Characteristics of plasmas produced by double beat wave interaction in the Neptune facility at UCLA

Cathodeless electron sources have received a great deal of attention recently. In a similar scheme for generating a high current relativistic electron beam described here, two beat waves are used: one to setup an accelerating structure, and another to locally perturb this structure in order to trap background electrons from the resonant density plasma. This is called the "double beat wave injector" scheme. We report the characterization of plasmas formed by the superposition of two beating electromagnetic wave pairs with peak intensities greater than the tunneling ionization threshold for hydrogen. The plasmas produced by the beat waves are diagnosed using optical imaging and time resolved Thomson scattering, separately as well as when both beat waves interfere with each other. The brightness of the plasma is maximum near the resonant fill pressure, as expected. Preliminary results are presented.