Complete multipactor suppression in an X-band dielectric-loaded accelerating structure

Abstract

Multipactor is a major issue limiting the gradient of rf-driven Dielectric-Loaded Accelerating (DLA) structures. Theoretical models have predicted that an axial magnetic field applied to DLA structures may completely block the multipactor discharge. However, previous attempts to demonstrate this magnetic field effect in an X-band traveling-wave DLA structure were inconclusive, due to the axial variation of the applied magnetic field, and showed only partial suppression of the multipactor loading [Jing et al., Appl. Phys. Lett. 103, 213503 (2013)]. The present experiment has been performed under improved conditions with a uniform axial magnetic field extending along the length of an X-band standing-wave DLA structure. Multipactor loading began to be continuously reduced starting from 3.5 kG applied magnetic field and was completely suppressed at ∼8 kG. Dependence of multipactor suppression on the rf gradient inside the DLA structure was also measured.

Summary report of working group 3: Laser and high-gradient structure-based acceleration

“…The tests demonstrated the total suppression of multipactor once the external magnetic field exceeded 7.5 kG, and the dependence of the required magnetic field on the accelerating gradient was weak. Modeling and experimental results demonstrated excellent agreement [10]. Other ideas proposed to suppress multipactor included grooved dielectric linings, both transverse and longitudinal, as well as TiN coatings.…”

Development and high-power testing of an X -band dielectric-loaded power extractor

“…DLSs were first used for particle acceleration in the late 1940s [42,43]. Since then, steady progress has been made including an increased frequency range from GHz to THz [12-15, 19, 44], comparable shunt impedance as the metallic disk-loaded structure by using low loss microwave ceramic materials [14,21], tunability with a second layer of nonlinear ferroelectric [15], higher order modes (HOMs) damping with segmented conducting boundaries [45], multipacting suppression by external magnetic field [46,47], and GV/m level gradient in rf breakdown tests [48] as well as CWA experiments [19], etc. Despite this progress, high power rf pulse generation beyond 100 MW with drive bunch train excitation in the TBA approach was yet to be demonstrated for DLS.…”

A Compact, Low-Field, Broadband Matching Section for Externally Powered X-Band Dielectric-Loaded Accelerating Structures

“…absorbing material. However, there are still some potential challenges for DLA structures in a high-power RF environment, such as dielectric breakdown [13], thermal heating and multipactor [14][15][16][17]. In dielectric breakdown studies, a dielectric surface field breakdown threshold of 13.8 GV/m [18] has been observed at THz regime.…”