Coaxial two-channel high-gradient dielectric wakefield accelerator

Abstract

A new scheme for a dielectric wakefield accelerator is proposed that employs a cylindrical multizone dielectric structure configured as two concentric dielectric tubes with outer and inner vacuum channels for drive and accelerated bunches. Analytical and numerical studies have been carried out for such coaxial dielectric-loaded structures (CDS) for high-gradient acceleration. An analytical theory of wakefield excitation by particle bunches in a multizone CDS has been formulated. Numerical calculations are presented for an example of a CDS using dielectric tubes with dielectric permittivity 5.7, having external diameters of 2.121 and 0.179 mm with inner diameters of 2.095 and 0.1 mm. An annular 5 GeV, 6 nC electron bunch with rms length of 0.035 mm energizes a wakefield on the structure axis having an accelerating gradient of $600 MeV=m with a transformer ratio $8:1. The period of the accelerating field is $0:33 mm. If the width of the drive bunch channel is decreased, it is possible to obtain an accelerating gradient of >1 GeV=m while keeping the transformer ratio approximately the same. Full numerical simulations using a particle-in-cell code have confirmed results of the linear theory and furthermore have shown the important influence of the quenching wave that restricts the region of the wakefield to within several periods following the drive bunch. Numerical simulations for another example have shown nearly stable transport of drive and accelerated bunches through the CDS, using a short train of drive bunches.

Formation of a novel shaped bunch to enhance transformer ratio in collinear wakefield accelerators

“…Moreover, the gradient of the accelerators in the TBA scheme seems to be limited to $120 MV=m, particularly for conventional metallic disk-loaded accelerating structures operated in the microwave regime [15]. A coaxial wakefield device in principle can combine the advantages of collinear and TBA schemes [16,17], but it also faces great challenges in drive beam formation, structure construction, beam transport, etc.…”

Comparison of experimental tests and theory for a rectangular two-channel dielectric wakefield accelerator structure

“…Nevertheless, the presence of deflection in a rectangular DWFA is an intrinsic feature [17] that is a consequence of its lack of symmetry. A more promising choice for accelerator application should be a coaxial structure where symmetry can cure this unwanted deflection [12,15]. The rectangular version-studied [14,[16][17][18] and developed [14,16] by our group-nonetheless delivers a useful example that is very well suited to check theory and our understanding of how wakefields in a two-channel structure manifest themselves.…”

“…However, achievement of high TR is subject to limitations dictated by bunch stability requirements for both the accelerated and drive bunches, or drive trains [1,[12][13][14]. Recently, we explored a version of the two-channel structure with favorable symmetry, namely, a coaxial dielectric wakefield accelerator [12,15]; in this structure, lateral forces on the test bunch vanish to lowest order.…”

Three-dimensional analysis of wakefields generated by flat electron beams in planar dielectric-loaded structures

“…To date, cylindrically symmetric DLW's have been extensively studied both theoretically [10,[16][17][18] and experimentally [19][20][21][22]. Since the angular divergence of the beam also increases during focusing it is hard to maintain a low transverse size of the beam over a long propagation distance.…”