Tight Focusing of Proton Beam and Its Interaction with Targets

Abstract

A high-bright, self-magnetically insulated, coaxial ion beam diode, “Plasma Focus Diode” (PFD), was successfully developed and studied systematically. Using such the tightly focused beam, we investigated the ion beam energy deposition in the intense beam-target interaction. Experimental results on various diagnostics are reported briefly involving diode operation, ion-current density, beam-power density and energy spectra. The beam-target interaction experiment is described in detail, where the proton energy loss was measured by a time-resolvable Thomson-parabola spectrometer (TPS). In comparison with the energy loss for cold target (calculated by Bethe equation), enhanced energy deposition was observed for aluminium targets of 7 μm thick with maximum enhancement ratio of ∼ 1.5. Theoretical efforts involve diode behaviour analysis and simulations of beam-target interaction. We analyzed diode behaviour through calculations of field distribution, electron and ion densities and diode impedance. In the simulation of beam-target interaction, we applied bound electron and free electron stopping power model, thermal equilibrium model, radiation and conduction model and hydrodynamic expansion model. The simulated results of proton energy loss in aluminium are in good agreement with the experimental data. Following above experimental and theoretical studies, physical understanding was obtained on PFD and the associated interaction with targets.