DESIGN OF A 3RD-HARMONIC ELECTRON-CYCLOTRON EMISSION DIAGNOSTIC FOR BALLOONING MODE FLUCTUATIONS IN PBX-M

A third-harmonic electron cyclotron emission diagnostic using ultrawide bandwidth (≈40 GHz) heterodyne receivers centered on 120 GHz with 14 channels per radial view is described for localized, long wavelength (5≲λ≲50 cm), fast time response (≈1 μs) fluctuation studies in the PBX-M tokamak. The optically gray emission signal will have a γñe/ne+(3/β)T̃e/T e dependence on temperature and density fluctuations where γ≤1 and 1≤β≤3 depending on local optical depth. Electron temperature fluctuation sensitivity is estimated to be 0. 2%≤T̃e/Te ≤2.9% depending on local optical depth and fluctuation frequency in the 0.1-1 MHz range. Spatial resolution of approximately 3 cm radially and 5 cm vertically are estimated for 2 keV plasmas with low suprathermal electron emission.