Abstract
A tall, dielectric-lined rectangular wakefield microstructure is analyzed as a possible element of an advanced linear wakefield accelerator. This accelerator would be driven by a train of fs electron microbunches that would be chopped out of a longer bunch using a powerful ${\mathrm{CO}}_{2}$ laser and then formed into a train of rectangular-profile bunches using a quadrupole. The bunches set up a periodic wakefield in the microstructure that can be built up to $400--600\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, for example, using a train of ten 3-fs 1-pC bunches. Two major issues are examined. First, interference is studied using the particle-in-cell code KARAT between transition radiation and Cerenkov wakefield radiation, both set up by the passage of a charge bunch through a dielectric structure of finite length. Of significance is the difference in propagation speeds of transition radiation and Cerenkov radiation (which travels almost at the vacuum light speed $c$) and the magnitude of the respective fields. Second, stability is examined for drive and accelerated bunches using computations of test particle orbits in the longitudinal and transverse wakefields excited by the drive bunches. It is found that nearly all test electrons in the drive bunches are confined within the structure for a travel distance of 30 cm or more, while test electrons located in an accelerated bunch can have stable motion over greater than 30 cm without passing through the structure walls.
Highlights
Acceleration of electrons in wakefields set up by a series of drive bunches in a dielectric structure has shown promise as the basis for a linear accelerator in which large acceleration gradients can be achieved [1,2]
This paper discussed the interference between transition radiation and Cerenkov wakefield radiation in a tall, planar dielectric microstructure, using the PIC code KARAT
We find that because of the difference between the propagation speeds of wakefield radiation and transition radiation, a train of periodic wakefields still is excited behind the bunch as it advances into the structure
Summary
Acceleration of electrons in wakefields set up by a series of drive bunches in a dielectric structure has shown promise as the basis for a linear accelerator in which large acceleration gradients can be achieved [1,2]. With the objective of realizing such an accelerator, we have recently studied wakefield generation and beam stability in tall, planar dielectric wakefield structures having micron-scale dimensions [3] Such structures are capable of precision fabrication using microcircuit technologies and have the capability of achieving very high field gradients: analysis has recently shown that a series of ten, 3-fs 1-pC charge bunches can set up an accelerating wakefield of 500 MV=m in a structure 18:8 m 150 m in cross section [4]. A TW-level CO2 laser would be used as a modulator [3] of the original ps, nC bunch provided by the linac to form such a sequence of short bunches, each having charge in the pC range These drive bunches, which can in principle be recycled, would in practice be followed by an accelerated bunch that is situated in the accelerating phase of axial electric field Ez which trails the drive bunch train. This large magnitude of stable acceleration gradient motivates the analysis in this paper, so as to work towards realization of an advanced high-gradient linear accelerator based on the principles enunciated here
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
