VACUUM BEAT-WAVE ACCELERATION

A vacuum beat wave accelerator (VBWA), in which two focused laser beam s of differing wavelengths generate a beat wave that can impart a net acceleration to particles, is analyzed and simulated, The mechanism re lies on the ponderomotive (vXB) force, thus circumventing the so-calle d Lawson-Woodward theorem. No gas, plasma, or other proximate material medium is required to achieve a net energy gain, The single-stage ene rgy gain of the VBWA is limited by diffraction of the laser beams, par ticle slippage, and radial walkoff. In the simulations the particles a re synchronous with the brat wave for a short interval of time and the energy gain has the nature of an impulse delivered near the focal reg ion. Simulations show that the problem of radial walkoff may be amelio rated by using a converging beam of particles, as naturally occurs for injection of a finite-emittance beam. For terawatt-level laser beams, with wavelengths 1 mu m and 0.5 mu m, and a 4.5 MeV finite-emittance electron beam, the energy can be increased to similar to 12.5 MeV in a nonsynchronous interaction over a distance of under 4 mm, with a peak acceleration gradient similar to 15 GeV/m and an estimated trapping f raction of similar to 1%. The simulated energy gain is compared with a nalytical predictions. Scaling is illustrated by increasing the inject ion energy to 50 MeV.