1. Système à vide du CLIC: activités en cours
C. Garion
VSC seminar, 9th October 2009

2. Outline CLIC: layout of the complex Vacuum system for the modules
vacuum chambers
pumping system
Interconnections
drive beam
main beam
wave guides
Next steps
Conclusions

3. CLIC Layout
CLIC module
 Main objective: CDR (End 2010)

4. Vacuum system of the module
Vacuum chambers
Accelerating structures
PETS
Drive beam
Spec: EDMS ,
PMB ~ 10nTorr
RiMBP 3 mm (now baseline is 4 mm)
material: copper (or Cu coated)
Spec: EDMS
 RiDBP 11.5 mm
~2m
Main beam
Vacuum chambers are mainly PETS or AS

5. Vacuum chambers of the drive beam
Drift tube
Quadrupole
Space limited by an aperture of 23 mm in diameter and a pole diameter of 26 mm for the quads.
For both cases, precision tubes in stainless steel, copper coated, can be used (23 *1 in 316L)
Pole
Quadrupole chambers can be centered with 2 “soft” rings (PEHMW)
Pipe
Ring

6. Vacuum chambers of the main beam quad
Constraints
Very tight space available  low conductance distributed pumping is mandatory
Unbaked system  vacuum is driven by water pumping
Proposal:
Stainless steel vacuum chamber, squeezed in the magnet
NEG strips sited in 2 antechambers
Copper coated (thickness to be defined)
Pole radius: 4-5mm
Stainless steel
Spacer
NEG strip
Ceramic support
8-10 mm
50 mm

7. Vacuum chambers of the main beam quad
Present design
Pressure in the central part is determined by the gap (Seff~h2/L)
 reduce the sheet thickness (0.3 mm for the prototype)
Spacers stamped in the shell (has to be improved)
Stability study
Tests are in preparation in building 101.

8. Pumping system Vacuum equipment (version sealed disk):
manifolds around the accelerating structures linked to a common tube
Tanks around the PETS linked to a common tube
MB and DB vacuum coupled via the common manifold and the waveguides
 pumping system: mobile turbomolecular station + holding ion and cartridge pumps
2 NEG cartridges pumps
4 linked Manifolds/AS
Ion pump
Large manifold

9. Pumping system performances: static vacuum
Non standard system with small conductances
Very simplistic approach (does not take into account adsorption desorption physics of water)!
150
80
Outgassing: q [mbar.l/s/cm2]
Conductance Ceq
S: 1 ion + 2 NEG pumps
Effective pumping speed: Seff with: 1/Seff=1/S+1/Ceq
P=Q/Seff=q*area/Seff
q~10-10mbar.l/s/cm2 (after 100 hours of pumping), area~2800cm2/AS
 P100h~6E-9 mbar

10. Pumping system performances: static vacuum Program of study
Study at 3 different levels:
global approach: pump an accelerating structure
semi global: measure of the apparent outgassing rate
Local approach: understand and model the water pumping process
P=f(t,S,geometry)
q(t)=P.S/surface
Desorption/adsorption phenomenon including coverage, residence time study
Gas (water) injection

11. Dynamic vacuum in the accelerating structures
Assumptions:
1012 H2 molecules released during a breakdown [Sergio et al.]
Gas is at room temperature (conservative)
Requirement: Pressure<10-8 mbar 20ms after breakdown
Monte Carlo simulation implemented in a FE code (Castem)
Sealed undamped
Sealed in tank
Pressure in the cell where breakdown occurs as a function of time
Sealed with manifolds
Vacuum degradation remains localized close to the breakdown
Longitudinal distribution as a function of time

12. General considerations
Interconnections
General considerations
Spec:
adjustment capability (maximum stroke for intermodule interconnections): ~0.27mm longitudinally, ~0.36 mm transversally
lifetime: 1000 cycles for main beam, cycles for drive beam (TBMWG 20/7/09)
Non-exhaustive list of points to be considered:
leak tightness
RF/electrical continuity
flexibility/uncoupling (w.r.t. which displacements)
accessibility
in-situ or pre-assembly
dismounting possibility? How many time? Cleanness?
reliability

