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  • 1
    Electronic Resource
    Electronic Resource
    Hot-ion Bernstein wave with finite k(parallel) (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1899-1906 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The complex roots of the hot plasma dispersion relation in the ion cyclotron range of frequencies have been surveyed. Consistent with current understanding, the cold plasma fast wave appears at low values of perpendicular wave number k⊥, followed by the well-known Bernstein wave at higher k⊥. At still higher k⊥ there can be two previously unappreciated hot plasma waves with relatively little sensitivity to frequency, in contrast to the Bernstein wave which is characterized by large changes in k⊥ for small changes in frequency or magnetic field. The latter waves exist only for relatively large k(parallel), the wave number parallel to the magnetic field. Both waves are strongly absorbed if the electron temperature is near the ion temperature, but not in a hot-ion, cold-electron, plasma. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871277
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  • 2
    Electronic Resource
    Electronic Resource
    Ion cyclotron range of frequencies heating and current drive in deuterium–tritium plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2427-2434 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871266
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  • 3
    Electronic Resource
    Electronic Resource
    Active core profile and transport modification by application of ion Bernstein wave power in the Princeton Beta Experiment-Modification (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 741-751 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Application of Ion Bernstein Wave Heating (IBWH) into the Princeton Beta Experiment-Modification (PBX-M) [Phys. Fluids B 2, 1271 (1990)] tokamak stabilizes sawtooth oscillations and generates peaked density profiles. A transport barrier, spatially correlated with the IBWH power deposition profile, is observed in the core of IBWH-assisted neutral beam injection (NBI) discharges. A precursor to the fully developed barrier is seen in the soft x-ray data during edge localized mode (ELM) activity. Sustained IBWH operation is conducive to a regime where the barrier supports large ∇ne, ∇Te, ∇νφ, and ∇Ti, delimiting the confinement zone. This regime is reminiscent of the H(high) mode, but with a confinement zone moved inward. The core region has better than H-mode confinement while the peripheral region is L(low)-mode-like. The peaked profile enhances NBI core deposition and increases nuclear reactivity. An increase in central Ti results from χi reduction (compared to the H mode) and better beam penetration. Bootstrap current fractions of up to 0.32–0.35 locally and 0.28 overall were obtained when an additional NBI burst is applied to this plasma. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871426
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  • 4
    Electronic Resource
    Electronic Resource
    Ion cyclotron range of frequency experiments in the Tokamak Fusion Test Reactor with fast waves and mode converted ion Bernstein waves (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2006-2012 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent experiments in the ion cyclotron range of frequencies (ICRF) in the Tokamak Fusion Test Reactor [Fusion Technol. 21, 13 (1992)] are discussed. These experiments include mode conversion heating and current drive, fast wave current drive, and heating of low (L)- mode deuterium–tritium (D–T) plasmas in both the hydrogen minority and second harmonic tritium regimes. In mode conversion heating, a central electron temperature of 10 keV was attained with 3.3 MW of radio-frequency power. In mode conversion current drive experiments, up to 130 kA of current was noninductively driven, on and off axis, and the current profiles were modified. Fast wave current drive experiments have produced 70–80 kA of noninductively driven current. Heating of L-mode deuterium and D–T plasmas by hydrogen minority ICRF has been compared. Finally, heating of L-mode D–T plasmas at the second harmonic of the tritium cyclotron frequency has been demonstrated. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871997
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  • 5
    Electronic Resource
    Electronic Resource
    Investigation of lower hybrid wave damping in the PBX-M tokamak (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 125-133 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lower hybrid (LH) current drive experiments on the Princeton Beta Experiment-Modified (PBX-M) [Phys. Fluids B 2, 1271 (1990)] have shown that the current profile can be changed by varying the phase velocity of the waves. The radial profile of the current carrying electrons was deduced from two-dimensional hard x-ray tomography. For a certain range of phase velocities, there is a correlation between the peak of the fast electron profile and the launched wave spectrum, despite the presence of a wide spectral gap between the phase velocity and the thermal electron energy distribution. A new model is proposed to explain how first-pass wave damping is possible in such plasmas. The rf power can form a tail of energetic electrons, and subsequently waves with moderate phase velocity can damp on them. For waves with very fast phase velocity, there must be an upshift of the n(parallel) spectrum for any damping to occur. These hypotheses are supported by ray tracing results which are coupled to relativistic Fokker–Planck calculations of the electron distribution function. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872122
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  • 6
