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A unified theory of resonant excitation of kinetic ballooning modes by energetic ions/alpha particles in tokamaks

Description: A complete theory of wave-particle interactions is presented whereby both circulating and trapped energetic ions can destabilize kinetic ballooning modes in tokamaks. Four qualitatively different types of resonances, involving wave-precessional drift, wave-transit, wave-bounce, and precessional drift-bounce interactions, are identified, and the destabilization potential of each is assessed. For a characteristic slowing-down distribution function, the dominant interaction is that which taps thos… more
Date: October 1, 1991
Creator: Biglari, H. & Chen, L.
Partner: UNT Libraries Government Documents Department
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The interpretation of reflectometry measurements of plasma fluctuations

Description: Wave reflections from density fluctuations with magnitudes and frequencies typical of drift waves have been investigated. Both drift waves and the reflected phase and amplitude depend on the density gradient scale length, and this common feature implies that both the angular deviation of a normally propagating wave and the phase change on reflection are of order unity. Thus the surface will always appear rough'' and amplitude variations will always be large. For smaller amplitude waves numerica… more
Date: October 1, 1991
Creator: Bretz, N.
Partner: UNT Libraries Government Documents Department
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Generation of radiation by intense plasma and e. m. undulators

Description: This program involves the generation of short wavelength optical radiation by intense plasma and e.m. undulators. In this concept a relativistic electron beam is wiggled by either the oscillating electric field of an intense plasma wave, or by a laser beam causing it to radiate. For both types of undulators the designed parameters are a{sub w} > 0.1, N {approximately} 100 and {lambda}{sub w} = 100 {mu}m for plasma wave or 10.6 {mu}m for laser light. This progress report describes the work to-da… more
Date: January 1, 1988
Creator: Joshi, C.
Partner: UNT Libraries Government Documents Department
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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
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Study of roughness-induced diffuse and specular reflectance at silver-air and silver-liquid interfaces. Final report, July 1, 1979-August 31, 1980

Description: Results of an extended investigation of surface plasma-wave absorption and roughness-induced optical scattering from an interface of silver and air are described. In particular, the position of the surface plasma resonance minimum in reflectivity for a stochastically roughened metal silver surface has been studied as a function of a number of distinct roughness perturbations. In the case of a transparent liquid-silver boundary the frequency red shift of the resonance minimum has been determined… more
Date: July 1, 1980
Creator: Sari, S.O.
Partner: UNT Libraries Government Documents Department
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Analysis of sawtooth relaxation oscillations in tokamaks

Description: Sawtooth relaxation oscillations are analyzed using the Kadomtsev's disruption model and a thermal relaxation model. The sawtooth period is found to be very sensitive to the thermal conduction loss. Qualitative agreement between these calculations and the sawtooth period observed in several tokamaks is demonstrated.
Date: July 1, 1982
Creator: Yamazaki, K.; McGuire, K. & Okabayashi, M.
Partner: UNT Libraries Government Documents Department
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The interaction of energetic alpha-particles with intense lower hybrid waves

Description: Lower hybrid waves are a demonstrated, continuous means of driving toroidal current in a tokamak. When these waves propagate in a tokamak fusion reactor, in which there are energetic {alpha}- particles, there are conditions under which the {alpha}-particles do not appreciably damp, and may even amplify, the wave, thereby enhancing the current-drive effect. Waves traveling in one poloidal direction, in addition to being directed in one toroidal direction, are shown to be the most efficient drive… more
Date: June 1, 1992
Creator: Fisch, N. J. & Rax, J. M.
Partner: UNT Libraries Government Documents Department
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Measurements of beat wave accelerated electrons in a toroidal plasma

Description: Electrons are accelerated by large amplitude electron plasma waves driven by counter-propagating microwaves with a difference frequency approximately equal to the electron plasma frequency. Energetic electrons are observed only when the phase velocity of the wave is in the range 3v{sub e} < v{sub ph} < 7v{sub e} (v{sub ph} was varied 2v{sub e} < v{sub ph} < 10v{sub e}), where v{sub e} is the electron thermal velocity, (kT{sub e}/m{sub e}){sup {1/2}}. As the phase velocity increases, fewer elect… more
Date: June 1, 1992
Creator: Rogers, J.H. (Princeton Univ., NJ (United States). Plasma Physics Lab.) & Hwang, D.W. (California Univ., Davis, CA (United States). Dept. of Applied Science Lawrence Livermore National Lab., CA (United States))
Partner: UNT Libraries Government Documents Department
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Maryland controlled fusion research program

Description: In this paper, we summarize the technical progress in four major areas of tokamak research: (a) L/H transition and edge turbulence and transport; (b) active control of microturbulence and transport; (c) major disruptions; and (d) the sawtooth crash.
Date: January 1, 1992
Creator: Griem, H. R. & Liu, C. S.
Partner: UNT Libraries Government Documents Department
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Excitation of high-n toroidicity-induced shear Alfven eigenmodes by energetic particles and fusion alpha particles in tokamaks

