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Leakage of runaway electrons from tokamaks

Description: Runaway electron orbits are calculated in a tokamak magnetic field. It is shown that these electrons tend to drift towards a larger major radius with a velocity v Vector/sub R/ = qcE/B/sub 0/ R. This effect may be relevant to some recent experimental observations in tokamaks.
Date: February 1, 1982
Creator: Wong, K. L.
Partner: UNT Libraries Government Documents Department

An alpha particle diagnostic based on measurements of lower hybrid wave fluctuations

Description: It is shown that the one-dimensional alpha particle velocity distribution function can be determined from the fluctuation- dissipation theorem based on measurements of lower hybrid wave fluctuations in an equilibrium plasma. This method uses collective Thomson scattering data with large signal-to-noise ratio, but it is applicable only when the alpha particles have an isotropic velocity distribution. 16 refs., 1 fig.
Date: July 1, 1989
Creator: Wong, K.L.
Partner: UNT Libraries Government Documents Department

Experimental observation of current generation by unidirectional electron plasma waves

Description: A slow wave structure was used to launch electron plasma waves traveling preferentially in one direction. The current generated by the waves was observed. The magnitude of the current can be estimated from momentum conservation in the wave-particle interaction process.
Date: August 1, 1978
Creator: Wong, K.L.
Partner: UNT Libraries Government Documents Department

Externally launched ion Berstein wave in the ACT-1 toroidal device

Description: In a hydrogen plasma (T/sub e/ = 2.5 eV, T/sub i/ = 1.5 eV), excitation of ion Bernstein waves by an externally placed electrostatic antenna has been investigated for ..omega.. approx. = 2 ..cap omega../sub i/. Mode transformation of the electron plasma wave at ..omega.. approx. = ..omega../sub pi/ without observable reflection was observed, followed by strong excitation of the ion Bernstein wave. Detailed measurements of k/sub perpendicular to/(..omega..,k/sub parallel/) and of the wave packet trajectory show excellent agreement with theory.
Date: June 1, 1980
Creator: Ono, M. & Wong, K.L.
Partner: UNT Libraries Government Documents Department

Assessment of eddy current effects on compression experiments in the TFTR tokamak

Description: The eddy current induced on the TFTR vacuum vessel during compression experiments is estimated based on a cylindrical model. It produces an error magnetic field that generates magnetic islands at the rational magnetic surfaces. The widths of these islands are calculated and found to have some effect on electron energy confinement. However, resistive MHD simulation results indicate that the island formation process can be slowed down by plasma rotation.
Date: May 1, 1986
Creator: Wong, K.L. & Park, W.
Partner: UNT Libraries Government Documents Department

Effects of ion cyclotron harmonic damping on current drive in the lower hybrid frequency range

Description: We investigate the ion cyclotron harmonic damping effects on slow and fast waves in the lower hybrid frequency range for tokamak reactor parameters. Inclusion of the higher order terms in the hot plasma dielectric tensor introduces ion cyclotron harmonic damping; these terms also contribute to the real part of the dispersion relation and affect the wave trajectories. However, wave absorption by 15 keV deuterium and tritium ions can be avoided by choosing the slow wave frequency above the lower hybrid frequency and the fast wave frequency below the lower hybrid frequency. But preliminary estimates show that energetic alpha particles tend to absorb both the slow and the fast waves. This absorption may become a serious obstacle for fusion-reactor current drive in the lower hybrid frequency range.
Date: November 1, 1983
Creator: Wong, K.L. & Ono, M.
Partner: UNT Libraries Government Documents Department

Excitation of drift waves by lower hybrid waves

Description: The excitation of low frequency oscillations by lower hybrid waves at electric fields lower than the thresholds of other parametric decay processes is reported. The frequencies and wavelengths of these oscillations agree with the collisional drift wave dispersion relation. The excitation is localized deep inside the plasma density gradient. The excited drift waves change the density profile and the lower hybrid wave trajectory.
Date: March 1, 1977
Creator: Wong, K. L. & Bellan, P.
Partner: UNT Libraries Government Documents Department

Non-resonant parametric decay of lower-hybrid waves in the ACT-1 toroidal device

Description: Non-resonant parametric decay of lower-hybrid waves, observed in a number of high-power tokamak rf heating experiments, is positively identified as a decay into ion-cyclotron quasi-modes. The decay-wave spectrum, wavelength and amplitude profile are measured inside a toroidal plasma with pump frequency f/sub 0/ approx. 3.5 f/sub ..pi../ approx. 25 f/sub ci/.
Date: February 1, 1981
Creator: Wong, K.L. & Ono, M.
Partner: UNT Libraries Government Documents Department

Parametric excitation of ion Bernstein waves by a fast wave antenna in the ion cyclotron frequency range

Description: Parametric excitation of ion Bernstein waves is observed with an ICRF fast wave induction loop antenna in the ion cyclotron frequency range (..omega../sub o/ approx. 2..cap omega../sub i/ - 4..cap omega../sub i/). Important features of the decay process are investigated and discussed.
Date: November 1, 1983
Creator: Skiff, F.; Ono, M. & Wong, K.L.
Partner: UNT Libraries Government Documents Department