13. Interconnections - Drive beam
Free space: 30mm
Free space: 20mm
PETS/BPM
QUAD/PETS
QUAD/PETS IC
(or QUAD/drift tube IC)

14. Drive beam – QUAD/PETS intramodule interconnections
Working position
Vacuum enclosure delimited by a bellows and knife flanges
Installation position
23
Electrical continuity done by a copper based flexible element

15. Drive beam – QUAD/PETS intramodule interconnections
Gasket/flange assembly (with screws)
Stainless steel bellows:
ID:45 mm, OD: 58 mm, 4 * 0.1mm, pitch: 4.4 mm
Stainless steel flange brazed on the PETS
Copper rings
Spring washers
Flexible “tube”
Other interconnections of the drive beam are based on the same concept and components

16. Design Algorithm of optimization of bellows expansion joints (Based on EJMA)
Minimise the objective function:
inequality constraints:
bellows convoluted length
inner diameter
outer diameter
bellows maxi compression
membrane stress
membrane & bending stress
fatigue life
column buckling
in-plane squirm
Inputs:
Lbmax = 20 mm
Dmin ~ 45 mm
Dmax = 53 mm
Chosen solution

17. Drive beam – QUAD/PETS intramodule interconnections
~2mm
Schematic artistic view of the flexible element
Thin foil (0.1mm) in copper based material

18. Drive beam interconnections
Fatigue life of flexible elements and material choice
Rough estimations of strains:
Installation cycle: ~1%
Axial cycle (thermal cycle): ~0.1%
Transverse cycle (0.36 mm): ~0.3%
~2mm
Schematic artistic view of the flexible element
Simple Manson Coffin law:
Assumptions:
10 “installation” cycles
Miner Law (linear cumulative damage)
Number of cycles to failure: ~9800
Number of cycles to achieve and loadings have to be reviewed.

19. Drive beam interconnections
Fatigue life of flexible elements and material choice
~2mm
Schematic artistic view of the flexible element
Initial and deformed shape
Plastic strain field
Superellastic alloy (CuAlBe) could improve the behavior (being discussed):
Decrease of plastic strain
Could avoid structural ratcheting

20. Interconnections - Main beam
15mm
Free space: 30mm
20 mm
AS/BPM IC
(or AS/AS IC)
AS/AS
QUAD/AS

21. Main beam – QUAD/AS intramodule (intermodule) interconnections
Solution with a gap and damping material (under study)
QUAD/AS intermodule is the same with longer bellows and flexible element

22. Main beam – AS/AS intermodule interconnections
Sealed version with gap
Damping material

23. Interconnections – inter beam waveguide flanges
Existing SLAC design:
non symmetric gasket cross section
Two different flanges
sealing mechanism by shearing
FE model
Gasket deformation
Plastic strain field
Contact pressure
A new design has been proposed to reduce the RF attenuation (smooth transition) and the cost
Gasket
Flange Δ w
New CLIC design concept
Symmetry
Optimization has been done
Prototypes have been manufactured

24. Interconnections – inter beam waveguide flanges
Qualification tests are on going:
Leak tightness tests
3 standard leak tightness tests: OK
3 severe leak tightness tests with thermal shocks: OK
Geometrical tests
Done with correct results
RF tests
3 samples in preparation: leak tests of the wave guide soldering done, assembly done, leak test of the assembly next week
Tests at CERN (low power) and at SLAC
> 0.1 mm
Flange
Gasket

25. Next steps & conclusion
A lot of things being done:
Tests of the quad vacuum chamber
Tests of the wave guide flanges
Definition of the interconnection components
Study of a copper based flexible element
A lot of things to be done or in preparation:
Tests of cavity
Tests for the understanding of the pump down of non baked system
Outgassing measurement
 Re-evaluation of the vacuum properties
Tests of interconnection concept
3 module prototypes should be assembled next year in a lab.
Other modules should be produced for CLEX.
 A lot of work of design, fabrication, assembly, operation and qualification.