WG3b since Snowmass

1
WG3b since Snowmass

• S. Guiducci
• LNF-INF
• On behalf of ILC Working Group WG3b
• GDE meeting
• LNF 7-9 December 05

2
Baseline Configuration recommendation

• Coordination of DR activity started at 1st ILC
  Worksop, KEK, November 2004
• Injector conveners G. Dugan, M. Kuriki, S.
  Guiducci
• Progress was reviewed at the 2nd ILC Workshop at
  Snowmass, in August 2005. We were not ready at
  that time to make any recommendations.
• Final results were reported at the damping rings
  meeting at CERN, November 2005.
• Damping Ring conveners J. Gao, S. Guiducci, A.
  Wolski
• Participants in the meeting agreed
  recommendations on the DR configuration.

3
Baseline Configuration recommendation

• Nearly 50 participants Contributions from more
  than a dozen institutions in all the three
  regions.

D. Alesini (INFN) A. Babayan (YPI) I. Bailey
(CI) K. Bane (SLAC) D. Barber (DESY) Y. Cai
(SLAC) W. Decking (DESY) A. Dragt (UM) G. Dugan
(Cornell) E. Elsen (DESY) L. Emery (ANL) J.
Gao (IHEP) G. Gollin (UIUC) S. Guiducci
(LNF) S. Heifets (SLAC) J. Jones (ASTeC) E.-S.
Kim (POSTECH)
H. S. Kim (CHEP) K. Kubo (KEK) M. Kuriki
(KEK) S. Kuroda (KEK) O. Malyshev (ASTeC) L.
Malysheva (CI) F. Marcellini (LNF) C. Mitchell
(UM) T. Naito (KEK) J. Nelson (SLAC) K. Ohmi
(KEK) Y. Ohnishi (KEK) K. Oide (KEK) T. Okugi
(KEK) M. Palmer (Cornell) M. Pivi (SLAC) P.
Raimondi (LNF)
T. Raubenheimer (SLAC) I. Reichel (LBNL) M.
Ross (SLAC) D. Rubin (Cornell) D. Schulte
(CERN) G. Stupakov (SLAC) A. Tomonori (KEK) J.
Urakawa (KEK) J. Urban (Cornell) M. Venturini
(LBNL) L. Wang (SLAC) R. Wanzenberg (SLAC) A.
Wolski (LBNL) M. Woodley (SLAC) G. Xia
(DESY) A. Xiao (ANL) F. Zimmermann (CERN)
34 participants in the DR meeting at CERN,
November 9-11, 2005
4
Status of the debate
Snowmass - WG3b Summary

• The injection/extraction kickers should be
  strip-line (or similar) devices powered by fast
  pulsers.
• Conventional kicker technology has developed so
  that 17 km or 6 km damping rings are feasible. 3
  km rings may also be possible, but at present
  have higher technical risk.
• It is still important to document thoroughly the
  work that has been done on alternative kicker
  technologies.
• 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)
• Other options need further information and
  debate.
• We have an organized international effort to
  produce the necessary information.
• We have a plan for presenting a well-documented
  recommendation to the GDE.

5
Seven representative lattices were assembled by
end of April 2005

• The goal was to apply analysis tools and
  procedures systematically to each of the seven
  reference lattices.
• An arbitrary naming scheme was chosen to
  promote objectivity.
• We did not set out to choose one of the lattices.
  Our goal was to understand the issues based on
  the results of studies of these reference
  lattices, and use that understanding to make a
  recommendation for a configuration, not a design.

