The permittivity of a plasma at cyclotron resonance in large amplitude e.m. fields

The permittivity of a collisionless plasma as a function of field parameters is measured in standing and in travelling waves. In both experiments the permittivity remains finite at cyclotron resonance; the resonance is broadened and shifted towards higher values of the magnetic field strength. The results are in quantitative agreement with theoretical predictions which follow from a cold-plasma, large-signal analysis. The loss tangent of the plasma is measured. The loss is found to be due to the escape of accelerated particles