High-power, kilojoule laser interactions with near-critical density plasma

Abstract

Experiments were performed using the Omega EP laser, which provided pulses containing 1kJ of energy in 9ps and was used to investigate high-power, relativistic intensity laser interactions with near-critical density plasmas, created from foam targets with densities of 3-100 mg=cm 3. The effect of changing the plasma density on both the laser light transmitted through the targets and the proton beam accelerated from the interaction was investigated. Two-dimensional particle-in-cell simulations enabled the interaction dynamics and laser propagation to be studied in detail. The effect of the laser polarization and intensity in the two-dimensional simulations on the channel formation and electron heating are discussed. In this regime, where the plasma density is above the critical density, but below the relativistic critical density, the channel formation speed and therefore length are inversely proportional to the plasma density, which is faster than the hole boring model prediction. A general model is developed to describe the channel length in this regime. V

Magnetic field generation during intense laser channelling in underdense plasma

“…Analysis using particle tracing simulations showed that the electric field profile was consistent with the channel electron density profile, i.e., the electric field peaks were situated at the same positions as the channel's walls, where charge has accumulated due to ponderomotive expulsion from inside the channel. Further simulations and experiments have been conducted using similar setups considering the effects of near critical density plasmas 23 and polarisation effects 24 upon channel formation. Along with the electric fields, magnetic fields are also generated during channelling.…”

Relativistic critical density increase and relaxation and high-power pulse propagation

“…8 However, in the relativistic regime it is difficult to determine the critical surface and the critical density accurately in both experiments 12 and simulations, 5 especially for linear polarization (LP). 15 The propagation velocity of the pulse front is found to be neither the group velocity nor the hole boring velocity; [12][13][14][15] the accurate calculation of this propagation velocity is still an open problem.…”

“…9,10 In particular, an increase of the critical density n c makes the fast particle transport and heat losses more easily to be controlled in laser plasma interactions, [11][12][13][14] and it provides a higher, more favourable laser energy coupling to the compressed core in fast ignition schemes. 8 However, in the relativistic regime it is difficult to determine the critical surface and the critical density accurately in both experiments 12 and simulations, 5 especially for linear polarization (LP).…”

Electron heating in subpicosecond laser interaction with overdense and near-critical plasmas

“…Ion acceleration with these targets relies on an efficient volumetric heating in the low-density layer [37][38][39][40] combined with a neat charge separation granted by the solid foil. Under suitable conditions [19,[22][23][24], a significant enhancement of both total accelerated charge and maximum ion energy has been observed.…”