Simultaneous observation of ultrafast electron and proton beams in TNSA

The interaction of ultra-intense high-power lasers with solid-state targets has been largely studied for the past 20 years as a future compact proton and ion source. Indeed, the huge potential established on the target surface by the escaping electrons provides accelerating gradients of TV/m. This process, called target normal sheath acceleration, involves a large number of phenomena and is very difficult to study because of the picosecond scale dynamics. At the SPARC_LAB Test Facility, the high-power laser FLAME is employed in experiments with solid targets, aiming to study possible correlations between ballistic fast electrons and accelerated protons. In detail, we have installed in the interaction chamber two different diagnostics, each one devoted to characterizing one beam. The first relies on electro-optic sampling, and it has been adopted to completely characterize the ultrafast electron components. On the other hand, a time-of-flight detector, based on chemical-vapour-deposited diamond, has allowed us to retrieve the proton energy spectrum. In this work, we report preliminary studies about simultaneous temporal resolved measurements of both the first forerunner escaping electrons and the accelerated protons for different laser parameters.

Proton energy spectrum with the DAMPE experiment

The DAMPE (DArk Matter Particle Explorer) experiment, in orbit since December 17th 2015, is a space mission whose main purpose is the detection of cosmic electrons and photons up to energies of 10 TeV, in order to identify possible evidence of Dark Matter in their spectra. Furthermore it aims to measure the spectra and the elemental composition of the galactic cosmic rays nuclei up to the energy of hundreds of TeV. The proton analysis and the flux with kinetic energy ranging from 50 GeV up to 100 TeV, at the end of two years of data taking, will be presented and discussed.

ONE DIMENSIONALITY OF DEUTERON VELOCITY DISTRIBUTION FOR CLUSTER-IMPACT FUSION

In cluster-impact fusion, the width of the proton energy spectrum gives information about the temperature of the fusing deuterons, and its shape reflects the dimensionality of their velocity distribution. The observed symmetrical spectrum implies a one-dimensional distribution, whereas a three-dimensional distribution would result in a skewed spectrum. One dimensionality implies either extremely rapid thermalization in the beam direction, or the possibility of beam ion fusion.

Cosmic rays in an evolving universe

If the most energetic cosmic rays that have been detected are of extragalactic origin, and their sources were strong radio emitters, the radio-astronomical evidence suggests that the output from such sources must have been very much greater in the past than at present, varying roughly as t−3 over a long period. In this case, the importance of interactions between the universal flux of microwaves and intergalactic cosmic-ray protons and nuclei above 1015 eV is greatly increased, because of "red shifts" in the energies of the nuclei and the microwaves, and changes in density. The probable result is shown to be a steepening in the proton energy spectrum from a slope of –1.5 to –2.2 over the range 1016 to 1018 eV, as is observed, if the energy spectrum at production is always simply E−1.5.This could mean that the "ankle" in the observed spectrum near 3 × 1018 eV is related to the interaction mentioned, and is not a transition from galactic to extragalactic rays.Difficulties remain in accounting for the spectrum above 3 × 1019 eV.