedness, and orientation of the polarization ellipse. In cases where the information of interest to the investigator depends upon the relatively slow modulations of a carrier and not upon the frequency of the carrier itself, the preprocessing of the spectral information as described here allows the investigator to sample the data at a much reduced rate, or with a narrower bandwidth, without loss of information. We have implemented the circuits described in our investigation of electromagnetic waves in the ULF (3 mHz–3 Hz) frequency band and have achieved a reduced demand for storage and processing capacities in the project.

Notes: Systematic errors in conductimetric measurements are often encountered due to partial screening of interelectrode current paths resulting from adhesion of bubbles on the electrode surfaces of the cell. A method of assessing this error quantitatively by a simulated electrolytic tank technique is proposed here. The experimental setup simulates the bubble-curtain effect in the electrolytic tank by means of a pair of electrodes partially covered by a monolayer of small polystyrene-foam spheres representing the bubble adhesions. By varying the number of spheres stuck on the electrode surface, the fractional area covered by the bubbles is controlled; and by measuring the interelectrode impedance, the systematic error is determined as a function of the fractional area covered by the simulated bubbles. A theoretical model which depicts the interelectrode resistance and, hence, the systematic error caused by bubble adhesions is calculated by considering the random dispersal of bubbles on the electrodes. Relevant computed results are compared with the measured impedance data obtained from the electrolytic tank experiment. Results due to other models are also presented and discussed. A time-domain measurement on the simulated cell to study the capacitive effects of the bubble curtain is also explained.

Notes: The design and the operation of a rapid (∼10 s), accurate (±1%), moderate resolution (∼50 cm−1) system for measuring inelastic electron tunneling spectra are described. The utility of this system is discussed, and an example of its use is presented.

Notes: An experimental system is described with which exothermic solid-state phase transformations can be made to occur isothermally and their kinetics studied in times as short as 1 s. The system has been applied to the study of the crystallization rate of metallic glasses heated to temperatures well above their glass formation temperatures. Strips of the metallic glass 0.2 cm wide and 5 cm long are resistively heated over a portion of their length to the reaction temperature. They are heated within a 0.3-cm-i.d. tube through which flows a cooling gas. The gas flow rate and electrical current are controlled so as to maintain the sample at constant temperature during the reaction. The rate of reaction is measured by monitoring the intensity of diffraction peaks from the small crystallites which form within the ribbon. The x-ray flux from a bending magnet beam line at the Stanford Synchrotron Radiation Laboratory (SSRL) provides sufficient diffracted intensity to monitor the full development of the crystalline diffraction peaks in times as short as 1 s.

Notes: We have developed an X-band electron resonance apparatus incorporating a diamond anvil cell to generate pressures up to 100 kbar. The system can operate down to 1.5 K and the pressure can be changed and calibrated via ruby fluorescence while at low temperature. The system differs from a conventional EPR cavity system in that the pressure gasket acts as the microwave resonator. For an initial application, the system is used to examine the pressure dependence of the magnetic properties of a chromium chalcogenide spinel, CdCr2Se4.

Notes: An ultrahigh-vacuum compatible sample manipulator which incorporates rotation and a Dewar for sample cooling is described. The rotation is accomplished using a differentially pumped rotary seal made of two Teflon O rings and the temperature of the sample can be controlled from 30 K to over 1600 K.

Notes: A very simple and inexpensive method of converting a barrel plasma etching system into a planar system is described. Details of structure and operating characteristics of the planar reaction chamber are shown.

Notes: A local magnetic field diagnostic, based on the Zeeman splitting of lithium atoms is under development at Los Alamos. A modified duoPIGatron ion source1 is used in conjunction with an 80-kV accelerator to produce a high-density atomic lithium beam, permitting access to plasmas with a wide range of parameters. Detection of the Zeeman pattern in the plasma will be enhanced by the use of a dye laser, either using fluorescence or intracavity absorption (ICA). While the sensitivity of resonance fluorescence is well known, that of ICA is less well understood where short time scales are involved. Experiments to study the time/concentration trade-offs in ICA have been performed on lithium vapor, and show that the sensitivity of ICA is at least equal to that of fluorescence (assuming a dark background), under conditions of submillisecond detection times. ICA is also 103 times more sensitive than single-pass absorption under these conditions. Optimization of the atomic beam and integration with the dye laser systems are in progress.

Notes: The increase in the radial line integral of the electron density in the NBS theta pinch plasma due to the ionization of titanium impurity has been measured with the use of a He–Ne laser heterodyne quadrature interferometer. Titanium is injected as an impurity into the base gas of hydrogen with the use of a coaxial gun discharge with titanium electrodes. The abundance of the Ti X ion density in the plasma is deduced in each discharge from the measured increase in electron density by knowing the temporal charge state distribution of Ti ions obtained by spectroscopic methods.