6
DR Configuration Study Task Forces were formed to
co-ordinate activities

• 1 Acceptance Issues
• Y. Cai and Y. Ohnishi
• 2 Vertical Emittance Tuning
• J. Jones and K. Kubo
• 3 Classical Instabilities
• K. Bane, S. Heifets, G. Stupakov
• 4 Space-Charge Effects
• K. Oide and M. Venturini
• 5 Electron-Cloud Effects
• K. Ohmi and M. Pivi
• 6 Fast-Ion Effects
• E.-S. Kim, D. Schulte, F. Zimmermann
• 7 Polarization
• D. Barber
• 8 Kicker Technology
• M. Ross and T. Naito
• 9 Cost Estimates
• S. Guiducci, J. Urakawa and A. Wolski
• 10 Availability

An enormous amount of work was completed in a
little over six months. Results are being written
up far too many results to do justice in a short
presentation. There were close to 50
contributors, with activities co-ordinated by the
Task Force leaders. Most Task Forces carried out
thorough studies of all (or nearly all) reference
lattices. Results were continually cross-checked
between two or more researchers.
7
Configuration studies were concluded in early
November

• Two reports are now in preparation, containing
  the results of the configuration studies and the
  configuration recommendations
• ILC Damping Rings Configuration Recommendation
  Summary Report
• http//www.desy.de/awolski/ILCDR/DRConfigurationS
  tudy_files/DRConfigRecommend.pdf
• Completed.
• ILC Damping Rings Configuration Studies Detailed
  Report
• http//www.desy.de/awolski/ILCDR/DRConfigurationS
  tudy_files/DRConfigRecommendSummary.pdf
• In progress (180 pages).
• Nearly all contributions have been collected.
• Expected completion in early 2006.
• Configuration Recommendation has been presented
  to the GDE Executive Committee by Andy Wolski
  (SLAC, November 17th)
• http//cbp.lbl.gov/people/wolski/Wolski-DRConfigRe
  commend-2.pdf

8
BC recommendation meeting

• CERN, November 9-11,
• Thanks to Gilbert Guignard for hosting the
  meeting at CERN.
• 34 participants
• 21 presentations on the results of the task
  forces were presented. and are available on the
  web
• http//www.desy.de/awolski/ILCDR/CERNDampingRingP
  roceedings.htm
• One afternoon and the following morning were
  devoted to discussions.
• For each configuration item, the participants
  agreed on
• the relevant issues and their significance
• the risks associated with each issue for each of
  the configuration options
• a recommendation for the baseline and
  alternative configurations.

9
Nominal Parameters and performance specifications
10
Circumference and Layout

• The critical choice for the DR was the
  circumference and layout recommendation
• Ill describe the options, the issues and the
  process which led to the recommendations.
• For each issue was attributed a significance for
  the circumference choice (A,B,C) and a risk
  parameter (from 1 to 4).
• Final recommendations came from the discussion,
  not a mathematical formula.

11
Classification of Significance and Risk
12
Circumference optionsfrom TESLA dogbone 17 Km to
6 3 Km
3 or 6 km rings can be built in independent
tunnels dogbone straight sections share linac
tunnel
3 Km
6 Km
Two or more rings can be stacked in a single
tunnel
13
Issues for the circumference choice

• Kickers
• Injection/extraction kickers are more difficult
  in a shorter ring.
• RD programs are proceeding fast, it is expected
  a demonstration for a 6 km circumference.
• Electron cloud effect
• Shorter rings have a closer bunch spacing, which
  greatly enhances the build-up of
• electron cloud. Electron cloud density is
  dominant in the wiggler and in the dipole.
  Electron cloud instability could limit the stored
  current or increase the vertical beam size in the
  positron ring. RD programs on mitigation
  tecniques are in progress at different storage
  rings.
• Acceptance
• Given the high average injected beam power
  injection efficiency has to be 100 for the
  nominal positron distribution. The dogbone
  damping rings have a small acceptance, while the
  nearly circular 6 km ring has the largest
  acceptance.
• Ion effects
• Fast ion instability could limit the current in
  the electron ring. Fill pattern and vacuum
  pressure are more significant than the
  circumference for the severity of the effect.
  Gaps in the fill and very low vacuum levels will
  be necessary to mitigate ion effects.