Description: The stability of high-n toroidicity-induced shear Alfven eigenmodes (TAE) in the presence of fusion alpha particles or energetic ions in tokamaks is investigated. The TAE modes are discrete in nature and thus can easily tap the free energy associated with energetic particle pressure gradient through wave particle resonant interaction. A quadratic form is derived for the high-n TAE modes using gyro-kinetic equation. The kinetic effects of energetic particles are calculated perturbatively using t… more
Date: July 1, 1992
Creator: Fu, G. Y. & Cheng, C. Z.
Partner: UNT Libraries Government Documents Department
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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 … more
Date: June 1, 1982
Creator: Ono, M.; Wong, K. L. & Wurden, G. A.
Partner: UNT Libraries Government Documents Department
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Locked modes and magnetic field errors in MST

Description: In the MST reversed field pinch magnetic oscillations become stationary (locked) in the lab frame as a result of a process involving interactions between the modes, sawteeth, and field errors. Several helical modes become phase locked to each other to form a rotating localized disturbance, the disturbance locks to an impulsive field error generated at a sawtooth crash, the error fields grow monotonically after locking (perhaps due to an unstable interaction between the modes and field error), a… more
Date: June 1, 1992
Creator: Almagri, A. F.; Assadi, S.; Prager, S. C.; Sarff, J. S. & Kerst, D. W.
Partner: UNT Libraries Government Documents Department
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Detection of lower hybrid waves within a plasma by microwave scattering

Description: The spatial distribution and intensity of electrostatic waves injected into a hot plasma may be inferred from the scattering of millimeter microwaves. We report measurements on the 30/sup 0/ scattering of 8.6 mm microwaves by a 500 W, 2.45 GHz slow wave excited in a linear plasma by a phased array of two waveguides. From the magnitude of the scattered signal and auxiliary measurements with probes, we infer that a large fraction of the injected power penetrates to the center of the overdense tes… more
Date: March 1, 1978
Creator: Motley, R. W.; Paoloni, F. J.; Bernabei, S. & Hooke, W. M.
Partner: UNT Libraries Government Documents Department
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Nonlinear evolution of resistive tearing mode instability with shear flow and viscosity

Description: The nonlinear evolution of the tearing mode instability with equilibrium shear flow is investigated via numerical solutions of the resistive magnetohydrodynamic equations. The two-dimensional simulations are in slab geometry, are periodic in the x-direction, and are initiated with solutions of the linearized MHD equations. The magnetic Reynolds number S was varied from 10{sup 2} to 10{sup 5}, a parameter V that measures the strength of the flow in units of the average Alfven speed was varied, a… more
Date: December 1, 1991
Creator: Ofman, L.; Morrison, P.J. (Texas Univ., Austin, TX (United States). Inst. for Fusion Studies) & Steinolfson, R.S. (Southwest Research Inst., San Antonio, TX (United States). Dept. of Space Sciences)
Partner: UNT Libraries Government Documents Department
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Ideal ballooning stability near an equilibrium magnetic island

Description: The stability properties of ideal ballooning modes on toroidal flux surfaces near a quasistatic magnetic island is examined. On these surfaces, magnetic field-line trajectories tend to bunch on that part of the magnetic surface closet to the X-point of the magnetic island. Because of this preferential bunching, the stabilizing effect of field-line bending due to magnetic shear can be reduced. Eigenfunctions localized in helical angle near the X-point and in poloidal angle on the bad curvature s… more
Date: March 1, 1992
Creator: Hegna, C. C. & Callen, J. D.
Partner: UNT Libraries Government Documents Department
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Compton harmonic resonances, stochastic instabilities, quasilinear diffusion, and collisionless damping with ultra-high intensity laser waves

Description: The dynamics of electrons in two-dimensional, linearly or circularly polarized, ultra-high intensity (above 10{sup 18}W/cm{sup 2}) laser waves, is investigated. The Compton harmonic resonances are identified as the source of various stochastic instabilities. Both Arnold diffusion and resonance overlap are considered. The quasilinear kinetic equation, describing the evolution of the electron distribution function, is derived, and the associated collisionless damping coefficient is calculated. Th… more
Date: April 1, 1992
Creator: Rax, J.M.
Partner: UNT Libraries Government Documents Department
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Nonlinear mechanisms for drift wave saturation and induced particle transport

