Research Instruments  RI  and Thales have been pro  ducing the first two prototype 1.5 GHz fundamental power couplers for the VSR  Variable pulse length Storage Ring  DEMO since early 2021 and delivered these prototypes in late March 2023. These couplers are designed to provide up to 16 kW CW power to two 1.5 GHz superconducting cavities of the VSR DEMO module and provide variable coupling with a Qext range from 6 106 to 6 107. The paper describes the challenges in fabricating a scaled coupler and provides details on the modifications to the design as a re  sult of these challenges. The impact of the late stage design modification is discussed along with how this affects future conditioning plan

Dürr, V.

Knobloch, J.

Schendler, S.

Sharples Milne, E.

V lez, A.

Undetermined

HZB Repository

PRODUCTION OF THE 1.5 GHZ FUNDAMENTAL POWER COUPLERSFOR VSR DEMOE. Sharples-Milne1∗† , V. Dürr1, S. Schendler1, A. Velez1,2, J. Knobloch1,31 Helmholtz-Zentrum Berlin ür Materialien und Energie, Berlin, Germany2 Technische Universität Dortmund, Faculty o Physics, Dortmund, Germany3 Universität Siegen, Faculty o Physics, Siegen, GermanyAbstractResearch Instruments (RI) and Thales have been pro-ducing the rst two prototype 1.5 GHz undamental powercouplers or the VSR (Variable pulse length Storage Ring)DEMO since early 2021 and delivered these prototypes inlate March 2023. These couplers are designed to provideup to 16 kW CW power to two 1.5 GHz superconductingcavities o the VSR DEMO module and provide variablecoupling with a Qext range rom 6×106 to 6×107. The paperdescribes the challenges in abricating a scaled coupler andprovides details on the modications to the design as a re-sult o these challenges. The impact o the late stage designmodication is discussed along with how this aects utureconditioning plans.INTRODUCTIONInitially conceptualised as an upgrade to BESSY II atthe Helmholtz-Zentrum Berlin (HZB), VSR DEMO is anSRF technology research and development project. VSRDEMO aims to validate SRF technology to achieve highcurrent (300 mA) - high gradient (20 MV/m) – continuouswave (CW) operation enabling uture storage ring projectsto manipulate the longitudinal bunch phase space. To dothis an SRF module [1] equipped with two 1.5 GHz SRFcavities and two undamental power couplers (FPCs) alongwith ancillary components will be commissioned at highpower. The couplers must provide 16 kW CW power andvariable coupling with Qext rom 6×106 to 6×107.The design started by scaling the 1.3 GHz Cornell couplerdesign [2, 3] or operation at 1.5 GHz. This initial scaleddesign can be seen in [4], however as the design progressedit became clear that the complex nature o VSR [5, 6] sig-nicantly aected the design. Thus modications such asxing the cold coax dimensions to reduce HOM propaga-tion and modiying the tip design were made to meet VSRrequirements, see [7–9] or details o these modications.MANUFACTURING CHALLENGESThe couplers are being manuactured by Research Instru-ments (RI) in partnership with the sub-vendor Thales. Figure.1, shows the nal FPC design at the start o coupler manu-acture in early 2021. However, several small changes weremade as a result o discoveries during abrication along withthe larger change to the waveguide to coax transition o the∗ emmy.sharples@helmholtz-berlin.de† Work supported by grants o the Helmholtz-AssociationFigure 1: A technical drawing o the ull coupler, with the 4key coaxial parts labelled and the waveguide to coax transi-tion highlighted by the red box.coupler, where the RF eeds into the coupler, this is detailedbelow. In addition to this certain components required morequalication than expected most notably the ceramics, whichis detailed in [9] and the copper coating which is detailed inthe section below.Copper Coating QualifcationSince couplers or SRF applications must deal with cryo-genic temperatures at the cavity side and room temperatureat the RF waveguide side, each coupler spans 5-300 K. Thismeans the coupler must be as thermally insulated as possi-ble, to avoid heating the cavity and causing a quench. Thusa high quality copper coating is critical to provide goodRF transmission while remaining thin enough to maintainthermal insulation.Copper coating was