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Gyrokinetic Theory for Arbitrary Wavelength Electromagnetic Modes in Tokamaks

Description: A linear gyrokinetic system for arbitrary wavelength electromagnetic modes is developed. A wide range of modes in inhomogeneous plasmas, such as the internal kink modes, the toroidal Alfvén eigenmode (TAE) modes, and the drift modes, can be recovered from this system. The inclusion of most of the interesting physical factors into a single framework enables us to look at many familiar modes simultaneously and thus to study the modifications of and the interactions between them in a systematic way. Especially, we are able to investigate self-consistently the kinetic MHD phenomena entirely from the kinetic side. Phase space Lagrangian Lie perturbation methods and a newly developed computer algebra package for vector analysis in general coordinate system are utilized in the analytical derivation. In tokamak geometries, a 2D finite element code has been developed and tested. In this paper, we present the basic theoretical formalism and some of the preliminary results.
Date: October 1, 1997
Creator: Qin, H.; Rewoldt, G. & Tang, W.M.
Partner: UNT Libraries Government Documents Department

Data analysis of tokamak experiments with singular value decomposition. Final report

Description: Under the grant, the applicant has developed a method of identifying poloidal and toroidal modes active in tokamak plasmas. Except complicated situations the method has shown to work well. Even with the limited applications, the advantage from the method is significant and even crucial. The method can be used to identify: (1) responsible coherent modes such as MHD or Resistive modes activity in plasma; (2) onset of instabilities; and can be used for (3) plasma controls. The method has been applied to the DIII-D tokamak experimental data, and some results are presented in this report. The authors also present how the method can be used for plasma controls.
Date: April 20, 1997
Creator: Kim, J.S.
Partner: UNT Libraries Government Documents Department

Ballooning-mirror instability and internally driven Pc 4--5 wave events

Description: A kinetic-MHD field-aligned eigenmode stability analysis of low frequency ballooning-mirror instabilities has been performed for anisotropic pressure plasma sin the magnetosphere. The ballooning mode is mainly a transverse wave driven unstable by pressure gradient in the bad curvature region. The mirror mode with a dominant compressional magnetic field perturbation is excited when the product of plasma beta and pressure anisotropy (P{sub {perpendicular}}/P{sub {parallel}} > 1) is large. From the AMPTE/CCE particle and magnetic field data observed during Pc 4--5 wave events the authors compute the ballooning-mirror instability parameters and perform a correlation study with the theoretical instability threshold. They find that compressional Pc 5 waves approximately satisfy the ballooning-mirror instability condition, and transverse Pc 4--5 waves are probably related to resonant ballooning instabilities with small pressure anisotropy.
Date: March 1, 1994
Creator: Cheng, C.Z.; Qian, Q.; Takahashi, K. & Lui, A.T.Y.
Partner: UNT Libraries Government Documents Department

Dissipation of Magnetohydrodynamic Waves on Energetic Particles: Impact on Interstellar Turbulence and Cosmic Ray Transport

Description: The physical processes involved in diffusion of Galactic cosmic rays in the interstellar medium are addressed. We study the possibility that the nonlinear MHD cascade sets the power-law spectrum of turbulence which scatters charged energetic particles. We find that the dissipation of waves due to the resonant interaction with cosmic ray particles may terminate the Kraichnan-type cascade below wavelengths 10{sup 13} cm. The effect of this wave dissipation has been incorporated in the GALPROP numerical propagation code in order to asses the impact on measurable astrophysical data. The energy-dependence of the cosmic-ray diffusion coefficient found in the resulting self-consistent model may explain the peaks in the secondary to primary nuclei ratios observed at about 1 GeV/nucleon.
Date: January 17, 2006
Creator: Ptuskin, V.S.; /Troitsk, IZMIRAN /Maryland U.; Moskalenko, Igor V.; /Stanford U., HEPL; Jones, F.C.; /NASA, Goddard et al.
Partner: UNT Libraries Government Documents Department

