Review of the CLIC Two-Beam Module lab program Conclusions

1. Review of the CLIC Two-Beam Module lab programConclusions F. Bertinelli, E. Jensen, Ph. Lebrun, D. Missiaen, D. Schulte Review held at CERN on 6 November 2013 Reported to CASC on 19 November 2013

2. Background • The Two-Beam Modules (TBM), whichintegrate the RF, magnet, vacuum, supporting, alignment and stabilizationfunctions of the drive-beam and main-beamlinacs, constitute the backbone of CLIC and a high stake of itsprojectpreparation phase 2013-2017 • A first generation of TBM prototypes is in the process of beingconstructed, tested and experimentallyvalidated • in the laboratory (withoutbeam): geometrical, mechanical, thermal and vacuum measurements • in the CLEX area of CTF3 (withbeam): functional tests, two-beamacceleration • It isforeseenthat a second generation of TBM prototypes willfollow, integrating the developments of the CLIC study and the resultsfrom the first-generation tests Review of the CLIC TBM lab program

3. Review charge • The CLIC Accelerator SteeringCommittee (CASC) has decided to conductreviews of the Two-Beam Module (TBM) program, in order to getadvice on the development and testingstrategy of the prototype TBMs: • Review the progress of the developmentwork on prototype TBMs, • Assess the results of prototype TBM tests, • Lay out the roadmap for the continuation of the module development and test program, • Provideelements of decision for optimal resource allocation to fulfilthis program • The review panel will report to the CASC • This first reviewwill address the TBMs for the laboratory test program Review of the CLIC TBM lab program

4. Review panel • Francesco Bertinelli, MME group leader, EN department • Erk Jensen, RF group leader, BE department • Philippe Lebrun, DG unit (chair) • Dominique Missiaen, ABP-SU section leader, BE department • Daniel Schulte, ABP-CC3, BE department Review of the CLIC TBM lab program

5. Agenda Review of the CLIC TBM lab program

6. General • The Committee acknowledges the good preparation of the review and expresses thanks to the organizers and speakers for the information provided • The CLIC TBMs are highly complex objects, integrating several advanced technologies and requiring highly specialized work for design, construction, assembly and testing • The prototype TBM program, the purpose of which is to provide relevant information for and technical validation of the CLIC design, is by nature long-term and costly in resources. It was defined several years ago and has developed large momentum, with the risk of taking attention away from its original purpose or not undergoing the adaptations rendered necessary by the evolution of the CLIC design • The Committee therefore welcomes the establishment of regular reviews of this program, while being conscious that the possibilities of steering it on a modified course remain limited • The Committee however strongly reaffirms that such reviews will never replace proper guidance of the program by a competent, responsible person empowered with the necessary authority and provided with adequate resources • The Committee also wishes to recall that while there is certainly need for integrated tests at some stage of the R&D program, it is often more efficient, under a constraint of limited resources, to address specific technical issues via dedicated test set-ups Review of the CLIC TBM lab program

7. Objectives, strategy & presentstatus • A table of generaltolerances and requirements for the TBMswaspresented, some of whichappearverydemanding • The Committeeis not convinced of the consistency of the differenttolerances on basic components, subassemblies, assemblies and reference points, in relation to alignment and beamrequirements • Consequently, the Committee suspects insufficientintegratedunderstanding of the chain of tolerancesfrom the basic components to the beam • The Committeethereforerecommendsthat a single personwiththisunderstanding has the completeview and responsibility of the requirements and theirconsequences on design, fabrication, assembly and alignment • The TBM program presentedextends over severalyearsand requires a large, sustained effort in material budget and personnel. • It appearsthatseveral objectives of the TBM labprogram could have been or were in factbetterreachedthroughsimpler, dedicatedmock-ups and test setups • The Committeethereforerecommends to periodicallyreview the activity for optimal steering • Most of the program isalreadycommitted and cannoteasilybere-directed on a different course. The committee has howeveridentifiedseveralunsettled issues, addressed in the following, on which program decisions must betaken • Stabilization tests werementioned as one of the objectives of the program: the Committee notes thatthisvery important issue has not been addressed Review of the CLIC TBM lab program

8. TBM type 0 • The Committeewishes to acknowledge the important amount of design, construction and assemblyworkperformed on TBM type 0, as reflected in the presentation • The prototype TBMs are inhomogeneousassemblies of functional components and mock-ups, resulting in verycomplexobjectswhichstillsubstantiallydifferfrom real CLIC TBMs, and thus have limitedpotential for complete validation of CLIC technological issues. The Committeerecommendsthatthis issue beanalysed in detail • The results of straightnessmeasurements on AS presented show • significantdifferencesbetweenmanufacturers, • substantial amplification of the errorsfromsubcomponent to completeassembly, • values welloutsidespecifiedtolerances. Whilethese out-of-tolerance AS canprobablybeused as mock-ups for the TBM lab program, the Committee expresses concernthatthismayrevealdifficulty to attain the requestedtolerances on industriallyproduced AS, and recommends to address this issue and analyse the consequencesitmay have on CLIC performance • The geometricalerrorspresentedwerepeak-to-peak: the Committee notes that RMS errors are also relevant to a number of requirements and shouldthereforebeconsidered Review of the CLIC TBM lab program

