CYCLOTRON HARMONIC RADIATION FROM ELECTRON BEAM INJECTION INTO AN AFTERGLOW PLASMA

A pulsed electron beam was injected into an afterglow produced by a P.I.G. discharge in low pressure argon. The beam and the afterglow form concentric posts in X-band waveguide on which accurate microwave measurements were made. Radiation at the cyclotron harmonics was observed from the simultaneous beam and afterglow plasmas when the beam was too low to generate its own radiating plasma. Radiation was enhanced when the experimental parameters were consistent with the Bernstein electrostatic dispersion relations. Observations of the width of the third harmonic radiation resonance as the plasma frequency was varied are in qualitative agreement with the theory of Auer and Stone. Space charge fluctuations at the receiver frequency (9.2 Gc) were also observed when the radiation occurred. (Author)