On a nonintrusive spectroscopic method to determine fluctuating electric fields in hot plasmas (abstract)

Abstract

A nonintrusive method to measure low level stochastic electric fields in hot plasmas is being investigated in the TJ-I tokamak (R=30 cm, a=10 cm, Ip<60 kA, BT<1.5 T). It is based on the measurement of ion temperature of particles with different masses, i.e., protons and impurities, by the Doppler line width of their emission lines. It is hypothesized that its difference is due to gross mass motion produced by Ẽ×B. As a guide for data interpretation, we compare our results with typical values of fluctuating electric fields obtained by Langmuir probes at the plasma periphery. The ion temperatures of representative impurities like C V and O V, have been measured by the Doppler line width of near UV lines 2271 and 2781 Å, respectively. The proton temperature has been measured analyzing the Hβ and Hα line wings whose emission is due to highly energetic neutrals. Results of fluctuating electric fields obtained by this method as a function of radius and plasma density will be presented. The deduced fluctuating electric fields are higher at the plasma periphery than at the plasma center and in the latter much higher at low than at high densities. An approach to distinguish between radial and poloidal electric field fluctuations is being addressed by modeling experimental results with a simulation code.