Post on 22-Feb-2016
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TaCoTuner-adjustable waveguide Coupler
A new generation of waveguide couplers for standing wave cavities
Publication: CERN-ATS-Note-2011-085
Frank Gerigk, Jean-Michel Giguet, Rolf Wegner, Patricia Ugena
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Outline
• why adjustable couplers for standing wave cavities
• principles of couplers and their adjustment
‘nozzle’ coupler, T-type coupler, TaCo
• TaCos for Linac4/SPL
• TaCo prototype
• Advantages and potential applications of TaCo
09/12/11 TaCo // Tuner-adjustable waveguide Coupler
TaCo // Tuner-adjustable waveguide Coupler
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Unpredictable Q-value variations
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EB weldingshrinkage 0.2 to 0.3 mmdQ/Q ~ 1%
tuning elementsdQ/Q ~ 1..2%
surface roughnessdQ/Q ~ 3..5%
TaCo // Tuner-adjustable waveguide Coupler
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Why adjustable couplersCritical coupling of cavities (with beam) to minimise reflected power
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dd,unpred.bd,exp.
ext
PPPP
dunpred .0
coupling factor
(critical coupling: βd = 1)
small adaptation of coupling factor desired to compensate for unpredictable variation
=> safety margin (often adjustment in one direction only; proton Linacs: cavities often have different dimensions)
TaCo // Tuner-adjustable waveguide Coupler
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“nozzle” coupler
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‘nozzle’ coupler
adaptationΔβ / β0
courtesy of Jim Stovall & Craig Deibele
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T-type coupler
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adjustment of coupling factor: LS
principle: compensation of reactance by stub line
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T-type coupler, adaptation
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1st Step: movable
short circuitLS
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T-coupler, adaptation
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2. machining of appropriate short circuit (vacuum)
(+ copper plating)
delay
3. installation(helicoflex joint, 30 bolts M12)
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TaCo – Tuner adjustable w.g. coupler
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plunger tuner
1. Cavity (slightly) detuned to compensate stub line reactance
2. Coupling factor can be decreased as well as
increased
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TaCo for LINAC4/SPL
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0 20 40 60 80 100 120 1400
20
40
60
80
100
L_t [mm]
b_re
l [%
]
0 20 40 60 80 100 120 1400
0.5
1
1.5
2
2.5
3
L_t [mm]
Em
ax [M
V/m
]
0 20 40 60 80 100 120 1400
2
4
6
8
10
L_t [mm]
P_1
0% [W
]
xt = 350 mmzt = 0 mmLS = 311 mmøt = 83 mmRRt = 10 mm
vacuum section
Pin=1 MW, cavity: ES~33 MV/m
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TaCo, increase of coupling factor
0 20 40 60 80 100 120 140 1600
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
b_rel [%]
Em
ax [M
V/m
]
xt=100,zt= 0xt=290,zt= 0xt=350,zt= 0xt=470,zt= 0xt=290,zt= 200xt=290,zt=-250
increase of coupling factor
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TaCo prototype
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70 80 90 100 110 120 130 1400
5
10
15
20
25
L_t [mm]
Em
ax [M
V/m
]
xt = 292 mmzt = -345 mmLS = 420 mmøt = 43 mmRRt = 2.0 mmLt = 113 mm
70 80 90 100 110 120 130 1400
0.5
1
1.5
2
2.5
3
L_t [mm]
simulationmeasurement Pin=1 MW
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TP= 0.8 ms,frep= 2 Hz,ttest= 72 h
high power test:
Pin= 1.1 MW,Es,m= 8 MV/m
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TaCo prototype
no breakdownsno multipactor
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Advantages of TaCo• Coupling factor can be increased as well as decreased
=> cavity design for desired coupling=> safety margins included in coupler design
• TaCo machined in one process(T-type: short circuit machined after RF measurements -> delay)
• RF matching simple and quick (final RF contact between coupler and cavity)
• Change of beam current => exchange of plunger tuner
• Movable tuner => variable coupling during operation
• TaCo applications: Linac4 / SPL
26 TaCos (20 x decrease β, 5 x increase β, 1 x variable β)
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