Review of the CLIC Two-Beam Module lab program

Conclusions

F. Bertinelli, E. Jensen, Ph. Lebrun, D. Missiaen, D. Schulte

Review held at CERN on 6 November 2013Reported to CASC on 19 November 2013

Review of the CLIC TBM lab program

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Background• The Two-Beam Modules (TBM), which integrate the RF, magnet, vacuum,

supporting, alignment and stabilization functions of the drive-beam and main-beam linacs, constitute the backbone of CLIC and a high stake of its project preparation phase 2013-2017

• A first generation of TBM prototypes is in the process of being constructed, tested and experimentally validated– in the laboratory (without beam): geometrical, mechanical, thermal and vacuum

measurements– in the CLEX area of CTF3 (with beam): functional tests, two-beam acceleration

• It is foreseen that a second generation of TBM prototypes will follow, integrating the developments of the CLIC study and the results from the first-generation tests

Ph. Lebrun

Review of the CLIC TBM lab program

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Review charge

• The CLIC Accelerator Steering Committee (CASC) has decided to conduct reviews of the Two-Beam Module (TBM) program, in order to get advice on the development and testing strategy of the prototype TBMs:– Review the progress of the development work on prototype TBMs,– Assess the results of prototype TBM tests,– Lay out the roadmap for the continuation of the module development and test

program,– Provide elements of decision for optimal resource allocation to fulfil this program

• The review panel will report to the CASC• This first review will address the TBMs for the laboratory test program

Ph. Lebrun

Review of the CLIC TBM lab program

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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

Ph. Lebrun

Review of the CLIC TBM lab program

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Agenda

Ph. Lebrun

Review of the CLIC TBM lab program

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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

Ph. Lebrun

Review of the CLIC TBM lab program

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Objectives, strategy & present status• A table of general tolerances and requirements for the TBMs was presented,

some of which appear very demanding– The Committee is not convinced of the consistency of the different tolerances on

basic components, subassemblies, assemblies and reference points, in relation to alignment and beam requirements

– Consequently, the Committee suspects insufficient integrated understanding of the chain of tolerances from the basic components to the beam

– The Committee therefore recommends that a single person with this understanding has the complete view and responsibility of the requirements and their consequences on design, fabrication, assembly and alignment

• The TBM program presented extends over several years and requires a large, sustained effort in material budget and personnel.– It appears that several objectives of the TBM lab program could have been or were

in fact better reached through simpler, dedicated mock-ups and test setups– The Committee therefore recommends to periodically review the activity for optimal

steering– Most of the program is already committed and cannot easily be re-directed on a

different course. The committee has however identified several unsettled issues, addressed in the following, on which program decisions must be taken

• Stabilization tests were mentioned as one of the objectives of the program: the Committee notes that this very important issue has not been addressed

Ph. Lebrun

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TBM type 0

• The Committee wishes to acknowledge the important amount of design, construction and assembly work performed on TBM type 0, as reflected in the presentation

• The prototype TBMs are inhomogeneous assemblies of functional components and mock-ups, resulting in very complex objects which still substantially differ from real CLIC TBMs, and thus have limited potential for complete validation of CLIC technological issues. The Committee recommends that this issue be analysed in detail

• The results of straightness measurements on AS presented show– significant differences between manufacturers,– substantial amplification of the errors from subcomponent to complete assembly,– values well outside specified tolerances.While these out-of-tolerance AS can probably be used as mock-ups for the TBM lab program, the Committee expresses concern that this may reveal difficulty to attain the requested tolerances on industrially produced AS, and recommends to address this issue and analyse the consequences it may have on CLIC performance

• The geometrical errors presented were peak-to-peak: the Committee notes that RMS errors are also relevant to a number of requirements and should therefore be considered

Ph. Lebrun

Review of the CLIC TBM lab program

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Thermo-mechanical tests

• Analysis of thermo-mechanical behavior certainly constitutes one of the most relevant justifications for testing complete prototype TBMs