Notes: A new method has been found to measure the ion temperature of a hot D–T plasma. The new method makes use of two new neutron dosimetry reactions, 54Fe(n,2n)53Fe and 27Al(n,2n)26Al. What makes these reactions special is that their threshold energies are quite close to the centroid of the energy distribution of the neutrons emitted from a D–T plasma. This makes their reaction yields sensitive to only the upper half of the neutron energy distribution and therefore sensitive to both changes in the centroid and the width of the neutron energy distribution. The sensitivity to the width of the neutron energy distribution allows one to measure the ion temperature. If the plasma is in thermal equilibrium the ion temperature can be calculated from the ratio of the yields of the 54Fe(n,2n)53Fe reaction to the 27Al(n, p)27Mg reaction or a similar nonsensitive reaction. No absolute measurements are needed. Using both of the new dosimetry reactions the asymmetry of the neutron energy distribution for nonequilibrium conditions (neutral beams) can be measured. The 54Fe(n,2n)53Fe reaction is sensitive enough to monitor a single shot in TFTR.

Notes: Time-resolved radial profile measurements of neutron source strength and Ti are required to determine ion energy balance especially during sawtooth oscillations and adiabatic compression. We describe the Tokamak Fusion Test Reactor (TFTR) vertical multichannel (10) collimator, two channels of which are now being completed. ZnS detectors will be used (Bicron 720) to reject γ rays and scattered neutrons, and operated in both count rate and current modes. The frequency response is limited by counting statistics and sampling times, but resolves compression times (approximately-equal-to)15–30 ms and Ti collapse times during sawtooth (approximately-equal-to)2–3 ms. The collimator consists of the 6-ft test cell floor plus ∼2-ft detector shield. Detector cross talk is calculated to be negligible. The dynamic range of the detectors is (approximately-greater-than)106, covering the range from ohmically heated deuterium (2.5 MeV neutron emissions of (approximately-greater-than)1013 s−1) to deuterium-beam heated tritium plasmas (14 MeV, (approximately-less-than)1019 s−1).

Notes: A high-efficiency, good resolution neutron spectrometer can obtain time-resolved fusion rates and mean ion energies from yield and Doppler width measurements of the 2.5 -MeV neutron peak. Gas scintillation spectrometers are capable of operating at high data rates. In order to obtain adequate energy resolution large light yields and uniform light collection over the active detector volume are required. We have measured the absolute light yield from He–Xe gas mixtures. With a high light collection efficiency the detected photon yield from the 3He(n, p)t reaction due to D–D neutrons will give adequate statistics for resolutions of a few percent. Calculations have been performed to model the detector optics in an effort to optimize the light yield and the uniformity of response. Measurements of detector resolution and time response have been made.

Notes: We discuss two approaches to obtain neutron detectors of very high temporal resolution. In the first approach, a uranium-coated cathode is used in a streak tube configuration. Secondary electrons accompanying the fission fragments from a neutron-uranium reaction are accelerated, focused through a pinhole, and streaked. Calculations show that 20-ps time resolution can be obtained. In the second approach, a uranium-coated cathode is integrated into a transmission line. State-of-the-art technology indicates that a time resolution of 20 ps can be obtained by gating the cathode with a fast electric pulse.

Notes: A 2 × 30-cm three-layer, microchannel-plate (MCP) assembly has been constructed with 120 anodes to collect electrons. It has a gain of up to 5 × 108 in the pulse counting mode. The device displays an unexpectedly high per-anode count rate. The original device had major problems: 5 × gain variation along its length and 150% FWHM/gain ratio. It is shown through a model distribution function that both effects can be due to the space charge limiting of pulses that cross the interstage gaps. One detector was rebuilt with greatly reduced interstage gaps and now displays 60% FWHM/gain and a 30% gain variation. This has significantly improved the pulse counting capability of the spectrometer.

Notes: A laser triggered photoconductive switch based microchannel-plate (MCP) gating system has been developed. The gating pulse provided to the MCP has a fall time on the order of 200 ps. Use of this system has resulted in increased signal-to-noise ratio on three MCP intensified x-ray spectrometers during recent x-ray experiments at the Novette laser facility. The x-ray signals of interest have a duration of approximately 300 ps while background in the same spectral region continues for several nanoseconds. As a result, signal-to-noise ratio is maximized by turning the MCP off just after the signals of interest are recorded. The MCP's are turned on by charging to approximately 1 kV with a slow rise-time (500 ns) pulse and rapidly gated off by a photoconductive switch connected to the MCP through transmission lines. Staggering the turnoff times of three microstrip lines across the MCP by 250 ps provides some time resolution. Details of the system, including pulse charging system, trigger beam delivery optics, and system diagnostics will be discussed.

Notes: A design study of a small-size neutral particle analyzer using a silicon surface barrier detector (SSD) is performed. The SSD is very sensitive to x rays or photons, so that a pair of 45° sector magnets to separate a reionized neutral from x rays and photons will be used for this analyzer. In order to examine the performance, the SSD was applied to measure the species ratio of the prototype neutral beam injector for JT-60. It was confirmed that the energy resolution was 12% at 40 keV and the linear relation between the incident energy of particles and the pulse height was held over the energy range from 16.7 to 100 keV. The species ratio measured by the SSD was in good agreement with that by the Doppler-shift spectrometer. The SSD has a sufficient capability for the energy analysis of fast neutrals.

