Millimeter wave generation through stimulated scattering with an intense relativistic electron beam and a controlled zero-frequency pump

Several megawatts of radiation, at 1 < λ < 2mm, have been generated by the interaction of a cold beam with a rippled magnetic field, in a scaled-up version of an earlier experiment. In one mode of operation, the beam propagates in an evacuated cylindrical waveguide along a solenoidal field (Bo ≈ 10 kG) which includes a periodic iron structure, or undulator. The short-wavelength radiation output maximizes at Bo which depends on waveguide diameter and beam γ. A new pulsed-current, nonferro-magnetic undulator with adjustable ripple period (≤ 1 cm) gives similar performance but with a sharper magnetic resonance; the field ripple amplitude can be increased up to 6%. The output power increases exponentially with ripple amplitude.