Abstract
A time dependent expression for an electron plasma wave driven by optical mixing of two electromagenetic waves is derived in a target plasma which has a small amount of high-energy electrons in addition to cold main-body electrons. Numerical analysis indicates that, for counterpropagating electromagnetic waves, the wave amplitude is strongly reduced by the Landau damping of a small amount of high-energy electrons in the target plasma. The resonant excitation of the electron plasma wave is experimentally observed when the difference in frequency between counterpropagating microwaves is equal to the electron plasma frequency. Using a capacitive probe the wave amplitude δn/n0 is found to be proportional to the incident microwave power and is 0.8% at the incident microwave power of 40kW. The experimental results are in reasonable agreement with that expected from the optical mixing theory with damping terms. The dominant damping is ascribed to the Landau damping of high energy electrons co-existing in the background plasma.
