W.P. Leemans, P.E. Catravas, E. Esarey, G. Fubiani, M. Pilloff, B.A. Shadwick, J. van Tilborg, J.S. Wurtele, S. Chattopadhyay (LBNL)
Laser driven plasma based acceleration offers the possibility of developing compact high gradient accelerators. In experiments, high intensity (I>10^18 W/cm^2) laser pulses are focused onto gaseous targets producing high density (10^18 - 10^19 electrons/cm^3) plasmas and exciting plasma waves with longitudinal electric fields > 10 GV/m that propagate with a phase velocity close to the light speed. In the self-modulated laser wakefield regime (SM-LWFA), the laser pulse duration is long compared to the plasma period and extremely large plasma wakes susceptible to wavebreaking can be generated. Results are presented of SM-LWFA experiments at LBNL on generation of relativistic electron beams using 50 q 200 fs, high power (<10 TW) laser pulses produced by a 10 Hz Ti:sapphire laser. To reduce the large energy spread (100 %) and relatively low mean energy (few MeV) inherent to this method, laser triggered injection methods have been proposed. Experimental progress is reported on the colliding laser pulse scheme, which operates in the standard laser wakefield regime (laser pulse duration matched to plasma period). Two additional collinear but counter-propagating laser pulses are injected to provide a low phase velocity accelerating structure that captures background electrons which can subsequently be accelerated in the fast phase velocity plasma wave.
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* This work was supported by the Director, Office of Science, Office of High Energy & Nuclear Physics, High Energy Physics Division, of the U.S. Department of Energy, under Contract No. DE-AC03-76SF00098.
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