required or the ollowing couplerparts: the warm inner conductor (WIC), the warm outerconductor (WOC), and the cold outer conductor (COC), allshown in Fig. 1, and all including at least one bellow. Theollowing tolerances were initially specied; 20m ± 5mor tubes and fanges including those at <5K and 20m ±10m -0 m or bellows. Ater discussion with Thales,the tolerances were relaxed to 25m ± 30% or all parts(max 32.5m and min 17.5 m), as this better refectedwhat Thales had been able to achieve in previous couplerprojects [10]. This was urther relaxed to a maximum o35 m with a minimum o 17 m or the warm parts, anda minimum o 15m or the cold parts, ater the bellowsub-supplier and design were xed.The coating qualication o each part was an iterativeprocess. First a simple sample was used or initial coatingtests, and then once the process was perected, a one-to-one sample was used or the nal coating test. Coatingqualication started in April 2021, the WIC was approvedin early July 2021, closely ollowed by the WOC in late July14th International Particle Accelerator Conference,Venice, Italy JACoW PublishingISBN: 978-3-95450-231-8 ISSN: 2673-5490 doi: 10.18429/JACoW-IPAC2023-WEPA1603022 MC7.T07: Superconducting RFWEPA160 WEPA: Wednesday Poster Session: WEPAContent from this work may beused under the terms of the CC BY 4.0 licence (© 2022). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.Figure 2: An illustration o the iterative copper coating quali-cation process or the WIC. The simple sample and the oneto one sample (WIC 1) are shown including measurementlocations and corresponding results.2021 and nally the COC in September 2021, meaning thewhole qualication process took 5 months.Figure. 2 shows this process or the WIC, with the mea-surements points labelled or both the simple and one to onesamples. The red lines in the results graph o Fig. 2 indicatethe minimum and maximum specied values, anything out-side o these lines is out o tolerance. Though the nal one toone sample WIC 3 was out o tolerance, Thales identied theissue (poor masking too long in bath) and showed with sam-ple 3 that tolerances could be met. As expected the bellowswere the critical parts, with areas out o tolerances localisedto the extremes o the bellows as seen in Fig. 3. This wasmore o an issue or the external parts as the bellows herewere only 6 convolutions (rather than the 18 convolutionsin the WIC) and coating was dependent on how much theycould be expanded during the process.Figure 3: The copper coating o the peak o the bellow othe WOC, showing over tolerances on the extremes.Ater discussion with colleagues rom XFEL [10], it wasound that these over tolerances on the bellows were commonand could be accepted. Overall the quality o the coatingwas high and so ar no issues with inclusions or bald spotshave been identied.Waveguide Coax Transition RedesignDuring the later stages o abrication, it became clear thata signicant redesign was required to the waveguide to coaxtransition o the coupler, where RF eeds into the coupler,see red box in g 1. This is where the WIC connects tothe WOC and it is critical to have both a vacuum seal, topreserve the isolation vacuum o the coupler, and an RF seal,in the orm o an RF spring, to avoid RF leakage. For the1.3 GHz Cornell coupler shown in Fig. 4 it can be seen thatboth the RF spring and the CF vacuum connection sit on theback ace o the conical part o the inner conductor.Figure 4: The waveguide to coax transition area or the 1.3GHz Cornell coupler.However, when scaling to 1.5 GHz and optimising or bestRF transmission [4], the dimensions o the inner conductorwere reduced. This meant the available space was signi-cantly reduced, and both the RF and vacuum seal could notbe placed behind the cone part o the warm inner conductor.The CF vacuum connection remained behind the cone butthe RF spring connection was moved to sit on top o thecone, as seen in the let-hand side o Fig. 5 (original design).This eventually led to two signicant problems: rstly, theplacement o the RF spring was not simple and requiredspecic tooling. Secondly, because the RF spring requiresgood contact between inner and the outer conductor, the topace o the inner conductor cone sat very close to the outerconductor. This