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Latest Plasma Wakefield Acceleration Results from the FACET Project

SLAC’s new Facility for Advanced Accelerator Experimental Tests (FACET) had its second user run in April– June, 2013. Several new milestones were reached during this run, including the achievement of beam driven plasma wakefield acceleration of a discrete witness bunch for the first time, and energy doubling in a noble gas plasma source. The FACET beam is a 20GeV electron bunch with a charge of 3.2 nC that can be compressed and focused to a size of 20μm× 20μm× 20μm rms. To create the twobunch, drive/witness beam structure, a chirped and overcompressed beam was dispersed horizontally in a chicane and a bite was taken from its middle with a tantalum finger collimator, corresponding to a longitudinal notching of the beam due to the head-tail energy correlation. A new 10 terawatt Ti:Sapphire laser was commissioned and used during this run to pre-ionize the plasma source in order to increase the efficiency of energy transfer from the beam to the wake. Ultimately, a witness beam of hundreds of pC in charge was accelerated by a drive beam of similar charge in a preformed lithium plasma with a density of 5 × 10 cm, experiencing gradients reaching several GV/m in magnitude.