27 research outputs found
Recommended from our members
MEASUREMENTS OF BEAM-ION CONFINEMENT DURING TANGENTIAL BEAM-DRIVEN INSTABILITIES IN A BEAM TOKAMAK EXPERIMENT
Astrophysical gyrokinetics: kinetic and fluid turbulent cascades in magnetized weakly collisional plasmas
We present a theoretical framework for plasma turbulence in astrophysical plasmas (solar wind, interstellar medium, galaxy clusters, accretion disks). The key assumptions are that the turbulence is anisotropic with respect to the mean magnetic field and frequencies are low compared to the ion cyclotron frequency. The energy injected at the outer scale scale has to be converted into heat, which ultimately cannot be done without collisions. A KINETIC CASCADE develops that brings the energy to collisional scales both in space and velocity. Its nature depends on the physics of plasma fluctuations. In each of the physically distinct scale ranges, the kinetic problem is systematically reduced to a more tractable set of equations. In the "inertial range" above the ion gyroscale, the kinetic cascade splits into a cascade of Alfvenic fluctuations, which are governed by the RMHD equations at both the collisional and collisionless scales, and a passive cascade of compressive fluctuations, which obey a linear kinetic equation along the moving field lines associated with the Alfvenic component. In the "dissipation range" between the ion and electron gyroscales, there are again two cascades: the kinetic-Alfven-wave (KAW) cascade governed by two fluid-like Electron RMHD equations and a passive phase-space cascade of ion entropy fluctuations. The latter cascade brings the energy of the inertial-range fluctuations that was damped by collisionless wave-particle interaction at the ion gyroscale to collisional scales in the phase space and leads to ion heating. The KAW energy is similarly damped at the electron gyroscale and converted into electron heat. Kolmogorov-style scaling relations are derived for these cascades. Astrophysical and space-physical applications are discussed in detail
Howes et al. Reply
Howes et al. Reply to Comment on "Kinetic Simulations of Magnetized Turbulence in Astrophysical Plasmas" arXiv:0711.435
Intrinsic momentum transport in up-down asymmetric tokamaks
Recent work demonstrated that breaking the up-down symmetry of tokamak flux
surfaces removes a constraint that limits intrinsic momentum transport, and
hence toroidal rotation, to be small. We show, through MHD analysis, that
ellipticity is most effective at introducing up-down asymmetry throughout the
plasma. We detail an extension to GS2, a local gyrokinetic code that
self-consistently calculates momentum transport, to permit up-down asymmetric
configurations. Tokamaks with tilted elliptical poloidal cross-sections were
simulated to determine nonlinear momentum transport. The results, which are
consistent with experiment in magnitude, suggest that a toroidal velocity
gradient, , of 5% of the
temperature gradient, , is
sustainable. Here is the ion thermal speed, is the ion
toroidal mean flow, is the minor radial coordinate normalized to the
tokamak minor radius, and is the ion temperature. Since other intrinsic
momentum transport mechanisms scale poorly to larger machines, these results
indicate that up-down asymmetry is the most feasible method to generate the
current experimentally-measured rotation levels in reactor-sized devices
Recommended from our members
Charge exchange and fusion reaction measurements during compression experiments with neutral beam heating in the tokamak fusion test reactor
Adiabatic toroidal compression experiments were performed in conjunction with high power neutral beam injection in the Tokamak Fusion Test Reactor (TFTR). Acceleration of beam ions to energies nearly twice the injection energy was measured with a charge exchange neutral particle analyser. Measurements were also made of 2.5 MeV neutrons and 15 MeV protons produced in fusion reactions between the deuterium beam ions and the thermal deuterium and3He ions, respectively. When the plasma was compressed, the d(d, n)3He fusion reaction rate increased by a factor of five, and the3He(d, p) α rate by a factor of twenty. These data were simulated with a bounce averaged Fokker-Planck program, which assumed conservation of angular momentum and magnetic moment during compression. The results indicate that the beam ion acceleration was consistent with adiabatic scaling. © 1986 IOP Publishing Ltd
Recommended from our members
Acceleration of beam ions during major-radius compression in the tokamak fusion test reactor.
Tangentially coinjected deuterium beam ions were accelerated from 82 up to 150 keV during a major-radius compression experiment in the tokamak fusion test reactor. The ion energy spectra and the variation in fusion yield were in good agreement with Fokker-Planck code simulations. In addition, the plasma rotation velocity was observed to rise during compression. © 1985 The American Physical Society