Limiting current of helical electron beams in gyrotrons

Potential depression (PD) and limiting current (LC) of helical electron beams (HEB) are investigated. Nonneutral electron beams and two velocity distributions: uniform and Rayleigh distribution are taken into account. For Rayleigh distribution electron reflection from magnetic mirror is taken into account. It is shown that velocity spread may lead to substantial reduction of LC for real values of the mean pitch-factors of helical trajectories. PD and LC are an unmonotonous functions of the velocity spread for Rayleigh distribution. A connection of PD with the change of gyrofrequency and with the beam broadening in gyrotron operating space is retraced.