INFN-MI: Status

1
INFN-MI Status

• Angelo Bosotti, Nicola Panzeri, Paolo Pierini

2
Planning

• 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 b1 cavities
  (Angelo Bosotti)

3
LFD compensation at high gradients (Dn KL E2)
Evolution of the tuner concept, with integration
of the fast LFD action 1.3 GHz system under
fabrication right now
4
Cavity A characterization
Parameter Value
Design Frequency 704.4 MHz
Geometrical b 0.47
Iris radius 40 mm
Cell to cell coupling 1.34
R/Q 180 Ohm
G 160 Ohm
Epeak/Eacc 3.57
Bpeak/Eacc 5.88 mT/(MV/m)
Stiffening ring radial position 70 mm
Cavity longitudinal stiffness (Kcav) 1.248 kN/mm
Frequency sensitivity (longitudinal) -353.4 kHz/mm
Vacuum freq. coeff. (constrained) 84.7 Hz/mbar
Vacuum reaction force at boundary 3.7 N/mbar
Lorentz coefficient (constrained) 3.7 Hz/(MV/m)2
Lorentz reaction force at boundary 0.177 N/(MV/m)2
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.
5
Where did we stand in tests with cavity A?

• Vertical tests 3 at Saclay, 3 at JLAB

Huge spread in static measurements! And off by a
factor 10
6
Influence of boundary conditions

• Linear superposition of 2 effects
• Shape deformation (fixed boundary)
• Cavity shortening (cavityboundary combined
  stiffness)

Analytical derivation of full behavior requires
solution of only 2 load cases
7
Cavity 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

8
The RF test frames
Saclay tests in 2004
Jlab tests in 2003/2005
Q Are they sufficiently stiff?
9
JLAB frame

• Cavity is held at He tank disks with a bar
• Dish stiffness is greatly reduced!

Large tube (FPC) side Large tube (FPC) side
Nominal KDbig 26 kN/mm
JLAB load case 2 kN/mm
Large tube (FPC) side Large tube (FPC) side
Nominal KDsmall 40 kN/mm
JLAB load case 2.1 kN/mm
Component Stiffness
Ti rods (4) 142 kN/mm
Support plates (2) 11 kN/mm
He tank dish, coupler side 2 kN/mm
He tank dish, opposite side 2.1 kN/mm
Overall stiffness 0.93 kN/mm
10
Saclay frame
Displacement load condition Displacement load condition
dz 1 mm
Reaction force 2.536 kN
Force load condition Force load condition
Applied force 1.000 kN
Max dz 0.444 mm
Average frame stiffness Average frame stiffness
kframe 2.39 kN/mm
A NO, both are not stiff enough
11
Correlation with measured KL

• Mechanical models assume perfect joints and no
  slack contacts between components
• In reality joints, screws, etc.

12
Alternative 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 Dn/DP 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 Dn/DP 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

13
Summary 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
  concerning the 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

14
Requirements 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 mm 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

15
Tuner 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

Actual experimental stiffness including leverage
(TTF)
16
On the road to finalize tuner design
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
Will ask for bids in late 2005 and Order main
tuner mechanical components before end of
year (INFN contribution is available) Then
fabrication time will take 4-6 months