| The plasma beat-wave accelerator in the Neptune Laboratory at UCLA uses a ∼1 terawatt two-wavelength CO2 laser pulse to tunnel ionize hydrogen gas at conditions of resonance for driving a relativistic plasma wave. This plasma wave is used as an accelerating structure for an externally injected, ∼12 MeV, electron beam from the Neptune Photo-injector. The accelerated electron energy spectrum is measured using an electron spectrometer, consisting of a dipole magnet, and an array of surface barrier detectors and phosphors. Accelerated electrons have been detected out to ∼50 MeV using this setup. These experiments are also modeled in 2-D particle-in-cell simulations. These simulations show the self-channeling of the laser beam due to ion motion, which overcomes the defocusing caused by ionization induced refraction, effectively increasing the interaction length between the injected electrons and the plasma wave. Simulations are also performed to study the guiding of shorter (50–500 fs), but more intense, 0.8 μm laser pulses by preformed plasma channels. The three laser acceleration schemes, laser wake-field acceleration, plasma beat-wave acceleration, and self-modulated laser wake-field acceleration, are explored. |
