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.[1] 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.[2] 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.
[1] E. Esarey et al., IEEE Trans. Plasma Sci. PS-24, 252 (1996) : W.P. Leemans et al., ibidem, 331.
[2]D. Umstadter et al., Phys. Rev. Lett. 76, 2073 (1996): E. Esarey et al., Phys. Rev. Lett. 79, 2682 (1997): C.B. Schroeder et al., Phys. Rev. E 59, 6037 (1999).
* 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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