Effect of beam pre-bunching and guide magnetic fields on gain and efficiency in slow wave free electron laser

摘要

A pre-bunched electron beam on slow wave free electron laser offers considerable enhancement in growth rate, gain and efficiency when a guide magnetic field is used in the free electron laser device. The growth rate, efficiency and gain were evaluated based on experimentally available parameters relevant to slow wave free electron laser. It was found that the growth rate, efficiency and gain of the slow wave FEL increases with the modulation index DELTA and has the largest value when the modulation index DELTA approx 1.0 in addition to the frequency and wave number of the pre-bunched beam are comparable to that of the radiation wave. When the slow wave free electron laser has a guide magnetic field B_(s), the transverse electron velocity is enhanced via cyclotron resonance. This leads to a reduction in beam parallel velocity and reduction in radiation frequency (omega)_(1). For modulation index (DELTA)(velence)0, i.e., without modulated beam, the value of the growth rate GAMMA approx8.3X10~(8) rad./sec. The growth rate of the slow wave free electron laser instability decreases monotonically with the radiation frequency. The scheme seems to work well at millimeter wavelength radiation.