skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Two and three dimensional simulation of disk-loaded travelling-wave output structures for high-power klystrons

Abstract

The authors have developed algorithms for designing disk-loaded travelling-wave output structures for X-band klystrons to be used in the SLAC NLC. They use either a four or five cell structure in a {pi}/2 mode. The disk radii are tapered to produce an approximately constant gradient. The matching calculation is not performed on the tapered structure, but rather on a coupler whose input and output cells are the same as the final cell of the tapered structure, and whose interior cells are the same as the penultimate cell in the tapered structure. 2-D calculations using CONDOR model the waveguide as a radial transmission line of adjustable impedance. 3-D calculations with MAFIA model the actual rectangular waveguide and coupling slot. A good match is obtained by adjusting the impedance of the final cell. In 3-D, this requires varying both the radius of the cell and the width of the aperture. When the output cell with the best match is inserted in the tapered structure, they obtain excellent cold-test agreement between the 2-D and 3-D models. They use hot-test simulations with CONDOR to design the structure with maximum efficiency and minimum surface fields. The azimuthal asymmetry due to the coupling iris can increasemore » the peak fields by 20 to 30 percent. They can reduce this problem by making the final cavity with a non-circular cross section. With proper dimensions, they can keep a good match while reducing the azimuthal asymmetry to 6 percent. They have designed circuits at 11.424 Ghz for several different perveances. At 440 kV, microperveance 1.2, they calculate 83 MW, 54 percent efficiency, peak surface field 76 MV/m. At microperveance 0.8, they calculate 60 MW, 58 percent efficiency, peak field 67 MV/m. At 465 kV, microperveance 0.6, they calculate 55 MW, 62 percent efficiency, peak field 63 MV/m.« less

Authors:
 [1]
  1. Stanford Linear Accelerator Center, CA (United States)
Publication Date:
OSTI Identifier:
63088
Report Number(s):
CONF-940604-
ISBN 0-7803-2006-9; TRN: IM9527%%139
DOE Contract Number:
AC03-76SF00515
Resource Type:
Book
Resource Relation:
Conference: 1994 Institute of Electrical and Electronic Engineers (IEEE) international conference on plasma science, Santa Fe, NM (United States), 6-8 Jun 1994; Other Information: PBD: 1994; Related Information: Is Part Of 1994 IEEE international conference on plasma science; PB: 252 p.
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING NOT INCLUDED IN OTHER CATEGORIES; 43 PARTICLE ACCELERATORS; KLYSTRONS; WAVEGUIDES; LINEAR COLLIDERS; COMPUTERIZED SIMULATION; TWO-DIMENSIONAL CALCULATIONS; THREE-DIMENSIONAL CALCULATIONS; PERFORMANCE; MESH GENERATION; THEORETICAL DATA

Citation Formats

Eppley, K.R.. Two and three dimensional simulation of disk-loaded travelling-wave output structures for high-power klystrons. United States: N. p., 1994. Web.
Eppley, K.R.. Two and three dimensional simulation of disk-loaded travelling-wave output structures for high-power klystrons. United States.
Eppley, K.R.. 1994. "Two and three dimensional simulation of disk-loaded travelling-wave output structures for high-power klystrons". United States. doi:.
@article{osti_63088,
title = {Two and three dimensional simulation of disk-loaded travelling-wave output structures for high-power klystrons},
author = {Eppley, K.R.},
abstractNote = {The authors have developed algorithms for designing disk-loaded travelling-wave output structures for X-band klystrons to be used in the SLAC NLC. They use either a four or five cell structure in a {pi}/2 mode. The disk radii are tapered to produce an approximately constant gradient. The matching calculation is not performed on the tapered structure, but rather on a coupler whose input and output cells are the same as the final cell of the tapered structure, and whose interior cells are the same as the penultimate cell in the tapered structure. 2-D calculations using CONDOR model the waveguide as a radial transmission line of adjustable impedance. 3-D calculations with MAFIA model the actual rectangular waveguide and coupling slot. A good match is obtained by adjusting the impedance of the final cell. In 3-D, this requires varying both the radius of the cell and the width of the aperture. When the output cell with the best match is inserted in the tapered structure, they obtain excellent cold-test agreement between the 2-D and 3-D models. They use hot-test simulations with CONDOR to design the structure with maximum efficiency and minimum surface fields. The azimuthal asymmetry due to the coupling iris can increase the peak fields by 20 to 30 percent. They can reduce this problem by making the final cavity with a non-circular cross section. With proper dimensions, they can keep a good match while reducing the azimuthal asymmetry to 6 percent. They have designed circuits at 11.424 Ghz for several different perveances. At 440 kV, microperveance 1.2, they calculate 83 MW, 54 percent efficiency, peak surface field 76 MV/m. At microperveance 0.8, they calculate 60 MW, 58 percent efficiency, peak field 67 MV/m. At 465 kV, microperveance 0.6, they calculate 55 MW, 62 percent efficiency, peak field 63 MV/m.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1994,
month =
}

