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Regimes of operation in the Princeton Large Torus

Description: In the quest for optimum discharge conditions in the Princeton Large Torus (PLT), a variety of discharge regimes have been produced. These separate broadly into two main categories - those regimes with m greater than or equal to 2 oscillatory MHD instabilities and often hollow electron profiles for tungsten limiters, and those regimes for which the electron temperature is sufficiently peaked to support the internal sawtooth or near-sawtooth (m = 1) instability. The internal sawtooth regime is found to be optimum for confinement but to be more difficult to select when low-Z impurity concentrations have been reduced with low power discharge cleaning or gettering to permit extension of the high density operation limit. Gas programming is used to cool the plasma periphery, thereby reducing the high-Z impurity concentrations and causing the current channel to constrict into the sawtooth regime, and then to attain the desired plasma density. With discharges selected in this manner, gross energetic confinement times up to approx. 100 msec have been obtained at densities of approx. 10/sup 14/ cm/sup -3/, and very high ion and electron temperatures have been produced with neutral beam injection heating at lower densities with no observable deleterious effect on energy confinement.
Date: October 1, 1979
Creator: Hosea, J.C.
Partner: UNT Libraries Government Documents Department

ICRF heating in large tokamaks

Description: When projected to PLT-size tokamaks, the preliminary results for ..omega.. approx. 2..omega../sub ci/ fast wave heating obtained in the ST and ATC tokamaks indicate that very efficient heating of the central plasma region as opposed to the surface region should ensue when the rf energy is suitably coupled to the plasma waves. Ion banana orbit losses become negligible and a large number of propagating waves are available so that the radial rf energy disposition pattern can be properly selected at last. It is vital to the potential use of ICRF (Ion Cyclotron Range of Frequencies) heating in reactor scale plasmas that surface heating be controlled and minimized relative to heating the plasma core. A demonstration that this is possible in existing large tokamaks is essential to the development of the ICRF heating schemes for reactor use. Projections to TFTR and larger devices are considered briefly.
Date: November 1, 1976
Creator: Hosea, J. C.
Partner: UNT Libraries Government Documents Department

Fast wave heating in the Princeton Large Torus

Description: Fast wave heating in the ion cyclotron range of frequencies (ICRF) is being studied on the Princeton Large Torus (PLT) to evaluate its potential for heating large reactor-scale toroidal plasmas. Of primary interest are the two-ion and pure second harmonic heating regimes which, with proper control of the ion energy distribution and the rf power deposition profile, permit substantial energy glow into the bulk plasma ions. Initial heating experiments have been conducted with a single 1/2 turn antenna up to wave powers of P/sub rf/ approx. = 350 kW for durations of greater than or equal to 100 ms in the two-ion regime under conditions for which direct fundamental cyclotron damping on the minority ion species dominates the wave absorption. Ion-ion coupling serves to heat the majority ions and for energetic minority ion energy distributions, energy flow to the electrons results from electron drag. Substantial ion heating is found for D-p mixtures; ..delta..T/sub d/(0) approx. = 600 eV for 350 kW with anti n/sub e/ approx. = 2 x 10/sup 13/ cm/sup -3/. The deuteron heating efficiency is improved by about a factor of approx. 2 in D/sup -3/He mixtures; ..delta..T/sub d/(0) approx. = 500 eV for 150 kW with anti n/sub e/ approx. = 2.1 x 10/sup 13/ cm/sup -3/.
Date: October 1, 1979
Creator: Hosea, J.C.; Arunasalam, V. & Bernabei, S.
Partner: UNT Libraries Government Documents Department

Multichannel wave interferometry

Description: The analysis of multichannel wave interferometry for a variety of density profiles reveals that the phase shift as a function of horn position normalized to that through the center of the plasma, is relatively insensitive to K = n/sub o//n/sub c/ (the ratio of maximum density to cutoff density) when refraction effects are minimized. Thus, this ratio may be easily inverted to obtain a reasonably accurate measurement of the density profile even for values of K approaching 1.
Date: December 1, 1975
Creator: Hosea, J. C. & Jobes, F. C.
Partner: UNT Libraries Government Documents Department

Ordinary-mode fundamental electron cyclotron resonance absorption and emission in the Princeton Large Torus

