Use of few-cycle PW-range laser pulses in fusion research

This talk refers to recent developments of ultrashort TW laser pulses having pulse durations in the order of 10 femto-seconds and less [1]. It describes plans at MPQ to upgrade these pulses to few-Joule energies with PW power. These pulses will be ideally suited for wakefield acceleration, producing very efficiently ultra-bright low-emittance monoenergetic electron beams in the bubble wakefield regime [2]. In this ultra-relativistic regime of laser plasma coupling, the laser pulse drives the wake so strongly that it breaks after the first oscillation and forms a solitary wake, which contains the driving laser pulse in its front-half and traps plasma electrons in its rear-half, accelerating them up to GeV energies [3]. These electron bunches may be converted into secondary beams of X-rays, ions, and other nuclear species. Here we discuss applications to fast ignition research. Fast ignition of precompressed ICF targets depends on efficient coupling of ignitor beam energy to the precompressed fuel core through strongly overdense plasma. This transport involves currents in the order of 100 MA which is dominated by strong magnetic fields and plasma instabilities, in particular current filamentation and coalescence [4]. Also for cone-guided fast ignition, this transport problem arises, be it on a reduced spatial scale. Understanding and control of these nonlinear dynamics is of central importance to make the fast ignition scheme work. The dynamics occur on femtosecond timescales and smaller. Ultrabright X-ray bunches (duration 100 as - 10 fs) produced from bubble electron bunches or also via high harmonics generation from plasma surfaces may open a possibility to time resolve the FI transport instabilities in pump-probe experiments. (Author)