Progress on Petawatt level experiments at BELLA Center for electron acceleration*

In 2014, electron beams with energy up to 4.3 GeV were obtained using 9 cm-long capillary discharge plasma waveguides and laser pulses with peak power 310 TW [1]. Although the laser power available was 1 PW, at that time it was not possible to increase the electron beam energy further since effective laser-guiding of the 60 micron focal spot at lower density was not possible. Usually the capillary radius would be reduced to increase the plasma channel depth and achieve matched guiding of the laser, but for PW laser pulses significant capillary damage would typically occur. The concept of inverse bremsstrahlung heating inside a capillary waveguide was proposed to address this problem [2]. Results will be shown on the optimization of heating and laser-guiding, which has allowed for guiding of laser pulses with PW peak power and 60 micron radius over tens of centimeters, and the generation of electron beams with increased energy.

[1] W. P. Leemans et al., Phys. Rev. Lett. 113, 245002 (2014). [2] N.A. Bobrova et al., Phys. Plasmas 20, 020703 (2013).