Suppressing parasitic effects in a long dielectric wakefield accelerator

Abstract

Abstract. Dielectric wakefield acceleration is a promising concept for increasing the accelerating gradient above the limits of conventional accelerators. Although superior gradients are reported in short dielectric wakefield accelerator tubes, problems arise when it comes to efficiency and multi-meter long interaction lengths. Here we discuss possible issues and provide some solutions backed by simulations.

Limiting effects in drive bunch beam dynamics in beam-driven accelerators: instability and collective effects

“…For example, the BBU instability that stems from transverse defocusing due to the quadrupole-like wakefields in DWA can be controlled with a magnetic quadrupole FODO lattice superimposed on the wakefield structure as explained above. The necessary magnetic fields are only achievable with small-aperture, permanent magnet quadrupoles, and effective suppression requires axial alignment of the quadrupoles with approximately 1µm accuracy [26,48]. This accurate alignment is extremely challenging, and with less accurate alignment the BBU mitigation technique will be significantly less effective.…”

“…"Vice-to-virtue" techniques exploiting the transverse wakefields, such as self-generated quadrupole-like modes to assist in damping in plasma [71], provide creative solutions. In structurebased wakefield acceleration, an effective way to reduce instability is by using the proper geometry for very wide elliptical beams in planar structures [37] or using round beams with a periodic change to the structure orientation providing natural quadrupole focusing [39,48,49]. It should be noted that the self-generated transverse wakefields can be harnessed and are already employed in traditional accelerator systems, for example in longitudinal diagnostics [72], where the wakefields generated in small aperture structures streak the beam for longitudinal profilometry with high-resolution beyond what can be provided by RF-powered devices such as deflecting cavities.…”

“…To achieve effective focusing, the sign of the quadrupole wakefield must alternate. This is possible to achieve by periodically changing orientation of the consequent sections of the rectangular waveguide by 90 degrees, as illustrated in figure 5 [39,48,49]. A similar alternating focusing idea was proposed in [50], although the planar waveguide accelerating geometry described in [50] cannot be technically classified as colinear acceleration.…”