Investigations Into X-Band Dielectric Assist Accelerating Structures for Future Linear Accelerators

Abstract

Dielectric assist accelerating (DAA) structures are being studied as an alternative to conventional disk-loaded copper structures. This paper investigates numerically an efficient Xband DAA structure operating in a higher order mode of TM02-π. This accelerating structure consists of dielectric disks with irises arranged periodically in a metallic enclosure. Through optimizations, the RF power loss on the metallic wall can be significantly reduced, resulting in an extremely high quality factor = and a very high shunt impedance ′ = MΩ/m. The RF-to-beam power efficiency reaches 51% which is significantly higher than previously-reported CLIC-G structures with an efficiency of only 33.5%. The optimum geometry of the regular and the end cells is described in detail. Due to the wide bandwidth from the dispersion relation of the accelerating mode, the DAA structure is allowed to have a maximum number of 72 regular cells with a frequency separation of 1.0 MHz, which is superior to that of conventional disk-loaded copper structures. In addition, the DAA structure is found to have a short-range transverse wakefield lower than that of the CLIC-G structure.

Analytical RF Pulse Heating Analysis for High Gradient Accelerating Structures

“…( 5) and Boris method agree perfectly with each other, a fact that allows us to justify and validate the simplification made in the third equation of the system (2) of disregarding the term proportional to the magnetic field H 0 . The analytical approximation (6) gives reasonable values for the electron trajectory, although the fact that its validity is restricted to very small times means that as time goes by the approximate trajectory differs from the full equation (5). In Fig.…”

“…The advantage of the DAA structure is that it has an extremely high quality factor and a very high shunt impedance at room temperature since the electromagnetic field distribution of the accelerating mode T M 02 reduces greatly the losses on the metallic wall as compared to that of a T M 01 mode of the pillbox cylindrical cavity. Several DAA designs have been presented in the literature, and even some prototypes have been build and tested [4], [5], [6]. Although their good performance in terms of quality factor and shunt impedance has been demonstrated with measurements, it has also been found that DAA structures suffer multipactor during operation.…”

Dielectric assist accelerating structures for compact linear accelerators of low energy particles in hadrontherapy treatments

“…The DAA structures [39,42] consist of axially symmetric dielectric cylinders with irises periodically arranged in a metallic enclosure operating in standing wave π-mode, as illustrated in Figure 1.…”

“…Based on these technologies, a Dielectric Assist Accelerating (DAA) structure proposed by Satoh et al [39][40][41] at C-band frequency is of particular interest since it achieved extremely high quality factor and shunt impedance. Later, this design was studied at X-band as a proposal for future linear accelerators [42] due to its high field holding capability. Building on these developments, a DAA structure for low beta particles operating at low frequency (S-band) is studied for the first time in this work, as a solution for compact linear accelerators of low energy and low beam current, such as medical accelerators for Hadrontherapy treatments.…”

“…Building on these developments, a DAA structure for low beta particles operating at low frequency (S-band) is studied for the first time in this work, as a solution for compact linear accelerators of low energy and low beam current, such as medical accelerators for Hadrontherapy treatments. Unlike the case of study of [42], hadrontherapy treatments make use of very low current (0.1-1 nA) [43]. Consequently, wakefields are not excited in this kind of accelerators.…”