ANALYSIS OF ICRF (OMEGA-LESS-THAN-OR-EQUAL-TO-OMEGA-CI) PLASMA PRODUCTION IN LARGE-SCALE TOKAMAKS

The paper studies the possibility of target plasma radiofrequency (RF) production in the ion cyclotron range of frequencies (ICRF) (omega less-than-or-equal-to omega(ci)) in large scale tokamaks before the startup of an Ohmic discharge. A number of experimental and theoretical studies on dense plasma production in the ICRF in toroidal magnetic devices are reviewed. The criteria for optimal development of the RF discharge stages are analysed, i.e. for RF breakdown of the neutral fill gas in the vicinity of the antenna (non-wave stage, n(e) much less than n(a), where n(e) and n(a) are the densities of electrons and atoms), and the wave stages of initial ionization (n(e) < n(a)) and neutral gas burnout (n(e) approximately n(a)) in the whole volume of the plasma torus. A number of requirements for the design of the antenna system are formulated for all stages of dense plasma ICRF production. A scenario for plasma ICRF production with slot type antennas in the ITER tokamak is proposed. Numerical simulations with a 0-D transport code show that in ITER a target plasma with an electron density of almost-equal-to 3 x 10(12) cm-3 can be produced by coupling 3-6 MW of RF power to the plasma at a frequency of almost-equal-to 3 MHz. Such a level of RF power is sufficient not only for full ionization of the neutral gas but also for heating the produced plasma to electron temperatures of approximately 80 eV.