Report from the 5 th meeting of CLIC ACE

1. Report from the5th meeting of CLIC ACE Markus Huening, Alban Mosnier, Pantaleo Reimondi, Vladimir Shiltsev, Nobu Toge, Thomas Roser, and Tor Raubenheimer (Lyn Evans, Tsumoru Shintake) Feb 5, 2010

2. Charge Committee has been asked to comment on: Layout and schedule for the CDR. Schedule of the CLIC feasibility demonstrations and timing of the CDR. Technical and/or design status of the following subjects drawn from the “list of CLIC critical issues”.

3. Where CLIC effort is, and it goes - Overview (1) • Findings: • Committee heard the following: • Critical issue is for CERN council in 2011 to determine whether the CLIC efforts should proceed into the next stage of design development (technical design). • Keyword that is introduced in aiding this evaluation process by the CERN council is whether “technical feasibility” of the “CLIC concept” is at hand. • CDR is a vehicle to convey the message - “CLIC concept is technically feasible so that it is ready for the next stage design development”.

4. Where CLIC effort is, and where it goes – Overview (2) • Observations: • If an objective, qualitative and quantitative definition for technical feasibility is absent, the relation between “technical feasibility of the concept” vs “readiness for the next step” is reduced into something of simple tautology. • J-PD has his definition of “feasibility” in this regard. • Recommendations: • Clarify the context of “technical feasibility of CLIC concept” upfront, in CDR i.e. what it is, and what it is not. In addition, • CLIC group should quantify and qualify - • What has been demonstrated wrt what is needed at CLIC. • What is planned to do at the TDR stage with goals, deliverable, milestones and budget for all significant parts of it. • (How the outcome from activities during the TD stage would relate to the launch of the project. ) • CLIC group should offer the explanations in reasonable details for the above sub-bullets in the CDR, besides the design description of CLIC which is already planned in the outline for CDR.

5. Main Beam Accelerator Structures Committee’s understanding of Primary Objectives Demonstrate nominal CLIC structures with damping features at the design gradient, pulse length and breakdown rate 100 MV/m, 240 ns, < 3.10-7 (pulse.m), efficiency (RF to beam) 30% Findings T18 structures (no HOM damping) After ~500 - 900hrs of processing BD rate of a few x 10-6 at 90MV/m 230ns Approaching the CLIC goal. TD18 (w. HOM damping) struc at SLAC, BD rate is comparable to that of T18s above, when it is processed up to 100MV/m, 100-300ns for 300-350 hrs. Including the ones under processing, within CY2010, the following acc structures will be tested at CERN, SLAC and KEK 2 x T18, 2 x TD18, 3 x T24, 4 x TD24 (one at CLEX) CERN is accelerating its effort in preparing its infrastructure + capability for acc struc construction and testing in support of TDR efforts.

6. Main Beam Accelerator Structures Observations Committee feels that there are good reasons to believe TD24, which is close to CLIC main beam acc struc, would clear a BD performance required at CLIC in a CLIC-like operational conditions, i.e. ~100MV/m, ~240ns, HOM damping, efficiency (but without the actual HOM absorbers) Objectives are (nearly) in hand (see T18 results) CERN-SLAC-KEK collaboration highly productive. Recommendations Should go full steam ahead with RF testing of the acc structures in pipeline, with emphasis on TD24. Take advantage of any chances for further schedule optimization. Try to make some statement on the struc life time on the basis of available data. Besides the ongoing work toward CDR, Testing of more accelerator structrues highly recommended in the future to enhance confidence in the statistical and technical sense. Clarify implications of difference in the current testing environment (i.e. absence of beam, beam-loading) wrt actual CLIC operational conditions, to pre-avoid confusion in the community. Address lifetime issues. Validated HOM damping performance. CERN efforts on its own infrastructure (fab + testing) strongly encouraged.

7. Drive Beam Accelerator Structure • Committee understanding of primary objectives • Demonstrate nominal PETS structures with damping features at the design power, pulse length, breakdown rate and on/off capability, efficiency • 135 MW, 170 ns, < 1.10-7 (pulse.m), on/off < 20 ms, efficiency 90% • Findings • Testing with Klystron (SLAC) • Power and pulsed length OK, but breakdown rate high • Testing with drive Beam (CTF3: Two Beam Test-stand): • RF re-circulation is required due to the current actually available through • < 30 A and last tests were limited due to breakdown in recirculating waveguides • Overall performance of PETS tested with ~130 MW, 170 ns • Breakdown rate an order of magnitude still higher than the goal likely due to the RF systems issues • Comments & Recommendations • Toward completion of CDR • ON/OFF operation has to be demonstrated (with the new scheme; integrated reflector) • HOM will not be immediately measured and remains to be an outstanding concern. • Ditto for damage and lifetime aspects in a recirculator-aided setting. • Ultimate goal has to be remembered: DB-driven test all features with a 100 A beam .

8. Drive Beam Generation Drive beam generation was successfully demonstrated at CTF3 with beam parameters that can reasonably be extrapolated to CLIC values. Progress in demonstrating the stability requirement is still needed. Efficient RF acceleration and frequency-multiplication with delay loop and combiner rings have been achieved. Pulse-shape control for beam-loading compensation and critical system-level issues including tolerances, beam-loss controls and reliability / machine protection remain to make this technology viable. The total average beam power of the CLIC drive beam (70MW) is 105 times larger than at CTF3 (1 kW) and also much larger than at any other existing electron or hadron beam facility. Control of both chronic and catastrophic beam losses needs to be carefully studied for machine protection and to limit equipment activation. It might not be feasible to keep the beam losses at the CLIC Drive Beam system low enough.

