1. Towards a Coordinated R&D Plan for ILC Damping Rings Impedance Issues Andy Wolski University of Liverpool and the Cockcroft Institute 28 September, 2006

2. 2 Impedance Issues: Milestones 1.Produce initial technical designs for: (a) vacuum system (~ 2 years for ~ 2 FTEs), and (b) RF cavities (> 2 years). 2.Produce preliminary impedance model based on general specifications and scaling from existing machines/designs. (~ 1 year time frame for 1 FTE). 3.Make preliminary estimates of thresholds, growth rates, HOM heating etc. based on preliminary impedance model. (~ 1 year time frame) 4.Construct detailed impedance model based on initial technical designs for vacuum system and RF cavities. (as information from milestone 1 becomes available; ~ 1 year 4½. Specify feedback system model. 5.Characterize the impedance-related collective effects. (follows 4; ~ months) 6.Specify revised design parameters, and produce optimized technical designs (low risk and cost) for vacuum system and RF cavities. (following TDR) 7.Produce revised impedance model and updated characterization of impedance- related collective effects. (following TDR) 8.Prototyping and testing (in parallel with 6 and 7).

3. 3 Impedance Issues: Milestones 1.Produce initial technical designs for (a) vacuum system, and (b) RF cavities. R&D WBS 3.1.1.1: Specify vacuum chamber material and geometry. R&D WBS 3.1.1.2: Develop engineering design of principal vacuum chamber components. R&D WBS 3.5.1.2: Develop physics designs for kicker striplines. R&D WBS 3.6.2.1: Develop physics designs for 650 MHz RF cavities. Technical studies of damping rings vacuum system are needed to: –specify chamber geometry (including antechamber), material, coating (for low SEY or NEG), pumping locations, etc. –produce technical designs for all chamber components, including kickers (for injection/extraction and feedback systems), septa, bellows, tapers, BPMs (in consultation with diagnostics group), pumping ports etc. (Need to prioritize items for design and impedance modeling based on initial estimates and experience.) Technical design is needed for main RF cavities to specify HOM spectrum. Studies are needed of higher-harmonic RF system for bunch shortening.

4. 4 Impedance Issues: Milestones 2.Produce preliminary impedance model based on general specifications and scaling from existing machines/designs. Use basic parameters based on general specifications (apertures, numbers of components…) Need to fix the parameters and general specifications! Need to lay out structure and organisation and tools (parameter database, including designs and impedance information…)

5. 5 Impedance Issues: Milestones 3.Make preliminary estimates of thresholds, growth rates, HOM heating etc. based on preliminary impedance model.

6. 6 Impedance Issues: Milestones 4.Construct detailed impedance model based on initial technical designs for vacuum system and RF cavities. R&D WBS 2.2.1.1: Develop single-bunch impedance models. R&D WBS 2.2.2.1: Develop long-range wakefield models. …including short-range (single-bunch) and long-range (multibunch) wakefields. Groups of adjacent components should be modeled together where appropriate, to take account of “interference” effects.

7. 7 Impedance Issues: Milestones 5.Characterize the impedance-related collective effects. R&D WBS 2.2.1.2: Characterize single-bunch impedance-driven instabilities. R&D WBS 2.2.2.2: Characterize multi-bunch instabilities. R&D WBS 2.2.2.3: Characterize the effects of injection transients. Use the impedance model to characterize instabilities, including: –potential well distortion; –single-bunch longitudinal and transverse instabilities (threshold effects: emittance growth and “bursting” type); –multi-bunch instabilities. Use the impedance model to characterize transients: –equilibrium phase transients from beam-loading variations; –non-equilibrium effects during injection/extraction process. Include model of fast feedback systems as appropriate (coordinated with diagnostics specifications and designs). Use the vacuum system technical design and impedance model to estimate higher-order mode heating of vacuum chamber components. Consider impact of other relevant effects, e.g. IBS, space-charge, CSR, electron cloud, ion effects etc.

