ELI-NP Thematics - Ions / Solid Target / High Intensity Interaction

Laser-driven Ion Acceleration

Ion acceleration can be driven via laser-matter interaction. The intense electromagnetic field of the laser is able to accelerate electrons to relativistic energy, creating a charge unbalance in the plasma, which in turn generates strong currents of electrons and ions. With the existing multi-petawatt lasers, intensities of the order of 10²² Wcm^-2 can be achieved. Such high intensities can easily accelerate ions to many tens of MeV per nucleon. Record high energies of 150 MeV for protons and 110 MeV/u for carbon ions have been achieved at ELI-NP employing the 10 PW laser system. Several mechanisms are recognized to be able to accelerate ions, resulting in different beam characteristics. Still, much research is needed to understand and optimize such acceleration mechanisms with respect to laser and target features. This research topic is of interest to several applications, among which are Nuclear Physics and Cancer therapy.

10 PW Interaction chamber with a typical ion acceleration and diagnostics setup

Target Normal Sheath Acceleration

Target normal sheath acceleration (TNSA) is a cutting-edge method used to accelerate protons and heavier ions to high speeds using ultra-intense laser pulses. When a powerful laser hits a target with a thickness of micron scale, it creates a dense cloud of electrons on the target's surface. These electrons quickly move away from the target, creating a strong electric field that pulls positively charged ions, or protons, from the back of the target and accelerates them forward at a fraction of the speed of light. This technique is compact and efficient compared to traditional particle accelerators, offering exciting possibilities for applications in medical treatments, scientific research, and advanced manufacturing technologies.

Particle-In-Cell simulation of the Tagret Normal Shealth Acceleration mechanism

The last moments before the peak of the ultraintense laser pulse approaches the initially solid foil, it is transformed into expanding plasma. The rate of such expansion influences the properties of accelerated ions which can be understood either as a drawback or an opportunity.

Laser-driven Gamma Generation

A high-power laser can generate an intense burst of gamma from electrons accelerated to a very high Lorentz factor γ. At the high laser intensity of up to sub -10²³ W/cm², such as available at ELI-NP, a new regime in laser-plasma interaction has been foreseen, where the QED processes start playing a significant role. Such strong interaction will inevitably affect the laser-driven ion acceleration processes, appreciably altering their scaling laws and the energy repartition among the secondary sources of particles. The efficiency of gamma-ray generation can greatly vary with laser intensity, and while the bremsstrahlung emission is almost independent of the laser intensity, the synchrotron-like radiation rapidly increases with laser intensity. The dominance of one process or the other strongly depends on the laser intensity, as reported in I.C.E. Turcu et al., RRP, 68, 2016 (see Fig 3). The exploration of synchrotron-like radiation at high laser intensities is relevant for fundamental physics and also for applications, as the yield of gamma emission predicted is very high: up to 20% of the laser energy can be converted into gamma photons. In consideration of all these aspects and the wide potential applications of a powerful gamma flash, it is very important to deeply study the physics underlying the gamma generation from laser-drive plasma processes.