E-320 experiment at FACET-II

The present proposal is intended to support the participation of Dr. Gianluca Sarri and his PhD student, Mr. Niall Cavanagh, of The Queen's University of Belfast to the experimental campaign E-320 at the FACET-II beamline of the Stanford Linear Accelerator (SLAC). The investigator of this proposal is a central member of an international collaboration of world-leading Universities and research institutes, including Princeton, Stanford, Ecole Polytechnique, the Max-Planck institute for Nuclear Physics, and UCLA that recently was awarded, in an extremely competitive environment, beam time at FACET-II for a series of ground-breaking experiments on Strong-Field Quantum ElectroDynamics (SFQED). In a nutshell, the experiments aim at studying the dynamics of the 13 GeV electron beam provided by the FACET-II accelerator as it propagates through the focus of a 20 TW laser system, already installed and operational. Peak intensities exceeding 1x1020 Wcm^-2 can be realistically achieved, allowing to reach a peak electric field, in the rest frame of the electrons, of the order of 70% of the Schwinger field, or critical field of QED. This value significantly exceeds what previously obtained at SLAC in the late 90s and, more recently, by the PI and collaborators using the Gemini laser at the Central Laser Facility in the UK. We plan to further advance previous work by performing precision measurements and collecting extensive data sets to provide sufficient statistics to study in detail iconic phenomena in SFQED, such as quantum radiation reaction, strongly non-linear Compton scattering, and pair production. The collected data will shed light at the current intensity frontier of high-power lasers, allowing one not only to test numerical and analytical models currently used in this physical regime, but also to optimise experimental techniques for the operation of the next generation of ultra-intense laser facilities.