Emission spectroscopy of ECRH non-axisymmetric helium mirror plasmas

Summary Form only given, as follows. Emission spectroscopy in the 3000 to 5000-AA range has been utilized to determine the electron temperature of helium plasmas produced by the Michigan Mirror Machine (MIMI). The plasma is generated and heated by whistler-mode electron-cyclotron resonance waves at 7.43 GHz and 500 W in 400- mu s pulses. Gas is puffed into the midplane region, where a quartz window is used to observe the plasma in a direction perpendicular to the mirror axis. Emission spectra are obtained using a 0.275-m spectrograph coupled to a gated optical multichannel analyzer. These spectra are interpreted using a model of the important collisional and radiative processes occurring in the plasma. From the analysis of line intensity ratios for neutral helium, the electron temperature is determined and its dependences upon the gas pressure, microwave power, and mirror and quadrupole field strengths are measured. The electron temperature is found to be independent of the power of the ECRH microwaves. The mirror and quadrupole currents have a small effect upon the electron temperature. This is probably a spatial effect due to a change in the location of the resonance planes where electrons are heated. By far the most important parameter is the pressure of the helium fill gas; the electron temperature ranges from 50 eV to 20 eV over the operating regime of MIMI (1*10/sup -5/ to 1*10/sup -3/ torr).<>