Converging Shock-induced Blow-off Acceleration (CSBA): Towards laser acceleration of protons at nearly the speed of light

The recent advancements in both laser and target fabrication techniques have led to the enhancement of the accelerated proton cutoff energies close to 100 MeV. However, the energy spectra show a wide spread, which reduces the effective beam current to be utilized. In order to widen the possibility for high energy proton acceleration, here, we consider a different approach using micron-scale spherical hydrogen clusters, alternative to that using solid thin film targets. Recently, we have presented a new scheme using prominent characteristics of cluster targets for achieving to the level of 300 MeV quasimonoenergetic proton bunch acceleration with a low angular divergence by utilizing the internal degree of freedom (d.o.f.). In this scheme, the collisionless shock dynamics inside the micron-scale cluster subsequently coupled with relativistically induced transparency (RIT) effect of high-intensity laser plays an important role. The external d.o.f. associated with the cluster expansion due to the sheath field is also incorporated. These multiple processes can be synchronized in a self-consistent manner once suitable conditions for the laser and the cluster are satisfied, leading to the quasimonoenergetic proton bunch acceleration. We named this process Converging Shock-induced Blow-off Acceleration (CSBA).The result of a proof-of-principle experiment for the quasimonoenergetic proton bunch acceleration via interaction of micron-scale hydrogen cluster targets with PW-class laser pulses, conducted using the J-KAREN-P laser facility at KPSI-QST, will be presented.Workshop on Laboratory Astrophysics: Novel Development in Nonlinear Plasma Physics with Laser