S. Guiducci

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 RD 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 dont 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 charge but 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

_at_5GeV, b50m
q0.6mrad or
Kick angle
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 time3.2ns 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. SEYlt1 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