resulted in a very tight t, which made dis-assembly ater heat treatment impossible without damagingthe coupler.Due to these two actors and the resultant damage to thecoupler, it was critical that the waveguide to coax transitionbe redesigned. In the redesign both the RF and vacuum sealsare positioned behind the cone part o the inner conductor,as in the Cornell design. This was possible due to the in-crease in warm inner conductor dimension made to improvecooling. Though the warm inner conductor dimension wasmodied beore manuacture started [8], the waveguide tocoax transition was not modied then as the issues detailedabove were not know. In addition to the moving o both seals,more space was created where the inner conductor and outer14th International Particle Accelerator Conference,Venice, Italy JACoW PublishingISBN: 978-3-95450-231-8 ISSN: 2673-5490 doi: 10.18429/JACoW-IPAC2023-WEPA160MC7.T07: Superconducting RF 3023WEPA: Wednesday Poster Session: WEPA WEPA160Content from this work may beused under the terms of the CC BY 4.0 licence (© 2022). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.Figure 5: A comparison o the original (let) and the re-designed (right) waveguide to coax transition.conductor sit parallel to one another to avoid the issue otight tting. These changes can be seen in the right-handpart o Fig. 5 (redesign).CURRENT STATUSThe parameters or the e-beam welding changed with theredesign so required re-optimisation to ensure successulwelds. This process has taken approximately 3 months andresulted in two unsuccessul welds, one which required theremoval and eventual disposal o a warm ceramic due tosignicant copper depositions on the inner surace and theother which required a repair, see Fig. 6.Figure 6: The second ailed e-beam weld (above) and thesuccessul repair (below).This repair entailed creating a small plug o high-qualitycopper to patch the hole seen in Fig. 6. This plug was weldedinto place by laser welding and then smoothed with a low-power e-beam weld. Ater the rst e-beam pass the repairappeared successul however the leak test o the part ailedand on closer inspection, there was not ull penetration o theweld. A second low-power smoothing pass was perormedand the second leak test passed. This was then inspectedone nal time, using a borescope to check the inner suraceand small amounts o copper deposition were ound on theedge o the ceramic on the inner surace.The source o the copper depositions likely comes rombeing unable to correctly place the protection or the ceramicduring welding as a direct result o the required redesign.Due to the damage to the parts as a result o the close tthe ceramic was cut away rom the confat unit on one sideand then re-welded to the redesigned part. For these weldspositioning the weld protection required sliding it the ulllength o the WIC (roughly 500 mm) and then securing it,rather than placing the protection around the ceramic andthen positioning the remaining parts o the WOC ready orwelding.Though this copper deposition is ar rom ideal, urtherrework would be time consuming and may not lead to abetter result. Thereore, a nal leak test o the warm partswas perormed and they were assembled into the prototypecouplers or heat treatment and residual gas analysis (RGA).These parts underwent a nal actory acceptance test (FAT)in March 2023 and were then shipped to HZB, or assemblyand conditioning.In light o the copper deposition on the inner surace o theprototype coupler ceramics, a new conditioning plan must beormed to analyse just how much power these couplers canhandle. The initial goal will be to reach low power (< 1 kW)CW operation, or 6 hrs at thermal equilibrium. This will bedone with extra monitoring o the warm window using anIR sensor or camera pointed down the RF waveguide. I 1kW CW is achieved then urther conditioning in which thepower is increased by small increments will be perormed,with continued close monitoring until the couplers eitherreach 16 kW or ail.CONCLUSIONAter a long manuacturing process the prototype couplersare now on site at HZB and being prepared or conditioning.Assembly ready or testing has begun with the initial cleanroom assembly o the cold parts and nal leak test. Thiswill then be moved