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The advent of multi-PW laser facilities world-wide opens new opportunities for nuclear physics. With this perspective, we developed a high efficiency neutron counter taking into account the specifics of a high intensity laser environment. Using GEANT4 simulations and prototype testings, we report on the design of a modular neutron-counter based on boron-10 enriched scintillators and high-density polyethylene moderator. This detector has been calibrated using a plutonium-beryllium neutron source and commissioned during an actual neutrons producing laser experiment at theLULI2000 facility (France). An overall efficiency of 4.37(59)% has been demonstrated during calibration with a recovery time of a few hundreds microseconds after laser-plasma interaction. We also tested using units of this detector in neutron time-of-flight configuration during the commissioning of the 1PW arm of the Apollon laser facility. Neutrons produced by the conversion of proton accelerated by the 1PW arm of the Apollon facility have been detected, of which we will present preliminary results.

We present results of the first laser-driven proton acceleration experiment with two ultrashort laser pulses at the Arcturus laser facility in Dusseldorf. The Ti:sapphire laser provides two laser pulses (30fs, 2.3J; 30fs, 3.7J) which reaches focused intensities up to 1020 W/cm2. The second pulse has a contrast of 108 on a picosecond timescale. A plasma mirror enhances the contrast of the first pulse by three orders of magnitude on a picosecond timescale. The scheme of the experiment is as follows. The first laser pulse irradiates a thin foil and accelerates ions according to the target normal sheath acceleration mechanism. 10s of femtoseconds after the first pulse the second pulse is interacting with the expanding plasma and enhances the acceleration process of the ions. In the experiment the pulses were spatially overlapping on a 5μm thin Titanium foil. The delay between the pulses was varied from 10s to 100s of femtoseconds. As a main diagnostic a Thomson Parabola was employed in combination with a micro-channel-plate. In a second part of the experiment a time-and-space-resolved-interferometer (TASRI) was used to determine the electron density and temperature at the rear side of the foil with a 3μm spatial and 3ps temporal resolution. Two regimes were observed, which were only present in the two-beam configuration. One regime is dominated by a large number of different (up to 13) ion species - namely carbon, nitrogen, oxygen and titanium ions. But in this regime only a relatively low maximum proton energy was observed. In contrast to this is the other regime, where only a few weak ion species were present. In return protons with relatively high energy could be measured. The proton maximum cut-off energy in this regime was distinctly higher compared to the single-beam configuration. First simulations with the particle-in-cell code EPOCH indicate the enhanced acceleration mechanism is driven by a second push of the electrons from the second laser pulse.

Summary form only given. Collisionless shocks are relevant to a variety of astrophysical scenarios, such as the generation of highly energetic particles and cosmic rays during supernova explosions, and have recently been the focus of several laboratory plasma investigations employing high-power lasers. We present here a study of the generation and evolution of collisionless shocks in tenuous plasma, carried out at the VULCAN laser facility, Rutherford Appleton Laboratory. The shocks are generated during the expansion of a warm plasma, produced after the irradiation of a thin solid foil by a long (∼1ns) and intense (∼1015 W/cm2) laser pulse, into a tenuous (∼ 1016 cm−3), non magnetized background plasma. Shock structures are seen to develop at the interface between the two plasmas. The shocks are probed via a proton projection imaging (PPI) technique [1], which allows one to measure the electric field distribution at the shock front with high spatial resolution (∼ µm), and temporally resolve its propagation within a ps scale. The temporal evolution of electrostatic shocks in ambient plasma has been observed and the associated electric field has been reconstructed in a number of different conditions. In particular, we have identified in the data the transition from an unipolar field profile, typical of a double layer structure, into a bipolar electric field, and the subsequent formation of a collisionless, electrostatic shock. This structure is then seen to propagate in the ambient plasma with a Mach number ∼3.5. A PIC simulation supports the existence of high Mach number (∼3.3) shocks launched by collision of plasma clouds of equal electron and ion temperatures [2].