量子科学技術研究開発機構学術機関リポジトリ

The interaction of relativistically intense short pulse (~few tens of fs) laser pulse with solid material
generates quasi-static electric fields with strengths of > TV/m are produced within a short
distance of less than m [1]. Thanks to the very strong field gradient, the field can accelerate
ions beyond MeV within a micron. Unlike the acceleration of low-Z ions, acceleration of the
high-Z ion is more complicated because charge state distribution should be controlled for pursuing
higher acceleration efficiency or for manipulating a spectral shape of the ions. However, all
the proposed laser-driven acceleration mechanisms, including the most investigated and easy to
implement mechanism, Target Normal Sheath Acceleration (TNSA) [2], are far from being fully
understood in the sense of ionization mechanisms. To address this issue, we investigate the ionization
mechanisms in HED plasma produced by a laser pulse of peak intensity ~5x1021 Wcm????2
interacting with a silver 500 nm target by using J-KAREN laser system KPSI, QST [3]. Even the
J-KAREN laser is high contrast laser system the pulses show not completely ideal (Gaussian-like)
temporal shape. The existence of the rising edge is an inherent feature of high power laser systems
based on highly non-linear processes and eliminating this rising edge is challenging, even when
applying pulse cleaning techniques such as plasma mirrors and/or a plasma shutter. The rising
edge interacts with target in advance to the main pulse and can prematurely expand the target
resulting in reduction of proton cutoff energies. This is a serious barrier for not only proton acceleration,
however we found this temporal shape can be a beneficial effect on heavy ion acceleration
from the bulk of the target. In the experiment we observed that silver ions with a charge state of
~ +40 are accelerated up to ~15 MeV/u with the particle number of (2±1)x106 ion/shot within an
energy range of 10-15 MeV/u. With the help of hydrodynamic, particle-in-cell (PIC) simulations
and analytical estimates, we find out that the ions in the contaminant layer pre-expands and effectively
detaches from the target, still keeping the target material intact, so that the bulk ions
are exposed to stronger sheath fields and accelerated to higher energies. The highly charged energetic
silver ions are generated via electron collisions in the hot (~6 keV electron temperature) solid
plasma. The reported heavy ion acceleration mechanism is in unexplored physical regime, which
has been generated for the first time via interaction with a laser with an ultra-high intensity using
the state-of-the-art laser system J-KAREN.

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Laser-Plasma Accelerator Workshop 2019参加

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2019-05-06

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2023-05-15 18:51:13.190535

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Highly charged heavy ion acceleration from a high temperature solid heated by J-KAREN laser system

× 西内, 満美子

× Dover, NicholasPeter

× 畑昌育

× Sakaki, Hironao

× Kondo, Kotaro

× 宮原巧

× Kiriyama, Hiromitsu

× Kevin Koga, James

× 岩田夏弥

× Alkhimova, MARIYA,

× Pirozhkov, Alexander

× Anatory, FAENOV,

× Tatiana, PIKUZ,

× Sagisaka, Akito

× Watanabe, Yukinobu

× Kando, Masaki

× Kondo, Kiminori

× Yasuhiko, Sentoku

× Nishiuchi, Mamiko