WG3b - Damping ring size and layout

1. WG3b - Damping ring size and layout S. Guiducci

2. DR configuration recommendation • Circumference and layout • ~ 17 km dogbone • 3 km or 6 km ring • Single rings • Stacked rings • (all task forces involved, at least 1 lattice for each length)

3. Task forces have been charged to study the key issues • The task forces (and co-ordinators) are: • Acceptance (Y. Cai, Y. Ohnishi) • Emittance (J. Jones, K. Kubo) • Classical Instabilities (A. Wolski) • Space-Charge (K. Oide, M. Venturini) • Kickers and Instrumentation (T. Naito, M. Ross)\ • Electron Cloud (K. Ohmi, M. Pivi, F. Zimmermann) • Ion Effects (E.-S. Kim, D. Schulte, F. Zimmermann) • Cost Estimates (S. Guiducci, J. Urakawa, A. Wolski) • Polarization (D. Barber) • The various configuration options are being studied, using the seven “reference” lattices as a basis, and applying a consistent set of analysis techniques and tools. • The goals of the task forces are to produce information that can be used to inform the configuration selection. • Work is in progress. There are roughly 30 active participants altogether, and 36 talks have been given. All three regions are strongly represented.

4. The Next Steps From WG3b Summary • The Task Forces will complete their studies by mid November 2005. The results of the studies will be documented in a report that will: • describe the seven “reference” lattices • describe the analysis tools and methods • present the analysis results • provide an “executive summary”: • configuration recommendations • remaining R&D that is required • We shall hold a mini-workshop in mid November 2005 to reach consensus on the configuration recommendations, and prepare (at least) the executive summary. • It has been proposed to hold the workshop at either CERN or TRIUMF. • A systematic process for reaching consensus on the configuration options will be drafted by the WG3b conveners, and agreed by the community in advance.

5. Layout and circumference - Discussion • Why don’t we recommend the TESLA dogbone? • We want to recommend the shortest ring that fulfills all the requirements and allows some flexibility (increase charge, number of bunches, gaps in the filling pattern) • Choice of dogbone was dictated by the anavailability of kickers: now we are confident that kickers for a 6 Km ring are feasible (low risk). • Pros • Larger ring has more potential for luminosity, you can increase charge and number of bunches • More safe for e-cloud instability • Cons • 3 different dogbone lattices have marginal DA while 6 Km rings, at present status of the study, show much better acceptance. • Dogbone ring needs to rely on coupling bumps to get rid of space charge? Does coupling bump perform well? Answer can be based only on simulations. Alternative is to increase energy (7 GeV) • Installation in the linac tunnel: stray fields sensitivity, difficulties for commissioning and operability

6. Layout and circumference - Discussion • 3 Km rings • High technical risk for kickers • Short bunch distance is bad for e-cloud instability • 6 Km rings • Low risk for kickers • Risk due to short bunch distance for e-cloud instability still to be well understood • Reasonably safe for space chargebut needs further studies • Large flexibility in lattice design and filling pattern • Single ring / 2 rings in the same tunnel • E-cloud claims for large bunch spacing: a second ring could be added if it is needed to double bunch spacing (or bunch number) • Space charge claims for short ring or higher energy • Two 6 Km rings: same bunch spacing as one 12 Km but half the space charge tune shift

7. Layout and circumference - Discussion • Further studies are needed to make a firm decision on the circumference. • However, a very promising option appears to be a 6 km circumference ring, possibly using rings in pairs to provide adequate bunch spacing (for electron cloud, bunch number increasing…)

8. Task force 5 - Kickers & Instrumentation • Kicker requirements @5GeV, b~50m Kick angle q~0.6mrad or Stability 7x10-4 Rep. Rate 3MHz 2800 bunches (for 1 ms) DR length Rise time of pulse 3 ns  3 km 6 ns  6 km 20 ns  17 km

