Abstract:

A conventional linear accelerator consists of (at a minimum) a particle source, a power source and an accelerating structure that provides accelerating fields. With RF technology, the accelerating gradient in such a structure is limited to fields roughly less than 100 MeV/m. Laser driven plasma based acceleration, on the other hand, offers the possibility of developing compact high gradient accelerators.[1] Ultra-high gradients in excess of 100 GV/m have been reported and beams of accelerated electrons have been observed with maximum electron energy as high as 100 MeV. Unfortunately, these beams had an energy spread of 100%.

In experiments, high intensity laser pulses are focused onto gaseous targets producing high density 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. In the standard laser wakefield regime the laser pulse duration is matched to plasma period.

Although high gradients have been demonstrated, to successfully build a high energy laser driven accelerator one must provide: (1) a means to extend the diffraction distance of a focused high intensity laser beam such that the interaction distance is sufficiently long, and (2) a controlled injection mechanism to reduce the energy spread. An overview will be presented of the current status of experiments and modeling of laser driven plasma based acceleration at the l'OASIS laboratory of the Center for Beam Physics at LBNL. We recently succeeded in producing electron beams using 50 200 fs, high power (<10 TW) laser pulses from a 10 Hz Ti:sapphire laser as well as guiding a laser beam in a plasma channel. Laser triggered injection methods will be discussed that have the potential to significantly reduce the energy spread of the accelerated electron beams.[2] Applications of these novel accelerators for high energy physics and future light sources will be discussed.

[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).