Notes: We are constructing and testing a diagnostic instrument to investigate, in detail, ions emanating along magnetic field lines from the plasma region of the TMX-U tandem-mirror experiment. This analyzer (of Tokamak Fusion Test Reactor design) contains parallel electric and magnetic fields, which yield ion mass and energy spatial separation, respectively. A two-dimensional array of 128 copper collector plates detects the particles. The entering ion flux is first well collimated and then focused onto the detector plane during the 180° bending in the magnetic field. This instrument is designed to measure higher particle energies than the present gridded end-loss analyzers as well as determine the energy spectra more accurately. Tandem-mirror plasma parameters to be investigated with this analyzer include end-plug potential, average central-cell-ion energy, and plasma potential in the thermal barrier and nearby regions. We plan a time resolution of up to 2 kHz for each detector.

Notes: A proton space charge having multi-MeV kinetic energy was injected through a thin ground plane to extract electrons and produce a time-dependent autoneutralization space potential. An electron-emitting floating-potential resistive divider was used to measure the space potential during 20 ns of the proton current pulse. During this time, proton kinetic energy fell from 10.6 to 8.5 MeV and thus the space potential (taken as 1.09× the floating potential) fell from 5.8 to 4.6 kV.

Notes: A new method combining Li0-beam probing and spectroscopic techniques has been developed to measure local magnetic fields in a bumpy torus. A collimated thermal Li0 beam is injected into the plasma. The Zeeman pattern of the lithium resonance radiation (22S–22P, 6708 A(ring)) is observed with a Fabry–Perot interferometer. The strength of the local magnetic field is determined from the splitting between two π components of the 22S1/2–22P1/2 transition with the spatial resolution of about 7 mm. The magnetic fields from 2 to 4 kG were measured with accuracy of ±2%. This method is applicable to plasmas of a line-integrated electron density below 5×1012 cm−2.

Notes: The sequence of radiative cascades following charge transfer between energetic neutral atoms and C6+, N7+, and O8+ are readily observed in high-temperature plasma devices where the field of view of a vacuum spectrometer includes a neutral heating beam. These charge exchange excited (CXE) lines have well defined relative intensities that are not strongly dependent on the theory used to compute the primary excitation.1 They have been exploited in the ISX-B tokamak as an in situ method of measuring the relative response of a grazing incidence spectrometer from 102 to 1164 A(ring). Mixing of energy levels by external fields or by collisions are shown to have little effect on treating l as a good quantum number when computing the ratios of effective emission cross sections.

Notes: A directly heated lanthanum hexaboride tapered filament has been tested in a plasma generator. A uniform temperature distribution at 1820 K has been achieved. The heating and cooling power calculated from measured quantities are balanced. A maximum arc current of 80 A was obtained, limited only by the power supply and plasma generator. The corresponding hydrogen ion current density was 0.6 A/cm2 when the arc voltage was 80 V and the filament heater current was about 5 A. The filament was capable of emitting 100 A of current at an operating temperature of 1900 K. The estimated lifetime for this filament is 900 h.

Notes: Operation of a compact, corona-preionized, XeCl excimer laser producing average output power in excess of 1 W at pulse repetition frequencies of up to 750 Hz is reported. This device is simple in construction and utilizes all commercially available components.

Notes: A method has been developed for measuring the spatial profile of the output beam of an iodine laser at 1.315 μm, which requires only using two optical fibers, one for collecting a reference signal and the other for detecting the laser intensity at a given point of the wavefront. The precision is sufficient for laser engineering purposes.

Notes: We have developed a slit-scan flow cytometer for recording the transient, simultaneous light scattering and fluorescence waveforms from individual metaphase chromosomes flowing through a focused laser beam. The two waveforms are recorded on a single-memory waveform recorder by delaying one of the waveforms and switching between them. The light scattering and fluorescence waveforms contain complementary information on chromosome structure. The delay and switching electronics developed here may be useful in other contexts.

Notes: The primary diagnostic on PBX for ion temperature measurements is charge exchange recombination spectroscopy of low Z ions, wherein fast neutrals from the heating neutral beams excite spectral lines from highly excited states (n〉4) of hydrogenic O, C, and He via charge exchange collisions with the respective fully stripped ions. Since the neutral beams on PBX provide relatively low-velocity neutrals (i.e., D° beams at 44 keV), best signals are obtained using the near-UV lines of O7+ (e.g., n=8–7, 2976 A(ring)). Off-line analysis of the Doppler broadened and shifted line profiles includes nonlinear least-squares fitting to a model line profile, while a simplified on-line fast analysis code permits between-shot data analysis.

