Interaction of relativistically intense laser pulses with long-scale near critical plasmas for optimization of laser based sources of MeV electrons and gamma-rays

Abstract

Experiments were performed to study electron acceleration by intense sub-picosecond laser pulses propagating in sub-mm long plasmas of near critical electron density (NCD). Low density foam layers of 300-500 μm thickness were used as targets. In foams, the NCD-plasma was produced by a mechanism of super-sonic ionization when a well-defined separate ns-pulse was sent onto the foamtarget forerunning the relativistic main pulse. The application of sub-mm thick low density foam layers provided a substantial increase of the electron acceleration path in a NCD-plasma compared to the case of freely expanding plasmas created in the interaction of the ns-laser pulse with solid foils. The performed experiments on the electron heating by a 100 J, 750 fs short laser pulse of 2-5×10 19 W cm −2 intensity demonstrated that the effective temperature of supra-thermal electrons increased from 1.5-2 MeV in the case of the relativistic laser interaction with a metallic foil at high laser contrast up to 13 MeV for the laser shots onto the pre-ionized foam. The observed tendency towards a strong increase of the mean electron energy and the number of ultra-relativistic laseraccelerated electrons is reinforced by the results of gamma-yield measurements that showed a 1000fold increase of the measured doses. The experiment was supported by 3D-PIC and FLUKA simulations, which considered the laser parameters and the geometry of the experimental set-up. Both, measurements and simulations showed a high directionality of the acceleration process, since the strongest increase in the electron energy, charge and corresponding gamma-yield was observed close to the direction of the laser pulse propagation. The charge of super-ponderomotive electrons with energy above 30 MeV reached a very high value of 78 nC.

Forward-looking insights in laser-generated ultra-intense γ-ray and neutron sources for nuclear application and science

“…The effective temperature of the DLA accelerated electrons exceeds more than one order of magnitude the ponderomotive potential and their energies extend up to 100 MeV, already at moderate relativistic laser intensities 55 , 56 . The reason for this behavior is a long acceleration path in a NCD plasma ensured by pre-ionized sub-mm thick foams and a relatively long sub-ps laser pulse duration.…”

“…These different intensity regimes were achieved by different focusing systems 56 . Polymer aerogel-foams with a mean density of 2 mg/cm 3 and sub-millimeter thickness 65 were used for the production of a NCD-plasma via the mechanism of super-sonic ionization 55 , 66 by sending a well-controlled nanosecond-pulse before the main relativistic pulse. A fully ionized plasma corresponds to 0.64 × 10 21 cm −3 electron density or 0.64 n cr ( n cr = 10 21 cm −3 ).…”

Parametric Study of Proton Acceleration from Laser-Thin Foil Interaction

“…The TPS has an acceptance angle of 2 µSr and is capable of detecting protons with energy from 30 keV up to several MeV in a single shot. We also used a calibrated electron spectrometer [25] based on magnetic deflection with image plates to measure the temperature of the electrons along the target normal direction. This spectrometer has an acceptance angle of 0.3 mSr and can measure up to several of tens of MeV.…”

Clean source of soft X-ray radiation formed in supersonic Ar gas jets by high-contrast femtosecond laser pulses of relativistic intensity

“…It was shown in Refs. [6][7][8] that the application of foam nanostructure targets resulted in a significant increase of X-ray emission from a laser plasma [9] . Unfortunately for most of the cases, the production of these targets is a complicated many-step process, which makes such target application rather expensive for wide use.…”