Radiation from a charge q moving in a helix in magnetoplasmas is investigated theoretically. When its speed ν is much larger than the thermal velocity, (m−1 kT)½, of the plasma electrons and the gyration frequency is much smaller than the plasma frequency ω0, the radiation power from the charge is (q2 ω02/2ν) ln (ν2/m−1 kT). Cyclotron radiation from an electron with nonrelativistic speed decreases to zero as plasma density increases. For a positron in a dilute plasma, however, the radiation is strengthened. This strengthened radiation from a positron again decreases with increasing ω02/ωH2 and becomes zero for ω02/ωH2 ≥ 2 (ωH = gyration frequency of the plasma electron). Damping of the Cerenkov radiation due to collisions of plasma electrons is also discussed.
Contribution to the theory of magnetic pumping of an inhomogeneous collisional plasma