9. Thermo-mechanical tests • Analysis of thermo-mechanicalbehaviorcertainlyconstitutes one of the most relevant justifications for testingcomplete prototype TBMs • The Committeehoweverwishes to emphasizethattemperaturemapping of TBM components constitutesonly part of thermo-mechanical tests, and thatdeformations and displacementsinduced by steady-state and transient thermal regimes are most important to the validation of the TBM design for CLIC • A large number of temperaturemeasurementswereperformed in a variety of elementaryheating cases. The Committeewouldlike to see a completeanalysis of theseresults, particularly as concerns: • Paths and balance of power flow • Transient time constants • Indications of temperature on other components whichmay influence transientbehaviour • Simulation of CLIC operational and failure scenarios • The Committeereaffirms the need to integrate the thermal test program withgeometry and alignmentmeasurements, as well as to provideuseful feedback to design Review of the CLIC TBM lab program

10. Geometry and alignment [1/2] • Four objectives weredefined for geometry and alignment tests, and resultspresented on each of them, showing good progress of the program • 1) Measurementmethods • Micro-triangulation and AT401 weretested and cross-checked, withadequateresults • Alternative methodswith good complementaritypotential are still to betested • 2) Pre-alignmentstrategy • The concept of performing component pre-assembly on a CMM maybeadequate for prototype work, the Committeethinksthatitis not applicable for series production • A pendingtechnicalchoiceisthat of linearactuators vs cammovers: the Committeethinksitisnecessary to clarifywhoisleading the engineering design of this system • The supports design may need to be reviewed (choice of V-supports, tolerances of support surfaces, number and positioning of support points with respect to stiffness of the structure) • The observeddegradation of the articulation point isconsidered a critical issue by the Committee, needinganalysis and redesign • 3) Intercomparisonbetweenalignmentsystems on short range • The Committee encourages studies on the opticalwirepositioning system as alternative to capacitive sensors Review of the CLIC TBM lab program

11. Geometry and alignment [2/2] • 4) Stability of alignmentunderchanging conditions • A large number of measurementswereperformed: theyneedthoroughanalysis, still to bedone, in order to extractuseful information and help steer the continuation of the test and measurement program • In particular, the Committeewishes to emphasizethatdeformations and displacements must beanalysedunder conditions simulatingrealisticoperation and failure modes, not only the variations in tunnel air flow and temperaturewhichwerepresented • The present design of the vacuum system is not suited to resist pressure forces withinalloweddeformations: the problemshouldbealleviated by the foreseen suppression of the central vacuum tank and new configuration of vacuum pumps • Two measurement campaigns of modal analysis showed lower natural frequencies than the expected 50 Hz: this implies need for analysis, including possible engineering redesign • The Committeerecommendsthat the TBM design and development team provides more input and better guidance to the geometry and alignmentstudies Review of the CLIC TBM lab program

12. Vacuum tests • The Committee notes that due to the leakfound in TBM0-1, the UHV behaviourwasaddressed on an independent, dedicatedset-up, leading to fasterresults in a more flexible and cost-effective way • The Committeeappreciatesthat the measured UHV performance meets the specification, in good agreement with the simulations. The large outgassing of SiC, at least at the beginning of pumping, willhoweverrequirefurtherstudies • The Committeewelcomes the potential simplification and improvementbrought by the new vacuum system and encourages furtherdevelopmentworkalongthis line, includingitsimplementationat the first possible stage, i.e. in TBM1 • The Committeewishes to underlinethatthe foreseenredesign of the TBM vacuum system shouldintegrate all aspects of operation and maintenance, including replacement of faulty components (e.g. need for isolation valves) Review of the CLIC TBM lab program

13. Nextsteps and future plans [1/2] • The Committeewaspresentedwith a maximum test plan TT1 to TT5, including transport test after TT2 Review of the CLIC TBM lab program

14. Nextsteps and future plans [2/2] • Somemeasurements and analysis are still to bedone on the present configuration (TT1), to simulaterealistic CLIC operating conditions as well as somefailure modes • Selectedmeasurements and analysisfound relevant from TT1 experienceshouldberepeated on the TT2 configuration • The Committeewaspresentedwith justification for the transport test after TT2 and supports it. The Committeewishes to underlinethat, depending on the outcome, transport of the TBMsmayrequire a dedicatedstudy and test program, whichmaythereforecompete for the use of prototype TBMs and thusinterferewith the lab program • The Committeedoes not see an absolute justification for conductingsequentially TT3 and TT4, and out of the two tests, favours TT4 on the grounds of itshigheradded value • Consideringthatmost of the added value of TT5 consist in stabilization tests, for which the labis not adequatelysuited, and thatotherbenefitsof integratingTBM4 are limited, the Committeedoes not support TT5 • The Committeerecommendsthat design of nextgenerationTBMs not startbefore the test program on first-generationTBMsbeconcluded, and all relevant information analysed and resultsfedinto the process Review of the CLIC TBM lab program