Notes: A Jarrell-Ash 0.27-m triple grating spectrometer with a high-speed intensified diode array detector has been used to perform time-resolved surveys of the visible emission (2200-7000 A(ring)) from the OHTE plasma. Using a 512 diode array, spectra are obtained every 516 μs during the shot. The spectral width of the scan is 150, 300, or 1200 A(ring) depending on the grating selected. Surveys at up to 500 kA for OHTE plasmas indicate a complete absence of metal emission lines with the graphite bead vacuum liner. In the 5200-A(ring) region, a clear iindow has been identified for optical bremsstrahlung measurements. Other details of the spectra will be discussed.

Notes: A grazing incidence spectrograph which operates in the EUV (40 to 350 A(ring)) that has multispectral, temporal, and spatial resolving capabilities is being constructed for plasma fusion diagnostics. The spectrograph achieves a simultaneous spectral coverage of 20 and 60 A(ring) when centered on 40 and 350 A(ring), respectively, with ∼1-A(ring) resolution. The detector consists of an image intensifier fiber optically coupled to 3 area array detectors (CCDS), which can be read out in 5 ms, thereby determining the time resolution of the instrument. The spatial resolution is accomplished by using the astigmatism inherent to a concave grating in grazing incidence, coupled with the pinhole camera effect produced by an entrance slit of limited height. The spectrograph can view ∼54 cm of plasma which is 2 m away from the entrance slit with 4- and 8-cm resolution at 350 and 40 A(ring), respectively. We will present the results of a feasibility study, the spectrograph design, and the results of the data reduction and interpretation codes which are under development.

Notes: K-shell spectroscopy is commonly used to diagnose laboratory plasmas, such as those produced in Z-pinches or laser targets. Neon-like systems are also of special interest because they produce the next simplest spectra, and because of applications to x-ray lasers. High-resolution spectroscopy and the acquisition of complex atomic physics data make it feasible to do diagnostics directly on neon-like systems. We present a model which calculates the 3-3 and 3-2 transitions of neon-like selenium. The ground state, n=3, and n=4 excited states are included explicitly; the n=5 through n=10 states are each lumped into one generic level. The model includes collisional and radiative transitions among these levels, and solves steady-state rate equations for the populations. The code includes graphics to plot line ratios and synthetic spectra. The model is analyzed for possible diagnostic use and is compared with experimental results.

Notes: Single shot, multipoint ion temperature and plasma rotation profiles have been routinely obtained on the Doublet III tokamak for 32 consecutive time slices with 20-ms resolution. A six-chord tangentially viewing spectroscopic diagnostic has been built to look at radiation emitted by fully stripped low-Z impurity ions (He, C, O) that have undergone charge exchange recombination with hydrogen atoms from a 3-MW heating beam. The main components of the instrument are a single monochromator for wavelength dispersion, a single image intensifier tube for photon gain, and a pair of 1024-element linear photodiode arrays for detection. A special arrangement of fiber optics allows simultaneous data acquisition from all chords without the use of scanning mirrors or other moving parts. Ion temperature profiles taken under a variety of plasma conditions will be presented.

Notes: Intensity and line profile measurements of the spectra of light hydrogenic ions which are excited by charge exchange reactions with fast neutral atoms are being widely used as diagnostics for fusion plasma research. This technique, which is referred to as charge exchange recombination spectroscopy, allows measurements of the densities of fully stripped impurity ions and particle transport coefficients with only minor uncertainties arising from atomic processes. The excitation of long-wavelength transitions in light ions such as He+, C5+, and O7+ allows relatively easy measurements of ion velocity distributions to determine ion temperatures and plasma rotation velocities. Among its advantages for such measurements are the facts that fiber-optic coupling between a remote spectrometer and the immediate reactor environment is possible in many cases, the measurement is localized by the intersection region of a neutral beamline and viewing sightline, and intrinsic ions can be used so that injection of potentially perturbing impurities can be avoided. A particularly challenging application of this technique lies in the diagnosis of alpha particles expected to be produced in the present generation of Q≈1 tokamak experiments.

Notes: A 20-channel interferometer has been developed which utilizes a linear, one-dimensional microbolometer array to obtain single-shot density profiles from the UCLA Microtor tokamak plasma. The interferometer has been used to study time-dependent phenomena in the plasma density profile. Observations of the sawtooth instability clearly show the growth of the m=0 mode from a localized oscillation (r=1 cm) on axis to an oscillation of the entire plasma. Also, measurements during the initial startup phase of the discharge show evidence of hollow density profiles. In addition, a simultaneous measurement of the poloidal magnetic field has been developed which provides 20 channels of polarimetry. Interferometry and polarimetry both use the same imaging system and the spatial resolution of both measurements has been tested using plastic and crystal-quartz test objects. The signal-to-noise ratio for the polarimeter has also proved adequate for the expected Faraday rotation angle (αmax=7°, Ip=70 kA, n=5×1013 cm−3).

