Tri-stage quasimonoenergetic proton acceleration from a multi-species thick target

Abstract

We show that quasimonoenergetic proton beams can be generated through a multi-ion thick target irradiated by a circularly polarized laser pulse. After disrupted by the transverse instabilities in the laser pressure acceleration process, heavy ions as majority species can still provide a co-moving electric field. Different from the dynamics using ultrathin foil, protons with small doped rates can experience a full tri-stage quasimonoenergetic acceleration (hole boring, sheath boosting, and free expansion stages) in this scenario. A theoretical model is developed to explain the proton energy evolution in detail and verified by two-dimensional particle-in-cell simulations. The scaling of proton energy with laser intensity indicates that the 200 MeV proton beam with narrow energy spread (3%–10%) and sufficiently large charges (1010–1011) required for medical applications can be obtained using 100s TW class laser systems in near future.

Transverse instability in the "light sail" ion acceleration

“…Among other possibilities to improve the LS performance, it is worth to mention the multi-species targets, where heavy ions provide a co-moving electrostatic field for protons even after the plasma is disrupted by the in-stability [31][32][33][34][35]. Another proposed alternative is to use an extremely intense single-cycle laser to provide acceleration on a time before the instability develops [36].…”

Two-stage laser acceleration of high quality protons using a tailored density plasma

“…In case of a laser pulse matched to the plasma density, electrons are completely blown out from the wake, and ψ max ∝ a 0 [37,38]. In order to estimate T h , we may consider balance between the plasma electron energy area density and the absorbed laser energy area density [39]. Assuming a uniform temperature in NCD plasma region balance equation reads 3k B T h L 1 n e = ηIτ laser , where I is laser intensity, τ laser is the laser pulse duration, and η is the laser to electron conversion efficiency.…”