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  • 1
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The first experiments utilizing high-power radio waves in the ion cyclotron range of frequencies to heat deuterium–tritium (D–T) plasmas have been completed on the Tokamak Fusion Test Reactor [Fusion Technol. 21, 13 (1992)]. Results from the initial series of experiments have demonstrated efficient core second harmonic tritium (2ΩT) heating in parameter regimes approaching those anticipated for the International Thermonuclear Experimental Reactor [D. E. Post, Plasma Physics and Controlled Nuclear Fusion Research, Proceedings of the 13th International Conference, Washington, DC, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 239]. Observations are consistent with modeling predictions for these plasmas. Efficient electron heating via mode conversion of fast waves to ion Bernstein waves has been observed in D–T, deuterium-deuterium (D–D), and deuterium–helium-4 (D–4He) plasmas with high concentrations of minority helium-3 (3He) (n3He/ne(approximately-greater-than)10%). Mode conversion current drive in D–T plasmas was simulated with experiments conducted in D–3He–4He plasmas. Results show a directed propagation of the mode converted ion Bernstein waves, in correlation with the antenna phasing. © 1995 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2414-2422 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The reflection of electromagnetic waves from a plasma cutoff layer has been used to examine properties of density fluctuations in fusion plasmas. In this paper an exact one-dimensional model is used to show the relation between changes in the phase of the reflected wave and the location, magnitude, and correlation properties of density fluctuations. For long-wavelength density perturbations the reflected phase can be simply related to the amplitude of fluctuating density and the density scale length, Ln, near the cutoff layer. However, the phase response falls substantially as the fluctuation wavelength approaches the free space wavelength of the reflected wave, λ0, and the location of the maximum response moves out in front of the cutoff layer following the wave matching condition kΛ= 2k ≈ 2η(x)k0. Thus, a measurement of the reflected phase is strongly weighted to and localized for phenomena whose wavelength is longer than the characteristic scale (λ20Ln)1/3. Because of this weighting and because the region of maximum response moves away from the cutoff layer for short-wavelength fluctuations, there is also a limitation in any estimate of the density correlation length from the reflected phase. The correlation of phases between several different probe frequencies can be used to estimate a density correlation length no less than about four times the free space probe wavelength.
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  • 3
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Toroidal Alfvén eigenmodes (TAE) were excited by the energetic neutral beam ions tangentially injected into plasmas at low magnetic field in the Tokamak Fusion Test Reactor (TFTR) [Proceedings of the 11th International Conference on Plasma Physics and Controlled Fusion Research (IAEA, Vienna, 1987), Vol. 1, p. 51]. The injection velocities were comparable to the Alfvén speed. The modes were identified by measurements from Mirnov coils and beam emission spectroscopy (BES). TAE modes appear in bursts whose repetition rate increases with beam power. The neutron emission rate exhibits sawtoothlike behavior and the crashes always coincide with TAE bursts. This indicates ejection of fast ions from the plasma until these modes are stabilized. The dynamics of growth and stabilization were investigated at various plasma currents and magnetic fields. The results indicate that the instability can effectively clamp the number of energetic ions in the plasmas. The observed instability threshold is discussed in light of recent theories. In addition to these TAE modes, intermittent oscillations at three times the fundamental TAE frequency were observed by Mirnov coils, but no corresponding signal was found in BES. It appears that these high-frequency oscillations do not have a direct effect on the plasma neutron source strength.
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  • 4
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ohmic plasma size scans have been carried out in the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)] to measure the influence of the major radius upon energy confinement. The major radius, minor radius, and aspect ratio were varied over wide ranges (R=2.08–3.2 m, a=0.4–0.9 m, and R/a=2.9–8.0) at constant qc. The energy confinement determined from kinetic diagnostics varies strongly with major radius. The data set is less well suited to determine minor radius scaling, but it appears to be distinctly weaker than the major radius scaling. The anomaly in ion thermal conductivity over neoclassical predictions appears to decline with increasing aspect ratio, which is a better ordering parameter for the magnitude of the anomaly than either the minor radius or the major radius. © 1994 American Institute of Physics.
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  • 5
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The final hardware modifications for tritium operation have been completed for the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. These activities include preparation of the tritium gas handling system, installation of additional neutron shielding, conversion of the toroidal field coil cooling system from water to a FluorinertTM system, modification of the vacuum system to handle tritium, preparation, and testing of the neutral beam system for tritium operation and a final deuterium–deuterium (D–D) run to simulate expected deuterium–tritium (D–T) operation. Testing of the tritium system with low concentration tritium has successfully begun. Simulation of trace and high power D–T experiments using D–D have been performed. The physics objectives of D–T operation are production of ≈10 MW of fusion power, evaluation of confinement, and heating in deuterium–tritium plasmas, evaluation of α-particle heating of electrons, and collective effects driven by alpha particles and testing of diagnostics for confined α particles. Experimental results and theoretical modeling in support of the D–T experiments are reviewed.
