1. SPL RF coupler: integration aspects
V.Parma, TE-MSC
with contributions from WG3 members:
Th.Renaglia, U.Wagner, P.Coelho, N.Bourcey, A.Vandecraen
Review of SPL coupler, CERN 16th-17th March 2010

2. β=1 cryo-module in SPL layout (drwg SPLLJL__0014)

3. Cryogenic scheme (under discussion)

4. Cavity/coupler assy
Part of interest
Double-walled-tube

5. Coupler integration functionalities (non-exhaustive list)
Functionality
Requirement
Comment
RT/atm. to 2K/vacuum penetrations
minimise static HL;
leak-tight penetration (o-ring);
mechanical decoupling from vacuum vessel (if not a support);
- Optimise thermal design
Isolation between coupler and beam vacua
leak tight window
vacuum gauge outside cryostat
- Single ceramic window for HP RF
Gas cooling of double-walled tube (5 K-300 K)
cryostat feedthrough of cooling line:
leak-tight
avoid atm. moisture (T>dew point)
- externally-mounted manual valves (presetting);
- Heater for control (Ofelia’s talk)
Coupler maintenance
Maintenance-free
No in-situ intervention
Coupler as support (option under study)
support/position cavities;
coupler flange mechanically fixed to vacuum vessel;
fix longitudinal position of cavities;
mechanical support of thermal shield
- impact of gas cooling on position (Ofelia’s talk);
- Vacuum vessel as mechanical reference

6. Transversal position of cavities inside cryostat
BUDGET OF TOLERANCE (preliminary)
Step
Sub-step
Tolerances (3σ)
Total envelopes
Cryo-module assembly
Cavity and He vessel assembly
± 0.1 mm (TBD)
Positioning of the cavity w.r.t. beam axis
± 0.5 mm
Supporting system assembly
± 0.2 mm (TBD)
Vacuum vessel construction
Transport and handling (± 0.5 g any direction)
N.A.
Stability of the cavity w.r.t. beam axis
± 0.3 mm
Testing/operation
Vacuum pumping
Cool-down
RF tests
Warm-up
Thermal cycles

7. Possible supporting schemes
“standard” supporting scheme
RF coupler
Invar longitudinal positioner
Inertia beam
Fixed support
Sliding support
External supports (jacks)

8. Possible supporting schemes
“standard” supporting scheme
RF coupler
Invar longitudinal positioner
Inertia beam
Fixed support
Sliding support
External supports (jacks)

9. Possible supporting schemes
Coupler supporting scheme
RF coupler + longitudinal positioner + vertical support
Intercavity support structure
External supports (jacks)

10. Coupler position: top ...? Contras:
Interferes with bi-phase tube  move sideways
Waveguides/coupler more exposed to personnel/handling (damage, breaking window?)
Pros:
Easier connection of waveguides
Easier access (needed?)

11. Coupler position: ...or bottom?
Contras:
Space needs for waveguides under cryostat
If coupler not a support (bellows) support on top, i.e. centered tube not possible
Pros:
Centered bi-phase tube symmetry
Waveguides/coupler protected

12. RF coupler assembly constraints
Defines minimum diameter of “pipeline” type vessel:
Lenght of double-walled tube
Integration of thermal shield
Note: drwgs for information only (concept not final)

13. Mid plane symmetry

14. Need guiding? Layout Equivalent sketch No - If sag small enough
- If strenght OK
- isostatic l
Yes
- couple cavities
- hyperstatic
inter-cavity guides 2l
mid cavities most critical: sag reduces only to ½

15. Mass loads on internal supports (preliminary)
Description
Load
Comment
Cavity/he vessel/tuner
~2.0 kN
per assembly (x 8 per cryomodule)
Piping/thermal shield/MLI
0.8 kN
equally shared on coupler tube
Transport accelerations
± 0.5 g
each direction

16. Max sag: “to guide or not to guide?”
Stiffening of coupler/cavity assembly necessary
 Guiding between cavities is most probably necessary

17. “standard” supporting
Max. sag minimized at a/L=0.20.
 A 3rd central support seems mandatory

18. comparing solutions A) Coupler supporting scheme
B) “standard” supporting scheme
Pros
Contras
Design simplicity
Vacuum vessel:
Stiffness (thickness, stiffeners)
Dim. stability
Precision machining
Cost
Single cavity adjustment at assy
Positioning stability (thermal, weld relieving...)
Inter-cavity guiding
Mid cavities guiding sufficient?
Pros
Contras
Cavities mechanical isolation from external perturbations: dim. changes (thermal, weld relieving), vibrations...
Design complexity
Vacuum vessel simplicity:
Reduced machining precision
reduced thickness
Central support needed (?)
Complex cavity adjustment at assy

19. Summary
Coupler length (double-walled tube) sets minimum diameter of cryo-module
Coupler could be used as cavity support and is an interesting option
Vacuum vessel become of paramount importance for mechanical positioning/stability
Guiding between cavities probably needed (relieve cantilever)
In case of “standard” supporting solutions, coupler design considerations still valid  mechanical decoupling with bellows