Demonstration of Plasma Beat Wave Acceleration of Electrons from 2 MeV to 20 MeV

We describe the results from recent experiments1 on the plasma beat wave accelerator (PBWA) scheme at UCLA. A relativistic electron plasma wave (which is the accelerating structure) is resonantly excited in a plasma by the beating of two co-propagating electromagnetic waves (obtained from a CO2 laser operating simultaneously on two wavelengths). A 2 MeV, 200 mA (peak-current) electron beam, roughly 1 nsec (FWHM) in duration is used as a source of test particles for measuring the longitudinal fields of the plasma wave which itself is moving with a relativistic Lorentz factor of about 34. Accelerated electrons are energy-selected with an imaging sector magnet and detected simultaneously with a cloud chamber and surface barrier detectors. Initial experiments show that electrons are accelerated up to 20 MeV over roughly 1 cm (the uniform length of plasma) indicating an gradient of acceleration of more than 1.8 GeV/m.