7 Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023
thEnhanced pointing and charge stabilities for electron beams from few-TW laser
wakefield acceleration with a shaped sub-mm gas jet
Ming-Wei Lin , Dang Khoa Tran , Po-Wei Lai , Shou-Wei Chou ,Hsu-Hsin Chu , Shih-Hung Chen , and Jyhpyng Wang
Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu, Taiwan
Department of Physics, National Central University, Zhongli, Taiwan
Center for High Energy and High Field Physics, National Central University, Zhongli, Taiwan
Institute of Atomic and Molecular Science, Academia Sinica, Taipei, Taiwan
e-mail (speaker): mwlin＠mx.nthu.edu.tw
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4Invention a scheme of laser wakefield acceleration(LWFA) applicable with few-TW or even sub-TW pulses
enables the high-repetition-rate generation of electron
beams driven by modern diode-pumped lasers. It is aprerequisite here to create a dense target capable ofproviding a plasma electron density ne >> 1019 cm-3, suchthat a high intensity can be resulted for the self-focusedand self-modulated pump pulse to drive plasma waves
for electron acceleration [1,2]. In addition, implementing
a target with a shaped density profile can improve
properties of output electrons, primarily for the enhanced
charge stability and the reduced beam pointing
fluctuation as demonstrated in this work.
Figure 1(a) illustrates the experimental setup in which
1-TW, 40-fs pulses were focused onto nitrogen gas jetsfor electron generation and pulses of the shadowgraphy
probe beam were applied to measure density profiles ofplasmas with a wavefront sensor. Gas jets were produced
by a 178-μm diameter orifice as shown in Fig. 1(b),while a blade was placed with a height of 100 μm above
the orifice and a coverage C = 0 % is defined when theblade edge is aligned with the back edge of the orifice
exit. When 1-TW pulses were introduced to interact withgas jets produced with a backing pressure of 400 psi, thedensity profiles of nitrogen plasmas shown in Fig. 1(c)indicate that the shaped gas jet/ plasmas produced with
C= 100 % exhibited an asymmetric density profile with areduced length and a shortened density-down ramp whencompared to the default one produced without using theblade. For the output electrons, the results shown in Figs.
1(d) and 1(e) indicate that using the shaped target canresult in a greatly increased beam intensity and, more
importantly, significantly reduced pointing fluctuations,which decreased from ∆θ# = 22.1 mrad and ∆θ$ = 11.4
mrad for beams from default nitrogen jets to ∆θ# = 2.6
mrad and ∆θ$ = 5.1 mrad for those from shaped jets.
Meanwhile, as shown in Figs. 1(f) and 1(g) for thedispersed electron distributions, using the shaped jets canobviously improve the output beams for their charge
stabilities. As the charge and associated deviation wereestimated to be 4.9 pC and 134 % for electrons (> 3 MeV)
generated from the default jets, an increased charge of
12.1 pC and an inhibited deviation of 10.7 % wereacquired with the shaped gas jets, which greatly
facilitates the downstream applications of few-TW
LWFA with satisfactory beam properties
References[1] M.-W. Lin et al, Phys. Plasmas, 27, 113102 (2020).
[2] P.-W. Lai et al, Phys. Plasmas, 30, 010703 (2023).

Figure 1. (a) Schematic diagram of LWFA experiment. (b) Illustration for the position of the blade edge relative to the orifice (nozzle) exit, (c) With
400-psi backing pressure fed to the nozzle, the shadowgrams and associated electron density distributions for the nitrogen plasmas produced with thedefault gas jet and the shaped one with the coverage C = 100 %. Corresponding (d) transverse profiles of output electron beams. Comparison for (c)pointing fluctuations and (f) images of dispersed distribution of 20 consecutive electron beams. (g) Representative energy spectra for results in (f).