infn-mi: status mi.pdf · hippi05 4 28-30 september 2005 – hippi05 meeting cavity a...
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INFN-MI: StatusINFN-MI: StatusAngelo Bosotti, Nicola Panzeri,
Paolo PieriniAngelo Bosotti, Nicola Panzeri,
Paolo Pierini
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gPlanning
• Milestones :– Report on final tuner design by end 2005– Tuner construction and testing by mid 2006
• Parallel “historical” tuner activity– Started within TTF, now ILC/XFEL – In CARE/JRA1/WP8
• Report in preparation for 1.3 GHz β=1 cavities (Angelo Bosotti)
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gLFD compensation at high gradients (Δν = KL E2)
Stroke
Force
Displ
Structure
Piezo
δmax
Fmax
Evolution of the tuner concept, with integration of the fast LFD action1.3 GHz system under fabrication right now
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gCavity A characterization
JLAB Z501 Tests
1.0E+08
1.0E+09
1.0E+10
1.0E+11
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Eacc
Q
Test #1Test #2Test #3Design
Multipacting Cable failures...
0.177 N/(MV/m)2Lorentz reaction force at boundary
3.7 Hz/(MV/m)2Lorentz coefficient (constrained)
3.7 N/mbarVacuum reaction force at boundary
84.7 Hz/mbarVacuum freq. coeff. (constrained)
-353.4 kHz/mmFrequency sensitivity (longitudinal)
1.248 kN/mmCavity longitudinal stiffness (Kcav)
70 mmStiffening ring radial position
5.88 mT/(MV/m)Bpeak/Eacc
3.57Epeak/Eacc
160 OhmG
180 OhmR/Q
1.34 %Cell to cell coupling
40 mmIris radius
0.47Geometrical β
704.4 MHzDesign Frequency
ValueParameter
Previous estimation [7 Hz/(MV/m)2] only on half-cell geometry, but also, mechanical load condition was overestimated by a factor of 2. Present calculation on the full geometry.
1
X
YZ
-2841
-2453-2066
-1678-1290
-902.697-515.087
-127.477260.133
647.743
JUN 21 200513:45:48
ELEMENTS
PRES
X
YZ
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gWhere did we stand in tests with cavity A?
• Vertical tests: 3 at Saclay, 3 at JLAB
0 20 40 60 80 100 120 140 160 180 200
-3000
-2000
-1000
0
KL = -31
KL = -24
KL = -47
KL = -35
KL = -20
KL = -32
Δν[Hz]
E2acc [(MV/m)2]
Z502 Test #1 Z502 Test #2 Z502 Test #3 Z501 Test #1 Z501 Test #2 Z501 Test #3
Huge spread in static measurements!And off by a factor 10
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gInfluence of boundary conditions
cavext
accLL KK
EFzfKK
+∂∂
+=∞
∞2 • Linear superposition of 2 effects:
Shape deformation (fixed boundary)Cavity shortening (cavity+boundarycombined stiffness)
Analytical derivation of full behavior requires solution of only 2 load cases
-60
-50
-40
-30
-20
-10
0
1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06K ext [N/mm]
K L [
Hz/
(MV
/m)2 ]
AnalyticalANSYS
KL = -3.7Hz/(MV/m)2
KL = -54Hz/(MV/m)2
Cavity stiffness, Kcav
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gCavity frequency response under arbitrary b.c.
• Frequency response of the cavity can be then understood as a function of the external boundary condition
• Using values from the cavity mechanical characterization and Slater perturbation theorem
( )
( )⎪⎪⎩
⎪⎪⎨
⎧
+−=
+−−=
Hz/mbarin248.1
58.13077.84
Hz/(MV/m)in248.1
55.627.3 2
extextP
extextL
KKK
KKK
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gThe RF test frames
Saclay tests in 2004Jlab tests in 2003/2005
Q: Are they sufficiently stiff?
