Abstract
The effects of fast electron confinement and plasma
temperature on the lower hybrid current ramp-up efficiency are
investigated. The production of reverse runaways in a toroidal geometry
is calculated with a Monte Carlo particle following code, which includes
collisions and both neoclassical and relativistic effects. When
anomalous fast electron diffusion in the configuration space is taken
into account, the ramp-up efficiency is found to be enhanced for
increasing loss rate of runaway electrons. The enhancement is in
accordance with a simple analytical model that expresses the efficiency
as a function of the average runaway electron confinement time and the
runaway fraction of current carrying electrons. A larger runaway
production rate is found for the electrons orbiting on outer magnetic
surfaces, because their trapping region in velocity space is wider. The
runaway rate is also significantly enhanced, as the thermal velocity is
increased up to and above one sixth of the runaway velocity vR.
The range of the phase velocity spectrum where the waves efficiently
ramp up the current in large tokamaks is limited by these effects to
velocities below 1.3vR
Original language | English |
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Pages (from-to) | 887 - 894 |
Number of pages | 8 |
Journal | Nuclear Fusion |
Volume | 33 |
Issue number | 6 |
DOIs | |
Publication status | Published - 1993 |
MoE publication type | A1 Journal article-refereed |