Notes: Long wavelength density fluctuations can be observed by scattering even with a probe beam of much shorter wavelength provided the scattering angle is small enough. This paper is concerned with experiments in which the scattering angle is comparable with the probe beam divergence so the scattered and incident radiation never achieve spatial separation. Under these circumstances, the role of diffraction is preeminent and Fourier optics methods are used to describe the propagation of the beam, which is taken to be TEM00 mode Gaussian. Interaction between the probe beam and the plasma disturbance is described by refraction and no appeal is made to explicit scattering theory. Analysis of the effect of a monochromatic wave disturbance confined to a plane perpendicular to the probe beam (a plane grating in effect) reveals oscillations at the wave frequency induced on the probe with an intensity varying over the beam profile in a regular pattern symmetric about the beam axis. Detail of the pattern depends on the wavelength of the disturbance, its direction, and its axial position relative to a local beam waist. These oscillations are readily identified as due to radiation scattered by the plasma wave into diffraction orders, beating with the unperturbed part of the beam. Indeed, it can be shown1 that Fourier optics plus refraction produce almost the same result as conventional scattering theory,2 the small discrepancy being traceable to the neglect in the latter of incident beam wavefront curvature. The results of the two approaches coincide in the Fraunhofer limit. Computations of this sort have been confirmed by experiments using transducer-driven waves in air3 and by plasma experiments where the same regular patterns are observed from spontaneous plasma waves.4,5 Calculation suggests and experiments have demonstrated6 that additional information, such as the absolute direction of wave propagation, can be deduced from phase, measured with a multichannel detector array.Asymmetric profiles are frequently encountered in far forward scattering experiments in plasma, and they are attributed either to (1) the volume effect, that is, the finite width of a plasma wave, or (2) a pair of counter-propagating waves, such as poloidal waves in a torus met twice by a probe beam traversing a minor diameter. The first explanation rests on the difference between the multiple order scattering of a two-dimensional grating (Raman–Nath) and the single-order scattering of a three-dimensional crystal (Bragg). In a regime intermediate between these extremes, both +1 and −1 orders are present, but of unequal intensity, therefore giving rise to asymmetry in the beam profile. The Fourier optics treatment can be extended to describe a wave of arbitrary interaction length L, and a controlling parameter Q=κ2L/k (κ and k being wave numbers of the plasma wave and the probe radiation, respectively) which is (very-much-less-than)1 for Raman–Nath and (very-much-greater-than)1 for Bragg, determines the precise regime that prevails.7 Calculations describing the counter-propagating waves model have been performed and verified experimentally, again using transducer-driven waves in air.8 Profiles based on this model are currently providing best fits to data recently recorded from tokamak plasmas in TOSCA. A preliminary inspection of the results of these measurements reveals, from the orientation of the beam profile pattern, predominantly poloidal waves. Their maximum intensity is near 100 kHz and they fall away towards higher frequencies as ν−2.5. Evidence for coherent gross modes at lower frequencies is also seen. Wave numbers are in the range 1 cm−1〈κ⊥〈30 cm−1, bracketing the neighborhood where κ⊥ρi∼1. The strength of the relative density fluctuation ñe/n¯e of a few per cent is consistent with diffusion coefficients D⊥∼104 cm2 s−1, and there is evidence for inverse correlation between ñe/n¯e and confinement time τE.

Notes: The generalized H theorem of Boltzmann for a multiple gas mixture is written as the law of increase of entropy for small deviations from equilibrium by largely following a method first introduced by Prigogine. It is shown that the local rate of entropy production for such a mixture is a quadratic form of the generalized forces with the kinetic coefficients satisfying Onsager's principle and all the pertaining properties. The classical expression for the entropy flux of a multiple gas mixture is also derived by this method.

Notes: A Monte Carlo simulation of a solution of 1,2-dichloroethane in methyl chloride has been performed in the NPT ensemble. The solution serves as a model to study the differential solvation of the gauche and anti conformers of a polar solute in a polar solvent. The expected conformational change induced by the solvation in favor of the gauche conformer is well reproduced in the simulation. To explain it, the r−12, r−6, and r−1 contributions of the intermolecular potential functions (TIPS format) to the solute–solvent and solvent–solvent energies have been recorded during the simulation. The mean r−1 contributions are computed to be less than one-third of the sum of the r−12 and r−6 contributions; however, the computed difference of 2±0.5 kcal/mol between the gauche and anti solute–solvent mean energy is totally accounted for by the difference in the r−1 contributions. The analysis of the r−1 energy pair distribution shows that the main part of this difference comes from changes in the interaction of the solute with the nearest solvent neighbors. The gauche conformer shows at one and the same time more attractive and more repulsive interactions than the anti conformer. When the pure liquid, the anti and gauche solutions are compared, it is found that the solvent molecules experience, on the mean, nearly the same solvent–solvent interactions in the three cases.

Notes: An analysis of internal particle equilibrium in J. Chem. Phys. 81, 2489 (1984) is generalized by means of Lagrange's method of undetermined multipliers to show that a one-component crystalline particle of fixed size and shape is at equilibrium at constant temperature and pressure when the chemical potentials of molecular species, μi, μj, ..., and of vacancies μvi, μvj, ..., for sites i, j,... of different characteristic bond environments fit the relation μi−μvi=μj−μvj =⋅⋅⋅ . The chemical potential differences between molecular species and vacancies is shown to be the chemical potential for the component. The influence of surfaces on vapor pressures is predicted by setting the chemical potential of the component in the particle equal to that of its vapor. The predicted effects of surfaces are larger than those of classical theory but are in reasonable agreement with measurements for liquid drops.

