@misc{oai:repo.qst.go.jp:00076657,
 author = {Fukuda, Yuji and Fukuda, Yuuji},
 month = {Oct},
 note = {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. In order to widen the possibility for high energy proton acceleration, we consider a different approach using micron-scale spherical hydrogen clusters, alternative to that using solid thin film targets.
Here, we introduce a new acceleration scheme, what we call CSBA (Converging Shock-induced Blow-off Acceleration), using prominent characteristics of micron-scale hydrogen cluster targets for achieving sub-GeV (0.3 GeV) quasimonoenergetic (QME) proton bunch acceleration, while maintaining a narrow energy spread (∼10%) and a small half-divergence angle (∼5°) by utilizing the internal degree of freedom (d.o.f.) of the cluster. 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 conditions for the laser and cluster are satisfied, leading to the QME proton bunch acceleration. 
By using the PW-class J-KAREN-P laser facility at KPSI-QST and the micron-scale hydrogen cluster targets, the proof-of-principle experiment for the QME proton acceleration has been successfully conducted, although the maximum proton energy is much less than that of the ideal case. In order to access the sub-GeV (0.3 GeV) QME proton acceleration, the laser peak intensity well above 1.0 × 10^22 W/cm^2 with the spot size as large as possible and the high enough laser pulse contrast is required, which could be achievable only with the ELI-NP 10 PW laser facility. 
The details of the CSBA, the results of the proof-of-principle experiment at KPSI-QST, and the future outlook will be presented., 1st ELI-NP User Workshop},
 title = {A challenge towards generation of sub-GeV quasimonoenergetic protons via the Converging Shock-induced Blow-off Acceleration (CSBA)  with 10 PW laser pulses},
 year = {2019}
}