Speaker
Description
Fabricating a thin, dense gas target capable of providing a plasma electron density of > 10^{19} cm^{-3} enables the operation of laser wakefield acceleration (LWFA) with few-TW or even sub-TW pulses, as a strong laser intensity can be achieved for the self-focused and self-modulated pump pulse to drive plasma waves for electron acceleration. The high plasma density used here, however, results in a short dephasing length of < 100 µm, which substantially limits the energy gains for accelerated electrons and degrades the quality of the output beams. Based on the results of LWFA acquired with a 1-TW laser pulse and a default nitrogen gas jet characterized by a length of 670 µm and a peak electron density of 4.5 x 10^{19} cm^{-3}, we investigate the feasibility of improving beam properties by shaping the density profile of a gas jet with a shortened density-down ramp region to inhibit electron dephasing therein. Hence, by placing a blade above the nozzle to impede part of the gas flow, an asymmetric density profile featuring a reduced density-down ramp length of 150 µm and a lowered peak electron density of 3.9 x 10^{19} cm^{-3}was created, accordingly. Results showed that using the asymmetric/shaped nitrogen gas jet helped to reduce the horizontal pointing fluctuation to 5.3 mrad when compared to 19.2 mrad obtained with the default jet. The shaped gas jet also contributed to a higher bunch charge of 16.3 pC than that of 5.8 pC with the default jet, which can be attributed to the mitigated dephasing of accelerated electrons and the moderated depletion of pump pulse as shown by the related particle-in-cell simulation.
