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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1974-1976 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Three fast-scanning heterodyne receivers, swept between 75 and 110, 110 and 170, and 170 and 210 GHz have measured electron cyclotron emission on the horizontal midplane of the tokamak fusion test reactor (TFTR) plasma. A second-harmonic microwave mixer in the 170–210-GHz receiver allows the use of a 75–110-GHz backward wave oscillator as a swept local oscillator. Electron temperature profile evolution data with a time resolution of 2 ms and a profile acquisition rate of 250 Hz will be presented for gas-fueled and pellet-fueled ohmic and neutral beam heated plasmas with toroidal fields up to 5.2 T. Recent results from a new swept-mode absolute calibration technique which can improve the accuracy and data collection efficiency during in situ calibration will also be presented.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1538-1543 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Most microwave scattering measurements in tokamaks are done with the polarization of the incident radiation approximately parallel to the toroidal field (ordinary mode) and at a frequency which is sufficiently above the plasma frequency ωpe that refraction effects are small. However, as confinement devices get hotter, drift wave turbulence is expected to occur at longer wavelengths. In order to observe density fluctuations associated with these phenomena with good spatial resolution, the ideal probe wavelength λi is near or beyond the ordinary cutoff at λi=2πc/ωpe. As a result, we have considered the propagation and scattering of the extraordinary (X) mode where the incident polarization is nearly perpendicular to the confining fields and where the cutoff density is significantly higher than in the ordinary mode. We have modeled the propagation of the X mode in a tokamak field geometry and shown that the polarization typically remains perpendicular to the local field along the ray path, simplifying the interpretation of the scattering results. We have calculated the single-particle cross section and give a formula for X-to-X-mode scattering. An apparatus for carrying out these measurements on TFTR at λi=0.5 cm will be described. For BT=5.0 T, the X-mode cutoff density in this case is 1.5×1014 cm−3, so that a major part of the operating density range can be studied by this technique.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1565-1567 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A 200-kW, ∼60-GHz gyrotron will be used on TFTR during D–T operation for collective Thomson scattering diagnostics of confined alpha-particle velocity distribution and density. Scattering angles of up to 120° are under consideration using x-mode propagation to increase the density cutoff limit. Useful signal-to-noise ratios will be possible in plasmas where ne(approximately-greater-than)5×1013 cm−3, nα(approximately-greater-than)2×1011 cm−3, and the background emission is (approximately-less-than)30 eV equivalent blackbody level.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1593-1598 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Measurements of the superthermal electron distribution can be made by observing the polarized electron cyclotron emission. The emission is viewed along a constant magnetic field surface. This simplifies the resonance condition and gives a direct correlation between emission frequency and kinetic energy of the emitting electron. A transformation technique is formulated which determines the anisotropy of the distribution and number density of superthermals at each energy measured. The steady-state distribution during lower hybrid current drive and examples of the superthermal dynamics as the runaway condition is varied are presented for discharges in the PLT tokamak.
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  • 5
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Most magnetically confined plasma devices cannot take advantage of standard electron cyclotron emission (ECE) diagnostics to measure temperature. They either operate at high density relative to their magnetic field (e.g., ωp(very-much-greater-than)Ωc in spherical tokamaks) or they do not have sufficient density and temperature to reach the blackbody condition (τ〉2). The standard ECE technique measures the electromagnetic waves emanating from the plasma. Here we propose to measure electron Bernstein waves (EBW) to ascertain the local electron temperature in these plasmas. The optical thickness of EBW is extremely high because it is an electrostatic wave with a large ki. For example, the National Spherical Torus Experiment (NSTX) will have an optical thickness τ(approximate)3000 and CDX-U will have τ(approximate)300. One can reach the blackbody condition with a plasma density (approximate)1011 cm−3 and Te(approximate)1 eV. This makes it attractive to most plasma devices. The serious issue with using EBW is the wave accessibility for the emission measurement. Simple accessibility arguments indicate the wave may be accessible by either direct coupling or mode conversion through an extremely narrow layer ((approximate)1–2 mm). EBW experiments on the Current Drive Experiment-Upgrade (CDX-U) will test the accessibility properties of the spherical tokamak configuration. © 1999 American Institute of Physics.