• The Committee however wishes to emphasize that temperature mapping of TBM components constitutes only part of thermo-mechanical tests, and that deformations and displacements induced by steady-state and transient thermal regimes are most important to the validation of the TBM design for CLIC

• A large number of temperature measurements were performed in a variety of elementary heating cases. The Committee would like to see a complete analysis of these results, particularly as concerns:– Paths and balance of power flow– Transient time constants– Indications of temperature on other components which may influence transient

behaviour– Simulation of CLIC operational and failure scenarios

• The Committee reaffirms the need to integrate the thermal test program with geometry and alignment measurements, as well as to provide useful feedback to design

Ph. Lebrun

Review of the CLIC TBM lab program

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Geometry and alignment [1/2]

• Four objectives were defined for geometry and alignment tests, and results presented on each of them, showing good progress of the program

• 1) Measurement methods– Micro-triangulation and AT401 were tested and cross-checked, with adequate

results– Alternative methods with good complementarity potential are still to be tested

• 2) Pre-alignment strategy– The concept of performing component pre-assembly on a CMM may be adequate for

prototype work, the Committee thinks that it is not applicable for series production– A pending technical choice is that of linear actuators vs cam movers: the

Committee thinks it is necessary to clarify who is leading 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 observed degradation of the articulation point is considered a critical issue by the Committee, needing analysis and redesign

• 3) Intercomparison between alignment systems on short range– The Committee encourages studies on the optical wire positioning system as

alternative to capacitive sensors

Ph. Lebrun

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Geometry and alignment [2/2]

• 4) Stability of alignment under changing conditions– A large number of measurements were performed: they need thorough analysis,

still to be done, in order to extract useful information and help steer the continuation of the test and measurement program

– In particular, the Committee wishes to emphasize that deformations and displacements must be analysed under conditions simulating realistic operation and failure modes, not only the variations in tunnel air flow and temperature which were presented

– The present design of the vacuum system is not suited to resist pressure forces within allowed deformations: the problem should be alleviated 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 Committee recommends that the TBM design and development team provides more input and better guidance to the geometry and alignment studies

Ph. Lebrun

Review of the CLIC TBM lab program

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Vacuum tests

• The Committee notes that due to the leak found in TBM0-1, the UHV behaviour was addressed on an independent, dedicated set-up, leading to faster results in a more flexible and cost-effective way

• The Committee appreciates that 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, will however require further studies

• The Committee welcomes the potential simplification and improvement brought by the new vacuum system and encourages further development work along this line, including its implementation at the first possible stage, i.e. in TBM1

• The Committee wishes to underline that the foreseen redesign of the TBM vacuum system should integrate all aspects of operation and maintenance, including replacement of faulty components (e.g. need for isolation valves)

Ph. Lebrun

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Next steps and future plans [1/2]

• The Committee was presented with a maximum test plan TT1 to TT5, including transport test after TT2

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Next steps and future plans [2/2]

• Some measurements and analysis are still to be done on the present configuration (TT1), to simulate realistic CLIC operating conditions as well as some failure modes

• Selected measurements and analysis found relevant from TT1 experience should be repeated on the TT2 configuration

• The Committee was presented with justification for the transport test after TT2 and supports it. The Committee wishes to underline that, depending on the outcome, transport of the TBMs may require a dedicated study and test program, which may therefore compete for the use of prototype TBMs and thus interfere with the lab program

• The Committee does not see an absolute justification for conducting sequentially TT3 and TT4, and out of the two tests, favours TT4 on the grounds of its higher added value

• Considering that most of the added value of TT5 consist in stabilization tests, for which the lab is not adequately suited, and that other benefits of integrating TBM4 are limited, the Committee does not support TT5

• The Committee recommends that design of next generation TBMs not start before the test program on first-generation TBMs be concluded, and all relevant information analysed and results fed into the process

Ph. Lebrun