Diagnostics for Radial Electron Thermal Transport Measurements

Production and identification of electron temperature gradient (ETG) mode have been successfully demonstrated in a basic experiment in Columbia Linear Machine CLM [1]. ETG mode was excited by heating electrons of the core plasma. For local measurement of radial electron thermal transport we use miniature langmuir probes with special resolution $ < 1mm$ and frequency response $ > 2MHz$. Triple probes will be used to measure local temperature fluctuations. For significant improvement of the frequency response of the triple probe we used a capacitive probe as a single probe and used capacitive coupling of double probe's positive tip with the measuring circuit. Then cross- correlation of the electron temperature fluctuations and potential fluctuations will yield local thermal flux. A non-local measurement scheme based on a variation of perturbative transport method is attempted. Here we modulate (at $\sim$ 20-50kHz) the accelerating bias voltage which produces the electron heating. The resulting modulated $ \tilde {T_e}$ in the plasma core will be conducted / convected to the plasma edge, where it will be measured by a triple probe. $[1]$ X. Wei, V. Sokolov and A.K. Sen, Bulletin of 49th APS DPP, p.110, 2007.