Velocity ratio measurement using the frequency of the gyro backward wave
The operating diagram of a low quality factor, 8 GHz TE(o,01) gyrotron exhibits oscillations between 6.8 and 7.3 GHz. These oscillations are identified as the backward wave component of the TE(o,21) travelling mode. As the resonance condition of this mode depends on the average parallel velocity (v parallel) of the beam electrons (w(BW) approximately equal to omega(c)/gamma-k parallel(v parallel)), the measurement of w(BW) for given omega(c) and gamma is used as a diagnostic for the beam electrons with velocity ratio alpha = (v perpendicular)/(v parallel). The values of alpha, deduced from w(BW) through the linear dispersion relation for the electron cyclotron instability in an infinite waveguide, are unrealistic. A nonlinear simulation code gives alpha values that are in very good agreement with the ones predicted by a particle trajectory code (+10% to +20%). It is found numerically that the particles' velocity dispersion in v perpendicular and v parallel increases w(BW). This effect explains part of the discrepancy between the values of alpha inferred from w(BW) without velocity dispersion and the expected values.
Bibliographic Reference: Article: Physics of Fluids B, Vol. 3 (1991) No. 6, pp. 1315-1318
Record Number: 199111100 / Last updated on: 1994-12-02
Original language: en
Available languages: en