9. RF Power Generation TBL with 8 structures will be an important step. However, still a long ways to go to 90% extraction which is critical to CLIC concept. The 16 PETS test is closer to demonstration. HOM performance (PETS) is an outstanding concern, and requires thought. Need understanding of systems-level issues. Intensity stability/Timing stabilitynot too far off and I believe the remaining factor is achievable, but not necessarily within 2010 in CTF3.

10. Damping Ring • Appreciate good progress on • Lattice. • Magnet design, several feasible solutions on hand. • Collective effects under study. • Reducing fractional IBS growth seems promising. • E-Cloud dealing seems feasible • Ion-trapping not an issue. • Concerns • Space charge tune shift (0.2) very large, • 2GHz RF system seems very hard. No detailed calc or sim seem available. • Beam pipe diameter very small (10mm). • Bunch length very short (1mm). • HOM power studies not available.

11. Damping Ring, continued • Concerns / Suggestions • Large gap in the ring might cause a lot of difficulties for the RF system and RF and beam stability requirements. • Synchronous phase spread due to the gap transient is missing. • No studies made on single and multi bunch instabilities. • Feedback requirements missing. • Longitudinal dynamics (with RF cavities) has to be checked. • Committee feels that not enough data presented to judge the DR feasibility. • DR is one of the major performance drivers for any LCs. • Possibly into TDR • Ideally a DR modeling that includes everything should be developed and applied to the present DR design before the CDR deadline. This might not be possible given the lack of time and resources, in that case it might be risky to claim feasibility in the CDR.

12. Preservation of Low Emittance • Damping Ring to Linac • Details of studies seems sufficient for the CDR phase. No clear criticality seen. • Very complex system with several functions included • Acceleration • Bunching • Spin manipulation • Feed forwards • More than 20Km of beam transport • Tuning of the system needs a lot of work but probably ok for now.

13. Preservation of Low Emittance, continued • Main Linac • Emittance preservation has been extensively studied and is based on several techniques, some tested in several facilities, some already developed for different machine (e.g. NLC/ILC) and some specific for CLIC. The requirements for the hardware (alignment, BPM resolutions etc.) are met by the present technology and knowhow. • Tolerance on quads stability (1nm) seems also reachable. Useful to demonstrated for CDR. • Important to incorporate technical noise sources in evaluation of the LE preservation. • Beam phase and energy stability tools are ok.

14. Preservation of Low Emittance, continued • Beam Delivery System • Much progress done in the last year. Good enough for the CDR. • Solutions for different energies are well developed and seem OK. • Itra-train FDBK studies and MDI studies look promising. • Work on tuning procedure should continue into the future. • Beam pipe radius about 3mm. Need a “Machine Protection System“ study (don’t know how detailed it is at the moment) • Stability requirement of 0.15nm seems a major challenge into TDR. • General final remark is that very much everything is well on hand both for CDR and the next phase apart the Damping Ring feasibility that might have an impact on the final design performances.

15. Diagnostics and Beam Quality • Beam diagnostics at all mentioned are BPMs, Phase Monitors and BLMs • BPM resolution of 100nm ought to be reachable given the small beam pipes • Required dynamic range was a question. If too large why not make it switchable or interleave • At TTF phase monitors (40mm aperture) were demonstrated with 15fs (5µm) resolution in the machine (expected performance was 5fs). Nevertheless at CTF3 an RF based phase monitor is reasonable because of the available infrastructure • At FLASH glass fibers are used to monitor accumulated dose, for machine protection the fibers (Cherenkov) were too insensitive, use scinttillators instead • Detecting beam losses by ICT to 10-4 for machine protection does not sound completely unrealistic, might have been done already somewhere

16. Operation and Machine Protection

17. Global Recommendations for / beyond CDR Highly desirable to make concentrated efforts on the CTF3-TBL demo test With the goal of showing the probe beam acceleration Before the CERN council meeting (June 2011) For sake of CDR presentation Understand the audience (Council, Community around CERN, Community in the world, Community outside HEP) Do not be shy about the progress and accomplishment. Yet, be open and forthcoming about remaining issues. Be quantitative, whenever possible. Also, use tables to compare the specs, goals, achievements, projections, whenever possible.

18. On Systems-Level Issues The feasibility of many of the critical components for CLIC has been demonstrated in the sense of an existence prove. What is less well developed is the feasibility of systems. This includes the damping rings, two-beam acceleration structures, stability of the ML and final focus quadrupoles, extremely high power operation of the drive beam complex. It is clear that this can not be completed during the CDR phase and will need to be a main focus of the TDR phase.

19. Staging of CLIC / Activities in TDR The committee was presented with a list of tasks to be completed during the TDR phase. The focus was on technical designs of all critical components of CLIC and construction of prototypes. Enough prototypes will be build to judge the yield and lifetime. In addition, CTF3 will be expanded to facilitate more realistic testing of the two-beam acceleration structures (CTF3+). It was also proposed to build the first 10% of the CLIC drive beam linac. Recommendation: Develop a plan for the TDR phase that is focused on laying the groundwork for approval of CLIC construction, and include it in the CDR document. The committee supports including prototype development and testing as well as significant R&D items, in particular, realistic testing of the two-beam acceleration structures. Construction of the drive beam linac, however, could be part of “CLIC zero” as a first phase of CLIC construction. CLIC-zero would be on ly opportunity for the many systems-level demonstration of the CLIC concept. Important to think of a possible physics justifications for CLIC-zero.

20. Closing • Greatly appreciate the excellent presentations and efforts made by the team. Big thanks, as usual, to the colleagues at CLIC, led by J-P.D. for all the hard work, informative presentations, rapid responses to the late inquiries. • Big thanks to Alexia for all the logistical support.