Update on the W7-X phase contrast imaging diagnostic for OP 2 experiments

Recent experiments in high performance stellarator plasmas, such as W7-X, indicate that turbulence plays a dominant role in determining the transport of energy and particles [1]. A wide range of instabilities, including ITG and TEM modes can produce turbulence across a wide range of temporal and spatial scales. The W7-X phase contrast imaging (PCI) diagnostic is capable to measure turbulent density fluctuations with a bandwidth of 2 kHz to about 500 kHz, with higher frequency fluctuations detectable at lower signal levels, and a wavenumber range spanning 1.5 cm^-1 to 10 cm^-1, depending on the optical configuration used [2]. The implementation of water-cooled divertors in W7-X imposed major changes to the diagnostic system for the OP 2 campaign. This presentation will review the recently upgraded PCI diagnostic, its measurements capabilities, and an optical heterodyne upgrade that will create the possibility of ICRF wave detection. Some representative measurements from the OP1.2 experiments and the OP2 experiments, if available, will also be presented.



[1] M.N.A. Beurskens et al., Nucl. Fusion 61, 116072 (2021).

[2] Z. Huang et al., JINST 16, P01014 (2021).