EXCITATION OF CYCLOTRON-HARMONIC NOISE IN A BEAM-GENERATED PLASMA.
Abstract
Deliberate, controlled excitation of a special class of electrostatic waves was achieved in a pulsed electron-beam-generated hydrogen plasma. Microwave drive signals near the electron gyro frequency were applied to the electron beam in the form of transverse electric fields. With a change in the magnetic field, the beam plasma system could be made stable or unstable with respect to the emission of narrow-band, cyclotron-harmonic radiation. In the stable mode, the r-f drive fields, applied with a bifilar helix coupler, excited cyclotron harmonic waves propagating across the magnetic field inducing narrow-band radiation. For the radiation to be observable, the Doppler frequency shift condition had to be satisfied by appropriate values of beam voltage, drive coupler pitch, magnetic field, and drive frequency. With the system in the unstable mode, the rate of plasma generation was increased, using cyclotron frequency drive fields which resulted in radiation appearing earlier (at a given receiver sensitivity) in the beam voltage pulse. Under the same conditions, the frequency of the self-excited noise was shifted by enlargement of the plasma electron orbit caused by sufficiently strong drive fields. Whether the system was in the stable or unstable mode, noise could only be measured when the density was sufficiently high that the receiving frequency was less than the upper hybrid frequency. These stimulated noise emissions are closely related to the high-harmonic, nonthermal radiation at microwave frequencies reported in recent years. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1967
- Accession Number
- AD0812999
Entities
People
- Michael Roberts
Organizations
- Cornell University College of Engineering