Book:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this book.

Save / Share:
  • No abstract prepared.
  • Travelling wave output structures can in principle provide higher efficiency and lower surface gradients than a single output cavity. We discuss simulations of TW structures designed for X-band klystrons to be used in the SLAC NLC. The PIC Code CONDOR calculated efficiency over 50 percent for one such circuit. When the circuit was built in the SLAC XC7 klystron, the match was so poor that it had to be modified. When tested, the tube produced less than half the efficiency calculated. We subsequently found significant differences between the field distribution calculated by CONDOR versus that from the 3-D code MAFIA.more » We have now developed a procedure which gives much better agreement between the 2D and 3-D models. We use a {pi}/2 disk-loaded structure, with the waveguide coupling to an output cavity through an iris, rather than directly to the drift tube as in the XC7. The disk radii are tapered to produce an approximately constant gradient. The output coupling is adjusted to match to a uniform structure replicating the cell before the waveguide. The simulations predict 75 MW, 49 percent efficiency, with peak surface fields of 73 MV/m. from a 440 kV, 350 amp beam at 11.424 GHz.« less
  • Experiments involving backward wave oscillators having nonuniform amplitude slow wave structures (NBWOs) operating in the x-band frequency range have produced 500 MW of rf power with 20% efficiency. To elucidate the processes occurring in the NBWO, and to ascertain the possible advantage of using a nonuniform amplitude sow wave structure over one that is uniform, the authors have performed a simulation study involving several different tubes, nonuniform and uniform, using the 2.5D electromagnetic particle-in-cell code TWOQUICK. The simulations model experiments performed on the SINUS-6 electron beam accelerator at the University of New Mexico. Results of the simulation study are presented.more » They show that the slow phase velocity surface wave that interacts with the electron beam coexists with an ordinary waveguide mode, which forms a standing wave in both nonuniform and uniform BWOs. Analysis of BWOs using a single particle phase model that accounts for both fast and slow TM waves shows that it may be possible to increase the output power of these tubes in general by choosing the length of the slow wave structure to simultaneously optimize the coupling of the beam to the slow wave, while forcing a transit time interaction between the standing wave and the electron beam, which pumps beam energy directly into the ordinary waveguide mode. The authors discuss the possible advantages of using a NBWO to accomplish this. In addition, comparisons with SINUS-6 experiments are made.« less
  • As the power and the frequency of a relativistic klystron increase, design of both modulation and extraction cavities becomes increasingly difficult. If the gap is narrow, the rf electric field begins to exceed limits for electron emission or breakdown. On the other hand, if the gap width exceeds a small fraction of a wavelength, typical extraction modes do not couple well, and space charge potential energy reduces efficiency and limits the current that can cross the gap. The authors present theoretical investigations of a novel gap design which incorporates an inductively-loaded return-current structure. This structure serves to neutralize the dcmore » space charge of the beam, while sustaining the longitudinal rf field which extracts the microwave energy. With appropriate choice of resonant modes, it appears that gap widths exceeding a half wavelength can be used for modulation of high-current beams, as well as extraction of rf energy with high efficiency.« less