MEBT SAR BUNCHER CAVITIES Nagore Garmendia On behalf

MEBT SAR BUNCHER CAVITIES Nagore Garmendia (On behalf of Buncher Team) Bilbao, 27 March 2019

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

Buncher Team Task Description Team Beam dynamics simulations I. Bustinduy EM Design and simulations O. Gonzalez; J. L. Muñoz Mechanical Design and drawings A. Zugazaga; I. Rueda Thermomechanical simulations A. Paramo; J. L. Muñoz Manufacturing A. Zugazaga ; I. Rueda Vacuum Test A. Zugazaga; A. Conde; J. Martin RF Test bench + bead pull N. Garmendia; High power RF test N. Garmendia ; A. Kaftoosian Assembly and Integration A. Conde; J. Martin Coupler and tuners R. San Martin; I. Rueda Motion control and EPICs I. Mazkiaran Project Manager (MEBT; RF) I. Bustinduy ; P. Gonzalez MEBT SAR – Buncher cavities

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

Specifcations Specification Doors ID Description ACC. L 1 ESS. Sy. R-430 Nominal operational repetition rate 14 Hertz. ACC. L 1 ESS. Sy. R-450 Nominal operational beam pulse length 2, 86 ms ACC. L 2 ACC. Sy. R-19 For beam energies greater than 1. 0 Me. V, the nominal bunch frequency MEBT. EMR. Syr-36 MEBT. EMR. Sy. R-36 Cavity peak field; Kilpatrick Value 352, 21 MHz <1, 5 MEBT-L 4 -EMR-090 MEBT. EMR. Sy. R-37 Maximum gap voltage 150 k. V MEBT-L 4 -EMR-140 MEBT. EMR. Sy. R-42 Maximum coupled peak power into the cavity 18 k. W MEBT-L 4 -EMR-150 MEBT. EMR. Sy. R-43 RF coupler power handling 22, 5 k. W MEBT-L 4 -EMR-180 MEBT. EMR. Sy. R-46 Cavity aperture (diameter) 30 mm MEBT-L 4 -EMR-190 MEBT. EMR. Sy. R-47 Cavity longitudinal space (Lmax) MEBT SAR – Buncher cavities <190 mm

Requirements Parameter Particle Energy Description 3. 62 Me. V Max RF pulse width 3, 5 ms Max RF Duty Cycle 4. 9 % Maximum RF input peak power 22. 5 k. W Unloaded quality factor >18000 Tuner linearity > 15 k. Hz/mm Nominal cooling water temperature 25ºC +/-1º Coupling coupler coefficient 0. 95 -1. 05 MEBT SAR – Buncher cavities

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

Strategy (II) Manufacturing Phases PHASE DESCRIPTION PH 1 SS Machining and welding (local supplier) PH 2 Copper plating (GSI) Test Plan PHASE MT VT LPT PH 1 X X X PH 2 X X X MT: Metrology + rugosity VT: Outgassing (impurity) + Leak test (welding and sealing) LPT: Low Power RF Test+ Bead-pull CT: Conditioning test MEBT SAR – Buncher cavities CT X

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

Manufacturing (I) ● Considerations Ø Applicable standards: ISO 9606 -1; ISO 15614 -1 and ISO 5817 Ø Critical tolerance definition for a manufacturing from stainless steel copper plated (copper layer of 30 μm) Ø Certificated materials and thermal treatment for mechanical stress relief Ø Drawings and manufacturing procedure for Helicoflex for vacuum seal Ø Ø 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

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

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

Metrology Ø Ø 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 cavity: manufacturer SS and Cu cavity: ESS Bilbao MEBT SAR – Buncher cavities

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

Cooling system Ø Ø Ø Two independent circuits for body and cover cavity to optimised the design Specifications: static pressure test at 16 bar during 15 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

Vacuum test Ø Ø 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 Pressure Evolution MEBT SAR – Buncher cavities Leak Detection

Low power RF Test Ø Ø 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 Figure of Merit Test Res. Frequency, [MHz] T 01 HOM 2; HOM 3 (MHz) T 02 Quality factor T 03 Coupler coupling factor T 04 Pick-up coupling factor T 05 Cavity insertion loss T 06 Frequency tuning range T 07 Tuner linearity T 08 MEBT SAR – Buncher cavities

Bead-pull Ø Implementation of bead-pull test bench based in the Slater´s perturbation theory to obtain the accelerating field profile from the bead frequency shift Ø Main figures of merit: Ez, T, RT 2; Pdiss Ø Bead-calibration with a pillbox cavity to assure accurate results Bead calibration Bead-pull test bench Accelerating electric field profile MEBT SAR – Buncher cavities

Mechanical interfaces Port Description Dim. A Vacuum port CF 60 B Fixed Tuner CF 60 C RF input power coupler CF 60 D Movable tuner CF 60 E Pick-up port CF 40 F Gauge port CF 40 G Cavity support RAFT 2 MEBT SAR – Buncher cavities

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

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

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

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

Low Power and Bead-pull Test Results Figure of Merit BU-1 BU-2 BU-3 C/NC 352. 21 C Penetration Tuner 1, L 1[mm] 50 40, 5 40 C Penetration Tuner 2, L 2[mm] 32 40, 5 25 C 16. 3 16. 2 16. 3 C 0. 94 / 0. 136 1. 1 / 0. 15 1. 09 / 0. 14 C 9. 3 9 10 C Ql 8108 8125 8144 C Qo 16883* 18415 18250 C BW, [KHz] 43. 3 43 43. 2 C RTT/Q [Ω] 73. 85 76. 7 76. 9 C RTT [MΩ] 1. 25 1. 41 C ZTT [MΩ/m] 9. 89 11. 2 11. 14 C Transit Time Factor (T) 0. 654 0. 645 C Effective Voltage Vo. T [KV] 160/100 160/120 160/140 C Dissipated Power, Pd [Kw] 20. 5 / 8 18. 1 / 13. 8 18. 2 / 13. 9 C 9. 4 9. 36 9. 28 C Res. Frequency, [MHz] Sensitivity, [KHz/mm/tuner] βcoupler / βpickup_max IL_min(d. B) Max Acc. Field Ez_max [MV/m] MEBT SAR – Buncher cavities *for 160 k. V, the specifications is 150 k. V

Cavities in MEBT Ø 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. Parameter Eo. T sim (k. V) RTT/Q [Ω] Location in MEBT ESS official name BU#1 BU#2 BU#3 60 130 150 73. 85 76. 7 76. 4 1 st 2 nd 3 th MEBT 010: EMRTnk-001 MEBT SAR – Buncher cavities MEBT 010: EMR-Tnk. Tnk-002 003

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

Conditioning BUNCHER component Status Cavities Tested Pick-ups Tested Fixed tunners Tested Movable tuner + actuator Tested Motion control Tested MC EPICs integration Tested Coupler Manufacturing at ESSB (end of May) SSPAs Manufacturing at BTESA (end of July) RF Rack control To be provided by ESS MEBT SAR – Buncher cavities

Conclusions Ø Ø 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) Ø The SSPAs are under manufacturing (BETESA, Spain. 1 st for end of July)) Ø The RF control to be provided by ESS Ø Next step : Coupler and cavity conditioning strategy : ü ü Totally advisable at ESS Bilbao ( cavities delivery? ) Alternative: buncher versus test box to be study: time, cost, resources, delivery time, breakdown. MEBT risk, … SAR – Buncher cavities

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