Alternative mechanism to accelerate ions from magnetized thin foil using standing whistler wave.

Abstract

In the presence of an external magnetic field with strength exceeding a certain critical threshold, a right circularly polarized (RCP) laser pulse propagates through an otherwise opaque target. This significantly alters the conventional laser-plasma interaction dynamics, giving rise to a set of novel physical phenomena that are not observed in the absence of such a magnetic field. Periodic longitudinal electric field structures are generated inside the target due to the formation of a standing whistler wave. These structures play a crucial role in enhancing the acceleration of protons, particularly from thin foil targets with sub-micron thickness. Interestingly, the dependence of maximum proton energy on the applied magnetic field strength exhibits an oscillatory behavior, which is governed by the coupling of the periodic longitudinal electric field and suitable target parameters. Using this mechanism, a significant improvement in collimation and energy enhancement above 40% of the accelerated ions are observed from a thin foil target of thickness 200 nm in the presence of a high magnetic field using PIC simulations. To our knowledge, this is the first report on the possibility of achieving collimated and energetic ions for a given laser intensity by exploiting the concept of enhanced TNSA due to the combined effect of standing wave field and the sheath field in the overdense plasma.