An experimental investigation of the Buneman instability
The Plasma Betatron, a toroidal turbulent heating device, is modified so that a short (200 nsec duration) electric field pulse (maximum strength 650 V/m) is applied to accelerate electrons to a drift velocity vD much larger than the initial thermal velocity VTH. The device has a major radius of 19 cm and a minor radius of 3 cm, and a plasma having an electron density of 4 x 1016 ~ 1.2 x 1017 m-3 is prepared by rf ionization in a toroidal magnetic field of ~.2 T. A ratio of VD/VTH ~> 5 has been realized which is sufficient for the development of the electron-ion two stream instability. Rapid decay of the plasma current, concurrent turbulent electron heating and an anomalously high electron-ion collision frequency are also observed. However, the Buneman frequency is not observed. Following the collapse of the current, strong oscillations near the ion plasma frequency are detected. Most of the experimental results are in qualitative agreement with recent theoretical predictions.
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