to a designated assembly area where thewarm parts will be mounted and the whole system bakedout beore nally assembly into the cryostat. Conditioningis planned to start late summer 2023.The manuacturing process highlighted some issues withscaling a design to a higher requency, which will only be-come more extreme at higher requencies. These designchallenges have impacted the manuacture, potential per-ormance and conditioning plan o the 1.5 GHz prototypecouplers. However, learning rom this should acilitate suc-cessul production o the series couplers, though the e-beamwelding o the warm windows must be closely monitoredas a critical production step, and i necessary, the tooling toprotect the ceramic will be modied to ensure there are no de-position issues or the series coupler. The conditioning planor these couplers has evolved with their manuacture andnow includes a low power CW stage which can be omittedi the production issues are eliminated or the series.ACKNOWLEDGEMENTSThe authors would like to thank Wol Dietrich Moeller,our external coupler consultant or his input and assistancethroughout the manuacturing process.14th International Particle Accelerator Conference,Venice, Italy JACoW PublishingISBN: 978-3-95450-231-8 ISSN: 2673-5490 doi: 10.18429/JACoW-IPAC2023-WEPA1603024 MC7.T07: Superconducting RFWEPA160 WEPA: Wednesday Poster Session: WEPAContent from this work may beused under the terms of the CC BY 4.0 licence (© 2022). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.REFERENCES[1] F. Glöckner et al., “The VSR Demo Module Design– A Spacerame-Based Module or Cavities with WarmWaveguide HOM Absorbers”, in Proc. SRF’21, East Lans-ing, MI, USA, Jun.-Jul. 2021, pp. 233. doi:1.18429/JACoW-SRF221-MOPTEV13[2] V. Veshcherevich, S. Belomestnykh, P. Quigley, J. Reilly, andJ. Sears, “High power tests o input couplers or Cornell ERLinjector”, in Proc. SRF’07, Beijing, China, Oct. 2007, paperWEP26.[3] V. Veshcherevich et al., “Design o High Power Input Coupleror Cornell ERL Injector Cavities”, in Proc. SRF’05, Ithaca,NY, USA, Jul. 2005, paper THP54, pp. 590–592.[4] E. Sharples, M. Dirsat, J. Knobloch, and A. V. Velez, “De-sign o the High Power 1.5 GHz Input Couplers or BESSYVSR”, in Proc. IPAC’17, Copenhagen, Denmark, May 2017,pp. 978–981. doi:1.18429/JACoW-IPAC217-MOPVA51[5] H.-W. Glock et al., “Progress o the BESSY VSR ColdString Development and Testing”, in Proc. IPAC’19, Mel-bourne, Australia, May 2019, pp. 1434–1436. doi:1.18429/JACoW-IPAC219-TUPGW19[6] A. V. Velez et al., “The SRF Module Developments or BESSYVSR”, in Proc. IPAC’17, Copenhagen, Denmark, May 2017,pp. 986–989. doi:1.18429/JACoW-IPAC217-MOPVA53[7] E. Sharples, M. Dirsat, J. Knobloch, Z. Muza, and A. V. Vélez,“Design Development or the 1.5 GHz Couplers or BESSYVSR”, in Proc. SRF’19, Dresden, Germany, Jun.-Jul. 2019, pp.795–799. doi:1.18429/JACoW-SRF219-WETEB9[8] E. Sharples-Milne, V. Dürr, P. Echevarria, J. Knobloch, A.Neumann, and A. V. Vélez, “Final Design Studies or theVSR DEMO 1.5 GHz Coupler”, in Proc. IPAC’21, Camp-inas, Brazil, May 2021, pp. 2300–2303. doi:1.18429/JACoW-IPAC221-TUPAB343[9] E. Sharples-Milne, V. Duerr, S. Schendler, N. Wunderer,A. Velez, and J. Knobloch, “The 1.5 GHz Coupler orVSR DEMO: Final Design Studies, Fabrication Statusand Initial Testing Plans”, in Proc. SRF’21, East Lans-ing, MI, USA, Jun.-Jul. 2021, pp. 652. doi:1.18429/JACoW-SRF221-WEPTEV9[10] S. Sierra et al., “Status and Lesson Learned rom Manu-acturing o FPC Couplers or the XFEL Program”, in Proc.LINAC’16, East Lansing, MI, USA, Sep. 2016, pp. 572–574.doi:1.18429/JACoW-LINAC216-TUPLR4814th International Particle Accelerator Conference,Venice, Italy JACoW PublishingISBN: 978-3-95450-231-8 ISSN: 2673-5490 doi: 10.18429/JACoW-IPAC2023-WEPA160MC7.T07: Superconducting RF 3025WEPA: Wednesday Poster Session: WEPA WEPA160Content from this work may beused under the terms of the CC BY 4.0 licence (© 2022). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.

Production of the 1.5 GHz fundamental power couplers for VSR demo

https://www.helmholtz-berlin.de/pubbin/oai_publication?VT=1&ID=109732

Production of the 1.5 GHz fundamental power couplers for VSR demo

Abstract

Similar works

Full text

Available Versions

HZB Repository