Speaker
Description
Hydrodynamic [1,2] and conditioned hydrodynamic [3,4] optical-field-ionised plasma channels are promising candidates to support low-density, high repetition-rate multi-GeV laser wakefield accelerator (LWFA) stages. They are generated by focusing an ultrashort pulse into neutral gas, forming a hot column of plasma via optical field ionization, which expands hydrodynamically to form a plasma channel. Because they are freestanding, they can be operated at high repetition-rate [5]. An advantage of optically generated channels is the potential to sculpt the plasma density along the LWFA stage, for example to promote injection. Here we explore the use of a density down-ramp generated between neutral gas immediately prior to the channel and the channel itself to trap electrons. We present results of a recent experiment at the Gemini TA3 laser (RAL) in which ~ 1 GeV bunches, with percent-level energy spread, were generated by sub-100 TW laser pulses. The effect of the longitudinal and transverse position of the drive pulse focus on the generated electron bunches was investigated. These results, and particle-in-cell simulations, demonstrate that the channel entrance down-ramp is responsible for electron injection.
[1] Shalloo, RJ, et al, (2018). PRE, 97(5)
[2] Shalloo, RJ, et al, (2019). PRAB, 22(4)
[3] Picksley, A, et al, (2020). PRE, 102(5)
[4] Feder, L, et al, (2020). PRR, 2(4)
[5] Alejo, A, et al, (2022), PRAB, 25(1)
Acknowledgments
This work was supported by the UK Science and Technology Facilities Council (STFC UK) [grant numbers ST/P002048/1, ST/R505006/1, ST/S505833/1, ST/V001655/1]; the Engineering and Physical Sciences Research Council [EP/R513295/1, EP/V006797/1]. This material is based upon work supported by the Air Force Office of Scientific Research under award number FA9550-18-1-7005.
