ILCDR'07, 5-7 March, INFN-LNF, Frascati, Italy ILC Damping Rings Technical and Organizational Status Andy Wolski University of Liverpool and the Cockcroft Institute

2 IntroductionILCDR07 The RDR Configuration… One electron and one positron ring in a shared tunnel around the Interaction Region. 5 GeV beam energy. "OCS6" lattice: –6695 m circumference (harmonic number 14516). –24 MV, 650 MHz RF (gives natural bunch length of 9 mm). –Momentum compaction factor 4.2×10 -4.

Arc 1 (818 m) Arc 2 (818 m) Arc 3 (818 m) Arc 4 (818 m) Arc 5 (818 m) Arc 6 (818 m) short straight A (249 m) short straight B (249 m) short straight C (249 m) short straight D (249 m) long straight 1 (400 m) extraction long straight 2 (400 m) injection shaft/large cavern A shaft/large cavern C e+e+ 8 RF cavities 10 RF cavities wiggler small cavern 2 small cavern 1 IP wiggler OCS6: 6695 m, TME lattice

4 IntroductionILCDR07 Evolution of the configuration and design November 2005: CERN meeting recommended the baseline configuration, based on results of detailed studies of a range of different lattices and configurations: –5 GeV beam energy. –Roughly 6 km circumference. –Two positron damping rings (for mitigation of electron cloud) in one tunnel, and one electron damping ring in a second tunnel. –Natural bunch length 6 mm. Throughout 2006: Continuing studies, including more detailed cost estimates, led to a number of configuration and design changes: –6695 m circumference (h = 14516) to satisfy timing constraints. –Eliminated second positron damping ring. –Reduced the number of straight sections from 8 to 6. –Co-located two damping rings in a single, central tunnel. –Reduced RF voltage by increasing natural bunch length to 9 mm.

5 IntroductionILCDR07 The RDR "value" estimate: $675M

6 IntroductionILCDR07 The RDR "value" estimate: $675M

7 IntroductionILCDR07 Key questions for the next design iteration 1.What is the optimum circumference to satisfy the new timing constraints? Present circumference was chosen with regard to a second IR (which no longer exists in the baseline) and without regard to constraints from the electron source (subharmonic buncher). 2.What is the optimum layout from technical and cost considerations? An early assumption was that each straight section (with wiggler and RF) would need an access shaft and large alcove. In fact, only two shafts and alcoves exist in the present configuration. What can be done to ease requirements for the kickers? 3.How do we optimize the lattice for good dynamical performance and low cost? Beam dynamics considerations include: Dynamic aperture Sensitivity to errors; low-emittance tuning Sensitivity to collective effects, including: impedance-driven instabilities, ion effects, electron cloud, intrabeam scattering, etc. Affects choice of momentum compaction factor etc.

8 IntroductionILCDR07 Constraints on the circumference from the timing scheme…

9 IntroductionILCDR07 Constraints on the circumference from the timing scheme… Bunch spacing in linac should be "divisible by lots of 2's and 3's". Average linac current should be fixed at 9 mA; RF pulse length should be 970 µs.

10 IntroductionILCDR07 Low Emittance Tuning The vertical emittance of 4.5 pm achieved in KEK-ATF is still the lowest that has been achieved anywhere. The ILC damping rings are specified for a vertical emittance < 2 pm… so there is still some way to go. Considerations and implications of low-emittance tuning: –The vertical emittance is an important performance metric for the damping rings; but the scaling of machine luminosity with extracted emittance is not very strong. –The "ease of achieving" 2 pm vertical emittance will depend on details of the lattice design: magnet strengths and locations, machine tunes, lattice functions, etc. How do we compare 2 pm in ATF, for example, with the goal of 2 pm in the ILC damping rings? –To what extent do we trust simulations? The real world has many aspects that simulations do not usually include, for example: BPM dependence on current, random failures of BPMs and correctors… –Low emittance tuning is coupled to lattice design (sensitivity to alignment errors) and to the vacuum system design (BPM performance).

11 IntroductionILCDR07 Ion Effects Effects consistent with the Fast Ion Instability have been observed in several storage rings (ALS, PLS, ATF)… …but we cannot predict with confidence the impact of ion effects on the performance of the ILC electron damping ring. –What will be the residual gas pressure and composition in the vacuum chamber, as functions of time (conditioning) and position? –How will the beam interact with the ions? What will be the impact on performance of the damping rings under various conditions? –To avoid performance limitations from ion effects, what should be the specifications for: –the lattice (optics); –vacuum system; –bunch-by-bunch feedback system; –fill pattern (bunch charge, bunch spacing, and gaps). –There is a lack of quantitative data with which we can benchmark the simulation codes in the appropriate (low emittance) regime: further studies will be very important.

12 IntroductionILCDR07 Development of an R&D Plan for the Damping Rings The GDE R&D Board has set up a number of Task Forces to develop plans for tackling R&D in specific areas: –S0 Cavity Gradient R&D –S1 Cryomodule operating gradient R&D –S2 Linac Test Facility –S3 Damping Ring R&D –S4 Beam Delivery System R&D –S5 Positron Source R&D –S6 Control system R&D –S7 RF Power Source R&D The S3 Task Force has 10 members (Eckhard Elsen, Jie Gao, Susanna Guiducci, Tom Mattison, Mark Palmer, Mauro Pivi, Junji Urakawa, Marco Venturini, Andy Wolski, Mike Zisman). We have: –Reviewed the R&D objectives for the damping rings, classifying according to priority. –Collected information on available (or possibly available) resources. –Started preparation of an R&D plan, by drafting "Work Packages" on injection/extraction kickers, electron cloud effect, and impedance issues.

