Klystron Cluster RF Distribution Scheme Chris Adolphsen Chris Nantista SLAC.
L. Ge, C. Adolphsen, K. Ko, L. Lee, Z. Li, C. Ng, G. Schussman, F. Wang, SLAC, B. Rusnak, LLNL...
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L. Ge, C. Adolphsen, K. Ko, L. Lee, Z. Li, C. Ng, G. Schussman, F. Wang, SLAC, B. Rusnak, LLNL Multipacting Simulations of TTF-III Coupler Components *# TTF-III Coupler Comparison of simulations and measurements * This work was supported by DOE contract No. DE-AC02-76SF00515. # This work was performed under the auspices of the U. S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. • No multipacting activities in the bellows region Particle distribution at 2 nd period Particle distribution at 100th period During charging of SW cavity, reflection varies from 0% to 100 % . Partial SW field in coax shifts MP to lower order and power level. 0 0.2 0.4 0.6 0.8 1 1 1.2 1.4 1.6 1.8 2 R F InputP ow er(M W) A verage D elta third order fourth order fifth order sixth order seven order 0 500 1000 1500 2000 2500 3000 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 P rim ary electron energy:eV ILC C O UPLER S/S SAM PLE #4,CO NCAVE SIDE delta Multipacting Simulation – Track3P •3D parallel high-order finite-element particle tracking code for dark current and multipacting simulations (developed under SciDAC) •Track3P – traces particles in resonant modes, steady state or transient fields – accommodates several emission models: thermal, field and secondary •MP simulation procedure – Launch electrons on specified surfaces with different RF phase, energy and emission angle – Record impact position, energy and RF phase; generate secondary electrons based on SEY according to impact energy – Determine “resonant” trajectories by consecutive impact phase and position – Calculate MP order (#RF cycles/impact) and MP type (#impacts /MP cycle) •Track3P benchmarked extensively – Rise time effects on dark current for an X- band 30-cell structure – Prediction of MP barriers in the KEK ICHIRO cavity Cold Coax and Bellows Delta as a function of RF input power and z axis location • No Multipacting activities between coax pipes • High impedance coax supports MP at higher power level Delta as a function of RF input power and MP order Matching Taper Ceramic Window Region Impact energy and MP order versus input power for two-point multipacting particles between ceramic window and cold inner conductor A multipacting particle trajectory between ceramic window and taper region of inner conductor on the cold side Electric Field • Multipacting map in cold coax w/ and w/o reflection MP particle trajectory Reflection: 0.5 Input power level: 160KW Order: 5th order Impact energy: 542-544 eV •Coax is the first component for high power processing •After initial processing, the vacuum and electron pickup signal show multipacting bands in agreement with simulations Electron pickup 0 500 1000 1500 0 20 40 Pow erofklystron:kW mV 0 500 1000 1500 -100 -50 0 uA uA mV Simulated power (kW) 170~190 230~270 350~390 510~590 830~1000 Power in Coupler (kW) 43~170 280~340 340~490 530~660 850~1020 klystron power (kW) 50~200 330~400 400~580 620~780 1000~1200 Abstract: The TTF-III coupler adopted for the ILC baseline cavity design has shown a tendency to have long initial high power processing times. A possible cause for the long processing times is believed to be multipacting in various regions of the coupler. To understand performance limitations during high power processing, SLAC has built a flexible high-power coupler test stand. The plan is to test individual sections of the coupler, which includes the cold and warm coaxes, the cold and warm bellows, and the cold window, using the test stand to identify problematic regions. To provide insights for the high power test, detailed numerical simulations of multipacting for these sections will be performed using the 3D multipacting code Track3P. RF In RF Out Coupler component test stand layout • DESY TTF-III coupler experienced long processing time • Test stand built at SLAC to evaluate processing limitations • Multipacting simulations help identify processing barriers Multipacting Simulations of TTF-III Components Secondary emission yield (R. Kirby) Track3P simulation After high power processing
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Transcript of L. Ge, C. Adolphsen, K. Ko, L. Lee, Z. Li, C. Ng, G. Schussman, F. Wang, SLAC, B. Rusnak, LLNL...
