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Effects of dielectric discontinuity on the dispersion characteristics of the tape helix slow-wave structure with two metal shields

Published online by Cambridge University Press:  13 March 2012

Yu Zhang ,
Jinliang Liu ,
Shiwen Wang ,
Xuliang Fan ,
Hongbo Zhang  and
Jiahuai Feng
Yu Zhang*
Affiliation:
College of Opto-electronic Science and Engineering, National University of Defense Technology, Changsha, China
Jinliang Liu
Affiliation:
College of Opto-electronic Science and Engineering, National University of Defense Technology, Changsha, China
Shiwen Wang
Affiliation:
College of Opto-electronic Science and Engineering, National University of Defense Technology, Changsha, China
Xuliang Fan
Affiliation:
College of Opto-electronic Science and Engineering, National University of Defense Technology, Changsha, China
Hongbo Zhang
Affiliation:
College of Opto-electronic Science and Engineering, National University of Defense Technology, Changsha, China
Jiahuai Feng
Affiliation:
College of Opto-electronic Science and Engineering, National University of Defense Technology, Changsha, China
*
Address correspondence and reprint requests to: Yu Zhang, College of Opto-electronic Science and Engineering, National University of Defense Technology, Changsha 410073, China. E-mail: zyu841227@yahoo.com.cn
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Abstract

In the tape helix slow-wave system, discontinuous dielectrics have great effects on the dispersion characteristics. In this paper, the tape helix slow-wave system, including an inner and an outer metal shield, tape helix, nylon support, and de-ionized water as filling dielectric, was analyzed. Effects of dielectric discontinuity caused by the support dielectric and filling dielectric on the dispersion characteristics were studied in detail. The dispersion relations, phase velocities, slow-wave coefficients, and electric lengths of the spatial harmonics in the system were calculated. Results showed that, if the permittivity of support dielectric was smaller than that of the filling dielectric, frequencies of the spatial harmonics in the system rose, phase velocities and slow-wave coefficients increased, the slow-wave effect of the system was weakened so that the previous electric length was shortened. The reverse condition corresponded to the reverse results, and the electromagnetic simulation also proved it. By use of the helical pulse forming line of accelerator based on the studied tape helix slow-wave system, the electric lengths of the system were tested as 188.5 ns and 200 ns in experiments where the thicknesses of nylon support were 6 mm and 3 mm, respectively. The theoretical calculation results 198 ns and 211 ns basically corresponded to experimental results, which only had relative errors as 5 and 5.5%, respectively.

Keywords

AcceleratorDielectric discontinuityDispersion relationElectric lengthPulse forming lineSpatial harmonicsTape helix slow-wave structure
Type
Research Article
Information
Laser and Particle Beams , Volume 30 , Issue 3 , September 2012 , pp. 329 - 339
Copyright
Copyright © Cambridge University Press 2012

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