Global mirror modes in the magnetosheath

Description: A global stability analysis of mirror modes in the magnetosheath is presented. The analysis is based upon the kinetic-MHD formulation which includes relevant kinetic effects such as Landau resonance and gradient drift effects related to inhomogeneities in the background density, temperature, pressure and its anisotropy, magnetic field, and plasma flow velocity. Pressure anisotropy provides the free energy for the global mirror mode. The local theory of mirror modes predicts purely growing modes confined in the unstable magnetosheath region; however, the nonlocal theory that includes the effects of gradients and plasma flow predicts modes with real frequencies which propagate with the flow from the magnetosheath toward the magnetopause boundary. The real frequency is on the order of a combination of the diamagnetic drift frequency and the Doppler shift frequency associated with the plasma flow. The diamagnetic drift frequency provides a wave phase velocity in the direction of the magnetopause so that wave energy accumulates against the magnetopause boundary, and the amplitude is skewed in that direction. On the other hand, plasma flow also gives rise to a real phase velocity, but the phase velocity is smaller than the flow velocity. As a result, the wave amplitude is increased in the wake of the plasma flow and piles up against the bow shock boundary.
Date: May 1, 1996
Creator: Johnson, J.R. & Cheng, C.Z.
Partner: UNT Libraries Government Documents Department

Theory of semicollisional kinetic Alfven modes in sheared magnetic fields

Description: The spectra of the semicollisional kinetic Alfven modes in a sheared slab geometry are investigated, including the effects of finite ion Larmor radius and diamagnetic drift frequencies. The eigenfrequencies of the damped modes are derived analytically via asymptotic analyses. In particular, as one reduces the resistivity, we find that, due to finite ion Larmor radius effects, the damped mode frequencies asymptotically approach finite real values corresponding to the end points of the kinetic Alfven continuum.
Date: February 1, 1985
Creator: Hahm, T.S. & Chen, L.
Partner: UNT Libraries Government Documents Department

Hydromagnetic waves in high. beta. plasmas

Description: The wave propagation and damping properties in a collisionless thermal plasma for which ..beta.., the ratio of the plasma pressure to the magnetic pressure, is much greater than unity are determined. We achieve this by solving the full collisionless dispersion relation as an expansion in 1/..beta... To do this we develop a set of iteration methods which converge to this solution. We illustrate these results with two applications, the trapping of cosmic rays in supernovae remnants and the collisionless damping of hydromagnetic turbulence.
Date: February 1, 1979
Creator: Foote, E.A. & Kulsrud, R.M.
Partner: UNT Libraries Government Documents Department

Spectrum of resistive MHD modes in cylindrical plasmas

Description: A numerical study of the normal modes of a compressible resistive MHD fluid in cylindrical geometry is presented. Resistivity resolves the shear Alfven and slow magnetosonic continua of ideal MHD into discrete spectra and gives rise to heavily damped modes whose frequencies lie on specific lines in the complex plane. Fast magnetosonic waves are less affected but are also damped. Overstable modes arise from the shear Alfven spectrum. The stabilizing effect of favorable average curvature is shown. Eigenfunctions illustrating the nature of typical normal modes are displayed.
Date: July 1, 1983
Creator: Ryu, C.M. & Grimm, R.C.
Partner: UNT Libraries Government Documents Department

Kinetic theory of toroidicity and ellipticity-induced Alfven eigenmodes

Description: Toroidicity-induced Alfven eigenmodes (TAE) and ellipticity-induced Alfven eigenmodes (EAE) are currently of great interest because they may destroy the confinement of fast ions in a burning tokamak plasma. The present study focuses on kinetic effects, extending the non-perturbative kinetic analysis of the TAE to the EAE. One finds that the parameter which measures the kinetic character of the EAE is significantly smaller than it is for the TAE for elongated plasmas like DIII-D. The parameter is rather small for the lower mode numbers but attains values of order unity or larger for the higher mode numbers, since the parameter scales as the square of the mode number. Consequently, one expects the lower mode number EAE's to have a strongly magnetohydrodynamic (MHD) character, and to suffer only perturbative damping that depends linearly on the dissipative mechanisms. However, while the former is true, the latter is not necessarily the case. This work examines these kinetic T/EAE(KT/EAE) modes in further detail.
Date: October 1, 1992
Creator: Mett, R.R. & Mahajan, S.M.
Partner: UNT Libraries Government Documents Department

Analysis of the Giacobini-Zinner bow wave

Description: The cometary bow wave of P/Giacobini-Zinner has been analyzed using the complete set of ICE field and particle observations to determine if it is a shock. Changes in the magnetic field and plasma flow velocities from upstream to downstream have been analyzed to determine the direction of the normal and the propagation velocity of the bow wave. The velocity has then been compared with the fast magnetosonic wave speed upstream to derive the Mach number and establish whether it is ''supersonic'', i.e., a shock, or ''subsonic,'' i.e., a large amplitude wave. The various measurements have also been compared with values derived from a Rankine-Hugoniot analysis. The results indicate that, inbound, the bow wave is a shock with M = 1.5. Outbound, a subsonic mach number is obtained, however, arguments are presented that the bow wave is also likely to be a shock at this location. 11 refs., 4 figs., 2 tabs.
Date: January 1, 1986
Creator: Smith, E.J.; Slavin, J.A.; Bame, S.J.; Thomsen, M.F.; Cowley, S.W.H.; Richardson, I.G. et al.
Partner: UNT Libraries Government Documents Department

