Projection imaging with directional electron and proton beams emitted from an ultrashort intense laser-driven thin foil target

Abstract

Projection images of a metal mesh produced by directional MeV electron beam together with directional proton beam, emitted simultaneously from a thin foil target irradiated by an ultrashort intense laser, are recorded on an imaging plate for the electron imaging and on a CR-39 nuclear track detector for the proton imaging. The directional electron beam means the portion of the electron beam which is emitted along the same direction (i.e., target normal direction) as the proton beam. The mesh patterns are projected to each detector by the electron beam and the proton beam originated from tiny virtual sources of ~20 µm and ~10 µm diameters, respectively. Based on the observed quality and magnification of the projection images, we estimate sizes and locations of the virtual sources for both beams and characterize their directionalities. To carry out physical interpretation of the directional electron beam qualitatively, we perform 2D particle-in-cell simulation which reproduces a directional escaping electron component, together with a non-directional dragged-back electron component, the latter mainly contributes to building a sheath electric field for proton acceleration. The experimental and simulation results reveal various possible applications of the simultaneous, synchronized electron and proton sources to radiography and pump-probe measurements with temporal resolution of ~ps and spatial resolution of a few tens of µm.

Low divergent MeV-class proton beam with micrometer source size driven by a few-cycle laser pulse

“…Previously reported emittance value of laser-driven MeV protons from the mesh projection (or ‘pepper-pot’) methods are about 0.1 4 , 49 . Other measurements using mesh projection have recently reported emittance values of 0.01 π mm mrad 50 and 0.065 π mm mrad 6 . In alternate methods of micromachining groves at the target rear surface, the transverse emittance for nearly 10 MeV proton came to about 0.0013 7 , 15 , i.e., 100-fold better than conventional accelerators.…”

Proton imaging of high-energy-density laboratory plasmas

“…Using lowerintensity lasers (Orimo et al, 2007), one can image smaller or less dense objects, and a variant of this scheme uses a thin needle to produce protons and x rays (Ostermayr et al, 2020) along the same line of sight. This dual imaging has been shown with electrons as well (Nishiuchi et al, 2015;Faenov, Pikuz, and Kodama, 2016), which could be used to break the degeneracy between electric and magnetic fields. In this vein, the use of an x-ray free electron laser or coherent source colocated at a laser facility could provide significant advantages when proton and high resolution x-ray images are combined along the same line of sight.…”