9. ATF Kicker tests • 3 Fast pulsers tested with beam • FID pulser • DESY pulser(HTS-50-08-UF) • LLNL/SLAC solid state switch bank • rise time 3 ÷ 4 ns • Strip line length ~ 30 cm • ~ 10 strip lines to get required kick FID FPG5-3MHz Rise time~3.2ns Kick angle ~85mrad (calc. 94.7mrad) Expanded horizontal scale

10. Task force 5 - Kickers & Instrumentation • TF5 Schedule - fall 2005 • Proposed Tests: • Droop (KEK), FID durability(?), stability (SLAC/LBL), complementary pulse (KEK), high rate (DESY) • Proposed Design: Optics constraints for ~10 kickers, optimized stripline electrode • Evaluation and analysis: • Baseline document to include – demonstrated – and/or projected: • 6 ns performance (8 buckets of 1.3 GHz)  6.15ns bunch spacing • 3 ns performance (4 buckets of 1.3 GHz)  3.08ns) • Risk assessment  what RD is needed in 06. • Write-up • 6MHz for 5600 pulses operation not yet considered

11. Task force 5 - Kickers & Instrumentation • Other possibilities: • Adopt an inj/ectr scheme wich allows longer fall time (an indipendent positron source, conventional or Compton, allows more flexibility) • RF deflectors could be used, in conjunction with strip line kickers, to get half the bunch distance. • Longer pulse length allows: • Lower voltage (easier pulser) or • Larger kick angle (less strip lines electrodes) • At present 6 ns rise time kicker seems feasible • 3 ns rise time kicker has a higher risk

12. Task Force on Space Charge Good progress has been made. A number of lattice designs have already been analyzed, tune scans performed. Tentative current assessment for ideal lattices: Can a 2pm vertical emittance be maintained at design working point? 6 Km • Goals for the next 2 months • Understand/resolve some differences in results between the two codes (in particular for non-design working points) • Extend study to include lattice errors, realistic model of wigglers • Provide final assessment of lattices • People: • Oide & collaborators, MV; P. Spentzouris (FNAL) has volunteered much appreciated help to provide further bench-mark with his code, possibly using a strong-strong model.

13. Task force 6 - Summary • Task force 6 work is proceeding at good speed with good coordination between SLAC/CERN/KEK/DESY. • Results have small dependence on SEY models (1 and 2). • 17 km ring TESLA has moderate electron cloud build-up in BENDS, while in ARC DRIFTs is dominated by photoelectrons. • 3 km ring OTW has faster build-up and much larger electron cloud densities. SEY<1 in BENDs and large build-up in arc DRIFTs. • Still quadrupoles and wigglers simulations are needed to compile electron cloud density along each ring. • LARGER beam pipe dimensions are beneficial in all configurations! • Simulations benchmarking between different codes are ongoing. • Single-bunch instability and build-up will determine SEY limits. • Single-bunch instability simulations (see Ohmi-san presentation): • In particular, lower threshold in TESLA and slightly higher threshold in OTW. Higher thresholds are expected for BRU, MCH. • It is too early to come to conclusions

14. Discussion of Recommendation From Task Force 1 • Acceptance • Based on what we have learned so far • Pick 6 km ring with “circular” shape • more symmetric • better chromatic property, large moment aperture • large dynamic aperture with multipole errors and wigglers • More space in arcs, potentially leads more flexible lattice, emittance, momentum compaction factor, bunch length • Not yet to recommend any particular type of cell because we would like to have a lattice that achieve the maximum flexibility. • Try to optimize dogbone lattice until November meeting

15. DR configuration recommendation • Energy 5 GeV (TF4 Space Charge) • Is it needed 7 GeV to get rid of space charge in dogbone? • Injected beam parameters (agreed with WG3a, TF1- Acceptance) • Max DR acceptance gAx + gAy = 0.09 m-rad (Ax = 2Jx) • Max energy spread DE/E = ±0.5% • Extracted beam parameters (TF2- emittance,TF3 - Instabilities, TF4 Space Charge) • Extracted emittances (vertical gey = 2pm most challenging) • Extracted energy spread • Extracted bunch length