Spoke Cryomodules Sébastien BOUSSON (IPNO), Christine DARVE (ESS) On behalf of the CNRS/IPNOrsay and ESS teams April, 2016

Spoke cryomodule overview: Executive summary IPN Orsay is taking in charge the design of the ESS spoke cryomodules. The design activity is 99% achieved, up to a very high level of details. The only remaining design work to perform is to implement DC Bias capacity of the power coupler doorknob (for margins...). WP4 is in the design validation phase: prototypes of all sub-components have been fabricated and are under test to have an experimental validation of their performances before starting series productions. Excellent performances, well above specifications have been already reached on the spoke cavities prototypes allowing to start the procurements for the cavity mass production (niobium supply and cavity fabrication). Other validation steps, also on prototypes, are planned for the coming months: power coupler conditioning, tests at Uppsala University of cavity+coupler and of the prototype cryomodule at full power. Collaboration with UU well in place, with many technical exchanges and already common experiments performed on HNOSS (UU horizontal cryostat) with spoke cavities. IPN Orsay Infrastructure is being adapted to be ready for the mass production and tests of the spoke cryomodule components. 2

Schedule: main blocks Main objective: deliver to ESS the last (#13) spoke cryomodule for Xmas Reference milestones for the production phase: Cavity production start : May/June 2016 (2 months delay, no further consequences) Cryomodule production start : December 2016 First cryomodule shipped to Uppsala: 14 Aug 2017 RFI date (ready for installation): January 2018 Last cryomodule tested & validated in Uppsala: 20 Dec 2018 i.e. cryomodule production rate = 1 cryomodule every 5 weeks Achieved or estimated dates for the call for tender publication

Spoke cryomodule requirements & technical performances 4 The 13 spoke cryomodule composing the first superconducting acceleration stage. SCRF linac (T=2K) Warm linac The cryogenic distribution system for the spoke section (valve boxes, cryolines, cryo end box) The IPNO task includes all activities linked to the design, prototyping, series production, preparation, assembly and then testing of the spoke cryomodule components (cavities, power couplers, cold tuning systems, cryostat). The 13 cryomodule validation tests at nominal RF power will be done by the Uppsala University team, already strongly involved in the project, in their newly built and operational FREIA facility.

Spoke cryomodule requirements & technical performances Power Coupler Cold Tuning System Ceramic disk, 100 mm diameter 400 kW peak power (335 kW nominal) Antenna & window water cooling Outer conductor cooled with SHe Doorknob transition from coaxial to ½ height WR2300 waveguide Slow tuning (stepper motor): Max stroke: ~ 1.3 mm Tuning range: ~ 170 kHz Tuning resolution: 1.1 Hz Fast tuning (piezo-actuator): Applied voltage up to +/- 120V Tuning range at 2K: 675 Hz (min) Double Spoke SRF Cavities Double spoke cavity (3-gaps), MHz,  =0.50 Goal: Eacc = 9 MV/m [Bp= 62 mT ; Ep = 39 MV/m] 4.2 mm (nominal) Niobium thickness Titanium Helium tank and stiffeners Lorentz detuning coeff. : ~-5.5 Hz/(MV/m) 2 Tuning sentivity  f/  z = 130 kHz/mm

Spoke Cavities design & prototype performances 1/2 66 DOUBLE-SPOKE CAVITY Frequency [MHz] Beta_optimum0.50 Operating gradient [MV/m]9.0 Temperature (K)2 Bpk [mT]61 Epk [MV/m]38 G [Ohm]133 r/Q [Ohm]427 Lacc (=beta optimal x nb of gaps x λ /2) [m]0.639 Bpk/Eacc [mT/MV/m]6.8 Epk/Eacc4.3 P max [kW]335 3 spoke cavity prototypes have been fabricated and tested in vertical cryostat: #1 fabricated by SDMS (Fr), #2 and #3 fabricated by ZANON (It) Niobium is from Tokyo Denkai (Japan) ZA 02 Giulietta ZA 01 Romea SD 01 Germaine

Spoke Cavities design & prototype performances 2/2 Spoke cavity prototype test results (Jan15 – Feb16): Excellent performances, well within specifications (both on Eacc & Qo) Pcav<0.5W Ultra pure water high pressure rinsing Chemical etching

Cold tuning system design & prototype performances 1/2 CTS parameters / design results Cavity sensitivity128 kHz/mm Cavity stiffness20 kN/mm Max cavity deformation1.28 mm Course / Tuning range1.28 mm / 160 kHz Resolution1 Hz/step Piezo tuning K ~ 1.5 kHz ~ 800 Hz (tbc) Design features: Double lever arm tuner (“Saclay-type”). Actuators : one stepper motor and two piezos per tuner (one for redundancy).

Cold tuning system design & prototype performances 2/2 4 prototypes tuners fabricated by ESIM (Fr) and tested (Cryo, VT) With 50 mm piezos length  All specifications reached With 90 mm piezos length (purpose: extra margin  Bad performances. Analysis in progress: pre-load? high stress (differential thermal shrink)?... Coarse tuning range

Power coupler & prototype performances 1/2 Design features:  Coaxial geometry, capacitive coupling.  Ceramic: disk, 6 mm thick, TiN coated  Designed for 400 kW peak (25 kW CW)  Eq. average power : 25 kW CW.  3 cooling channels: water for ceramic window & antenna 5 K SC He for outer conductor Power coupler port 100 mm diameter 4 power coupler prototypes have been fabricated: #1 and #2 fabricated by SCT company (Fr) #3 and #4 fabricated by PMB Company (Fr)

Power coupler & prototype performances 2/2 First conditioning happened in end January 2016, at CEA premises (availability of RF source ) Due to an accidental disabling of all securities, the conditioning went on without any protection/interlock on… The second power coupler test is now being prepared. … and at ~100 kW, vacuum was too high, an arc discharge occurred and one of the coupler ceramic cracked.

