Laser plasma wakefield accelerations (LWFA) are the most promising candidates for future compact accelerators and also can be used for next-generation free-electron lasers (FELs). However, due to the insufficient electron beam quality, such as a few percent of energy spread, stability, and reproducibility, the electron beam from the LWFA has difficulty to be directly used for FELs with a range from soft X-ray to hard X-ray. To overcome this limitation of the beam quality from the laser wakefield acceleration using various injection techniques, one of the most reliable way is to use the electron beam with short duration, lower energy spread, and emittance from the RF photocathode.
This external injection technique is planning with conventional S-band RF photocathode gun and final energy of 70 MeV, few tens fs duration, and lower emittance at Pohang Accelerator Laboratory Injector Test Facility (PAL-ITF). In this presentation, we show a simulation result on the characterization of the electron beam from LWFA using external injection for soft X-ray free-electron lasers.
Femtosecond MeV electron beam generated by laser-plasma accelerators (LPA) is a promising source for ultrafast electron diffraction (UED) application. Compared to conventional UED instruments which limit temporal resolution to a few tens of fs, plasma electron accelerator-based UED is possible to make sub-10 fs temporal resolution because of no intrinsic time jitter between pump-probe pulses and ultrashort electron bunch length. Some groups have shown that a few MeV electron beam can be produced by using a few mJ laser pulse as it has shorter pulse duration (single- or few-cycle). In this regime, the laser pulse is tightly focused onto gas target, and thus electrons in relatively high density plasma (1020 cm-3) are self-injected and accelerated. However, the electron beam quality like energy spread and emittance should be still improved for applications. Here, we introduce plan of two laser pulses-based plasma electron acceleration research for UED application at Pohang Accelerator Laboratory (PAL). A laser pulse is separated to two pulses that one is used to drive plasma wakefield and the other one is delivered to induce electron injection in a plasma bubble. Since the driving pulse intensity is retained under threshold of self-injection to suppress electron injection, the electron injection occurs in a localized region the injection pulse is focused, resulting in the high quality electron generation. In addition, researches conducting for better electron beam quality are presented in this presentation.
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