Progress in the development of RF diagnostics for NSTX-U and WEST

Recent advances in computational tools have made it possible to locally compare the RF wave-field in scrape-off-layer (SOL) plasmas with simulations, which motivated the need for new RF diagnostics for wave characterization in the SOL of NSTX-U and WEST. To characterize and mitigate the high harmonic fast wave (HHFW) power flow in the SOL of NSTX-U, we have been developing an 8-channel homodyne RF detection system that will be connected to the RF Langmuir probes in the antenna and divertor regions of NSTX-U. This diagnostic will allow us to locally measure the RF voltage in the SOL to study RF rectification effects (R. J. Perkins et al., PoP 22, 042506 (2015)) and will support spectral analysis to study parametric decay instabilities (J. R. Wilson et al., AIP Conf. Proc. 787, 66 (2005)). In parallel, we have been assessing the possibility of installing an RF B-dot probe to a reciprocating probe system on WEST. COMSOL modeling of the probe's response at the WEST ICRF frequency (50 MHz) allowed us to optimize the probe's dimensions, and a prototype probe has been built and calibrated in the lab. This diagnostic will yield crucial data to validate recent full-wave simulations on the WEST tokamak and may support a study of parametric decay instabilities in the SOL of WEST.