7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Beam stabilization and control of laser wakefield acceleration
by laser near field shaping
Nobuhiko Nakanii1,2, Kai Huang1,2, Zhan Jin2,3, Kotaro Kondo1, Izuru Daito1,Hiromitsu Kiriyama1, Hosokai Tomonao2,3, Masaki Kando1,2,3
1
Kansai Institute for Photon Science(KPSI), QST, Japan
2
Laser Accelerator R&D Team, RIKEN SPring-8 Center, Japan
3
SANKEN, Osaka University, Japane-mail (speaker): nakanii.nobuhiko@qst.go.jp
Ever since laser wakefield acceleration (LWFA)
concept was proposed by Tajima and Dawson in 1979 [1],a laser-plasma accelerator, which has an acceleration
gradient that is thousand times higher than that ofconventional accelerators, has been studied anddeveloped as a next-generation compact accelerator [2].
The maximum energy of the LWFA electron beam havealready achieved to be 8 GeV [3]. Recently, as one of themilestones in this research area, self-amplified
spontaneous emission (SASE) free-electron laser (FEL)
has been demonstrated by Chinese group [4], and seeded
FEL has been demonstrated by a group of French andGerman researchers[5]. In Japan, we have a similar
project to demonstrate FEL with wavelengths aroundextreme ultraviolet (XUV) and vacuum ultraviolet(VUV) in the JST MIRAI program [6].
The stability of electron beams is crucial for thepractical application of laser-plasma accelerators, such asFELs. Here, we focus on the pointing stability. If thepointing of the beams is unstable, the electron beamcannot be transported to the beamline and guided to theundulator. The stability of the LWFA beams, including
the pointing stability, can be improved by stabilizing thelaser system and choosing appropriate injection methods.
However, the cause of the instability of the LWFA
electron beams still needs to be clarified. The typicalpointing fluctuations of the electron beams observed in
the experiments are three times larger than those of thedriving laser pulses.
We have performed LWFA experiment with near fieldshaping of high intensity laser pulse for stabilization andcontrol beam direction. The experiment have been
performed with J-KAREN-P laser system which is ahigh-contrast petawatt-class Ti:Sapphire laser system atKPSI[7].

In our experiment, we succeeded in stabilizing theelectron beams by simply placing an aperture in the lasertransport line before the focusing element, that is, anoff-axis parabolic mirror (OAP) as shown in Figure 1.
Shaping the near-field profile (NFP) of the laser pulse
with the aperture removes the outer part of the laser
pulse with unstable wavefront and intensity. This
improves the quality and stability of the focusing laser
pulse, and thus, the electron beam generated by this laser
pulse also becomes stable. This simple method isexpected to be a key technique for realizing anultracompact accelerator with LWFA, in the future[8].
This work was supported by the JST-MIRAI program(Grant No. JPMJMI17A1). This work used researchequipment shared in the MEXT program for Advanced
Research
Equipment
Platforms(GrantNo.
JPMXS0450300221). This work was partially supportedby JSPS KAKENHI (Grant No. JP22K12665,JP21H01103 and JP21K17998.)
References[1] T. Tajima and J.M. Dawson, Phys. Rev. Lett. 43, 267(1979).
[2] E. Miura et al., Appl. Phys. Lett. 86, 251501(2005). S.P.D.
Mangles et al., Nature 431, 535(2004). C.G.R. Geddes et al.,Nature 431, 538 (2004). J. Faure et al., Nature 431, 541(2004).
W.P. Leemans et al., Nat. Phys. 2, 696 2006).
[3] A.J. Gonsalves et al., Phys. Rev. Lett. 122, 084801(2019).
[4] W. Wang et al., Nature 595, 519(2021).
[5] M. Labat et al., Nat. Photon. (2022).
[6] Y. Sano et al., JST MIRAI project “Development anddemonstration of laser-driven quantum beam accelerators”
https://lpa.ims.ac.jp/[7] H. Kiriyama et al., Opt. Lett. 45, 1100(2020).
[8] N. Nakanii et al., Appl. Phys. Express 16, 026001(2023).

Figure 1 LWFA beam stabilization by near field shaping of high intensity laser pulse