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Microhollow electrode discharges (MHCD) [l] are gas discharges between closely spaced (submillimeter) electrodes containing openings with diameter, D, on the same order as the electrode gap. In previous experiments the reduction of the size of the cathode opening to 100 pm has allowed us to generate stable, direct current discharges in air up to atmospheric pressure [2]. The microhollow cathode discharges were operated at currents of up to 20 mA, corresponding to current densities of 250 A/cm2 and at average electric fields of 16 kV/cm. The gas temperature of the MHCD was determined by spectroscopic measurements of the excited vibrational states of the nitrogen molecules. First results indicate that the gas temperature at atmospheric pressure and currents of 20 mA is close to 2000 OK. Parallel operation of MHCDs can be achieved by ballasting each discharge resistively [3]. Without resistive ballast, the discharge itself needs to be resistive, that means the current voltage characteristic of the discharge must have a positive slope. Results of modeling [4] show an increase of the forward voltage with current at high current values. However, overheating of the electrodes prevents dc operation of parallel discharges in atmospheric air in this current range. In order to extend the range of operation into the high current mode, were the discharge becomes resistive, it needs to be pulsed. In pulsed operation, with pulse duration in the range from 1 to 100 microseconds, the current range could be extended to 80 mA. At higher current, glow-to-arc transition was observed. The results show, that pulsed operation at high current might allow to operate discharges in parallel without individual ballast.Further research on PIA (Brandenburg and Kline 1998) plasmas, glow discharge-type plasmas created in room air, is reported. These plasmas can be made in a modified 1 kW microwave oven (2.45 GHz) and can be sustained for an indefinite period by the microwaves. They have now been made in a much larger size using 915MHz industrial microwaves at 30-75kW of microwave power. These new plasmas range from roughly spherical and approximately 50cm in diameter to highly irregular and dynamic shapes of larger size. Thus it is demonstrated that the PIA phenomenon can be scaled upward in size and power. The properties of the 915MHz PIA plasmas appear similar to that made with 2.45GHz, except that visible spectra appear to display more bright bands. The plasma also appears to seek microwave sources, like a classic breakdown, rather than retreat from it, as is the behavior of the PIA at 2.45GHz. This suggests that the 915MHz plasmas may be more strongly driven and closer to a classical arc discharge in properties. Further measurements on PIA plasmas will be reported. We believe these plasmas are a new and unusual plasma state first reported by Manwaring and Powell and Finklestein (1 970) whom used 30kW at 75 MHz. Recent research results will be shown. Work supported by AFOSR.

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