L. Ge, C. Adolphsen, K. Ko, L. Lee, Z. Li, C. Ng, G. Schussman, F. Wang, SLAC, B. Rusnak, LLNL
Multipacting Simulations of TTF-III Coupler Components*# Multipacting Simulations of TTF-III Coupler Components*#
TTF-III Coupler
Comparison of simulations and measurements
* This work was supported by DOE contract No. DE-AC02-76SF00515.# This work was performed under the auspices of the U. S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.
• No multipacting activities in the bellows region
Particle distribution at 2nd period Particle distribution at 100th period
During charging of SW cavity, reflection varies from 0% to 100 % . Partial SW field in coax shifts MP to lower order and power level.
0 0.2 0.4 0.6 0.8 11
1.2
1.4
1.6
1.8
2
RF Input Power (MW)
Avera
ge D
elta
third order
fourth order
fifth ordersixth order
seven order
0 500 1000 1500 2000 2500 30000.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4
Primary electron energy: eV
ILC COUPLER S/S SAMPLE #4, CONCAVE SIDE
delta
Multipacting Simulation – Track3P
• 3D parallel high-order finite-element particle tracking code for dark current and multipacting simulations (developed under SciDAC)
• Track3P – traces particles in resonant modes, steady state or transient
fields– accommodates several emission models: thermal, field and
secondary
• MP simulation procedure– Launch electrons on specified surfaces with different RF
phase, energy and emission angle– Record impact position, energy and RF phase; generate
secondary electrons based on SEY according to impact energy– Determine “resonant” trajectories by consecutive impact phase
and position– Calculate MP order (#RF cycles/impact) and MP type
(#impacts /MP cycle)
• Track3P benchmarked extensively– Rise time effects on dark current for an X-band 30-cell
structure – Prediction of MP barriers in the KEK ICHIRO cavity
Cold Coax and Bellows
Delta as a function of RF input power and z axis location
• No Multipacting activities between coax pipes • High impedance coax supports MP at higher power level
Delta as a function of RF input power and MP order
Matching Taper
Ceramic Window Region
Impact energy and MP order versus input power for two-point multipacting particles between ceramic window and cold inner conductor
A multipacting particle trajectory between ceramic window and taper region of inner conductor on the cold side
Electric Field
• Multipacting map in cold coax w/ and w/o reflection
MP particle trajectoryReflection: 0.5Input power level: 160KWOrder: 5th orderImpact energy: 542-544 eV
• Coax is the first component for high power processing
• After initial processing, the vacuum and electron pickup signal show multipacting bands in agreement with simulations
Electron pickup
0 500 1000 15000
20
40
Power of klystron: kW
mV
0 500 1000 1500-100
-50
0
uA
uA mV
Simulated power (kW) 170~190 230~270 350~390 510~590 830~1000
Power in Coupler (kW) 43~170 280~340 340~490 530~660 850~1020
klystron power (kW) 50~200 330~400 400~580 620~780 1000~1200
Abstract: The TTF-III coupler adopted for the ILC baseline cavity design has shown a tendency to have long initial high power processing times. A possible cause for the long processing times is believed to be multipacting in various regions of the coupler. To understand performance limitations during high power processing, SLAC has built a flexible high-power coupler test stand. The plan is to test individual sections of the coupler, which includes the cold and warm coaxes, the cold and warm bellows, and the cold window, using the test stand to identify problematic regions. To provide insights for the high power test, detailed numerical simulations of multipacting for these sections will be performed using the 3D multipacting code Track3P.
RF In RF Out
Coupler component test stand layout
• DESY TTF-III coupler experienced long processing time
• Test stand built at SLAC to evaluate processing limitations
• Multipacting simulations help identify processing barriers
Multipacting Simulations of TTF-III Components
Secondary emission yield (R. Kirby)
Track3P simulation After high power processing
