FREQUENCY VARIATION OF THE MEAN ENERGY OF RF ELECTRON SWARMS

Starting from the general momentum and energy balance equations for ch arged particle swarms in a gas, as furnished by momentum-transfer theo ry, we obtain expressions for mean velocity and mean energy of an elec tron swarm in an r.f. electric field under spatially uniform condition s, in the frequency range omega tau(e) > 1, where tau(e) is the energy collisional relaxation time. If tau(e) is a decreasing function of en ergy, it is shown that the cycle-averaged mean energy reaches a maximu m at a certain frequency. Physical arguments are provided to support t his result and the prediction is verified for a constant elastic cross section model by direct numerical solution of Boltzmann's equation.