Description: Fundamental electron cyclotron resonance damping for 4 mm waves with ordinary polarization is measured for propagation along the major radius traversing the midplane of the plasma in the Princeton Large Torus (PLT). Optical depths obtained from the data are in good agreement with those predicted by the relativistic hot plasma theory. Near blackbody emission over much of the plasma midplane is obtained and, in conjunction with the damping measurements, indicates that the vessel reflectivity is high. The practical use of ordinary mode fundamental electron cyclotron resonance heating (ECRH) in existing and future toroidal devices is supported by these results.
Date: November 1, 1979
Creator: Efthimion, P.C.; Arunasalam, V. & Hosea, J.C.
Partner: UNT Libraries Government Documents Department

Turbulent temperature fluctuations in the PLT tokamak plasma

Description: The first experimental evidence for the existence of turbulent temperature fluctutations in plasmas is presented. The measurements of temperature turbulence were accomplished by a spectral analysis of black-body electron cyclotron emission. The fractional fluctuation in the mean electron energy F = (<delta epsilon/sup 2/>/<epsilon>/sup 2/)/super /sup 1///sub 2// = (< delta T/sup 2//sub e/>/T/sup 2//sub e/)/super /sup 1///sub 2// is about 10% for typical PLT discharges. The frequency spectrum of the temperature turbulence extends well beyond the electron diamagnetic drift frequency F and does not show any resemblance to the simultaneously existing turbulent drift wave density fluctuations.
Date: July 1, 1977
Creator: Arunasalam, V.; Cano, R.; Hosea, J. C. & Mazzucato, E.
Partner: UNT Libraries Government Documents Department

ICRF heating and current drive experiments on TFTR

Description: Recent experiments in the Ion Cyclotron Range of Frequencies (ICRF) at TFTR have focused on the RF physics relevant to advanced tokamak D-T reactors. Experiments performed either tested confinement in reactor relevant plasmas or tested specific ICRF heating scenarios under consideration for reactors. H-minority heating was used to supply identical heating sources for matched D-T and D only L-mode plasmas to determine the species scaling for energy confinement. Second harmonic tritium heating was performed with only thermal tritium ions in an L-mode target plasma, verifying a possible start-up scenario for the International Thermonuclear Experimental Reactor (ITER). Direct electron heating in Enhanced Reverse Shear (ERS) plasmas has been found to delay the back transition out of the ERS state. D-T mode conversion of the fast magnetosonic wave to an Ion Berstein Wave (IBW) for off-axis heating and current drive has been successfully demonstrated for the first time. Parasitic Li{sup 7} cyclotron damping limited the fraction of the power going to the electrons to less than 30%. Similar parasitic damping by Be{sup 9} could be problematic in ITER. Doppler shifted fundamental resonance heating of beam ions and alpha particles has also been observed.
Date: December 31, 1996
Creator: Rogers, J.H.; Hosea, J.C. & Phillips, C.K.
Partner: UNT Libraries Government Documents Department

Quasilinear theory of the ordinary-mode electron-cyclotron resonance in plasmas

Description: A coupled set of equations, one describing the time evolution of the ordinary-mode wave energy and the other describing the time evolution of the electron distribution function is presented. The wave damping is mainly determined by T/sub parallel/ while the radiative equilibrium is mainly an equipartition with T/sub perpendicular/. The time rate of change of T/sub perpendicular/, T/sub parallel/, particle (N/sub 0/), and current (J/sub parellel/) densities are examined for finite k/sub parallel/ electron-cyclotron-resonance heating of plasmas.
Date: November 1, 1983
Creator: Arunasalam, V.; Efthimion, P.C.; Hosea, J.C.; Hsuan, H. & Taylor, G.
Partner: UNT Libraries Government Documents Department

Some novel features of the ordinary-mode electron-cyclotron resonance heating of tokamak plasmas

Description: It is shown that the finite k/sub parallel/ linear theory of absorption predicts: first, that the Doppler effect splits the k/sub parallel/ = o resonance into two closely spaced resonances instead of the usual Gaussian broadening; and second, that although the total absorption is due to the finite size of the electron Larmor orbits, it is mainly determined by T/sub parallel/ and is only weakly dependent on T/sub perpendicular/ via cyclotron overstability type terms. Some consequences of these unique features on plasma heating and rf current drive are also examined.
Date: March 1, 1983
Creator: Arunasalam, V.; Efthimion, P.C.; Hosea, J.C.; Hsuan, H. & Taylor, G.
Partner: UNT Libraries Government Documents Department

