MEBT SAR BUNCHER CAVITIES

1. MEBT SARBUNCHER CAVITIES • Nagore Garmendia • (On behalf of Buncher Team) • Bilbao, 27 March 2019

2. Outline • Buncher team • Introduction • Specifications and requirements • Strategy: design, manufacturing and test plan • Design process • Manufacturing process • Test procedures • Cavity interfaces and elements • Experimental results • Conclusions and next steps • MEBT SAR – Buncher cavities

3. Buncher Team • MEBT SAR – Buncher cavities

4. Introduction: MEBT Bunchers MEBT: RFQ – DTL beam matching BU#3 BU#2 BU#1 Longitudinal focusing • MEBT SAR – Buncher cavities

5. Specifcations • MEBT SAR – Buncher cavities

6. Requirements • MEBT SAR – Buncher cavities

7. Strategy (I) 2 Design Manufacturing 1 corrections Manufacturing Prototype BU#1; BU#2;BU#3 Tests Test procedures CDR Integration plan • MEBT SAR – Buncher cavities

8. Strategy (II) Manufacturing Phases • MT: Metrology + rugosity • VT: Outgassing (impurity) + Leak test (welding and sealing) • LPT: Low Power RF Test+ Bead-pull • CT: Conditioning test Test Plan • MEBT SAR – Buncher cavities

9. Design process • Considerations • Taking into account the size and RF requirements ( Fr=352,2 MHz; EoT=150 kV) a nose-cone single gap type cavity is the optimal option • The internal buncher dimensions take into account electro-magnetic, thermo-mechanic, RF and beam dynamics • SS versus copper manufacturing has implications in vacuum sealing, cooling system, Rf perfmances,… BEAM DYNAMICS EMDESIGN THERMO-MECHANICAL • MEBT SAR – Buncher cavities

10. Manufacturing (I) • Considerations • Applicable standards: ISO 9606-1; ISO 15614-1 and ISO 5817 • Critical tolerance definition for a manufacturing from stainless steel copper plated (copper layer of 30 μm) • Certificated materials and thermal treatment for mechanical stress relief • Drawings and manufacturing procedure for Helicoflex for vacuum seal • The cavity resonant frequency deviations due to manufacturing are corrected by means of the fixed tuner (tuning range) • Finger strips are foreseen in coupler, tuners and pick-up to increase the cavity efficiency (Qo) FINGER STRIPS VACUUM SEAL • MEBT SAR – Buncher cavities

11. Manufacturing (II) SS THERMAL TREATMENT MACHINING PORTS: TIG WELDING COPPER PLATING • MEBT SAR – Buncher cavities

12. Test procedure Metrology Roughness CoolingSystem Vacuum: Outgassing + Leakage Low Power RF Bead-pull Not ready: • Coupler • SSPA • LLRF and RFLPS rack Conditioning • MEBT SAR – Buncher cavities

13. Metrology • Performed by the manufacturer after the manufacturing in SS by means of a three-dimensional measuring machine (CMM) in a temperature controlled room at 20 ± 1 ° • Repeated at ESS Bilbao Metrology facility before and after copper plating SS and Cu cavity: ESS Bilbao SS cavity: manufacturer • MEBT SAR – Buncher cavities

14. Roughness • Different roughness specifications are required for : • Helicoflex vacuum sealing contact • Assure the cavity efficiency ( Qo) • Performed by the manufacturer after the SS machining • Repeated at ESS Bilbao laboratory before and after copper plating SS and Cu cavity: ESS Bilbao SS cavity: manufacturer • MEBT SAR – Buncher cavities

15. Cooling system • Two independent circuits for body and cover cavity to optimised the design • Specifications: static pressure test at 16 bar during15 minutes with a decrease < 0.1 bar • Performed by the manufacturer after SS machining and repeated at ESS Bilbao after ESS Bilbao test Simulations Manufacturer test • MEBT SAR – Buncher cavities

16. Vacuum test • Leakage level specification <2*e-10 mbar*l/s • Tests: pressure evolution , outgassing (RGA) and leakage test performed by the manufacturer after SS machining and repeated after copper plating at ESS Bilbao vacuum lab RGA ESS Bilbao Vacuum Test bench Leak Detection Pressure Evolution • MEBT SAR – Buncher cavities

17. Low power RF Test • Implementation of a test bench with a automatic data acquisition for S- parameters and with a precise algorithm to determine the quality factor • The tuning system is validated with two manual dummy tuners • MEBT SAR – Buncher cavities

18. Bead-pull • Implementation of bead-pull test bench based in the Slater´s perturbation theory to obtain the accelerating field profile from the bead frequency shift • Main figures of merit: Ez,T, RT2; Pdiss • Bead-calibration with a pillbox cavity to assure accurate results Bead calibration Bead-pull test bench Accelerating electric field profile • MEBT SAR – Buncher cavities

19. Mechanical interfaces • MEBT SAR – Buncher cavities

20. Power coupling Coupler • Magnetic loop in charge of the transmission the RF power • to the cavity • ESS Bilbao design based in Alumina ceramic window (the peek coupler • design was rejected due to vacuum requirements) • Manufacturing and brazing under procedure validation in ESS Bilbao Welding Center Manufacturing EM simulations Drawings • MEBT SAR – Buncher cavities

21. Pick-up • The magnetic loop takes the RF sample for LLRF, • interlock and control system • ESS Bilbao design with an commercial flange and B A C D Manufacturing Drawings Test and validation EM simulations • MEBT SAR – Buncher cavities

22. Fixed Tuner • To compensate the frequency deviation due to the • manufacturing and copper plating tolerances • ESS Bilbao design to avoid the brazing between the copper cylinder and the commercial SS flange Manufacturing Test and validation EM simulations Drawings • MEBT SAR – Buncher cavities

23. Movable tuner • To compensate frequency deviation during the beam operation • Commercial linear actuator controlled by the LLRF system • Motion control test and EPICs integration done and validated Test and validation Drawings EM simulations • MEBT SAR – Buncher cavities

24. Low Power and Bead-pull Test Results *for 160 kV, the specifications is 150 kV • MEBT SAR – Buncher cavities

25. Cavities in MEBT • Taking into account the beam dynamics simulations the first buncher cavity requires less effective accelerating field and the last one is the most demanding, therefore the less and the most effective cavities are located as first and third in the MEBT after analysing all the experimental results. • MEBT SAR – Buncher cavities

26. Conditioning • A first version procedure has been defined for the conditioning: • Previous checking list • State machine and start-up procedure • Conditioning steps with a foreseen configurations: pulse width, frequency repetition rate (i.e. duty cycle ) and RF power level • MEBT SAR – Buncher cavities

27. Conditioning • MEBT SAR – Buncher cavities

28. Conclusions • The design, manufacturing and test procedure were defined and validated with a complete experimental characterization of a buncher prototype (BU#0) • The three buncher cavities have been measured with the low power RF test and the results are in agreement with the simulations and requirements. • The pickups, fixed tuner and movable tuner have been also measured and validated • The power alumina coupler is under manufacturing at ESS Bilbao facilities (brazing • end of May) • The SSPAs are under manufacturing (BETESA, Spain. 1st for end of July)) • The RF control to be provided by ESS • Next step : Coupler and cavity conditioning strategy : • Totally advisable at ESS Bilbao ( cavities delivery?) • Alternative: buncher versus test box to be study: time, cost, resources, delivery time, breakdown risk,… • MEBT SAR – Buncher cavities

29. THANK YOU FOR YOUR ATTENTION • Questions ? • MEBT SAR – Buncher cavities