Neoclassical diffusion of heavy impurities in a rotating tokamak plasma

Description: Particle orbits in a rotating tokamak plasma are calculated from the equation of motion in the frame that rotates with the plasma. It is found that heavy particles in a rotating plasma can drift away from magnetic surfaces significantly faster, resulting in a diffusion coefficient much larger than that for a stationary plasma. Particle simulation is carried out and the results offer a qualitative explanation for some experimental data from the Tokamak Test Reactor (TFTR). 13 refs., 2 figs.
Date: August 1, 1987
Creator: Wong, K.L. & Cheng, C.Z.
Partner: UNT Libraries Government Documents Department

Non-linear converging resonance cones

Description: The trajectory modification of a focused resonance cone due to ponderomotive force effects was investigated in the Princeton L-3 device. A single ring pulsed at f/sub 0/ approx. 50 MHZ (f/sub 1h/ much less than f/sub 0/ much less than f/sub pe/, f/sub ce/) launches a converging resonance cone in an argon plasma with n/sub e/ approx. 10/sup 9/ to 10/sup 10/, B approx. 400G to 1kG, T/sub e/ approx. 1 to 3 eV. At high driving power the strong localized electric fields modify the density through the ponderomotive force on the electrons, leading to a modification of the resonance cone trajectory. The cone is seen to bend in towards the axis and the focus moves toward the ring in agreement with the recent theory of Wang and Kuehl. The density perturbation at the focus propagates away and excites ion-acoustic waves. The wave dispersion relation was verified in He/sup +/, Ne/sup +/, Ar/sup +/, and Kr/sup +/ plasmas. Electron heating was observed which is consistent with collisional heating.
Date: July 1, 1979
Creator: Wilson, J.R. & Wong, K.L.
Partner: UNT Libraries Government Documents Department

Observation of the backward electrostatic ion cyclotron wave

Description: The backward branch of the electrostatic ion cyclotron wave has been observed, we believe, for the first time. The wave, which was driven by a phased antenna structure inserted in a neon plasma, exists in the parameter ranges 2T/sub i//m/sub i/ << (..omega../k/sub parallel/)/sup 2/ << 2T/sub e//m/sub e/, n..cap omega../sub i/ < ..omega.. < (n+1)..cap omega../sub i/, T/sub e/ greater than or equal to T/sub i/, and ..omega../sub pi/ > ..cap omega../sub i/. Double-tip probe interferomety data agree with the theoretical dispersion relation.
Date: December 1, 1984
Creator: Goree, J.; Ono, M. & Wong, K.L.
Partner: UNT Libraries Government Documents Department

Suppression of lower hybrid wave coupling due to the ponderomotive force

Description: The coupling efficiency from a slow-wave structure to lower hybrid waves is investigated experimentally. At moderate electric field strengths large edge density changes are observed. Wave trajectory modifications and departure from linear coupling are observed consistent with these changes and in good agreement with a simple nonlinear theory that includes the ponderomotive force.
Date: April 1, 1980
Creator: Wilson, J.R. & Wong, K.L.
Partner: UNT Libraries Government Documents Department

Vacuum vessel eddy current modeling for TFTR adiabatic compression experiments

Description: A relatively simple current filament model of the TFTR vacuum vessel is described. It is used to estimate the three-dimensional structure of magnetic field perturbations in the vicinity of the plasma that arise from vacuum vessel eddy currents induced during adiabatic compression. Eddy currents are calculated self-consistently with the plasma motion. The Shafranov formula and adiabatic scaling laws are used to model the plasma. Although the specific application is to TFTR, the present model is of generation applicability.
Date: July 1, 1985
Creator: DeLucia, J.; Bell, M. & Wong, K.L.
Partner: UNT Libraries Government Documents Department

Echo phenomenon associated with lower-hybrid-wave launching

Description: Lower hybrid waves at two different frequencies f/sub 1/ and f/sub 2/ are launched simultaneously from two localized antennas, and a third wave is observed to arise near the plasma edge at the frequency f = f/sub 2/ - f/sub 1/. This phenomenon can be explained by an echo effect near the plasma surface.
Date: June 1, 1983
Creator: Wong, K.L.; Skiff, F. & Ono, M.
Partner: UNT Libraries Government Documents Department

Resonant decay of finite extent cold electron plasma waves

Description: The parametric decay of a finite extent cold electron plasma wave (slow wave) was studied experimentally. Using a frequency of ..omega../sub 0/ approximately greater than 10..omega../sub pi/, it was found that the decay waves propagated along the pump wave rather than in the Vector E/sub 0/ x Vector B direction. This is in agreement with the recent theoretical predictions of finite length stabilization.
Date: February 1, 1978
Creator: Wong, K.L.; Bellan, P. & Porkolab, M.
Partner: UNT Libraries Government Documents Department

Summary and review of hydrogen theoretical equation-of-state models at Lawrence Livermore Laboratory