Determination of the time evolution of the electron-temperature profile of reactor-like plasmas from the measurement of blackbody electron-cyclotron emission

Description: Plasma characteristics (i.e., n/sub e/ greater than or equal to 1 x 10/sup 13/ cm/sup -3/, T/sub e/ greater than or equal to 10/sup 7/ /sup 0/K, B/sub psi/ greater than or equal to 20 kG) in present and future magnetically confined plasma devices, e.g., Princeton Large Torus (PLT) and Tokamak Fusion Test Reactor (TFTR), meet the conditions for blackbody emission near the electron cyclotron frequency and at few harmonics. These conditions, derived from the hot plasma dielectric tensor, have been verified by propagation experiments on PLT and the Princeton Model-C Stellarator. Blackbody emission near the fundamental electron cyclotron frequency and the second harmonic have been observed in PLT and is routinely measured to ascertain the time evolution of the electron temperature profile. These measurements are especially valuable in the study of auxiliary heating of tokamak plasma. Measurement and calibration techniques will also be discussed with special emphasis on our fast-scanning heterodyne receiver concept.
Date: April 1, 1982
Creator: Efthimion, P.C.; Arunasalam, V.; Bitzer, R.A. & Hosea, J.C.
Partner: UNT Libraries Government Documents Department

Gas injection in PLT: experimental overview

Description: Cold gas injection serves both the obvious role of a particle source at the surface of the plasma and a more subtle role as one element in the process by which the relative impurity concentration and the MHD activity of a discharge are determined. Evidence offered by PLT experiments in support of these two widely recognized roles is considered.
Date: January 1, 1977
Creator: Schmidt, G.L.; Bretz, N.I.; Hawryluk, R.J.; Hosea, J.C. & Johnson, D.W.
Partner: UNT Libraries Government Documents Department

Fast-scanning heterodyne receiver for measurement of the electron cyclotron emission from high-temperature plasmas

Description: A fast-scanning heterodyne receiver was developed that measures the fundamental cyclotron emission from the PLT plasma and thus ascertains the time evolution of the electron temperature profile. The receiver scans 60 to 90 GHz every 10 milliseconds and is interfaced to a computer for completely automated calibrated temperature measurements.
Date: March 1, 1979
Creator: Efthimion, P.C.; Arunasalam, V.; Bitzer, R.; Campbell, L. & Hosea, J.C.
Partner: UNT Libraries Government Documents Department

Modeling of ICRF heating in PLT

Description: Significant heating with the fast magnetosonic wave near the ion cyclotron frequency has been demonstrated in the present generation of tokamaks. Effective wave absorption and heating can be achieved either by using the second harmonic or by heating at the fundamental of a minority ion component. Recent experiments in PLT have facilitated the refinement of a heating model which both shows good agreement with experiment and predicts favorable scaling to hotter, denser plasmas. Details of the model, including full wave theory, power deposition, Fokker-Planck theory, and scaling are discussed.
Date: February 1, 1981
Creator: Colestock, P.L.; Davis, S.L.; Hosea, J.C.; Hwang, D.Q. & Thompson, H.R.
Partner: UNT Libraries Government Documents Department

ICRF heating during DT experiments on TFTR: System improvements and results

Description: In order to carry out a program of ICRF experiments in deuterium- tritium plasmas on the TFTR device a series of technical improvements have been made to the ICRF system. These improvements allow more flexible and reliable operation of the system which is crucial for the limited number of tritium discharges available. During the last year circuitry has been installed to feedback the plasma position on antenna loading, to lock the phase between antenna elements, and to detect arcs from the second harmonic content of antenna signals.
Date: August 1, 1994
Creator: Wilson, J. R.; Hosea, J. C. & Larue, P.
Partner: UNT Libraries Government Documents Department

New Electron Cyclotron Emission Diagnostic Based Upon the Electron Bernstein Wave

