1. ESS cavities interfaces
23rd of June 2015
Pierre Bosland

2. Cavities lifecycle Cavity lifecycle after factory acceptance:
Transport in a dedicated box to vertical test stand: cavity equipped for test in vertical cryostat with
The final RF pickup mounted on the cavity
The b=1 antenna mounted
Valve adapted for cold RF tests in superfluid helium.
Test in vertical cryostat: interfaces with cryostat and with handling tools
Transport to Saclay (same box as for 1)
Acceptance stand at Saclay
Assembly in cryomodule

4. Acceptance and transfer of ownership PROPOSAL
The cavity production is under the full responsibility of the LASA/STFC.
The factory acceptance criteria are established by LASA/STFC in agreement with ESS and the factory acceptance are under the responsibility of LASA/STFC.
The RFA (Ready For Assembly) acceptance criteria are established in a common agreement between CEA and ESS/LASA/STFC. The RFA acceptance tests (and controls: QC ?) will be performed by CEA.
The RFA acceptance of each cavity before assembly will be under the responsibility of ESS.
The transfer of the cavities ownership to ESS is effective after the RFA acceptance of the cavities.
Non conformities will be managed following a policy on which each party shall agree upon.
Date for criteria agreement to be defined now!

5. Cavities interfaces & requirements
Cavity physical interfaces before assembly in the cryomodule:
Beam flanges (closed by a blank flange + valve)
Power coupler flange (closed by a blank flange + b=1 antenna)
Pickup mounted on the cavity: RF pickup connector
Support of the cavity in the cryomodule (interfaces for rods fixations)
Magnetic shielding
Cold tuning system
Handling tools
Alignment tools interfaces
Cryogenic pipes: flange of the cooling helium pipe (to be suppressed by a welded tube or not ?) + welded tube to the 2 phases tube above the helium tank.

6. Beam flanges & « tuner ring »
Vacuum tightness
Alignement tools and reference
Blocking fixtures

7. Power coupler port Vacuum tigthness
External coupling Qext (height & position % cell iris)
The Qext sensitivity calculated with HFSS gives:
Medium beta cavity: D=61,26mm for Qext =7,5e5
High beta cavity: D=64,41mm for Qext =7,6e5

8. Pick-up antenna
Transmitted power required by LLRF: Pt > 20 dBm at nominal gradient
30 units ordered
Designed to transmit 30 dBm
Cavity beam tube
Alu gasket
RF connector at 90°
Pick-up port
Pick-up antenna

9. Cold tuning system Amplitude slow tuner: +/- 3 mm
Amplitude fast tuner (piezo): 3 µm
Medium beta
 High beta
Niobium thickness mm 4
3.6
Tank thickness 5
Lorentz Force Detuning coef. KL fixed ends
Hz/(MV/m)²)
-0.36
Lorentz Force Detuning coef. KL free ends
Hz/(MV/m)²
-23.35
-8.9
Cavity stiffness
kN/mm
1.286
2.59
Tuning sensitivity Df/Dz
kHz/mm
214.8
197

10. Multilayer insulation
Between helium tank and magnetic shield
Detailed design not yet finalized

11. Magnetic shielding

12. Cavity supporting system in the cryomodule

13. Helium supply and return
He return (welded)
He supply
Pressure test to be established

14. Cavity Handling tools Wheels Unpacking and handling horizontally
Horizontal support and rotation for visual inspection
Lifting
Transport, assembly and rotation

15. Some requirements L4
Cavity functional interface requirements (see DOORS):
F = 704,42 MHz at 2K
Acceptance F = XXX at the acceptance conditions to be defined
Eacc= 16,7MV/m (Mb) Eacc= 19,9MV/m (Hb) <= cryomodule nominal
Dangerous HOM frequencies: 5MHz away from integer multiples of the beam bunching frequencies (n*352,21MHz)
Power coupler Qext : 5,9E5 < Mb < 8E5 & 6,6E5 < Hb < 7,6E5 - see technical notes for Mb and Hb cavity couplers.
R/Q = 395 at bopt => Pmax close to 900kW for medium beta cavities to get the needed voltage . Need of a high R/Q value!
Pickup antenna Qt – no issue - requirement 20dBm at the pickup connector at the nominal field
Lorentz force detuning: 3µm max deformation with piezo stacks
PS = 1,04barg + V max LHe = 48 liters => article 3.3 according to PED …