Optimization and operation of the upgraded PCI system on Wendelstein 7-X

A phase contrast imaging (PCI) diagnostic using a CO2 laser at 10.6 µm wavelength has been implemented on the W7-X stellarator during the 2017 OP1.2a campaign [1]. PCI is an internal reference beam interferometric technique which provides a direct image of line integrated electron density fluctuations in a plasma. In OP1.2a, typical wave numbers and frequencies that could be measured with PCI were in the range of 1.5 < k(cm^-1) < 14 at 2 <f(kHz) < 2000. The diagnostic has been upgraded during the past year and new physics results will be presented in a companion paper [2]. Key upgrades during the past year include a new telescope design to expand the upper limit of measurable wave-numbers to 30 cm^-1, an additional detector employing a spatial filter to focus on different locations in the plasma, a feedback-controlled vibration compensation system, a new sound wave calibration system, and a memory upgrade to allow data acquisition for 75 s compared to 4 s in OP1.2a.

References

[1] E. Edlund, M. Porkolab, O. Grulke et al, Proc. HTPD2018 Conference, San Diego, 2018.

[2] M. Porkolab, E. Edlund, et al, at this conference.