Abstract
During the past two decades of research, the ultra-relativistic beam-driven plasma wakefield accelerator (PWFA) concept has achieved many significant milestones. These include the demonstration of ultra-high gradient acceleration of electrons over meter-scale plasma accelerator structures, efficient acceleration of a narrow energy spread electron bunch at high-gradients, positron acceleration using wakes in uniform plasmas and in hollow plasma channels, and demonstrating that highly nonlinear wakes in the ‘blow-out regime’ have the electric field structure necessary for preserving the emittance of the accelerating bunch. A new 10 GeV electron beam facility, Facilities for Accelerator Science and Experimental Test (FACET) II, is currently under construction at SLAC National Accelerator Laboratory for the next generation of PWFA research and development. The FACET II beams will enable the simultaneous demonstration of substantial energy gain of a small emittance electron bunch while demonstrating an efficient transfer of energy from the drive to the trailing bunch. In this paper we first describe the capabilities of the FACET II facility. We then describe a series of PWFA experiments supported by numerical and particle-in-cell simulations designed to demonstrate plasma wake generation where the drive beam is nearly depleted of its energy, high efficiency acceleration of the trailing bunch while doubling its energy and ultimately, quantifying the emittance growth in a single stage of a PWFA that has optimally designed matching sections. We then briefly discuss other FACET II plasma-based experiments including in situ positron generation and acceleration, and several schemes that are promising for generating sub-micron emittance bunches that will ultimately be needed for both an early application of a PWFA and for a plasma-based future linear collider.
Highlights
For the past three decades various advanced accelerator schemes that push the properties of accelerators beyond the present limits of performance have been under investigation motivated by a desire to keep increasing the center of mass energy and luminosity of high-energy charge-particle colliders [1]
The decadal challenge [10] for the plasma accelerator community is to demonstrate a single stage of a multistage plasma-based tera electron-volt (TeV) scale accelerator
On FACET II we propose to test a variation of this scheme that has the potential to generate even lower emittance beams
Summary
For the past three decades various advanced accelerator schemes that push the properties of accelerators beyond the present limits of performance have been under investigation motivated by a desire to keep increasing the center of mass energy and luminosity of high-energy charge-particle colliders [1]. We found that for a given plasma density, a certain positron beam current profile and bunch length can lead to a loaded wake where the electric field reverses sign (from decelerating to accelerating) in the middle of the single drive bunch [28]. This happens because the presence of the positrons pulls in the plasma electrons towards the axis. We have quantified the magnitude of the transverse wakefields that are excited by a misaligned beam inside a hollow plasma channel [32]
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