Data elaboration of proton beams produced by high-energy laser-generated plasmas

Abstract

The proton beam production from high-energy laser-generated plasma is increasingly becoming of special interest for investigations in the field of new techniques of ion acceleration, nuclear physics, astrophysics and radiotherapy. The evolution of short-pulsed lasers, from the nanosecond to the femtosecond pulse scale, has allowed for an increase in intensity from about 1010 W/cm2 to about 1020 W/cm2 with a consequent increase of the kinetic energy of the plasma-generated ions. Thus proton energy has increased from about 100 eV at low intensity to about 100 MeV at the actual femtosecond-terawatt lasers. Although the emitted ions are multi-energetic, the use of thin hydrogenated targets and a high repetition rate can be employed to obtain high proton energy, narrow energy spread, high ion directivity and high current. Literature data indicate that the proton energy, the equivalent plasma temperature and the Coulomb acceleration increase with the pulse intensity. The use of femtosecond-terawatt lasers may produce very intense electric fields in the non-equilibrium plasma, which accelerate ions up to tens of MeV/amu. Ponderomotive forces, supersonic plasma expansion in vacuum, self-focusing effects and the high plasma temperature influence the ion plasma acceleration. Literature data can be fitted by Coulomb–Boltzmann-shifted functions which permit a separation of the thermal contribution from the Coulomb one. The latter increases at very high laser intensities to a greater extent than its thermal counterpart.