Experimental Study of Beat Wave Excitation of High Phase Velocity Space Charge Waves in a Plasma for Particle Acceleration

In this paper we present the first detailed study of the excitation of high phase velocity plasma waves by colinear optical mixing. The plasma wave frequency and wavenumber, hence the phase velocity, are directly measured using Thomson scattering. The amplitude of the plasma wave and therefore the longitudinal electric field is inferred from the magnitude of the Thomson scattered light. For a modest laser intensity of ~I013 W/cm 2 in each frequency, the excited space-charge plasma wave has measured longitudinal electric fields of the order i GeV/m, in reasonable agreement with the fluid theory.