Experimental demonstration of an electromagnetic pulse mitigation concept for a laser driven proton source.

The targets that are used to produce high-energy protons with ultra-high intensity lasers generate a strong electromagnetic pulse (EMP). To mitigate that undesired side effect, we developed and tested a concept called the "birdhouse." It consists in confining the EMP field in a finite volume and in dissipating the trapped electromagnetic energy with an electric resistor. A prototype was tested at a 10 TW 50 fs laser facility. The recorded average EMP mitigation ratio is about 20 for frequencies from 100 MHz to 6 GHz. The EMP mitigation ratio attains the level of 50 in the frequency range of 1-2 GHz where microwave emission is maximal. We measured the intensity of proton emission in two directions: along the laser propagation direction and along the edge of the proton beam. We observed that the "birdhouse" induces a two-fold increase of the intensity in the center of the proton beam and a two-fold reduction of the intensity on its edge. We did not observe any modification of the proton beam normalized spectrum.

Generation of solid-density ultraintense ion beams by a picosecond laser pulse of circular polarization.

This contribution reports particle-in-cell numerical studies of deuteron beam acceleration by a picosecond laser pulse of circular polarization. The effect of laser wavelength λ and the I(L)λ(2) product (I(L) is laser intensity) on the ion beam parameters is investigated. It is shown that at the I(L)λ(2) product fixed, the beam parameters (, I(i), F(i)) as well as the laser-ions energy conversion efficiency quickly increase with a decrease in the laser wavelength and the best results are achieved for a KrF laser (λ = 0.248 µm). In particular, a 2-ps KrF laser pulse of I(L)λ(2) ∼ 2 × 10(20) Wcm(-2) µm(2) interacting with a 10-µm deuteron target produces a quasi-monoenergetic, solid-density deuteron beam of parameters approaching those required for inertial confinement fusion fast ignition.

Proton emission from thin hydrogenated targets irradiated by laser pulses at 10(16) W∕cm2.

The iodine laser at PALS Laboratory in Prague, operating at 1315 nm fundamental harmonics and at 300 ps FWHM pulse length, is employed to irradiate thin hydrogenated targets placed in vacuum at intensities on the order of 10(16) W∕cm(2). The laser-generated plasma is investigated in terms of proton and ion emission in the forward and backward directions. The time-of-flight technique, using ion collectors and semiconductor detectors, is used to measure the ion currents and the corresponding velocities and energies. Thomson parabola spectrometer is employed to separate the contribution of the ion emission from single laser shots. A particular attention is given to the proton production in terms of the maximum energy, emission yield, and angular distribution as a function of the laser energy, focal position, target thickness, and composition. Metallic and polymeric targets allow to generate protons with large energy range and different yield, depending on the laser, target composition, and target geometry properties.

Fast proton generation from ultrashort laser pulse interaction with double-layer foil targets.

The results of studies of fast-proton generation from foil targets irradiated by 1-ps laser pulse at 10(17) W/cm (2) are presented. It is shown that a considerable increase in proton energy and current is possible when a double-layer foil target containing a high- Z layer and a low- Z hydrogen-rich layer is used instead of a single-layer target. Proton energies and current increase with the Z of the high- Z layer and depend essentially on the target and the layer thicknesses. Above 10(9) forward-emitted protons of energy >100 keV have been recorded within a cone angle <3 degrees.