8. 8 Impedance Issues: Milestones 6. Specify revised design parameters, and produce optimized technical designs (low risk and cost) for vacuum system and RF cavities. Decide appropriate value for momentum compaction, and need for higher- harmonic cavities. Revise technical designs to mitigate the impact of impedance, as necessary. 7.Produce revised impedance model and updated characterization of impedance-related collective effects. 8.Prototyping and testing (in parallel with 6 and 7).

9. 9 Impedance Issues: Investigators 1. Produce initial technical designs for (a) vacuum system, and (b) RF cavities. 2.2.3.I: CESR-TF wiggler and electron cloud studies (John Byrd). 3.1.1.A: Damping rings wiggler and straights vacuum system (Steve Marks). 3.1.1.B: Damping rings vacuum studies (Oleg Malyshev). 3.1.1.C: Coordinate design of damping rings vacuum system and control the impedance budget (Sam Heifets). 3.1.1.D: Vacuum chamber studies (Dong Hai Yi). 3.1.1.E: Vacuum design of damping rings (Frank Zimmermann). 3.5.1.D: Development of fast injection/extraction kickers (George Gollin). 3.5.1.E: Development of stripline electrodes for fast kickers (David Alesini). 3.5.1.H: Development of reduced beam impedance kicker structure (Anatoly Krasnykh). 4.2.1.A: ATF kicker development (Stefano de Santis). 4.2.1.B: Development of fast rise/fall time kicker for ATF/ATF2 (Takashi Naito). 3.6.1.A: RF system specification (Roberto Boni). 3.6.1.B: RF system issues (Kazunori Akai). 3.6.2.A: Development of 650 MHz superconducting RF cavity (Mark Palmer).

10. 10 Impedance Issues: Investigators 2.Construct impedance model based on initial technical designs for vacuum system and RF cavities. 2.2.1.A: Develop and impedance budget and specify feedback systems (Karl Bane). 2.2.1.B: Develop single-bunch impedance models (Andy Wolski). 2.2.1.C: Characterize single-bunch collective effects (Jie Gao). 2.2.1.D: Calculate impedance of vacuum chamber components (Sam Heifets). 2.2.1.E: Simulate vacuum chamber and beamline components (Kwok Ko). 2.2.1.F: Single bunch impedance (Yong-Chul Chae). 2.2.2.A: Model impedance-driven coupled bunch instabilities (Andy Wolski). 2.2.2.E: Multi-bunch instability with Monte Carlo HOM modeling (Louis Emery). 3.1.1.C: Coordinate design of damping rings vacuum system and control the impedance budget (Sam Heifets).

11. 11 Impedance Issues: Investigators 3. Characterize the impedance-related collective effects. 2.2.1.A: Develop and impedance budget and specify feedback systems (Karl Bane). 2.2.1.B: Develop single-bunch impedance models (Andy Wolski). 2.2.1.C: Characterize single-bunch collective effects (Jie Gao). 2.2.1.F: Single bunch impedance (Yong-Chul Chae). 2.2.2.A: Model impedance-driven coupled bunch instabilities (Andy Wolski). 2.2.5.A: Characterize selected single-bunch instabilities (Mike Zisman). 2.2.5.E: Characterize classical single- and multibunch instabilities (Sam Heifets). 2.2.2.C: Characterize transient beam loading and injected-beam transient effects (Mike Zisman). 2.2.2.D: Fast feedback systems specifications (John Fox). 2.2.2.E: Multi-bunch instability with Monte Carlo HOM modeling (Louis Emery). 2.2.5.D: Characterize injection/extraction transients (Andy Wolski).

12. 12 Impedance Issues: Timescale 1.Produce initial technical designs for (a) vacuum system, and (b) RF cavities. By end of… 2.Construct impedance model based on initial technical designs for vacuum system and RF cavities. By end of… 3.Characterize the impedance-related collective effects. By end of… 4.Specify design parameters, and produce optimized technical designs for vacuum system and RF cavities. By end of… 5.Produce revised impedance model and updated characterization of impedance-related collective effects. By end of…