Development of Magnetically Insulated Baffled Probe Cluster for Measurement of Energy Flux and Particle Flux in the Texas Helimak

Progress is reported in employing magnetically insulated baffled (MIB) probes\footnote{\textit{RSI} 73, 3409, 2002; \textit{CPP} 44, 689 (2004); \textit{J. Phys. D} 44, 233001 (2011); \textit{RSI} 81, 10E129 (2010)} in the Texas Helimak\footnote{\textit{PoP} 21, 092302 (2014)}. Radial scans at the plasma edge of dc and ac space potential are presented. Like the Ball-Pen probe\footnote{\textit{CPP} 54, 279 (2014)}, the MIB probe shares the Langmuir probe simplicity and overcomes its shortcomings in the ability to make real-time measurements of plasma space potential, temperature, and energy/particle fluxes in magnetized plasma. By rotating the probe shaft to change the extent to which the baffle ``masks'' the probe collection area, the ratio between electron and ion probe current, and consequently the relative sensitivity of the floating-probe oscillations to space potential and electron/ion temperature, can be adjusted, thus allowing space potential fluctuations and electron/ion temperature fluctuations to be distinguished when measured at two different rotation angles. At the optimal rotation angle, the contribution of electron temperature and its fluctuations to the floating-potential measurement are eliminated and the space potential fluctuation phase is preserved.