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Giacone, R.

Paper Title Page
TPAE031 Simulations of Laser Pulse Coupling and Transmission Efficiency in Plasma Channels 2179
 
  • R. Giacone, D.L. Bruhwiler, J.R. Cary, D.A. Dimitrov, P. Messmer
    Tech-X, Boulder, Colorado
  • E. Esarey, C.G.R. Geddes, W. Leemans
    LBNL, Berkeley, California
 
  Funding: Work supported by U.S. DOE under contracts DE-FG03-02ER83557, DE-FC02-01ER41178, DE-AC03-76SF00098, DE-FG03-95ER40926 and use of NERC supercomputer facilities.

Optical guiding of the laser pulse in a laser wakefield accelerator (LWFA) via plasma channels can greatly increase the interaction length and, hence, the maximun energy of trapped electrons.* Energy efficient coupling of laser pulses from vacuum into plasma channels is very important for optimal LWFA performance. We present 2D particle-in-cell simulations of this problem using the VORPAL code.** Some of the mechanisms considered are enhanced leakage of laser energy transversely through the channel walls, enhanced refraction due to tunneling ionization of neutral gas on the periphery of the gas jet, ionization of neutral gas by transverse wings of the laser pulse and effect of the pulse being off axis of the channel. Using power spectral diagnostics,*** we are able to differentiate between pump depletion and leakage from the channel. The results from our simulations show that for short (≈λp) plasma ramp, very little leakage and pump depletion is seen. For narrow channel walls and long ramps, leakage increases significantly.

*C. G. R. Gedes et al., Nature 431 (2004), p. 538. **C. Nieter and J. R. Cary, J. Comp. Phys. 196 (2004), p. 448.***D. A. Dimitrov et al., Proc. Advanced Accel. Concepts Workshop (2004).

 
TOPA003 Optical Injection into Laser Wake Field Accelerators
 
  • J.R. Cary, D.L. Bruhwiler, J.R. Cary, R. Giacone, C. Nieter
    Tech-X, Boulder, Colorado
  • E. Esarey, C.G.R. Geddes, W. Leemans
    LBNL, Berkeley, California
 
  Funding: This work supported by the U.S. Department of Energy grants DE-FG02-04ER41317, DE-FG02-01ER41178, aand DE-FG02-03ER83857, and NSF grant 0113907.

The accelerating gradient of laser-generated wake fields in plasmas can be orders of magnitude greater than the gradients obtainable in traditional, rf structures. One of the hurdles to overcome on the road to practical utilization of said plasma wake fields for production of high energy particles is the creation of quality beams having significant charge, low emittance, and narrow energy spread. To generate appropriate beams, various injection methods have been proposed. Injection by conventional means of beam prepartion using conventional technology is very difficult, as the accelerating buckets are only tens of microns long. Therefore, the field has turned to all-optical injection schemes, which include injection by colliding pulses, plasma ramps, wave breaking, and self-trapping through pulse evolution. This talk will review the various concepts proposed for injection, including plasma ramps, colliding pulses, and self trapping. The results of simulations and experiments will be discussed along with proposed mechanisms for improving the generated beams. Parameter studies to find optimal beam generation scenarios will be presented.