Heating and current drive by ion cyclotron waves in the activated phase of ITER

Abstract

Waves in the ion cyclotron range of frequency (ICRF) are expected to play a central role in the heating of ITER plasmas during deuterium (D)–tritium (T) operation. These waves can also be used to drive current by direct electron damping of the fast wave, provided an appropriate antenna phasing is used. The corresponding current profile is peaked near the magnetic axis, and can have a beneficial effect on the discharge stability and performance. In this paper, two scenarios applicable during the activated phase of ITER operation are compared: second harmonic tritium heating and minority helium-3 heating, which differ in the addition of a small fraction of 3He ions (2%) in the DT mixture for the latter. The resulting change of the dominant ICRF heating scheme causes the discharge properties to differ appreciably. In this paper, a full-wave code is coupled to a Fokker–Planck solver and a current drive module to investigate in detail the effect of ICRF waves on the discharge. The impact of phasing on the scenario in terms of plasma heating and current drive efficiency is studied by simulating ICRF heating with various antenna toroidal spectra. It is found that despite a lower current drive efficiency, the addition of 3He in the discharge increases the single-pass absorption rate, the ion heating fraction, and makes the scenario essentially immune to details in the toroidal phasing and fast ion properties.

A new ion cyclotron range of frequency scenario for bulk ion heating in deuterium-tritium plasmas: How to utilize intrinsic impurities in our favour

“…The computed results are quite similar to those reported in Ref. [9] (however, a higher plasma density and temperatures were used in those simulations).…”

“…7), dominant absorption of RF power by Be ions in D:T=1:1 ITER plasmas was computed for X Be = 1%, f = 40 MHz and k (ant) = 4 m −1 . (d) In recent papers, where the ICRF scenarios for the activated phase of ITER were studied, a significant impurity absorption, mostly by argon, was reported [8,9]. Because the ICRF frequency was chosen to locate the 3 He resonance centrally, the argon resonance was placed at the very high field side edge.…”

“…Note that fully ionized argon ions have a charge-to-mass ratio (Z/A = 0.45) very similar to that of Be ions. Again this impurity absorption was considered as a parasitic effect; however, in [9] it was outlined that this effect deserves further investigation with respect to the ICRF operation in ITER.…”

“…ICRF scenarios relevant for the D-T plasmas were discussed in detail in Refs. [1,3,4,7], with the emphasis to ITER in, e.g., [8,9]. Many of these scenarios were studied experimentally during the past D-T experiments in JET and TFTR tokamaks [10][11][12][13][14].…”

“…Finally, we discuss how the current design of the ICRF system in ITER can be adapted to exploit the advantages of beryllium ICRF heating to their maximum. The proposed method is not restricted to the use of 9 Be only, but other impurities with a similar charge-to-mass ratio, such as 7 Li, 22 Ne, 40 Ar, etc. can be used as well.…”