NONLOCAL THEORY OF A WHISTLER PUMPED FREE-ELECTRON LASER

A cylindrical waveguide loaded with a magnetized plasma supports a sho rt wavelength whistler mode. In the presence of a relativistic electro n beam the whistler mode couples to a negative energy beam mode and a high-frequency electromagnetic mode giving coherent radiation. A nonlo cal theory of the process reveals that larger beam cross section is pr eferable for better coupling. The phase matching conditions give the f requency of operation as omega1 = (ck0z/eta0)[(eta0-eta)/(eta-eta1)] w here omega1 is the frequency of the free electron laser radiation, k0z is the wave number of the pump wave, c is the velocity of light in fr ee space, and eta(j)=ck(j)/omega(j), eta(j) = eta0, eta1, eta correspo nd to the pump, radiation signal, and the beam mode, respectively. The frequency of radiation is maximum when it propagates in the transvers e magnetic TM01 mode. As the frequency of the whistler approaches elec tron cyclotron frequency, the frequency of radiation is enhanced while the growth time also increases. The growth time scales as mega0-k0zup silon(b))2]1/2/(omega(pb)2omega1(1/2)).