Advances in Target Normal Sheath Acceleration with traditional and nanostructured targets

This PhD work we dedicated our study to the promising ion acceleration technique represented by Target Normal Sheath Acceleration (TNSA) which consists in a novel acceleration technique that exploit the laser interaction of ultra-intense (I>10^18 W/cm2) beams with micrometric foils to accelerate protons and light ions to energies exceeding tens of MeVs. This PhD thesis was aimed at acquiring a greater insight of TNSA, with a particular interest on the laser-plasma coupling that drives ion acceleration. The first part of this work was dedicated on the data analysis of two recent experimental campaigns, carried out in collaboration with the GIST institute (South Korea), which allowed to understand the role of important experimental parameters on TNSA with both traditional flat foils and novel nanostructured targets. The experimental conditions analyzed also represented the core of our theoretical and numerical investigation. In order to understand the physics of laser induced electron heating, we provided simple theoretical model in order to predict the hot electron temperature resulting from the interaction of an ultra-intense, ultra-short (tens of fs) laser pulse with a flat micrometric target, usually adopted in TNSA experiments. This study will be also extended to the case of novel nanostructured targets which have recently proposed as an evolution of the acceleration technique. The analytical work was supported by dedicated numerical simulations which represent a powerful tool to investigate the rich physical system. Our results were then combined with an existing model for TNSA to offer an evolution to the latter. At this point the theoretical predictions will be tested against the ample experimental data we analyzed in the first part of this PhD.

Questa tesi di dottorato è incentrata sullo studio di un'innovativa tecnica di accelerazione di ioni chiamata Target Normal Sheath Acceleration (TNSA) che sfrutta l'interazione fra laser ultra-intensi (I> 10^18 W/cm^2) con bersagli micrometrici per accelerare ioni a energie superiori al MeV. In particolare in questa tesi ci si è concentrati sullo studio teorico, supportato da simulazioni numeriche del fondamentale processo di riscaldamento di elettroni che determina le caratteristiche del fascio di ioni accelerato. Si è proposto un semplice modello per stimare la temperatura degli elettroni a seguito dell'interazione con l'impulso laser. Tale risultato è stato combinato con un modello per la TNSA capace, a partire dalla temperatura elettronica, di stimare l'energia massima degli ioni accelerati. Tali stime son state confrontate con i risultati di due recenti campagne sperimentali.