Direct spectroscopic determination of breakdown field in microwave discharges
- EEI, Pluckemin, NJ (United States)
The breakdown electric field E at microwave frequencies is usually determined as the result of a sequence of measurements of power, frequency, standing wave ratios, etc. Breakdown measurements are further complicated by impurity, plasma, and boundary effects. In contrast, the polarization-dependent Stark shift offers the possibility of direct measurement of E in microwave discharges. The magnitude of the shift depends on whether the light is viewed parallel or perpendicular to an applied electric field, as opposed to the isotropic collisional Stark broadening in dense plasmas. This technique has been used to measure electric fields in the cathode sheath of dc glow discharges. Kamp and Himmel report Stark splitting of Balmer series lines in low-pressure microwave (2.45 GHz) discharges irradiated by a supplementary microwave field (34.8 GHz) above the cutoff frequency to create a high electric field in the plasma. A similar method has been proposed for measuring electric fields near RF antennas in plasmas. Here we report low-resolution observations of the Stark shift of H alpha light (wavelength 656.3 nm) during breakdown from hydrogenic impurities in microwave discharges in argon at pressures p{ge}200 Torr. Fields of 2-5 kV/cm were measured. Our work differs from that of Kamp and Himmel in that it concerns the intrinsic, plasma-producing electric field in pulsed microwave discharges.
- OSTI ID:
- 212990
- Report Number(s):
- CONF-950749--
- Country of Publication:
- United States
- Language:
- English
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