Notes: Time autocorrelation and memory functions for segment orientation are derived for a general diffusion model of a linear polymer chain in solution. Exact analytical results for the orientation and alignment memories P1(t), P2(t) (averages of the first and second order Legendre polynomial of the cosine of the angle of rotation of a segment) are obtained as a function of the time autocorrelation function M1(t) of the segment vector. These expressions significantly depart from the results for the diffusional rotation of a sphere: P1=M1, P2=M31.

Notes: The infrared absorption spectrum of the ν4 fundamental band of (NO)2 has been recorded at 0.3 cm−1 resolution in a cell cooled down to 110 K. From the band contour analysis and comparison with a simulated spectrum accurate values of the rotational constants in the ν4 state are derived, showing a reduction of the van der Waals bond on vibrational excitation. Absorption measurements performed using the various lines emitted by an isotopic CO laser suggest an unresolved rotational fine structure. A lower limit of the time for energy redistribution of 50 to 100 ps is proposed. Also, infrared photopredissociation of (NO)2 has been directly observed in a crossed laser-molecular beam experiment using bolometric detection of the beam attenuation. An upper limit of the dissociation lifetime can be set to 10−3 s.

Notes: The effect of lifetime-vibrational interference in the carbon and oxygen ultra-soft x-ray emission (USX) spectra of CO is theoretically analyzed. Computed spectral functions are compared with high-resolution experimental recordings. A time dependent Franck–Condon formalism is employed in the theoretical treatment of the interference. The electronic states involved in the analysis are determined by means of large scale MCSCF and CI calculations and the nuclear wave functions are solved for numerically. Certain features of the spectra are found to be sensitively dependent on the interference and can hence be used as a monitor for the core state lifetime.

Notes: Explicit analytical expressions for the rate constants have been derived which take into account the distortion of the Maxwellian caused by chemical reactions. In contrast to simple systems involving a single chemical reaction, where the rate constant is usually not affected much by the distortion, the analytical expressions show how in complex reaction systems the frequency factors of the rate constants for the reactions with the higher threshold energies may be substantially less than the Arrhenius values. The validity of the analytical expressions is verified by comparison with exact numerical solutions.

Notes: The Ar++CO→CO+(v=0–6)+Ar charge transfer reaction is studied at thermal energy in a flowing afterglow and the vibrational state distribution is determined by laser-induced fluorescence on the CO+(A 2Π–X2Σ+) bands. The nascent vibrational state distribution is (0.06±0.04)v=0 @B:(0.07±0.02)v=1 @B:(0.09±0.02)v=2 @B:(0.15±0.03)v=3 @B:(0.21±0.03)v=4@B: (0.27±0.02)v=5 @B:(0.15±0.02)v=6. The rate constant for CO+(v=4) deactivation by CO is measured to be 6.0±2.5×10−10 cm3 s−1; the similarity of this rate constant to that for CO+(v=1) deactivation by CO (5.0±2.0×10−10 cm3 s−1) suggests that vibrational deactivation proceeds by a charge transfer mechanism. The Ar++CO reaction is described as proceeding via a bent ArCO+ intermediate that forms in a side-on attack. Vibrational excitation may then result from delocalization of the bonding electron density of CO and the corresponding dynamical changes in the CO bond length in the intermediate.

Notes: For one-electron diatomic systems, an iterative solution of the momentum-space Schrödinger equation is examined using the Fock transformation which enables us to expand the kernel of the integral equation by the four-dimensional spherical harmonics. Starting from the united atom (UA) and simple LCAO approximations, first iterated solutions are derived and their properties are analyzed. The corresponding approximate energy eigenvalues are also obtained as a function of the internuclear distance R. The result from the LCAO starting function is found to be reliable semiquantitatively: in the range of 0≤R≤20, the maximum errors of the ground-state electronic energy are 4.7% and 1.7%, respectively, for the H+2 and HeH2+ systems, when compared with the exact values.

Notes: As previously shown [M. Levy and J. P. Perdew, Phys. Rev. A (in press)], the customary Hohenberg–Kohn density functional, based on the universal functional F[ ρ], does not exhibit naively expected scaling properties. Namely, if ρλ=λ3ρ(λr) is the scaled density corresponding to ρ(r), the expected scaling, not satisfied, is T[ρλ]=λ2T[ρ] and V[ρλ]=λV[ρ], where T and V are the kinetic and potential energy components. By defining a new functional of ρ and λ, F[ ρ, λ], it is now shown how the naive scaling can be preserved. The definition is F[ρ(r), λ]=〈λ3N/2 Φminρλ (λr1... λrN)|Tˆ(r1...rN) +Vee(r1...rN)| λ3N/2Φminρλ(λr1...λrN)〉, where λ3N/2 Φminρλ(λr1... λrN) is that antisymmetric function Φ which yields ρλ(r)=λ3ρ(λr) and simultaneously minimizes 〈Φ|Tˆ(r1...rN) +λVee(r1...rN)|Φ〉. The corresponding variational principle is EvG.S.=Infλ, ρ(r){∫ drv(r) ρλ(r)+λ2T[ ρ(r)] +λVee[ ρ(r)]}, where EvG.S. is the ground-state energy for potential v(r). One is thus allowed to satisfy the virial theorem by optimum scaling just as if the naive scaling relations were correct for F[ ρ].

