Abstract
Using a periodic electron beam bunch train to resonantly excite plasma wakefields in the quasi-nonlinear (QNL) regime has distinct advantages over employing a single, higher charge bunch. Resonant excitation in the QNL regime can produce plasma electron blowout using very low emittance beams with a small charge per pulse: the local density perturbation is extremely nonlinear, achieving total rarefaction, yet the resonant response of the plasma electrons at the plasma frequency is preserved. Such a pulse train, with inter-bunch spacing equal to the plasma period, can be produced via inverse free-electron laser bunching. To achieve resonance with a laser wavelength of a few microns, a high plasma density is used, with the attendant possibility of obtaining extremely large wakefield amplitude, near 1 TV/m for FACET-II parameters. In this article, we use particle-in-cell simulations to study the plasma response, the beam modulation evolution, and the instabilities encountered, that arise when using a bunching scheme to resonantly excite waves in a dense plasma.
Highlights
In a beam-driven plasma wakefield accelerator (PWFA), electromagnetic fields are excited by an intense, relativistic particle beam driver
Introduced in 2004 [17], the inverse free electron laser (IFEL) technique for microbunching, was proposed as a means of generating high peak current bunch trains
Resonant PWFA excitation in the linear regime has been experimentally demonstrated by modulating an electron beam into a train of microbunches spaced at a laser wavelength of λL 1⁄4 10.6 μm through an inverse free-electron laser (IFEL) interaction at the BNL ATF facility [21]
Summary
In a beam-driven plasma wakefield accelerator (PWFA), electromagnetic fields are excited by an intense, relativistic particle beam driver. To quantify the goal of obtaining large PWFA fields, a train with bunch-tobunch spacing of 2 μm is resonant with a very high density plasma: n0 1⁄4 k2p=4πre 1⁄4 2.79 × 1020 cm−3 This density, in combination with assumptions of quasinonlinear waves approaching wave-breaking amplitude, EWB 1⁄4 mec2kp, implies extremely large-amplitude excited wakefields, up to TV/m, as discussed below. A 3.2 pC microbunched (2 μm period, 348 A peak current) beam with a normalized emittance of 50 nm rad [11] has a matched spot size, σx, of 13 nm comparable to a linear collider final focus [12] At this size, the beam creates enormous radial electric fields, near 1 TV/m, which will ionize the gas atoms in a high field process termed the barrier suppression regime [13]. The size of the simulation window and the particle per cell for the simulations running for a longer duration, i.e., 5000=ωp is specified below in the table containing the simulation parameters
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