Force balance limiting current for charged particle beams

Description: A limiting current for cold, relativistic, charged particle beams is derived. Arbitrary rotation and axial flow profiles are allowed. Only force balance is required. A comparison with the usual Brillouin condition reveals a significantly more restrictive scaling for ambitious beam parameters. 6 references, 2 figures, 1 table.
Date: July 1, 1984
Creator: Kadish, A.
Partner: UNT Libraries Government Documents Department

Differential equation for Alfven ion cyclotron waves in finite-length plasma

Description: One finds the fourth-order differential equation describing an Alfven-ion-cyclotron wave propagating along a magnetic field of varying intensity. The equation is self-adjoint and possesses non-trivial turning points. The final form of the equation is checked using MACSYMA, a system for performing algebra on a computer.
Date: September 7, 1977
Creator: Watson, D. C.; Fateman, R. J. & Baldwin, D. E.
Partner: UNT Libraries Government Documents Department

Extremely Fast Acceleration of Cosmic Rays in a Supernova Remnant

Description: Galactic cosmic rays (CRs) are widely believed to be accelerated by shock waves associated with the expansion of supernova ejecta into the interstellar medium. A key issue in this long-standing conjecture is a theoretical prediction that the interstellar magnetic field can be substantially amplified at the shock of a young supernova remnant (SNR) through magnetohydrodynamic waves generated by cosmic rays. Here we report a discovery of the brightening and decay of X-ray hot spots in the shell of theSNRRXJ1713.723946 on a one-year timescale. This rapid variability shows that the X-rays are produced by ultrarelativistic electrons through a synchrotron process and that electron acceleration does indeed take place in a strongly magnetized environment, indicating amplification of the magnetic field by a factor of more than 100. The X-ray variability also implies that we have witnessed the ongoing shock-acceleration of electrons in real time. Independently, broadband X-ray spectrometric measurements of RXJ1713.723946 indicate that electron acceleration proceeds in the most effective ('Bohm-diffusion') regime. Taken together, these two results provide a strong argument for acceleration of protons and nuclei to energies of 1 PeV (10{sup 15} eV) and beyond in young supernova remnants.
Date: October 23, 2007
Creator: Uchiyama, Y.; Aharonian, F. A.; Tanaka, T.; Takahashi, T. & Maeda, Y.
Partner: UNT Libraries Government Documents Department

Quasilinear theory of ion-cyclotron resonance heating of plasmas and associated longitudinal cooling

Description: It is shown from quasilinear theory that an initially isotropic magnetized plasma will be forced into an anisotropic state in ion-cyclotron resonance heating. Strong heating of perpendicular ion temperature and strong cooling of longitudinal temperature should occur simultaneously. The maximum temperature ratio predicted by quasilinear theory is in exact agreement with that predicted from basic thermodynamic arguments by Busnardo--Neto, Dawson, Kamimura and Lin. Heating by fast hydromagnetic wave is also examined. (auth)
Date: February 1, 1976
Creator: Arunasalam, V.
Partner: UNT Libraries Government Documents Department

Kinetic theory of toroidicity-induced Alfven eigenmode

Description: An analytic kinetic description of the toroidicity-induced Alfven eigenmode (TAE) is presented. The theory includes electron parallel dynamics non-perturbatively, an effect which is found to strongly influence the character and damping of the TAE --- contrary to previous theoretical predictions. We use a parallel conductivity model that includes collisionless (Landau) damping on the passing electrons and collisional damping on both trapped and passing electrons. Together, these mechanisms damp the TAE more strongly than previously expected. This is because the TAE couples (or merges) with the kinetic Alfven wave (KAW) if the gap is sufficiently thin and/or the magnitude of the conductivity is sufficiently small. The high damping could be relevant to recent experimental measurements of the TAE damping coefficient. In addition, the theory predicts a kinetic'' TAE, whose eigenfrequency lies just above the gap, whose existence depends on finite conductivity, and which is formed by the coupling of two KAWs.
Date: March 1, 1992
Creator: Mett, R.R. & Mahajan, S.M.
Partner: UNT Libraries Government Documents Department

