New waveguide-type HOM damper for ALS storage ring cavities. Page: 2 of 3
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Calculations were done and the plot was created with the
help of the ANSOFT HFSS code. The total power
dissipated in the ceramic loads for the worst-case ALS
operation scenario (40mA single bunch or 56mA two
bunch mode) will be about 150W that gives the average
power density 0.75[W/cm3]. Thermal stress analysis has
not been done yet but it should not be an issue since the
same material is operating successfully for years in the
PEP-II rf cavity damper with the peak power density up to
5.5[W/cm3] [2]. The minimum length of the HOM damper
waveguide is determined by the required attenuation of
the fundamental frequency of the rf cavity (the length of
the HOM damper waveguide has no impact on the damper
performance since the HOM power is almost completely
absorbed in the ceramic). For the waveguide used at the
wavelength greater than the cutoff frequency, there is no
real propagation and the fields are attenuated
exponentially. Power attenuation is:
Pei-k ____ -4n 'l-
-=exp(-2k,gz)=exP -2kz 1-( ) =exp -(
or in dB:P
P054.57 z 1- " [dB]
cutoffwhere:
kiong -longitudinal wave number
ktmn -transverse wave number =2t/Xcutoff
z -waveguide length
Xcutoff-cutoff frequency wavelength.
for:>ACUtoff ' ok = Jktrans 1 -
- ron 7_ans
The length of the waveguide chosen is 350mm which
gives the power attenuation factor for the fundamental
frequency of 47dB. The cross section of the new ALS
HOM damper is shown in Fig.2
Figure2TEST RESULTS
(1) The "cold" model of the ALS waveguide damper was
build and tested. Test results are presented in Figure 3.Longitudinal HOM spectrum of the ALS main RF cavity
red-no dampers
black-with E-type HOM damper
green-with E-type and waveguide dampers
blue/yellow lines- ALS long. stability threshold for 1.9/1.5 GeVQ
z
z10000000
0.5 0.81 1.03 1.33 1.38 1.56 1.81 1.89 2.13 2.27 2.35 2.45 2.85GHz
1000000
100000
10000
1000
100
10
1
1 2 3 4 5 6 7 8 9 10 11 12 13MODE NUMBER
Figure 3
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Kwiatkowski, Slawomir; Baptiste, Kenneth & Julian, James. New waveguide-type HOM damper for ALS storage ring cavities., article, June 28, 2004; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc781506/m1/2/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.