Radiation pressure acceleration: The factors limiting maximum attainable ion energy
Authors: Bulanov S.S., Esarey E., Schroeder C.B., Bulanov S.V., Esirkepov T. Zh., Kando M., Pegoraro F., Leemans W.P.
Autors Affiliation: Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
KPSI, National Institutes for Quantum and Radiological Science and Technology, Kizugawa,
Kyoto 619-0215, Japan
A. M. Prokhorov Institute of General Physics RAS, Moscow 119991, Russia
Physics Department, University of Pisa and Istituto Nazionale di Ottica, CNR, Pisa 56127, Italy
Physics Department, University of California, Berkeley, California 94720, USA
Abstract: Radiation pressure acceleration (RPA) is a highly efficient mechanism of laser-driven ion acceleration, with near complete transfer of the laser energy to the ions in the relativistic regime. However, there is a fundamental limit on the maximum attainable ion energy, which is determined by the group velocity of the laser. The tightly focused laser pulses have group velocities smaller than the vacuum light speed, and, since they offer the high intensity needed for the RPA regime, it is plausible that group velocity effects would manifest themselves in the experiments involving tightly focused pulses and thin foils. However, in this case, finite spot size effects are important, and another limiting factor, the transverse expansion of the target, may dominate over the group velocity effect. As the laser pulse diffracts after passing the focus, the target expands accordingly due to the transverse intensity profile of the laser. Due to this expansion, the areal density of the target decreases, making it transparent for radiation and effectively terminating the acceleration. The offnormal incidence of the laser on the target, due either to the experimental setup, or to the deformation of the target, will also lead to establishing a limit on maximum ion energy.
Journal/Review: PHYSICS OF PLASMAS
Volume: 23 Pages from: 056703-1 to: 056703-13
KeyWords: Radiation pressure acceleration (RPA)