Notes: Ab initio SCF and CI calculations are reported for the ground state and low-lying excited electronic states of CuO (i.e., within ∼20×103 cm−1 of the X˜ 2Π ground state), employing an ab initio effective potential for the Cu atomic core (1s–3p), and including comparisons of several atomic orbital basis sets. The calculated bond lengths, energy separation, and population analyses for the lowest two electronic states, X˜ 2Π and Y 2Σ+ [corresponding roughly to Cu+ (3d10) and O− (2p5), where the 2p oxygen hole is, repectively, 2pπ and 2pσ], do not vary appreciably among the basis sets tested (minimal and split valence bases on Cu, and a split valence basis on oxygen, with and without d-polarization functions and diffuse p functions on oxygen) and are in reasonable agreement with previous experimental and theoretical estimates. Most of the remaining excited states of CuO below ∼20×103 cm−1 may be rationalized in terms of atomic-like excitations originating from theX˜ 2Π ground state: 3d(Cu) → 4s(Cu) and 3d(Cu) → 2 pπ (O) (the latter formally corresponds to Cu2+O2−, though covalent 2p‘gs–4s bonding reduces the charge to ∼Cu+O−). Close agreement (rms deviation of ∼103 cm−1) is obtained between calculated (CI) and observed adiabatic transition energies for ten Σ, Π, and Δ doublet excited states (relative to the X˜ 2Π state), after the calculated excitation energies are reduced by ∼5×103 cm−1, a term which corrects primarily for limitations in the Cu atom basis set, and whose magnitude can be obtained both in terms of calculated and observed atomic quantities and by direct least-squares fitting of calculated and observed CuO transition energies. The calculations yield the first comprehensive assignment of Kronig symmetry (±) for the observed 2Σ states (δ 2Σ−, A 2Σ−, A′ 2Σ+, and G 2Σ+) and one which is consistent with recent analyses of experimental data. The extent of specific molecular correlation effects is analyzed, and found to be important in the assignment of several of the observed transitions. The CI mixing of different principal configurations may be significant for states involving the "Cu2+O2−'' configuration (as also suggested in previous studies), and the assignments based on the present CI results for these states are only tentative.

Notes: The model of a classical one-component plasma in the vicinity of a metallic hard wall is shown to be a limiting case of an ideally polarizable interface.

Notes: Higher-order semiclassical phase integral methods are applied to the determination of rigid asymmetric rotor eigenlevels from the eigenvalues of Lamé's equation. The method yields accurate eigenvalues for moderate J, J larger than ten, but is especially valuable for very large J because the accuracy of the method improves with increasing J with practically no increase in the computational cost per eigenlevel.

Notes: The lattice energy surface of crystalline pyrene, as a model of layered aromatic structures, is analyzed numerically as a function of molecular reorientation. Cooperative effects are simulated by concerted rotation of neighboring molecules and the preservation of translational symmetry. The potential energy surface calculated by intermolecular atom–atom potentials corresponds to those of more rigid binary units like metallocenes and π-molecular compounds of the charge-transfer type. Common features in physical properties and low-temperature phase transitions with crystal fracture, observed for all these compounds, are readily accounted for in terms of domain disorder, calculated for the room-temperature structures. Because of the high molecular symmetry, rotationally disordered arrangements 60° apart are difficult to distinguish crystallographically and the predicted order–disorder transition for pyrene has only been characterized spectroscopically.

Notes: Calculations of diffusion constants for rigid molecules of arbitrary shape are often based on hydrodynamic interactions between freely moving spheres. Molecules can be modeled as collections of spheres, and the interactions are approximated as pairwise additive. Singularities previously associated with nearly linear geometries and with geometries dominated by a large central element can be avoided by including torque-angular velocity and torque-velocity coupling, as well as the usual force-velocity coupling between spheres. I provide explicit formulas for these couplings for both nonoverlapping and overlapping spheres, and also show how to include effects of one sphere on the self-diffusion of another. This formulation is incorporated in an algorithm that involves neither Gauss–Seidel iterations nor direct inversion of a large matrix.