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A motional Stark effect (MSE) instrument to measure q(r) using the Torus Experiment for Technology (TEXT) neutral beam on the Alcator C-Mod tokamak has been designed and installed. The neutral beam is on the midplane, aimed radially, and designed to operate in hydrogen at 50 keV. The MSE optics view the outer half of the plasma −0.3〈(R−R0)/a〈1.05. This geometry results in a spatial resolution of 1 (edge)–3 (center) cm from a beam apertured horizontally to 2 cm. Estimates of the signal levels indicate for Hα that photoelectron statistical errors in the measurement of Bθ/Bφ can be less than 0.2% for ne0〈2.0×1014 cm−3 similar to other MSE instruments. The collection optics reside within the vacuum chamber reflecting and imaging the neutral beam through a vacuum window in the neutral beam port. The optics are designed so that beam emission spectroscopy can be carried out simultaneously with MSE measurements. Optical signals are transmitted to remote detectors by fiber optics. Low Verdet glass and dielectric mirrors are used to minimize polarization changes caused by the ambient fields. Polarization is measured by conventional techniques using photoelastic modulators, optical filters, and photomultipliers. © 2001 American Institute of Physics.
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  • 7
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A design for a tangential array interferometer for C-Mod operating at 1.06 and 0.53 μm is presented. This is a special type of two color interferometer in which a Nd:YAG laser is frequency doubled in a nonlinear crystal. Because the doubling efficiency is imperfect, two frequencies propagate collinearly through the plasma after which the 1.06 μm ray is doubled again mixing in the optical domain with the undoubled ray. The resulting interference is insensitive to path length but is affected by plasma dispersion in the usual way. A typical central fringe shift in C-Mod is expected to be 0.1–1.0, but the absolute and relative accuracy in nel measurements can be as high as in a conventional interferometer. This design uses a repetitively pulsed laser which is converted to a fan beam crossing the horizontal midplane. The chordal array is defined by internal retroreflectors on the C-Mod midplane which return the beam to the second doubler and a detector array. This interferometer design has beam diameters of a few millimeters and element spacings of a few centimeters, uses a repetitively pulsed, TEM00 Nd:YAG laser, fiber optic beam transport, commercial components, and a compact optical design which minimizes port space requirements. An optical system design is presented which is based on the performance of a tabletop prototype at Princeton Plasma Physics Laboratory. © 1997 American Institute of Physics.
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  • 8
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A large-angle, 60-GHz collective Thomson scattering (CTS) diagnostic system for localized measurements of DT alpha-particle velocity distribution and fraction is being implemented on TFTR. Calculations of expected CTS spectra, signal-to-noise ratio per receiver channel, and estimated error in determining the temperature and fraction of alpha particles are being carried out. The experimental spectra are simulated by adding noise to the theoretical calculation by a Monte Carlo technique. Error analysis is then performed by using a relative intensity calibrated nonlinear curve fitting code to calculate the desired plasma parameters (Ti, Tα, nα/ni). Simulation results indicate that expected background emission of 20 eV during Supershot in TFTR poses no problem to the experiment. Also short integration times (〈10 ms) can be used to resolve the energetic ion features, thus offering a possibility for the study of temporal evolution of energetic ion velocity distribution during a single plasma shot.
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  • 9
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In D-T plasmas, the understanding of the physics of confined α particles is extremely valuable for the future fusion plasma device. Among the various proposed α diagnostics, an X-mode collective Thomson scattering system employing a high-power gyrotron source (P(approximately-equal-to)200 kW, f=60 GHz, pulse length (approximately-equal-to)0.5 s, and modulation frequency=10–25 kHz) is being designed for TFTR. The detailed description of the gyrotron source, transmission lines, optical designs, beam and viewing dump design, and receiver system will be presented in this paper. In particular, the test results of the beam and viewing dump indicate that the stray light can be reduced by 60 dB. The background emission level (∼20 eV) near 60-GHz range during high Q discharge may also be reduced with beam and viewing dump further. The optical system is designed to measure the radial profile of α particles and to orient the incident wavevector (k0) to test the electromagnetic effects of the scattered spectrum. Prior to the study of α physics in D-T plasmas, this scattering system will be used to measure not only a bulk ion temperature but also the scattered spectrum due to fast ions produced by NB and ICRF heating in TFTR. This work was supported by the U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.
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  • 10
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A microwave reflectometer is in operation on TFTR for the measurement of density fluctuations. The system operates in the X mode and comprises three channels with fixed frequencies of 140, 132, and 125 GHz, and one with stepped frequency of 111–123 GHz. All channels use solid state Gunn oscillators and a heterodyne detection scheme. The system is located outside of the TFTR test cell with the power conveyed to the tokamak vessel by low-loss corrugated waveguides and remotely controlled parabolic mirrors. Preliminary results indicate that the level of density fluctuations with k⊥ 〈1 cm−1 is very small in the central region of Ohmic plasmas (ñ/n〈10−3), and that it increases monotonically with minor radius to values of ≈10−2 at r/a=0.9. This work supported by U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.
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