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Title: Multipactor discharge in a dielectric-loaded accelerating structure

Abstract

This paper presents a Monte-Carlo model to explain the multipactor discharge and its high-power absorption in a dielectric-loaded accelerating (DLA) structure reported recently [J. G. Power et al., Phys. Rev. Lett. 92, 164801 (2004)]. Susceptibility diagrams are constructed. Dynamic calculations for beam loading and its power absorption by the multipactor discharge are performed. It is found that the fraction of power absorbed by multipactor discharge at saturation is much larger than the case of a simple rf window, and it is sensitive to the incident power, which confirms the prior experimental results. This enhanced power absorption is due to the fact that the length of a DLA structure is much larger than the radius of the structure. A resonant condition of a maximum growth region has also been determined numerically and analytically. The difference between the resonant condition and saturation (due to beam loading) is clarified.

Authors:
;  [1];  [2]
  1. School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 Singapore (Singapore)
  2. (Singapore)
Publication Date:
OSTI Identifier:
20960120
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 1; Other Information: DOI: 10.1063/1.2435709; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ABSORPTION; BEAM-PLASMA SYSTEMS; BEAMS; DIAGRAMS; DIELECTRIC MATERIALS; HIGH-FREQUENCY DISCHARGES; MONTE CARLO METHOD

Citation Formats

Wu, L., Ang, L. K., and School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 Singapore and Institute of High Performance Computing, 117528 Singapore. Multipactor discharge in a dielectric-loaded accelerating structure. United States: N. p., 2007. Web. doi:10.1063/1.2435709.
Wu, L., Ang, L. K., & School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 Singapore and Institute of High Performance Computing, 117528 Singapore. Multipactor discharge in a dielectric-loaded accelerating structure. United States. doi:10.1063/1.2435709.
Wu, L., Ang, L. K., and School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 Singapore and Institute of High Performance Computing, 117528 Singapore. Mon . "Multipactor discharge in a dielectric-loaded accelerating structure". United States. doi:10.1063/1.2435709.
@article{osti_20960120,
title = {Multipactor discharge in a dielectric-loaded accelerating structure},
author = {Wu, L. and Ang, L. K. and School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 Singapore and Institute of High Performance Computing, 117528 Singapore},
abstractNote = {This paper presents a Monte-Carlo model to explain the multipactor discharge and its high-power absorption in a dielectric-loaded accelerating (DLA) structure reported recently [J. G. Power et al., Phys. Rev. Lett. 92, 164801 (2004)]. Susceptibility diagrams are constructed. Dynamic calculations for beam loading and its power absorption by the multipactor discharge are performed. It is found that the fraction of power absorbed by multipactor discharge at saturation is much larger than the case of a simple rf window, and it is sensitive to the incident power, which confirms the prior experimental results. This enhanced power absorption is due to the fact that the length of a DLA structure is much larger than the radius of the structure. A resonant condition of a maximum growth region has also been determined numerically and analytically. The difference between the resonant condition and saturation (due to beam loading) is clarified.},
doi = {10.1063/1.2435709},
journal = {Physics of Plasmas},
number = 1,
volume = 14,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • 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-bandmore » 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.« less
  • High power tests are currently being conducted on RF-driven dielectric-loaded accelerating (DLA) structures to determine their viability as traveling-wave accelerators. These tests are a collaborative effort between Argonne National Laboratory (ANL) and the Naval Research Laboratory (NRL). In a previous high power test, single-surface multipactor was reported to be capable of absorbing more than half of the RF power incident on an alumina-based DLA structure. In this paper, we report on the most recent set of high power tests that are attempting to further understand multipactor and eventually suppress it. Several methods were employed to suppress multipactor including: the usemore » of a magnetic field; a TIN surface coating; and a different dielectric material (Magnesium-Calcium-Titanate based). The effectiveness of these three methods are presented and discussed in the paper.« less
  • Efforts by a number of institutions to develop a Dielectric-Loaded Accelerating (DLA) structure capable of supporting high gradient acceleration when driven by an external radio frequency source have been ongoing over the past decade. Single surface resonant multipactor has been previously identified as one of the major limitations on the practical application of DLA structures in electron accelerators. In this paper, we report the results of an experiment that demonstrated suppression of multipactor growth in an X-band DLA structure through the use of an applied axial magnetic field. This represents an advance toward the practical use of DLA structures inmore » many accelerator applications.« less
  • High power tests are currently being conducted on RF-driven dielectric-loaded accelerating (DLA) structures to determine their viability as traveling-wave accelerators. These tests are a collaborative effort between Argonne National Laboratory (ANL) and the Naval Research Laboratory (NRL). In a previous high power test, single-surface multipactor was reported to be capable of absorbing more than half of the RF power incident on an alumina-based DLA structure. In this paper, we report on the most recent set of high power tests that are attempting to further understand multipactor and eventually suppress it. Several methods were employed to suppress multipactor including: the usemore » of a magnetic field; a TIN surface coating; and a different dielectric material (Magnesium-Calcium-Titanate based). The effectiveness of these three methods are presented and discussed in the paper.« less
  • Due to the high magnetic field-induced surface currents on its conducting sleeve, a conventional single layer Dielectric-Loaded Accelerating (DLA) structure exhibits a relatively high RF loss. One possible way to solve this problem is to use multilayered DLA structures. In these devices, the RF power attenuation is reduced by making use of the Bragg Fiber concept: the EM fields are well confined by multiple reflections from multiple dielectric layers. This paper presents the design of an X-band dual layer DLA structure as well as the results of bench tests of the device. We will also present results on the design,more » numerical modeling, and fabrication of structures for coupling RF into multilayer DLAs such as a novel TM{sub 03} mode launcher and a TM{sub 01}-TM{sub 03} mode converter using dielectric-loaded corrugated waveguide.« less