Description: A review and analysis of the hydrogen equations of state (EOS) at use at Lawrence Livermore Laboratory (LLL) are presented. Careful comparisons to experimental data and among EOS's are performed and evaluated. The new LLL hydrogen EOS (EOS95) and its representations produce the best agreement with experimental data and hydrodynamic simulation studies.
Date: February 1, 1980
Creator: Graboske, H.C. Jr. & Wong, K.L.
Partner: UNT Libraries Government Documents Department

Orbit effects on impurity transport in a rotating tokamak plasma

Description: Particle orbits in a rotating tokamak plasma are calculated from the equation of motion in the frame that rotates with the plasma. It is found that heavy particles in a rotating plasma can drift away from magnetic surfaces significantly faster with a higher bounce frequency, resulting in a diffusion coefficient much larger than that for a stationary plasma. Particle orbits near the surface of a rotating tokamak are also analyzed. Orbit effects indicate that more impurities can penetrate into a plasma rotating with counter-beam injection. Particle simulation is carried out with realistic experimental parameters and the results are in qualitative agreement with some experimental observations in the Tokamak Fusion Test Reactor (TFTR). 19 refs., 15 figs.
Date: May 1, 1988
Creator: Wong, K. L. & Cheng, C. Z.
Partner: UNT Libraries Government Documents Department

Effect of density fluctuations of lower hybrid resonance cone propagation

Description: Experimental measurements show that coherent, azimuthal density fluctuations (1) focus lower hybrid resonance cones azimuthally, and (2) modulate the radial location of the resonance cones. A simple theory based on wave refraction is presented; this theory is in good agreement with the experimental observations. The theory is extended to give a physical description of wave propagation through turbulent, isotropic (perpendicular to B) noise such as has been observed in tokamaks; it is found that the turbulence causes the lower hybrid wave-vectors to have an angular spread in the plane perpendicular to B.
Date: April 1, 1977
Creator: Bellan, P. M. & Wong, K. L.
Partner: UNT Libraries Government Documents Department

Effect of convective loss on the parametric decay of cold electron plasma waves

Description: The resonant decay of cold electron plasma waves was investigated in the Princeton L-3 device in an argon plasma with n approx. 10/sup 10/--10/sup 11/ cm/sup -3/, B approx. 700 G -2kG, f/sub 0/ approx. 50 to 80 MHz (omega/sub 0/ greater than or equal to 10 omega/sub LH/). The decay waves were identified to be ion-acoustic waves and cold electron plasma waves. Because of convective losses in the finite extent pump field, the threshold for parametric decay is considerably higher than the collisional threshold for the dominant anti E/sub 0 perpendicular/ x anti B coupling. Coupling due to E/sub 0''/ can be important in low density high magentic field plasmas. At high densities (n > 3 x 10/sup 10/cm/sup -3/), anti E/sub 0 perpendicular/ x anti B coupling becomes dominant. The anti E/sub 0 perpendicular/ x anti B decay convective threshold was measured at various antenna lengths; magentic field strengths and plasma densities.
Date: February 1, 1979
Creator: Wong, K.L.; Wilson, J.R. & Porkolab, M.
Partner: UNT Libraries Government Documents Department

Harmonic launching of ion Bernstein waves via mode transformation

Description: Ion Bernstein wave excitation and propagation via finite ion-Larmor-radium mode-transformation are investigated theoretically and experimentally. It is shown that in the ion cyclotron range of frequencies omega less than or equal to 4..cap omega../sub i/, with modest ion temperatures (T/sub i/ less than or equal to 10 eV), the finite-Larmor-radius effect removes the wave singularity at lower-hybrid resonance layer, enabling an externally initiated electron plasma wave to transform continuously into an ion Bernstein wave. In an ACT-1 hydrogen plasma (T/sub e/ approx. = 2.5 eV, T/sub i/ less than or equal to 2.0 eV), externally excited ion Bernstein waves have been observed for omega less than or equal to 2..cap omega../sub i/ as well as for omega less than or equal to 3..cap omega../sub i/. The finite ion-Larmor-radius mode transformation process resulting in strong ion Bernstein wave excitation has been experimentally verified. Detailed measurements of the wave dispersion relation and of the wave-packet trajectory show excellent agreement with theory. The dependence of the excited ion Bernstein wave on the antenna phasing, the plasma density, and on the neutral pressure (T/sub i/) is also investigated.
Date: June 1, 1982
Creator: Ono, M.; Wong, K.L. & Wurden, G.A.
Partner: UNT Libraries Government Documents Department

Far-infrared laser scattering in the ACT-I toroidal device

Description: A far-infrared laser scattering diagnostic has been built for the ACT-I toroidal device. The optical system uses a passively stabilized 447-..mu..m CH/sub 3/I laser. A polyethylene etalon is the beam splitter. The vacuum windows are plastic (TPX), which we found has the vacuum property Q 6.5 x 10/sup -9/ torr-liter/sec/cm/sup 2/. Using paraboloidal and ellipsoidal mirrors for detection optics improves the signal strength and allows a better rf enclosure design for the detector. The diagnostic was tested by scattering from an ion Bernstein wave, a technique which can be used for ion temperature diagnostics.
Date: December 1, 1984
Creator: Goree, J.; Mansfield, D.K.; Ono, M. & Wong, K.L.
Partner: UNT Libraries Government Documents Department