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

Laser-Plasma Acceleration Research at PAL
M. Kim, M. H. Cho, D. Jang and I. Nam
Pohang Accelerator Laboratory, POSTECH, Korea
e-mail (speaker): kms83@postech.ac.kr

Laser-plasma accelerators have been the most promising
candidates for future compact accelerators which can beused for next-generation free-electron lasers (FEL).
However, their poor stability and reproducibility limit theapplicationsofthelaser-plasma
accelerator.
Photocathode RF gun is a good candidate for stableelectron generation and has been utilized as a major
injector for X-ray free-electron laser at PAL(PAL-XFEL) because they provide electron beams withlow emittance[1,2].
The Injector Test Facility (ITF) at PAL was built todevelop the photocathode gun in 2012 and the results ofphoto-injector research contributed to successfulcommissioning of PAL-XFEL in 2016. Since then, theITF has been refurbished for the purpose as Electron
Linear Accelerator for Basic Science (e-LABs). The
e-LABs facility consists of two beamlines with separate
two RF electron guns. The first beamline is dedicated to
MeV ultrafast electron diffraction (UED) research, andthus it was designed for generation of a few of MeV
electron bunches. The second is a multipurpose beamline
capable of delivering 70 MeV electrons in maximum.
This conventional photocathode RF guns separate
electron beams with good qualities such as energy jitterof 0.01% and emittance of ~0.5 mm mrad which arerequired for user facilities.
The plasma acceleration with external injection using
these good quality electron beams from RF photocathodegun is very prospective research[3]. Compared to otherLPA techniques that accelerate the electrons in plasma
wakefield, electron beams from photocathode RF gun areused as an injector for LPA, resulting in better beam
quality. Figure 1 shows the planned experimental schemeof the second beamline at e-LABs for plasma accelerator
with the external injection method. Generated electron
beams from the photocathode gun are accelerated to 70
MeV through a short linear RF accelerator, then thebeams are focused to tens of micrometer by the plasmalens. Tightly focused electron beams can be inserted into
the laser wakefield driven by an intense laser pulse,
leading to acceleration to high energy. If the electron
beams have 3 GeV, they can be used to produce soft
X-ray FEL[4,5]. For this external plasma accelerator, wehave developed a capillary plasma source considering
diverse purposes, for example, plasma lens and plasma
acceleration shown in Figure 1[6]. The capillary block is
made of a sapphire since it can provide a long-lived
stable plasma source. Furthermore, we are preparing thelaser upgrade to a few hundred TW system to realize thehigh-energy laser-driven wakefield acceleration andbunch compression for shorter electron bunches for thebeam-driven wakefield acceleration and beam injection.
This work is supported by the NRF of Korea fundedby the MSIT under grant no. 2020R1C1C1011840,
2020R1C1C1010477, 2021R1C1C1003255, 2022R1A2
C2009768.
References[1] I. Eom et al, Appl. Sci. 12, 1010 (2022)[2] H. S. Kang et al, Nat. Photonics 11, 708-713 (2017)[3] R. W. Assmann et al, Eur. Phy. J. Special Topics 229,3675-4284 (2020)[4] S. H. Park et al, Rev. Sci. Instrum. 89, 055105 (2018)[5] H. Jang et al, Rev. Sci. Instrum. 91, 083904 (2020)[6] S. Lee et al, Appl. Sci. 13, 2564 (2023)

Figure 1. Schematic diagram of plasma accelerator based XFEL researh at e-LABs, PAL. The developled one-bodycapillary plasma sources can be used for plasma lens and plasma electron acceleration in laser-plasma acceleration
research.