    Electronic Resource
    Electronic Resource
    The simulation of hard x-ray images obtained during lower hybrid current drive on the Princeton Beta Experiment Modification (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 205-217 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: During lower hybrid current drive on the Princeton Beta Experiment Modification PBX-M [Bell et al., Phys. Fluids B 2, 1271 (1990)], suprathermal electrons in the 30–150 keV range are generated. These electrons emit hard x-ray bremsstrahlung in collisions with plasma ions; the radiation creates images in a hard x-ray pinhole camera. In order to interpret the hard x-ray images, a computer simulation code has been written; the "pbxray'' code, which is described in this paper. The code represents an extension of the Stevens code [Stevens et al., Nucl. Fusion 25, 1529 (1985)], which calculates the free–free and free–bound radiation for non-Maxwellian relativistic electron tail distributions. The pbxray code provides the chord integration in the bean-shaped plasma geometry on the PBX-M tokamak and integrates over photon energy. The simulations show that the location of the suprathermal electrons can be determined with an accuracy of approximately 2 cm in the plasma. In particular, discharges are analyzed whose characteristic "hollow'' images indicate off-axis lower hybrid current drive. A comparison of images taken with different absorber foils reveals that the suprathermal electrons have less than 150 keV parallel energy for the hollow discharges. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871092
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  • 7
    Electronic Resource
    Electronic Resource
    Experimental exploration of profile control in the Princeton Beta Experiment-Modified (PBX-M) tokamak (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2562-2570 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The experimental program of the Princeton Beta Experiment-Modified (PBX-M) tokamak [Phys. Fluids B2, 1271 (1990)] is directed toward tailoring plasma profiles to achieve greater stability and confinement and to gain access to the second stability region. Modification of the current density profile has been achieved with lower-hybrid current drive (LHCD), leading to a regime free of global magnetohydrodynamic modes, while raising the value of q(0) above unity. The diffusion of the fast electrons produced by LHCD has been examined using two-dimensional hard x-ray imaging. Ion Bernstein waves (IBW) have been used for ion heating: a preliminary analysis shows that ion heating was spatially localized and in agreement with theoretical calculations. Divertor biasing has modified the electric field inside the last closed surface, resulting in the formation of a transport barrier, which in turn has reduced the threshold power of neutral beam injection (NBI) for H-mode transition by 25%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860744
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  • 8
    Electronic Resource
    Electronic Resource
    The Hard X-ray Camera on the PBX-M tokamak (invited) (abstract)a) : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 585-585 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The modification and control of the plasma current profile by lower hybrid current drive is considered one of the most promising avenues to control MHD instabilities and improve the high beta performance of tokamaks. The Hard X-ray Camera on PBX-M records images of the bremsstrahlung emitted by suprathermal electrons that carry part of the plasma current during lower hybrid current drive. The Hard X-ray Camera is a pinhole camera that uses a 9 in. diam x-ray intensifier as detector. It provides a tangential view of the tokamak plasma and delivers 64 images with 128×128 pixels per plasma shot. The spatial resolution in the plasma is approximately 2 cm, and the time resolution 3 ms. The camera is sensitive to x rays between 30 and 200 keV. The photon energy (and the energy of the suprathermal electrons) is measured with an absorber foil method. Modeling of the x-ray emission has reproduced the experimental images with a better than 10% accuracy. In addition, two inversion techniques have been developed: one of these can be performed on line between shots. Illustrative examples of important applications of hard x-ray imaging will be given. The hard x-ray images provide information on the radial location of the absorption of the lower hybrid waves, on the velocity distribution of the suprathermal electrons, on the diffusion of superthermal electrons, and on anomalous hot electron transport induced by MHD instabilities. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146291
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  • 9
    Electronic Resource
    Electronic Resource
    Camera for imaging hard x rays from suprathermal electrons during lower hybrid current drive on PBX-M (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 1621-1630 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: During lower hybrid current drive on tokamaks, suprathermal electrons are generated that emit hard x-ray bremsstrahlung. A pinhole camera has been installed on the PBX-M tokamak that records 128×128 pixel images of the hard x-ray plasma bremsstrahlung emitted in the 30–200 keV photon energy range. The camera has a temporal resolution of 3 ms and a spatial resolution of 3–4 cm in the plasma. The detector is a 230-mm-diam hard x-ray image intensifier. This instrument has identified hollow radiation profiles on PBX-M, indicating off-axis current drive. A detailed account of the construction of the hard x-ray camera, its operation, and its performance is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144850
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