RF wave observations in beam-plasma discharge
Master of Science
The Beam Plasma. Discharge (BPD) has been produced in the large vacuum chamber at Johnson Space Center (2 x 3 m) using an energetic electron beam of moderately high perveance (K ~ 1.4 x 1^-6 A V^-3/2). A more complete expression of the threshold current IC taking into account the pitch angle injection dependence is given. Ambient plasma density inferred from wave measurements under various beam conditions are reported. It is observed that the maximum frequency of the excited RF band behaves differently than the frequency of the peak amplitude. The latter shows signs of parabolic saturation consistent with the light data. It is found that the beam plasma state (pre-BPD or BPD) does not affect the pitch angle dependence. Unexpected strong modulation of the RF spectrum at half odd integer of the electron cyclotron frequency (n + 1/2)fce is reported (5 < n < 1). Another new feature, the presence of wave emission around 3/2 Fce for Ib = Ic is reported.