A 94-GHZ free-electron laser (FEL) driven by the NSWC thor generator

THOR is a 3-MeV, 2-kA, 1-µsec, Marx-based pulse generator. We are developing a 94-GHz PEL that is driven by the THOR electron beam. The PEL uses a 2.5-m-long, 10-cm-period helical wiggler. The PEL is initially being configured as an oscillator, with simple annular mirrors defining the cavity. The high power and long pulse duration of the THOR beam make it attractive for several applications. Here, we present results of the PEL design study as well as preliminary experimental results. Simulations show efficient operation (∼8% with no efficiency enhancement) and a small-signal gain of ∼20 to 30 dB/m with a beam current of 500 A. We have transported a current of 500 A through the wiggler with no focusing other than that provided by the wiggler itself. Beam emittance measurements indicate adequate beam quality for the PEL, but voltage variation limits the output pulse duration to 100–200 nsec. Initial output power and frequency are lower than expected, because the beam is off axis. Methods to eliminate this problem are being implemented.