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  • 6
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mission of the National Spherical Torus Experiment (NSTX) is to extend the understanding of toroidal physics to low aspect ratio (R/a(similar, equals)1.25) in low collisionality regimes. NSTX is designed to operate with up to 6 MW of high harmonic fast wave (HHFW) heating and current drive, 5 MW of neutral beam injection (NBI) and co-axial helicity injection (CHI) for noninductive startup. Initial experiments focused on establishing conditions that will allow NSTX to achieve its aims of simultaneous high βt and high-bootstrap current fraction, and to develop methods for noninductive operation, which will be necessary for Spherical Torus power plants. Ohmic discharges with plasma currents up to 1 MA and with a range of shapes and configurations were produced. Density limits in deuterium and helium reached 80% and 120% of the Greenwald limit, respectively. Significant electron heating was observed with up to 2.3 MW of HHFW. Up to 270 kA of toroidal current for up to 200 ms was produced noninductively using CHI. Initial NBI experiments were carried out with up to two beam sources (3.2 MW). Plasmas with stored energies of up to 140 kJ and βt=21% were produced. © 2001 American Institute of Physics.
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  • 7
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Perturbative experiments on the Tokamak Fusion Test Reactor [Phys. Plasmas 4, 1736 (1997)] (TFTR) have investigated transport in reverse shear plasmas. On TFTR, reverse magnetic shear plasmas bifurcate into two states with different transport properties: reverse shear (RS) and enhanced reverse shear (ERS) with improved core confinement. Measurements of the 14 MeV t(d,n)α neutrons and charge-exchange recombination radiation spectra are used to infer the trace tritium and helium profiles, respectively. The profile evolution indicate the formation of core particle transport barriers in ERS plasmas. The transport barrier is manifested by an order-of-magnitude reduction in the particle diffusivity (DT,DHe) and a smaller reduction in the pinch within the reverse shear region. The low diffusivities are consistent with neoclassical predictions. Furthermore, DT and DHe(approximate)χeff, the effective thermal diffusivity. Although the measured coefficients imply no helium ash accumulation, the situation is uncertain in a reactor due to unknown χeff scaling.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 4065-4073 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that radial localization of optically thin electron cyclotron emission from superthermal electrons can be imposed by observation of emission upshifted from the thermal cyclotron resonance in the horizontal midplane of a tokamak. A new and unique diagnostic has been proposed and operated to make radially localized measurements of superthermal electrons during lower hybrid current drive on the Princeton Beta Experiment-Modified (PBX-M) tokamak [Bernabei, et al., Phys. Fluids B 5, 2562 (1993)]. The superthermal electron density profile as well as moments of the electron energy distribution as a function of radius are measured during lower hybrid current drive. The time evolution of these measurements after the lower hybrid power is turned off are given and the observed behavior reflects the collisional isotropization of the energy distribution and radial diffusion of the spatial profile. © 1996 American Institute of Physics.
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  • 9
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High or enhanced confinement (H-mode) plasmas have been obtained for the first time with nearly equal concentrations of deuterium and tritium in high-temperature, high poloidal beta plasmas in the Tokamak Fusion Test Reactor (TFTR) [McGuire, Phys. Plasmas 2, 2176 (1995)]. Tritium fueling was provided mainly through high-power neutral beam injection (NBI) with powers up to 31 MW and beam energies of 90–110 keV. A transition to a circular limiter H-mode configuration has been obtained, following a programmed rapid decrease of the plasma current. Isotope effects, due to the presence of tritium, led to different behavior for deuterium–deuterium (DD) and deuterium–tritium (DT) H-modes relative to confinement, edge localized magnetohydrodynamic modes (ELMs), and ELM effects on fusion products. However, the threshold power for the H-mode transition was the same in DD and DT. Some of the highest values of the global energy confinement time, τE, have been achieved on TFTR during the ELM-free phase of DT H-mode plasmas. Enhancements of τE greater than four times the L-mode have been attained. © 1995 American Institute of Physics.
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  • 10
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Tokamak Fusion Test Reactor (TFTR) (R. J. Hawryluk, to be published in Rev. Mod. Phys.) experiments on high-temperature plasmas, that culminated in the study of deuterium–tritium D–T plasmas containing significant populations of energetic alpha particles, spanned over two decades from conception to completion. During the design of TFTR, the key physics issues were magnetohydrodynamic (MHD) equilibrium and stability, plasma energy transport, impurity effects, and plasma reactivity. Energetic particle physics was given less attention during this phase because, in part, of the necessity to address the issues that would create the conditions for the study of energetic particles and also the lack of diagnostics to study the energetic particles in detail. The worldwide tokamak program including the contributions from TFTR made substantial progress during the past two decades in addressing the fundamental issues affecting the performance of high-temperature plasmas and the behavior of energetic particles. The progress has been the result of the construction of new facilities, which enabled the production of high-temperature well-confined plasmas, development of sophisticated diagnostic techniques to study both the background plasma and the resulting energetic fusion products, and computational techniques to both interpret the experimental results and to predict the outcome of experiments. © 1998 American Institute of Physics.
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