ICRF heating

This paper reports that radio-frequency (RF) power in the ion cyclotron range of frequencies (ICRF) has been chosen as the primary auxiliary heating technique for BPX. This decision is based on the wide success of ICRF heating in existing large-scale experiments (JET, TFTR, JT-60), the capability of ion cyclotron waves to penetrate the high-density plasmas of BPX, the ability to concentrate ICRF power deposition near the plasma center, and the ready availability of high-power sources in the appropriate frequency range. The primary task of the ICRF system is to heat to fusion temperatures. However, other important roles are envisaged, such as the stabilization of sawteeth, preheating of the plasma during current rampup, and study of plasma current profile control by means of fast-wave current drive. It is essential that the ICRF system be capable of coupling power to the plasma effectively for all planned operating modes and that the ICRF system not rely on the tokamak to provide an ideal plasma tailored for ICRF heating. The baseline heating scenario is to use 3He minority in the D-T fuel plasma. At full field, B0 = 9 T, this requires fRF ∼ 90 MHz. In lower field operation, B0 = 6 T, 3He minority at fRF ∼ 60 MHz and hydrogen minority at fRF ∼ 90 MHz will be used. The RF system will provide at least 20 MW coupled to the plasma in the frequency range of 60 to 90 MHz for pulses at least 15 s long. This is to be provided by 16 power sources. The possibility of an upgrade to 30 MW will be accommodated in the facility design. Operation in the range fRF = 120 to 135 MHz may also be possible at reduced power, permitting hydrogen minority or second-harmonic deuterium heating at full field