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gJLAB frame
• Cavity is held at He tank disks with a bar– Dish stiffness is greatly reduced!
~ 2.1 kN/mmJLAB load case
40 kN/mmNominal KDsmall
Large tube (FPC) side
~ 2 kN/mmJLAB load case
26 kN/mmNominal KDbig
Large tube (FPC) side
( ) 1kN/mm93.01111 −≈++=DsmallDbigframejlab KKKK
0.93 kN/mmOverall stiffness
~ 2.1 kN/mmHe tank dish, opposite side
~ 2 kN/mmHe tank dish, coupler side
11 kN/mmSupport plates (2)
142 kN/mmTi rods (4)
StiffnessComponent
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gSaclay frame
kN/mm39.2≈saclayK
2.39 kN/mmkframe
Average frame stiffness
0.444 mmMax δz
1.000 kNApplied force
Force load condition
2.536 kNReaction force
1 mmδz
Displacement load condition
A: NO, both are not stiff enough
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gCorrelation with measured KL
-60
-50
-40
-30
-20
-10
0
1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06K ext [N/mm]
KL
[Hz/
(MV
/m)2 ]
Semianalytical modelJLABSaclay
• Mechanical models assume perfect joints and no slack contacts between components– In reality: joints, screws, etc.
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gAlternative check
• From the Saclay data at low temperatures (2.2 to 1.7 K, where the bath pressure is more stable), an average value of Δν/ΔP of -462 Hz/mbar can be evaluated– Kext of 1.15 kN/mm can be estimated, coherent with the model
discussed before
• From the JLab data an average of Δν/ΔP of -1020 Hz/mbar in the same temperature range can be estimated. – Comparable to a nearly “free” cavity behavior (nominal -966
Hz/mbar), with a negligible external stiffness condition with respect to the cavity stiffness, again, coherent with the model discussed before
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gSummary on static KL
• RF test data is understood– Weak constraints for the cavity length– Low beta geometry very sensible to external boundary condition
(low cavity stiffness)
• Behavior of KL agains Kext allows to set tuner stiffness requirements under operating conditions
• Interaction with CEA (GD) has shown a nearly perfect agreement of static LFD modeling– both calculation modes based on Slater perturbation theorem, but
different and independent implementations, especially concerningthe mechanical part of the codes (ANSYS vs CASTEM)
• Planning for dynamic LFD calculations– harmonic analysis + Slater for cavity transfer function and piezo tf– time dependent analysis: overelongation?– need time for the development and check the procedures
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gRequirements for 704.4 MHz
• One of the uncertainties of the piezo materials is still their stroke capabilities at the low operating temperatures
• Assuming a 3 μm stroke to cavity (long piezos)– [safe? SRF/WP8 work in progress]
• a ~1000 Hz frequency offset can be compensated during the fast tuning action
• With a design accelerating field of 8.5 MV/m, this implies that the overall KL in the operating condition should be limited to around -10 Hz/(MV/m)2
– We took a 50% margin for dynamic LFD? [M.Liepe: factor 2]
• In order to achieve this condition with these rather soft cavities the combined stiffness of the He Tank and tuner system needs to provide ~ 10 kN/mm– At 20 kN/mm we are hitting limit with He tank dish stiffness
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gTuner requirements
• Extracting out the Tank and end dish stiffness contribution (total of 15 kN/mm), the requirement for the tuner becomes about 20 kN/mm
15 20 30
ktuner A kNÅÅÅÅÅÅÅÅÅÅÅÅÅmm
E
-12
-11
-10
-9
-8
LK
Actual experimental stiffness including leverage (TTF)
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gOn the road to finalize tuner design
Will ask for bids in late 2005 andOrder main tuner mechanical components before end of year(INFN contribution is available)Then fabrication time will take 4-6 months
Now we are fine-tuning the tuner stiffness by slight adjustments of the blade number length and slope for final optimization before emitting final drawings for Cavity A
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