Betatron Radiation from Underdense Plasma

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Plasma accelerators provide unique opportunities for the generation of high quality, short-pulse electrons beams which are an ideal basis for high quality radiation generation. To commission a new type of very high brightness betatron radiation source, I will first study a single 10 GeV beam generated in a plasma wakefield accelerator, as a 'typical' drive beam. This simple setup will provide "clean", relatively simple physics that can be compared to simulations and models and used to calibrate all devices and detectors. Following single-bunch commissioning, I will then use two 10 GeV bunches (drive and witness) in a typical plasma wakefield accelerator configuration with accelerating fields of ~10 GeV/m, followed by the wakeless plasma source. Comparing the two, we expect to see a less broad radiation spectrum from the witness bunch in the wakeless plasma, due to the constant beam energy (note: the drive beam loses energy in both cases). The plasma density will then be progressively lowered to observe the transition from high to low (~1) Ku, if possible. Next, I will repeat the two-bunch procedure above, but using the 100 MeV, low emittance witness beam provided by the planned photo injector near the experimental area of the FACET-II beamline. This configuration would provide a strong low Ku signal at low X-ray energy for the bent crystal detector system. Finally, I will attempt to generate and observe very high brightness X-ray betatron radiation from an ultra-bright, plasma-injected beam in a wakeless plasma. Progress in this part will depend also on progress in e.g. plasma injection programs, such as Trojan Horse, as well as plasma source development, which must provide a seamless transition from the plasma injection region (wide plasma column, high density) to the wakeless plasma region (narrow plasma column, possibly lower density).