13 th Advanced Accelerator Concepts Workshop. Santa Cruz, July 27-August 2, 2008 Seventh-Harmonic Multi-MW K-band Frequency Multiplier: Rf Source for for High-Gradient Tests* N.A. Solyak 1,2 , V.P. Yakovlev 1,2 , S.Yu. Kazakov 1,3 , and J.L. Hirshfield 1,4
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
13th Advanced Accelerator Concepts Workshop.
Santa Cruz, July 27-August 2, 2008Seventh-Harmonic Multi-MW K-band Frequency Multiplier: Rf Source for for High-Gradient Tests*
N.A. Solyak1,2, V.P. Yakovlev1,2, S.Yu. Kazakov1,3, and J.L. Hirshfield1,4
1Omega-P, Inc., New Haven, CT 06511, USA
2Fermi National Accelerator Laboratory, Batavia, IL, USA
3High Energy Accelerator Research Organization (KEK), Tsukuba, Japan
4Physics Department, Yale University, New Haven, CT 06520, USA
*Work supported by the U.S. Department of Energy
● In order to investigate the frequency scaling of breakdown, high power tests are necessary at frequencies from X-band upwards.
●Key elements for these tests are high power, 0.5-1 sec pulsed RF sources.
● A“ quick-and-cheap” high-power RF source, an Harmonic Multiplier, is proposed for this application and described in this talk.
Gun tank, portion of magnetic system, and quadrature WR-284 feeds into CARA accelerator in the Yale Beam Physics Laboratory that can be available for the proposed harmonic multiplier.
XK5 S-band klystron and overhead WR-284 evacuated transmission line with variable amplitude and phase splitters in the Yale Beam Physics Laboratory. Also seen is the 300-kV gun modulator and gun tank.
65-MW modulator that powers the S-band XK-5 klystron in the Yale Beam Physics Laboratory. Klystron and gun modulator are visible in the background.
20 GHz, waveguide 7th harmonic multiplier
[J.L. Hirshfield, et al, 2000]:
Sketch of the proposed two-cavity 7nd harmonic frequency multiplier based on the S-band SLAC:
Drive frequency: 2.856 GHz
Output frequency: 19.992 GHz
Drive power: 8.5-10 MW
Output power: 4-4.7 MW
Multiplication efficiency: 47%
Beam power: 5 MW
Beam voltage: 250 kV
Beam current: 20 A
Operating mode TE111 (drive cavity)
Operating mode TE711 (output cavity)
Magnetic circuit configuration, with 5 coils and 4 iron pole pieces. Plot at top shows the magnetic field profile generated by this circuit. Drawing at bottom shows drive cavity (left) and output cavity (right).
Beam particle energies (blue) and radial excursions (red) with the TE711 mode output cavity tuned to 19.992 GHz. Cavity outlines are also shown.
Drive Cavity Design
*Suggested by N. Solyak at 1985 for 7 GHz , 60 MW gyrotron.
High power RF devices based on such approach:
of the 7GHz, 60 MW Gyrocon (frequency multiplier)
● 11.4 GHz, 135 MW (BINP/KEK, 1991)
● 3 GHz, 80 MW
Proposal for CLIC 937 MHz, 50 MW MBK design
(CERN, 2005, I.Syrachev et al.,)
1-RF cavity; 2-collector
3-collector; 4-coupling holes.
The output cavity with incorporated mini-windows.
Theory of traveling wave coupling
WG width for a=21mm (inner radius)
Waveguide dimensions is defined from equation:
0=c/f – free space wavelength, c- critical wavelength in coaxial waveguide, which is defined from the equation:
Here a,b – waveguide radial dimensions, k=Nwg – azimuthal index.
(gradient limit) 6 < Nwg < 10 (dispersion)
Parameters for excitation Direct or Reverse traveling Waves
Ncav = 7(Considering 6 < Nwg < 10 only)
D - amplitude of a direct wave
R - amplitude of a reverse wave.
CASE 1: Configuration 7-8-9
Traveling waves in Cavity and Waveguide are rotating in opposite directions
CASE 2: Configuration 7-28-7
Direction of rotating of TW in cavity and waveguide are the same
Table: Waveguide dimensions for 7-8-9 configuration
Red line shows dimensions, which are close to standard waveguide - WR51: width x height = 12.954 x 6.477 mm.
It will be easy to mach them.
Configuration 7-8-9 (HFSS simulations)
Case 7-8-9: HFSS simulations (2)
Slot/2= 6 mm x 3º.
Freq = 20 GHz.
WG port #1.
Magnitude of electric field in cavity and waveguide at 0 phase.
Waveguide dimensions for 7-28-7 configuration
WR51: 0.51”x 0.255” = 12.954 mm x 6.477 mm.
WR42: 0.42” x 0.17” = 10.688 mm x 4.318 mm
No propagating modes!
WR51: 0.51”x 0.255” = 12.954 mm x 6.477 mm
Dimensions of matching
section in mm:
a = (0.1, 27.762); b = (5.536, 20.284);
c = (9.603, 25.228);
d = (6.578, 28.953)
S11 was matched at the level of 0.03 at the broad band
General Layout of the output cavity in 7th harmonic converter
Waveguides are penetrating through the gap between magnetic
Layout #1 of the output cavity inside magnetic system.
(blue-magnetic coil, grey – cavity, red – beampipe, magenta – waveguide).
● Through use of 8.5-10 MW S-band drive power from SLAC XK-5 klystron and the beam from the CARA gun, preliminary simulation results indicate that a simple two-cavity 7th harmonic multiplier can be designed and built to furnish ~4-5 MW of phase-stable RF power at 20 GHz for use in high gradient accelerator R&D.
● Theory is developed of the azimuthally-distributed coupling of the cavity with rotating whispering-gallery mode to the rectangular waveguide. Basing on this theory, the design of the output cavity with 28 coupling slots for the 7th harmonic multiplier is developed.
● The preliminary design of the 7th harmonic multiplier is made.