461 research outputs found
Perpendicular momentum injection by lower hybrid wave in a tokamak
The injection of lower hybrid waves for current drive into a tokamak affects
the profile of intrinsic rotation. In this article, the momentum deposition by
the lower hybrid wave on the electrons is studied. Due to the increase in the
poloidal momentum of the wave as it propagates into the tokamak, the parallel
momentum of the wave increases considerably. The change of the perpendicular
momentum of the wave is such that the toroidal angular momentum of the wave is
conserved. If the perpendicular momentum transfer via electron Landau damping
is ignored, the transfer of the toroidal angular momentum to the plasma will be
larger than the injected toroidal angular momentum. A proper quasilinear
treatment proves that both perpendicular and parallel momentum are transferred
to the electrons. The toroidal angular momentum of the electrons is then
transferred to the ions via different mechanisms for the parallel and
perpendicular momentum. The perpendicular momentum is transferred to ions
through an outward radial electron pinch, while the parallel momentum is
transferred through collisions.Comment: 22 pages, 4 figure
Verifying raytracing/Fokker-Planck lower-hybrid current drive predictions with self-consistent full-wave/Fokker-Planck simulations
Raytracing/Fokker-Planck (FP) simulations used to model lower-hybrid current
drive (LHCD) often fail to reproduce experimental results, particularly when
LHCD is weakly damped. A proposed reason for this discrepancy is the lack of
"full-wave" effects, such as diffraction and interference, in raytracing
simulations and the breakdown of raytracing approximation. Previous studies of
LHCD using non-Maxwellian full-wave/FP simulations have been performed, but
these simulations were not self-consistent and enforced power conservation
between the FP and full-wave code using a numerical rescaling factor. Here we
have created a fully-self consistent full-wave/FP model for LHCD that is
automatically power conserving. This was accomplished by coupling an overhauled
version of the non-Maxwellian TORLH full-wave solver and the CQL3D FP code
using the Integrated Plasma Simulator. We performed converged full-wave/FP
simulations of Alcator C-Mod discharges and compared them to raytracing. We
found that excellent agreement in the power deposition profiles from raytracing
and TORLH could be obtained, however, TORLH had somewhat lower current drive
efficiency and broader power deposition profiles in some cases. This
discrepancy appears to be a result of numerical limitations present in the
TORLH model and a small amount of diffractional broadening of the TORLH wave
spectrum. Our results suggest full-wave simulation of LHCD is likely not
necessary as diffraction and interference represented only a small correction
that could not account for the differences between simulations and experiment
Sawtooth period changes with mode conversion current drive on Alcator C-Mod
DEFC0299ER54512. Reproduction,Ā translation,Ā publication,Ā useĀ andĀ disposal,Ā in whole orĀ inĀ part,Ā byĀ orĀ forĀ theĀ UnitedĀ StatesĀ governmentĀ isĀ permitted. Submitted forĀ publicationĀ toĀ PlasmaĀ PhysicsĀ andĀ ControlledĀ Fusion. Sawtooth period changes with mode conversion current drive on Alcator C-Mo
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Pulsed lower-hybrid wave penetration in reactor plasmas
Providing lower-hybrid power in short, intense (GW) pulses allows enhanced wave penetration in reactor-grade plasmas. We examine nonlinear absorption, ray propagation, and parametric instability of the intense pulses. We find that simultaneously achieving good penetration while avoiding parametric instabilities is possible, but imposes restrictions on the peak power density, pulse duration, and/or rf spot shape. In particular, power launched in narrow strips, elongated along the field direction, is desired. 4 refs., 4 figs
The Kinematics and Metallicity of the M31 Globular Cluster System
With the ultimate aim of distinguishing between various models describing the
formation of galaxy halos (e.g. radial or multi-phase collapse, random
mergers), we have completed a spectroscopic study of the globular cluster
system of M31. We present the results of deep, intermediate-resolution,
fibre-optic spectroscopy of several hundred of the M31 globular clusters using
the Wide Field Fibre Optic Spectrograph (WYFFOS) at the William Herschel
Telescope in La Palma, Canary Islands. These observations have yielded precise
radial velocities (+/-12 km/s) and metallicities (+/-0.26 dex) for over 200
members of the M31 globular cluster population out to a radius of 1.5 degrees
from the galaxy center. Many of these clusters have no previous published
radial velocity or [Fe/H] estimates, and the remainder typically represent
significant improvements over earlier determinations. We present analyses of
the spatial, kinematic and metal abundance properties of the M31 globular
clusters. We find that the abundance distribution of the cluster system is
consistent with a bimodal distribution with peaks at [Fe/H] = -1.4 and -0.5.
The metal-rich clusters demonstrate a centrally concentrated spatial
distribution with a high rotation amplitude, although this population does not
appear significantly flattened and is consistent with a bulge population. The
metal-poor clusters tend to be less spatially concentrated and are also found
to have a strong rotation signature.Comment: 33 pages, 20 figure
Generation Of High Non-inductive Plasma Current Fraction H-mode Discharges By High-harmonic Last Wave Heating In The National Spherical Torus Experiment
1.4 MW of 30 MHz high-harmonic fast wave (HHFW) heating, with current drive antenna phasing, has generated a Ip = 300kA, BT (0) = 0.55T deuterium H-mode plasma in the National Spherical Torus Experiment that has a non-inductive plasma current fraction, fNI = 0.7-1. Seventy-five percent of the non-inductive current was generated inside an internal transport barrier that formed at a normalized minor radius, r/a {approx} 0.4 . Three quarters of the non-inductive current was bootstrap current and the remaining non-inductive current was generated directly by HHFW power inside r/a {approx} 0.2
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