1. Spoke Cavities developments in Europe CNRS/IN2P3/ IPN– Paris-Sud University Sébastien Bousson On behalf of the IPNO team

2. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Outlook R&D on spoke cavities for Eurisol Spoke Developments for ESS Spoke for MYRRHA (ADS) Conclusion

3. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  352 Driver Post-Accelerator Beam preparation RIB production Spoke cavities for EURISOL (1)

4. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab   =0.35  =0.15 Spoke resonators Two prototypes @ 352 MHz (  0.15 and  0.35) fabricated and tested. Cryogenic cold box Spoke cavity Cold tuning system Power coupler Horizontal cryostat Adapted to spoke cavities for 4K and 2K tests Spoke cavities for EURISOL (2)

5. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  A triple spoke cavity has been designed during the Eurisol DS. The cavity fabrication has been launched and achieved in sept. 2011. After a first surface preparation (chemical etching and high pressure rinsing), a first cryogenic test was performed in the beginning of 2012. First result in vertical cryostat: Maximum achieved Eacc was 3.5 MV/m, limited by a quench -> a new BCP will be done Spoke cavities for EURISOL (3)

6. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  In the meantime, adaptation of the CMO horizontal cryostat is in progress to integrate the fully equipped triple spoke. This experiment will allow to test a new type of tuning system: a niobium plunger inside the cavity volume (as developed by IPNO for Spiral-2), for the first time implemented on a spoke cavity. Spoke cavities for EURISOL (4)

7. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  - 7 - ESS Linac: High power proton accelerator, 5 MW - Pulse 2.86 ms - Rep. rate: 14 Hz - Protons (H+) - Low loss - High reliability >95% - Modular design for future upgrade Investment cost: 1478 M€ over ~ 10 years Operation cost:106 M€ / year Dismounting :346 M€ (2008 costs) ESS (European Spallation Source)

8. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  - 8 - ESS (European Spallation Source)

9. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) DOUBLE-SPOKE CAVITY SPECIFICATIONS Beam modePulsed (4% duty cycle) Frequency [MHz]352.2 Beta_optimal0.50 Temperature (K)2 Bpk [mT]70 (max) Epk [MV/m]35 (max) Gradient Eacc [MV/m]8 Lacc (=beta optimal x nb of gaps x λ /2 ) [m] 0.639 Bpk/Eacc [mT/MV/m]< 8.75 Epk/Eacc< 4.38 Beam tube diameter [mm]50 (min) P max [kW]300 (max) Specs from beam dynamics

10. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) Hspokebase Lcav Liris-to-iris Htop Hbottom Wcenter Rspokebase rtop1 rtop2 Hspokecenter Dspoke rtop3 Rbeamtube The main parameters to play with…

11. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) One example: beam tube aperture Rbeamtube : Variation from 15 to 35 mm. 28mm Epk/Eac c Bpk/Eacc Ratios increase from 28mm 25mm Vacc @ beta0.50

12. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) Spoke bar base diameter and cavity length Rspokebase (=radius of the spoke base) and Lcav (=overall length of the cavity from end-caps) Calculation n°1: Calculation n°1: Rspokebase varies (  d from 0 to 40 mm) and Lcav is fixed (=Lacc=639mm) Calculation n°2: Calculation n°2: Lcav varies : Rspokebase is fixed (=Lcav/8=80mm) and Lcav varies from 639 to 839 mm (  Lcav1 from 0 to 200 mm) Lcav=3*beta*lambda/2+Lcav1 Rspokebase= (Lcav/8)+d)

13. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) Results on case 1 (R_spoke_base): Epk/Eacc ratio is not sensitive to Rspokebase variation whereas Bpk/Eacc decreased continuously and was lowered by 17%.

14. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) Results on case 2 (cavity lenght): Epk/Eacc ratio is increasing continously whereas Bpk/Eacc decreased down to a minimum. Bpk/Eacc

15. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) Feedback from the two Single-Spoke resonators and Triple-Spoke resonator fabrication (EURISOL) Base (H field area): no racetrack shape  3D weld seams are not easy (Spoke bar-to-cavity body connection) no cylindrical shape  Hpk too high Conical shape is chosen Center (E field area): racetrack shape is ok

16. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) Mesh type Hexahedral (1.2 millions) Tetrahedral (650000) Beta optimal0.50  Epk/Ea4.964.47  Bpk/Ea [mT/MV/m]7.036.74  G [Ohm]133  r/Q [Ohm]428427  E field H field E field H field Hexahedral mesh Tetrahedral mesh Final RF results:

17. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) o Design: Spoke 3-gap cavity defined by RF analysis o Material: niobium o Thickness: 4 mm o Stiffeners: 2 Donut ribs 2 Ring ribs o Ports: 1xCoupler  int =100, 2xPick-up  int =28, 4x  int 28 HPR o 1 Bellows Cavity final configuration Donut ribs (left and right side) 2 Ring ribs Beam tubes 4 HPR Ports Coupler port Coupler collar Coupler Flange Bellows 2 Pick-up Ports Total weight: 77 Kg  int 480 994 mm 787 mm  int 56

18. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) o Material: titanium grade 2 o Thickness: 3 mm o 8 Stiffeners (handling tools and cold tuning system) o Helium Ports (cooling and filling) o 8 Supports for rods (proposal for the supporting within the cryomodule) Helium vessel Total weight: 29 Kg Helium ports Stiffeners Support for rod Helium port  ext 550 888 mm 690 mm

19. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) As the thermal expansions of the niobium and titanium from 300K to 2K are similar, rigid connections are possible.  Improvement of the stiffness of the cavity Rigid connections : o Ring ribs o HPR ports o Pick-up ports o Coupler port o Flange between a beam tube and the helium vessel Ring rib Pick-up flange Bellows Flange Coupler collar HPR flange Cavity + He vessel Assembly View 2: View 1 View 2 Total weight: 109 Kg View 1:

20. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) Umax = 0,24mm TEST IN CRYOMODULE 37 MPa Mecanical behaviour: Test in the cryomodule Loads: VACUUM in the cavity  Pext cavity = Pcryo VACUUM in the cryomodule  Pint helium vessel = Pcryo GRAVITY Boundary conditions: Helium vessel maintained by 8 rods Tuner not taken into account Criteria:  max < Re(Niobium at 20°C) 0 0 Pcryo Conclusion:  max > Re(Niobium at 20°C) for Pcryo > 0,15 MPa

21. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) Mechanical characteristics Stiffness of the cavity with its helium vessel Kcav [kN/mm]20. Tuning sensitivity  f/  z [kHz/mm]: Cavity and helium vessel with the supports of cold tuning system fixed330. 1mm imposed Supports fixed RF sensitivity due to the detuning Boundary conditions :

22. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) RF sensitivity due to helium pressure fluctuation Mechanical characteristics Cavity with a part of the end cups of the helium vessel Sensitivity to He pressure K P [Hz/mbar] (free ends)120. Sensitivity to He pressure K P [Hz/mbar] (fixed ends) 40. Static results of the simplified model (1/4) are verified on the entire model: (mm) Entire model (Mechanical Ansys) One free end:Fixed ends: (m) 1/4 model (Mechanical APDL - Ansys) 0.48mm 0.14mm

23. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) Lorentz Factor: K L =  f / E²acc Cavity with helium vessel For 8MV/m K L [Hz/(MV/m) 2 ] (one free end)K L =-5.3  f = 340 Hz K L [Hz/(MV/m) 2 ] (fixed ends)K L =-2.8  f = 180 Hz RF frequency change due to Lorentz detuning Lorentz pressure: P = ¼ (µ 0 H² -  0 E²) calculated from RF analysis (ANSYS) Distribution of the pressure on cavity walls: Boundary conditions: one free end Boundary conditions: fixed ends For Eacc = 8 MV/m Pmax = 619 Pa (Push out) Pmin = -2500 Pa (Pull in) (mPa) Configuration type cryomodule 0,95µm Remark: Bandwith  f = 1355 Hz

24. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) CTS data Mechanical resolution (1/20 bandwidth) 68Hz Expected Stiffness 200kN/mm Cavity sensitivity (CTS stiffness taken in account) 300kHz/mm LHe pressure coefficient (CTS stiffness taken in account) 47Hz/mbar Lorentz forces coefficient (CTS stiffness taken in account) 3.21Hz/(MV/m)² Lorentz forces detuning 205Hz CTS stroke 1.25mm Max tuning range 375kHz Max strength 25kN

25. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) Spoke Cryomodule (conceptual) for ESS

26. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ESS (IPNO) ESS SPOKE PROTOTYPE CRYOMODULE 2012201320142015 T1T2T3T4T1T2T3T4T1T2T3T4T1T2T3T4 PRODUCTION Spoke Cavity Fabrication Nb production for 3 cavities IPNO 3 cavities production ESS-Bilbao 2 cavities production Ancillaries Fabrication Power couplers production Cold tuning systems production Cryomodule parts production PARTS TESTING Vertical Test of the 3 IPNO Cavities Vertical Test of the 2 ESS-Bilbao Cavities Power coupler conditionning CTS tests CRYOMODULE ASSEMBLY CRYOMODULE TESTING Low power test at IPNO High Power tests at UPPSALA

27. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ADS (IPNO) SPECIFICATIONSESSMYRRHA Double-spokeSingle-Spoke Beam modePulsedCW Frequency [MHz]352 Beta optimal0.500.37 Bpk [mT]7050 to 70 Epk [MV/m]3525 to 35 Temperature (K)22 Nominal gradient Ea [MV/m]85 to 6 Beam tube diameter [mm]50 (min) 50 (min) to 60 (ideal) P max [kW]300 (450 upgrade)<10 Lacc (=beta optimal x nb of gaps x c / f) [m] 0.6390.158

28. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Spoke development for ADS (IPNO) Spoke Cryomodule (conceptual) for MYRRHA One spoke cavity will be ordered in january 2013 A complete MYRRHA soke cryomodule will be constructed and tested in 2015.

29. S. Bousson – TTC Meeting – 5 to 8 Nov. 2012- JLab  Many thanks to my colleagues from IPN Orsay contributing to this work: G.Olry, P. Duchesne, D. Reynet, N. Gandolfo, P.Duthil, F. Leseigneur, E. Rampnoux