[P-EM17] Space Plasma Physics: Theory and Simulation

[PEM17-06] Demonstration of laser wake field accleration of protons

*Shogo Isayama¹, Yasuhiro Kuramitsu², Yuki Abe³, Takumi Minami², Kentaro Sakai², Yumi Kaneyasu³, Yuji Fukuda⁴, Shih Hung Chen⁵, Masato Kansaki⁶, Takahumi Asai⁶, Shuta Tanaka⁷, Kohei Yamanoi³ (1.Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 2.Graduate School of Engineering, Osaka University, 3.Institute of laser engineering, Osaka University, 4.National Institution for Quantum and Radiological Science and Technology, KPSI, 5.National Central University, Taiwan, 6.Faculty of Maritime Sciences, Kobe Unversity , 7.Aoyama Gakuin University)

Keywords:laser wake field accleration , generation of relativistic proton

The laser-plasma interaction can generate high acceleration fields, which exceeds those of the conventional accelerators by orders of magnitude. Due to this excellent feature of large acceleration gradient, laser-driven proton acceleration possesses high potential to realize the compact high energy proton sources. Proton beams with energies beyond 100 MeV is necessary for a wide range of applications, including modern cancer therapies [1]. In the experiment, the currently reported highest proton energy is 94 MeV by Higginson et al. [2], 93 MeV by Kim et al. [3], and 85 MeV by Wagner et al. [4]. The accleration mechanism of Radiation Pressure Acceleration (RPA) and Target Normal Sheath Acceleration (TNSA) are used in these experiments. However, these acceleration mechanisms have limitations. In the RPA, electrons and ions/protons are acclerated simultaneously by laser light pressure. This accleration will be terminated when the target is curved and deformed due to the non-uniformity of the light pressure in the direction transverse to the laser traveling direction and finally the target is broken. In the TNSA, protons are acclerated by a sheath electric field created by hot electrons but the sheath electric fifeld is limited within the debye length. Therefore, it is difficult to accelerate protons over long time and long distance by the conventional acccleration methods.
Laser Wakefeild Acceleration (LWFA) of electrons has been experimentally demonstrated to produce a few GeV electrons. In the LWFA, the electrons are trapped in the plasma wave potential and synchronously acclerated by the propagating palsma wave (wakefield) over long time and distance. Therefore, the wakefield accleration has a potential which enhances the proton energy over 100 MeV.
We conducted the experiment to demonstrate the LWFA of protons by using J-KAREN laser (KPSI). To realize the lwfa of protons, the propagation speed of wakefield should be reduced by using the intermediate density (a few times of the critical density) target so that the heavy protons are trapped by the wakefield potential. In our experiment, we used the plastic (CH) foam shape target which density is about ten time lower than the usual solid density CH target. In this presentation, we will show the preliminary results of the experiment and discuss the accleration process by comparing with the simulation resutls.

[1] S. V. Bulanov and V. S. Khoroshkov, Plasma Phys. Rep. 28, 453 (2002).
[2] A. Higginson et al., Nat. Com., 9 724, 2018.
[3] I. J. Kim et al., Phys. Plasmas, 23 070701, 2016.
[4] F. Wagner et al., Phys. Rev. Lett., 116 205002, 2016.