Overview of Measurements from the Wendelstein 7-X Phase Contrast Imaging Diagnostic and Plans for the OP2 Campaign*

A phase contrast imaging (PCI) diagnostic was implemented on the W7-X stellarator starting in the OP$1.2$ experimental campaign.$^1$ The PCI diagnostic creates an image of plasma density fluctuations using light from a CO$_2$ laser that passes through the plasma which captures the line-integral of the fluctuations along the optical path of the laser. The typical measurement range spans frequencies of about $2$ kHz to $600$ kHz, and wavenumbers of approximately $1$ cm$^{-1}$ to $10$ cm$^{-1}$, although the actual range depends on the optical magnifications used. PCI measurements of both coherent Alfv\'enic modes and broadband fluctuations will be presented. Changes to the PCI diagnostic for the OP2 campaign will be presented, with an outlook to possible future additions to the diagnostic including an optical heterodyne system for detection of ion-cyclotron resonance heating (ICRH) waves and an alternate optical design that allows for simultaneous measurement of the plasma image and the Fourier spectra of the fluctuations.\\ $[1]$ E.~M. Edlund et al, Rev. Sci. Instr. 89, 10E105 (2018).