13 IntroductionILCDR07 Development of an R&D Plan for the Damping Rings The "Very High Priority" issues for the ILC damping rings are: –Injection/extraction kickers –Electron cloud effect –Impedance issues –Lattice design –Low-emittance tuning –Ion effects The intention is that a "Work Package" will be developed for each R&D topic, and that the R&D plan will state, for each Work Package: –the R&D objectives; –the detailed tasks that must be accomplished to achieve the objectives; –the people involved in the R&D, and how they will contribute; –the time and resources required (and compared with those available) to complete the R&D. ILCDR'06 (Cornell) ILCDR'07 (Frascati)

14 IntroductionILCDR07 Development of an R&D Plan for the Damping Rings Based on the discussions and contributions from ILCDR'06, draft Work Packages are being prepared for: –injection/extraction kickers, –electron cloud effects, and –impedance issues. In this workshop, we should provide input for the development of Work Packages for: –lattice design, –low-emittance tuning, and –ion effects.

15 IntroductionILCDR07 Evolution of the ILC organization for the EDR The Engineering Design Report (EDR) will contain sufficient engineering detail to allow "approval to construct" from the participating governments. The EDR should be completed by "GDE will expand to contain all persons working on ILC." Executive Committee will continue as before. Director (Barry Barish) Regional Directors Accelerator Directors For the EDR, a Project Management Team will be set up, led by a full-time Project Manager. Functions carried out by the three Boards (R&D, Change Control, and Design/Cost) will be reviewed.

16 IntroductionILCDR07 Evolution of the ILC organization for the EDR Executive Committee Project Management Team R&D Board Change Control Board Design Cost Board GDE

17 IntroductionILCDR07 Evolution of the ILC organization for the EDR From Brian Foster's talk at Beijing, 4 February 2007: "To improve efficiency and reduce duplication of effort, [we] propose to organise EDR phase by dividing the tasks into work packages which can be bid for by consortia, which would be encouraged, as well as by individual labs, universities etc."

18 IntroductionILCDR07 Evolution of the ILC organization for the EDR From Brian Foster's talk at Beijing, 4 February 2007: "We have to ensure that, having allocated work packages, we can when necessary amend their scope and even reallocate them at a later stage in the project." "In general the work packages will be organised in “Area Systems”, e.g. damping ring, positron source, etc - but “Technical System”-based work packages [will be] allowed if advantageous." "First ideas on the definition of work packages will be produced by an ad- hoc working group to be set up by the EC." "Bids for work packages “above threshold” will be ranked and recommended to EC by a Work Package Assignment group, to be chaired by PM. This committee will work purely with the technical issues; the final decisions, injecting other relevant factors such as regional balance etc., will be made by EC on basis of these recommendations."

19 IntroductionILCDR07 ILCDR'07 Goals 1.Review the changes required to the present lattice design, and outline a plan leading to an "optimised" lattice for the EDR (including possible alternatives to the baseline). 2.Review the techniques presently used for low-emittance tuning. Identify the strengths and weaknesses of the various techniques, and the requirements for lattice design, alignment, instrumentation etc. Discuss possible alternative tuning procedures, and outline a plan leading to a demonstration of the required 2 pm vertical emittance. 3.Discuss the present status of knowledge of ion effects, particularly fast ion instability in the regime of the ILC damping rings. Specify the design requirements for avoiding performance limitations from ion effects in the ILC damping rings. Describe the experimental studies required to validate predictions of ion effects in the ILC damping rings, and outline a plan for performing such studies. Detailed technical discussions are important, and should comprise the main part of this workshop!

20 IntroductionILCDR07 ILCDR'07 Schedule Monday, 5 MarchTuesday, 6 MarchWednesday, 7 March 09:30 IntroductionWolski Low Emittance Tuning Emery 2 Discussion/Summary Preps 10:00 Lattice Design Sun  Sagan 10:30 Emery 1 Cai 11:00 Coffee 11:30 Lattice Design Preger Low Emittance Tuning Milardi Summaries 12:00Palmer 1 Kubo 12:30 Bettoni Jones 13:00 MitchellIon EffectsXia 13:30 Lunch Lunch/End 15:00 Lattice Design Naito Ion Effects Lee 15:30Rubin 1 Rubin 2 16:00 BiaginiUrakawa 16:30 Coffee 17:00 Lattice Design Palmer 2 Ion Effects Drago 17:30 Byrd/Venturini 18:00 Reichel  Wang  18:30 End 20:00 Workshop Dinner

21 IntroductionILCDR07 Finally… …thank you to: –the many people who contributed to the Reference Design Report and costing; –all of you for coming to participate in this meeting, and to the conveners for their work in organising the programme; –Susanna and her colleagues at Frascati for hosting this meeting, and making all the local arrangements.