Co-axial laser triggered injection of electrons in PWFA can produce high quality witness bunches. In this study, angled injection was examined in a pursuit to increase the tolerance levels of synchronization and experimental misalignments while maintaining the high quality of the witness bunches.
Many works have highlighted the great potential of the plasma photocathode PWFA scheme as regards the production of ultrahigh quality witness bunches in terms of high brightness and low emittance. However, both the synchronization and the alignment of electron injection within the blowout are challenging. Although low intensity and energy laser pulses are much more manageable than ultrahigh intensity laser pulses, as a result, the margins of experimental errors are very narrow, jeopardising the stability of the witness bunch generation and the resulting system quality. In this work, various approaches on how to reduce the sensitivity towards temporal and spatial misalignments or jitter are discussed. The use of angled injection in combination with tailored and confined trapping potential looks very promising, aiming at an increase of the tolerance levels of both synchronization and misalignments, while maintaining the quality of the witness bunches.
The wakefield produced by the propagation of a FACET-II-grade electron driver in an underdense pre-ionized plasma channel, was selected as a starting point with future reference. A two gas mixture (with adequately different ionization thresholds) enabled the production of both the plasma and the laser released electrons. Softly focused, long and short laser pulses, with large spot size and at various angles to the central axis of the driver propagation, were examined. The generated geometry can enable scanning of the trapping area by the laser pulse ionization front and can lead to homogeneous electron injection. As expected theoretically and also as confirmed by simulations, the combination of the geometrical characteristics of the trapping area with the pulse spot size, has a great impact on both the amount of trapped charge and its quality and the tolerance levels during an experiment. The levelling effect of angled injection is accompanied by an easier experimental setup when compared to fully collinear injection. This is a crucial step to making the scheme much more resilient towards experimental jitters and shot-to-shot variations.
|Are you a student?||Yes|