Investigations of Low and Moderate Harmonic Fast Wave Physics on CDX‐U

Third harmonic hydrogen cyclotron fast wave heating studies are planned in the near term on CDX‐U to investigate the potential for bulk ion heating. In preparation for these studies, the available RF power in CDX‐U has been increased to 0.5 MW. The operating frequency of the CDX‐U RF transmitter was lowered to operate in the range of 8 – 10 MHz, providing access to the ion harmonic range 2Ω ∼ 4Ω in hydrogen. A similar regime is accessible for the 30 MHz RF system on NSTX, at 0.6 Tesla in hydrogen. Preliminary computational studies over the plasma regimes of interest for NSTX and CDX‐U indicate the possibility of strong localized absorption on bulk ion species.