ICRH on the High‐Density Plasmas in ATF

ICRH experiments on the ECH‐produced low‐density plasmas (ne≤1.0×1013 cm−3) in ATF showed loading which was less than the vacuum loading. Computations using the ORION code also supported this conclusion. To increase the loading and rf power penetration into ATF plasma, the density was increased by injecting a helium‐neutral beam into a deuterium plasma with a hydrogen minority. In this case we could still control the minority concentration. Simulations predicted 10 times higher loading, good penetration of rf power into the central region, and enhanced plasma heating. In experiments, with plasma densities ne≥5.0×1013 cm−3, 100 kW of rf power was successfully coupled to the plasma and higher loading was demonstrated as predicted by simulation. There was also a slight increase in stored energy.