Liquid cooled antenna for high power helicon source

Controlled Shear Decorrelation eXperiment (CSDX) is a helicon plasma device used to simulate scrape off layer and divertor plasmas to study turbulence, transport, helicon core formation and axial detachment. A helicon plasma source using an external antenna requires an insulating sleeve forming the vacuum boundary to allow the RF to penetrate. Recently, several high-power helicon devices have been designed [1, 2, 3], but heating issues with the RF window restrict plasma operation timescales. To mitigate this constraint, we have designed and built a novel water-cooled RF window which allows steady state operation. We use de-ionized water as the coolant, flowing within two concentric insulators as the RF window. We have successfully demonstrated the production of steady state, high density (n_e > 10¹⁹ m^-3, T_e ~ 5 eV) plasmas. We report results from several studies with and without water cooling, such as antenna loading, infrared imaging of the inner ceramic cylinder, calorimetric studies and plasma parameters from probes and spectroscopy. The results from CSDX will be used to answer critical engineering questions for the MPEX device at ORNL.

[1] B. D. Blackwell, et. al., PSST, 21 055033 (2012)

[2] J. Rapp, et. al., NF, 57 116001 (2017)

[3] I. Furno, et. al., EPJ, 157 03014 (2017)