Existence and damping of toroidicity-induced Alfven eigenmodes

Description: A new method of analyzing the toroidicity-induced Alfven eigenmode (TAE) from kinetic theory is presented. The analysis includes electron parallel dynamics non-perturbatively, an effect which is found to strongly influence the character and damping of the TAE -- contrary to previous theoretical predictions. The normal electron Landau damping of the TAE is found to be higher than previously expected, and may explain recent experimental measurements of the TAE damping coefficient. 11 refs., 1 fig., 1 tab.
Date: December 1, 1991
Creator: Mahajan, S.M. & Mett, R.R.
Partner: UNT Libraries Government Documents Department

Theory of Alfven wave heating in general toroidal geometry

Description: A general treatment of Alfven wave heating based on the linearized equations of ideal magnetohydrodynamics (MHD) is given. The conclusion of this study is that the geometry of the plasma equilium could play an important role on the effectiveness of this heating mechanism, and for certain geometries the fundamental equations may not possess solutions which satisfy prescribed boundary conditions.
Date: September 1, 1981
Creator: Tataronis, J.A. & Salat, A.
Partner: UNT Libraries Government Documents Department

Comments on proposed experimental study of fusion product losses from PLT and TFTR plasmas

Description: An experimental technique is proposed for measuring the fusion product leakage from the PLT and TFTR tokamaks. The experiment would use two detectors (one at the top and one at the outboard side of the torus) shielded, and facing away from the plasma so that fusion products can enter along gyro-helices. (MOW)
Date: October 1, 1978
Creator: Hively, L. & Miley, G.H.
Partner: UNT Libraries Government Documents Department

Alpha-driven fast magnetosonic wave heating in tokamak plasmas

Description: An alpha-driven fast magnetosonic wave instability is investigated in tokamak plasmas for propagation transverse to the external magnetic field at frequencies several times the alpha gyrorate. A two-dimensional differential quasi-linear diffusion equation is derived in cylindrical v/sub perpendicular/ - v/sub parallel/ geometry. The quasi-linear diffusion coefficients in the small parameter k/sub parallel/k/sub perpendicular/ are expanded and the problem is reduced to one dimension by integrating out the v/sub parallel/ dependence. Reactor relevant information is obtained using data from the one-dimensional formulation in a 1-1/2 dimensional tokamak transport code. Contour plots of the alpha threshold fraction are used to identify the instability regions in the n/sub e/-T/sub i/ plane. Alpha/background electron fractions as low as 10/sup -6/ to 10/sup -4/ may trigger the instability. For a typical reactor-size tokamak, an enhancement of the fraction of the alpha energy transferred to ions by as much as 1.5 can occur for T/sub i/ = T/sub e/ at 7 keV. Still, due to the rapid equilibration of electron and ion temperatures, a <1 to 2% increase in fusion power occurs overall.
Date: January 1, 1985
Creator: Miley, G.H.; Sutton, W.R. III & Sigmar, D.J.
Partner: UNT Libraries Government Documents Department

The Hard-Core Pinch. Part I

Description: It is well known that a pinch column with internal H/sub Z/ and external conducting shell can be made grossly stable, but that small-scale instabilities persist; especiaily in the tubular region of maximum current density. To investigate further these small-scale instabilities of the stabilized pinch,'' we are using 12-in.-i.d. linear pinch tube with a 3-in.-o.d. insulated center rod. By controlling a current along this rod, as well as a current along external conducting straps, and a third current in an external H/sub z/ coil, it is possible to create many grossly stable pinch configurations. The small-scale stability of the tubular region of maximum current density can thus be studied for a wide range of internal and external magnetic field vectors. The magnetic field distribution in each discharge is obtained by a string of 10 magnetic pick- up loops. The distribution of plasma density is determined by modulating the inner or outer wall current and measuring the radial velocity of the resultant compressional Alfven waves. In one experiment, an initial H/sub z/ is entrapped in plasma by preionization, and then pushed radially outward from the rod by a rising H/sub theta /. The resultant field distribution, in which H/sub theta / everywhere falls more rapidly than 1/r, should have absolute hydromagnetic stability. The persistence of small-scale instabilities, as observed by the magnetic probes, in this inverse stabilized pinch'' suggests that the basic trouble is nonhydromagnetic. It is also found that, when the magnetic field approximates a vacuum field distribution, perfectly smooth and reproducible probe signals can be obtained. The absolute plasma current densities at which nearvacuum field distributions have been found stable are larger than current densities at which the 'stabilized pinch'' and inverse stabilized pinch'' distributions have been found unstable. (auth)
Date: July 31, 1959
Creator: Birdsall, D.H.; Colgate, S.A. & Furth, H.P.
Partner: UNT Libraries Government Documents Department