Experimental investigations of the formation of a plasma mirror for high‐frequency microwave beam steering

The Naval Research Laboratory (NRL) has been studying the use of a magnetically confined plasma sheet as a reflector for high‐frequency (X‐band) microwaves for broadband radar applications [IEEE Trans. Plasma Sci. PS‐19, 1228 (1991)]. A planar sheet plasma (50 cm×60 cm×1 cm) is produced using a 2–10 kV fast rise time square wave voltage source and a linear hollow cathode. Reproducible plasma distributions with density ≥1.2×1012 cm−3 have been formed in a low‐pressure (100–500 mTorr of air) chamber located inside of a 100–300 G uniform magnetic field. One to ten pulse bursts of 20–1000 μs duration plasma sheets have been produced with pulse repetition frequencies of up to 10 kHz. Turn on and off times of the plasma are less than 10 μs each. The far‐field antenna pattern of microwaves reflected off the plasma sheet is similar to that from a metal plate at the same location [IEEE Trans. Plasma Sci PS‐20, 1036 (1992)]. Interferometer measurements show the critical surface to remain nearly stationary during the current pulse. Plasma density measurements and optical emissions indicate that the plasma is produced by a flux of energetic electrons formed near the hollow cathode. The sheet appears to be stable to driver voltage and current fluctuations (NRL Memorandum Report No. 7461, 28 March 1994, NTIS Document No. AD‐A278758).