Description: 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 or they do not have sufficient density and temperature to reach the blackbody condition. 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 k(subscript i). One can reach the blackbody condition with a plasma density approximately equal to 10(superscript 11) cm(superscript -3) and electron temperature approximately equal to 1 eV. This makes it attractive to most plasma devices. One serious issue with using EBW is the wave accessibility. EBW may be accessible by either direct coupling or mode conversion through an extremely narrow layer (approximately 1-2 mm) in low field devices.
Date: May 1, 1999
Creator: Efthimion, P.C.; Hosea, J.C.; Kaita, R.; Majeski, R. & Taylor, G.
Partner: UNT Libraries Government Documents Department

Effects of Radial Electric Fields on ICRF Waves

Description: Equilibrium considerations infer that large localized radial electric fields are associated with internal transport barrier structures in tokamaks and other toroidal magnetic confinement configurations. In this paper, the effects of an equilibrium electric field on fast magnetosonic wave propagation are considered in the context of a cold plasma model.
Date: June 18, 2001
Creator: Phillips, C.K.; Hosea, J.C.; Ono, M. & Wilson, J.R.
Partner: UNT Libraries Government Documents Department

Measurements of ICRF (ion cyclotron range of frequencies) loading with a ridged waveguide coupler on PLT

Description: An ICRF ridged waveguide coupler has been installed on PLT for measurements of plasma loading. The coupler was partially filled with TiO/sub 2/ dielectric in order to sufficiently lower the cutoff frequency and utilized a tapered ridge for improved matching. Vacuum field measurements indicated a single propagating mode in the coupler and emphasized the importance of considering the fringing fields at the mouth of the waveguide. Low power experiments were carried out at 72.6 and 95.0 MHz without any external impedance matching network. Plasma loading increased rapidly as the face of the coupler approached the plasma, and, at fixed position, increased with line-averaged plasma density. At the lower frequency, the reflection coefficient exhibited a minimum (<8%) at a particular coupler position. At both frequencies, measurements indicated efficient power coupling to the plasma. Magnetic probe signals showed evidence of dense eigenmodes suggesting excitation of the fast wave. 24 refs., 13 figs.
Date: November 1, 1987
Creator: Greene, G.J.; Wilson, J.R.; Colestock, P.L.; Fortgang, C.M.; Hosea, J.C.; Hwang, D.Q. et al.
Partner: UNT Libraries Government Documents Department

Modeling of ICRF heating of a tokamak plasma

Description: A model for wave propagation and absorption of the Ion Cyclotron Range of Frequencies (ICRF) has been constructed and fitted into the 1-D BALDUR transport code. The wave propagation is handled by ray tracing techniques. Wave absorption is calculated using the Fokker-Planck equation and quasilinear diffusion. The wave propagation and damping profiles are evolved in time according to the plasma evolution. A simulation of PLT hydrogen minority ICRF heating with a comparison to experimental data is given.
Date: May 1, 1983
Creator: Hwang, D.Q.; Karney, C.F.F.; Hosea, J.C.; Hovey, J.M.; Singer, C.E. & Wilson, J.R.
Partner: UNT Libraries Government Documents Department


Description: The National Spherical Torus Experiment Upgrade (NSTX-U) will operate at an axial toroidal field of up to 1 T, about twice the field available on NSTX. A 28 GHz electron cylotron resonance heating (ECRH) system is currently being planned for NSTX-U. A 1 MW 28 GHz gyrotron will be employed. Intially the system will use short, 10-50 ms, 1 MW pulses for ECRH-assisted discharge start-up. Later the pulse length will be extended to 1-5 s to study electron Bernstein wave heating (EBWH) during the plasma current flat top. A mirror launcher will be used to couple microwave power to the plasma via O-mode to the slow X-mode to EBW (O-X-B) double mode conversion. This paper presents a pre-conceptual design for the ECRH/EBWH system proposed for NSTX-U and includes ray tracing and Fokker-Planck modeling results for 28 GHz ECRH during plasma start-up and EBW heating and current drive during the plasma current flattop of a NSTX-U advanced H-mode plasma scenario.
Date: June 15, 2012
Creator: Taylor, G.; Ellis, R. A.; Harvey, R. W.; Hosea, J. C. & Smirnov, A. P.
Partner: UNT Libraries Government Documents Department