Coherent synchrotron radiation from an intense relativistic electron beam

When an intense relativistic electron beam traversed a magnetic field of novel configuration, ∼ 25 MW of narrow-band microwave power was emitted near the relativistic cyclotron frequency. The emitted waves are superluminous and propagate in a direction transverse to the applied magnetic field. The process is coherent, is driven by population inversion, and depends on the relativistic mass change.