Notes: Molecular dynamics simulation was performed on barium meta-fluorozirconate, BaZrF6, glass by using the Born–Mayer–Huggins pair potential. The cumulative F coordination numbers and the F correlation functions of Zr and Ba ions revealed that, in the simulated BaZrF6 glass, the number and the mean distance of the nearest neighboring F were about eight at 2.12 A(ring) for Zr ions and about ten at 2.75 A(ring) for Ba ions. This is consistent with the previous x-ray diffraction result of the glass. A little uncertainty of the cumulative coordination number, however, may admit the presence of small amounts of seven F-coordinated Zr, as deduced in the previous studies. On the other hand, the Zr–Zr pair correlation function disclosed that the F polyhedra of Zr are linked by sharing the edges and/or the corners, the edge-sharing/corner-sharing ratio in number being approximately 3:2. The glass transition temperature and the Zr–F symmetric stretching vibration spectrum generated for the simulated glass were favorably compared with the observed ones. The mean square displacements and the trajectories of F, Zr, and Ba ions clearly showed that fluorozirconate glasses might exhibit fluoride-ion conduction. The present successful simulation indicates the validity of the calculation procedure, especially of the evaluation of the repulsive parameters of Zr and Ba ions. Based on the previous Raman spectroscopy, differential thermal analysis, and x-ray diffraction studies and the present study, the overall structure of BaZrF6 may be described as follows: In BaZrF6 glass, most of Zr ions are dodecahedrally coordinated by eight F and a small amount of them, monocapped-trigonal prismatically by seven F. These polyhedra connect with each other by sharing the edges and/or corners to build up three-dimensional fluorozirconate network. Ba ions are present as the modifier ions in the interstices of the fluorozirconate network, being surrounded on the average by ten F.

Notes: Strontium nitrite monohydrate [Sr(NO2)2⋅H2O] has been studied at 294, 100, and 20 K by neutron diffraction. Integrated intensities of 2958 (294 K), 4239 (100 K), and 2154 (20 K) reflections were measured at the Brookhaven National Laboratory high flux beam reactor, resulting in 2068 (294 K), 2030 (100 K), and 1934 (20 K) independent structure factors. Structural refinement in monoclinic space group P21 led to R(F)=0.029 (294 K), 0.019 (100 K), and 0.034 (20 K). Lattice constants at 295 K are a=12.5831(4), b=8.94941(15), c=4.4860(2) A(ring), β=99.111(4)°; at 100 K, a=12.539(2), b=8.909(1), c=4.475(1) A(ring), β=99.086(20)°; and at 20 K, a=12.542(2), b=8.901(1), c=4.472(1) A(ring), β=99.030(20)°.The expansivity of all four lattice parameters is nonlinear, with α1=32.8×10−6 K−1, β1=76×10−9 K−2; α2=31.6×10−6 K−1, β2=44×10−9 K−2; α3=15.6×10−6 K−1, β3=15×10−9 K−2; α4=−2.8×10−6 K−1, β4=−21×10−9 K−2 for αTi =α295i [1+αiΔT+βi(ΔT)2], ΔT=T−295 K. The mean-square amplitude of Sr varies linearly with temperature between 20 and 294 K, and extrapolates to a zero-point value of 0.0010(2) A(ring)2. A survey shows that atoms with masses greater than about 80 have similar zero-point amplitudes which increase toward the maximum exhibited by H, with its zero-point amplitude of about 0.023 A(ring)2, as the atomic mass decreases. The coordination (9 and 10) of the two independent Sr2+ ions remains unchanged with temperature: the coordination shell radius decreases on average by 0.012 A(ring) from 294 to 20 K. Comparison with previous x-ray structural results on Sr(NO2)2⋅H2O shows the latter are influenced by scattering from the nitrogen atom lone-electron pair. Small but significant differences in N–O distances among the four independent NO−2 ions are detected at 294 K (0.020 A(ring)) and at 20 K (0.017 A(ring)). The mean N–O distance at 20 K for all four ions is identical at 1.253–1.254 A(ring). The maximum atomic displacement between 294 and 20 K is that by a nitrite ion oxygen, of 0.045 A(ring).

Notes: A calorimetric study of Cd(ClO4)2 ⋅ 6H2O from 20 to 345 K shows three phase transformations at 124.8, 238.45, and 271.62 K. Infrared spectra indicate that the low-temperature structure (below 124.8 K) contains one type of [Cd(OH2)6]2+, of symmetry C3 or C3v, and two types of ClO−4, both strongly distorted from tetrahedral symmetry. There appears to be some disorder in this phase. The sharp transition at 124.8 K leads to major spectral changes, which indicate that hydrogen bonding is weakened, distortion of the perchlorate ions is diminished, and [Cd(OH2)6]2+ symmetry is increased to D3d. The more gradual phase transition at 238.45 K involves no observable infrared spectroscopic changes and may correspond to an increase in ClO−4 disorder. The very sharp transition at 271.62 K involves only very minor changes in the infrared spectra and may involve an increased disorder of the [Cd(OH2)6]2+ units.

Notes: A Wiener integral model for stiff polymer chains is developed following the approach of Bixon and Zwanzig. The model is mathematically tractable yet retains the general physics of the crossover between a flexible chain and a rod. Previous approaches to this problem are reviewed and compared to this model in the context of their applicability to the study of nonideal stiff polymer chains.