An electron synchrotron maser based on an intense relativistic electron beam

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Abstract
An electron cyclotron maser has been operated with an output of ∼50 MW of coherent radiation at a frequency ∼8 GHz. A magnetic field configuration is described which effectively converts streaming electron energy into energy transverse to the streaming direction. The redistribution of beam energy makes available a source of free energy to be converted, via an instability, into radiation at the Doppler-shifted relativistic electron cyclotron frequency. A nonlinear theoretical analysis shows that the coherent synchrotron radiation is a relativistic negative mass type instability reflecting the fact that the cyclotron frequency is a function of the electron energy. The emission was narrow band with a coherence time ≳50 nsec, and was also spatially coherent being primarily radiated into the TE01 circular waveguide mode. The potential for making a frequency tunable maser by employing a tapered drift tube has also been demonstrated.