Description: A detailed theoretical study of the nonlinear dynamics of gyrokinetic particle simulations of electrostatic collisionless and weakly collisional drift waves is presented. In previous studies it was shown that, in the nonlinearly saturated phase of the evolution, the saturation levels and especially the particle fluxes have an unexpected dependence on collisionality. In this paper, the explanations for these collisionality dependences are found to be as follows: The saturation level is determine… more
Date: December 1, 1989
Creator: Dimits, A.M. (Maryland Univ., College Park, MD (USA). Lab. for Plasma Research) & Lee, W.W. (Princeton Univ., NJ (USA). Plasma Physics Lab.)
Partner: UNT Libraries Government Documents Department
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Non-linear theory of laser-plasma interactions

Description: Research progress on each of the following areas is briefly described: (1) optical ray retracing of Brillouin backscattering from a nonisothermal plasma; (2) electromagnetic oscillating two-stream instability of laser radiation; (3) second harmonic generation of upper hybrid radiation in a plasma; (4) nonlinear scattering of upper hybrid laser radiation by electron Bernstein modes in a plasma; and (5) destructive collisions of supersonic solitons. (MOW)
Date: January 1, 1980
Creator: Liu, C.S.
Partner: UNT Libraries Government Documents Department
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Evaluation of two-beam spectroscopy as a plasma diagnostic

Description: A two-beam spectroscopy (TBS) system is evaluated theoretically and experimentally. This new spectroscopic technique uses correlations between components of emitted light separated by a small difference in angle of propagation. It is thus a non-perturbing plasma diagnostic which is shown to provide local (as opposed to line-of-sight averaged) information about fluctuations in the density of light sources within a plasma - information not obtainable by the usual spectroscopic methods. The presen… more
Date: April 1, 1980
Creator: Billard, B.D.
Partner: UNT Libraries Government Documents Department
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(Ion temperature gradient instability and transport: Progress report)

Description: Anomalous ion thermal conductivity remains in open physics issue for the present generation of high temperature Tokamaks. It is now believed to be due to the Ion Temperature Gradient (ITG or n{sub i}) instability. The production and identification of this instability is being studied in the simpler and experimentally convenient configuration of the steady state Columbia Linear Machine (CLM). The slab branch of this instability has been produced (by two different heating methods), identified and… more
Date: January 1, 1992
Partner: UNT Libraries Government Documents Department
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Wave Dynamics of Regular and Chaotic Rays

Description: In order to investigate general relationships between waves and rays in chaotic systems, I study the eigenfunctions and spectrum of a simple model, the two-dimensional Helmholtz equation in a stadium boundary, for which the rays are ergodic. Statistical measurements are performed so that the apparent randomness of the stadium modes can be quantitatively contrasted with the familiar regularities observed for the modes in a circular boundary (with integrable rays). The local spatial autocorrelati… more
Date: September 1, 1983
Creator: McDonald, S. W.
Partner: UNT Libraries Government Documents Department
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Doppler model for adiabatic toroidal compressor driftwave frequency profiles

Description: Microwave and CO/sub 2/ laser scattering experiments on ATC (Adiabatic Toroidal Compressor) Tokamak have shown that there exists a spectrum of fluctuations with parallel bar f parallel bar = parallel bar ..omega../2..pi.. parallel bar less than or equal to 1 MHz at wavelengths lambda approximately 0.28 cm and with parallel bar f parallel bar less than or equal to 400 kHz for lambda approximately 1 cm. However, a typical maximum frequency calculated for given experimental density and temperature… more
Date: October 1, 1977
Creator: Koch, R.A. & Tang, W.M.
Partner: UNT Libraries Government Documents Department
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MHD computation of feedback of resistive-shell instabilities in the reversed field pinch

Description: MHD computation demonstrates that feedback can sustain reversal and reduce loop voltage in resistive-shell reversed field pinch (RFP) plasmas. Edge feedback on {approximately}2R/a tearing modes resonant near axis is found to restore plasma parameters to nearly their levels with a close-fitting conducting shell. When original dynamo modes are stabilized, neighboring tearing modes grow to maintain the RFP dynamo more efficiently. This suggests that experimentally observed limits on RFP pulselengt… more
Date: May 1, 1992
Creator: Zita, E.J.; Prager, S.C. (Wisconsin Univ., Madison, WI (United States). Plasma Physics Research); Ho, Y.L. & Schnack, D.D (Science Applications International Corp., San Diego, CA (United States))
Partner: UNT Libraries Government Documents Department
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Trapped particle dynamics in toroidally rotating plasmas

Description: A detailed single particle orbit analysis is toroidally rotating plasma yields new analytical formulas for the second adiabatic invariant, the bounce frequency, and the precession frequency up to the first order correction in {rho}{sub pi}(poloidal ion gyroradium)/L{sub v}(scale length of rotation velocity), for toroidal flow values of the order of ion thermal velocity. Toroidal plasma rotation effects on the trapped ion instabilities in tokamaks are investigated in the context of local theory.… more
Date: June 1, 1992
Creator: Hahm, T.S.
Partner: UNT Libraries Government Documents Department
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