Cryomodule design & prototyping 1/2 All cryomodule parts are fabricated and delivered Cold/warm transition Gate valves Inter-cavity belows Coupler/vacuum vessel interface Thermal shield Vacuum vessel & its Mechanical support Blankassembly of some parts

Cryomodule design & prototyping 1/2 First test at 80 K in the cryomodule (without the cavity package) in February 2016

Spoke cryomodule components Integration and Verification 14 Several test results are validation of components ability to perform as required by ESS and thus are mandatory before launching series production: Cavity test in vertical cryostat (achieve 9MV/m and nominal Qo) Required prior tendering for niobium production for series (December 2015) i.e. one successful test to be achieved in October 2015 at the latest Cavity with coupler test in HNOSS (RF coupling successful, achieve 9MV/m and CTS) The test requires around 100 kW of RF power Required prior tendering for the power coupler mass production (Dec. 2016) i.e. one successful test to be achieved in Dec 2016 at the latest Prototype cryomodule test (validate cryo, assembly, overall results) Required prior tendering for the series production of spoke cryomodules (Dec. 2016) i.e. one successful test to be achieved in Dec (ideally), or March 2017 (at the latest) Done ! On time (Summer 2016) On time (Nov – few margin)

Organization at IPN Orsay : an average of 12 FTE has worked on ESS WP4 (spoke) (it was 9 in 2014, 7 in 2012 & 2013) Projected for 2016, 2017 & 2018 is 14 FTE/year In total, in 2015, about 24 IPN Orsay persons have been working for ESS WP4

Spoke cryomodule Major Procurements 1/ Niobium procurement & lead time In progress - Cost estimated to ~ 2.0 M€ 2 good offers received Order all niobium for spokes in one single procurement Supplier strategy: only 1 (for the ~ 4 tons of Nb) Performance mitigation strategy: buy niobium equivalent to 3 more cavities. 2.Spoke cavities procurement & lead time In progress - Cost estimated to ~ 4.0 M€ 3 good offers received Order the 26 spoke cavities in one single procurement Supplier strategy: only 1 – it’s cost effective & less required work for fabrication follow-up (2 contractors is of course possible, but no clear advantages, not necessary for schedule reasons for instance) Performance mitigation strategy : buy 3 more if within allocated budget Allocated production lead time will allow 2 phases: - a pre-production (4 units) to check production processes and quality, constituting a Go/NoGo for phase 2. - a series production for the remaining 22 units

Spoke cryomodule Major Procurements 2/ Spoke power couplers procurement & lead time Scheduled between June 2016 and June Cost estimate: ~ 1.1 M€ Several companies worldwide & Europe – Prototypes: SCT (Fr) and PMB (Fr) Order the 26 power couplers in one single procurement, to a single supplier Spare strategy: no spare (ESS guideline), but with option for 1 or 2 spares Allocated production lead time will allow 2 phases: - a pre-production (2 to 4 units) to check production processes and quality, constituting a Go/NoGo for phase 2. - a series production for the remaining (22 or 24) 4.Spoke cold tuning systems procurement & lead time Scheduled between June 2016 and June Cost estimate: ~ 0.5 M€ 5.Cryomodule parts procurement/assembly & lead time Scheduled between July 2016 and Sept Cost estimate: ~ 4.0 M€

Top risks #1 (Main risk): success-oriented schedule: no room for a failure – Typically: a cavity VT failure, a cryomodule assembly failure implying a partial or full disassembly/re-assembly of a cryomodule. – Mitigation: anticipate as much as possible the series production, to give schedule margin during series production, without taking additional risk: this is the followed scenario with the intermediate validation tests. #2: No spare: neither for sub-components nor for a complete module – A failure during production of a sub-component, or a lower performing component (cavity, power coupler, cryomodule...). – Mitigation: integrate options in procurement for additional production (yield) and use whenever possible the prototype cryomodule parts (except for cavities). #3: Failure of a test/preparation facility: RF source, vertical cryostat,... – Cavity, coupler or cryomodule tests and preparations rely on heavy infrastructure that might have failures – Mitigation: have fallback solutions: for RF, several sources will be available at UU (FREIA) and 1 at IPNO; for cryo test, 2 VC will be available at IPNO,...

Next Six Months 19 Conditioning of the 2 sets of power coupler pairs Develop and validate several cavity procedures: Cavity H degassing at 550 °C to cure from Q-disease Cavity venting procedure without inducing particle contamination Achieve the prototype valve box fabrication Perform a test of a cavity + power coupler in HNOSS before sept Achieve preparation and assembly of the spoke cryomodule for Oct Start niobium and cavity mass production within 2 months

Summary 20 All 3 cavity prototypes already tested in VT and showed excellent performances, with important margins w.r.t. specifications Design of all components for the spoke cryomodule is 99 % achieved Fabrication and assembly of the spoke cryomodule prototype and valve box, close to completion; the prototype cryomodule should be ready for test in Oct The actual schedule allows us to deliver the last spoke cryomodule to ESS on time (Dec. 2018), with realistic time allocated for the different activities…but only little (no ?) margin to cover for potential failures.