14
Issues for the circumference choice

• Space charge
• The incoherent space-charge tune shift is
  proportional to the ring circumference. The
  coupling bumps used to reduce this effect in the
  dogbone ring could be some risk for the vertical
  emittance.
• Tunnel layout
• Sharing the linac tunnel reduces the time
  available for commissioning and reduces the
  availability.
• Stray fields in the linac tunnel could adversely
  affect the vertical emittance
• of the extracted beam.
• Cost
• Smaller rings have lower cost. Dogbone shape
  allows tunnel cost saving.

15
Issues for the circumference choice

• Availability (Significance C)
• The larger number of components in a larger ring
  is likely to have an adverse impact on
  reliability.
• Classical collective effects (Significance C)
• Classical collective effects as resistive-wall
  instability, HOM coupled-bunch instabilities,
  microwave instability, and intrabeam scattering
  are of potential concern. Issues such as bunch
  charge, bunch length, momentum compaction,
  beam-pipe diameter etc., are determinant rather
  than the circumference. These effects should be
  manageable in any of the proposed circumference
  options.
• Low-emittance tuning (Significance C)
• Achieving the specified vertical beam emittance
  in the damping rings is important for producing
  luminosity. However, there is an additive
  emittance dilution in all the systems downstream
  of the damping rings. There is little evidence
  that the circumference of the damping ring in
  itself has an impact on the emittance sensitivity
  to misalignments and tuning errors.
• Polarization (Significance C)
• Studies suggest that depolarization should not be
  a major issue in any of the configuration options
  under consideration.

16
Kickers

• The length of the TESLA DR and the idea of the
  dogbone shape (to save tunnel length) were
  originated by the anavailability of ultra fast
  kickers. 17Km were needed to accommodate 3000
  bunches with 20 ns bunch distance.
• Three different type of fast pulsers have been
  tested on a strip line kicker at ATF(KEK). All of
  them have very short rise/fall time (3ns) and
  fulfil nearly all of the requirements for the
  damping ring injection. RD programs are in
  progress in various laboratories both on the
  pulser and on the electromagnetic design of the
  electrode. With the ATF kickers strength, nearly
  10 stripline electrodes are needed to reach the
  required injection/extraction angle. RD programs
  are rapidly proceeding and the task force
  participants are confident that
• - kickers for a 6 Km (i.e. 6 ns bunch spacing)
  are a low risk issue
• - kickers for the 3 Km ring are considered at
  present a high risk.

17
Injection/extraction kickers beam test at ATF
kick angle ?rad
kick angle ?rad
kick timing ns
kick timing ns

• Rise/fall time lt 3ns
• a tail of a few percent extends for 7ns
• RD on the pulser
• Cancellation with two kickers at p

J. Urakawa, for ATF collaboration
18

• General considerations kicker length and pulse
  length

Tf-2L/c4?B/c
Generator pulse shape
ILC
VIN
VT
Lkicker length Trrise time length Tfflat top
length ?Bbunch length TBbunch spacing
Tf
2TB
t
t
Tr
Tr
2L/cTr
2L/cTr
Kicker impulse response (ideal case)
VT
Injected bunch
Stored bunches
2L/c
DA?NE Injection upgrade
VT
t
assuming Tr300ps
2TB
t
VT2.5 MV
19
Design completed
20
Y. Cai
21
Single bunch instability threshold and simulated
electron cloud build-up density
M. Pivi, K. Ohmi, F. Zimmermann, R. Wanzenberg,
L. Wang, T. Raubenheimer, C. Vaccarezza, X. Dong
22
ILC DR Task Force 6 Recommendation Summary

• The instability limit is more likely to be
  exceeded in smaller rings.
• Larger bunch spacing Damping Rings with a larger
  synchrotron tune and/or momentum compaction are
  preferable.
• In order of preference MCH, DAS, TESLA, BRUx2,
  OCSx2, BRU, OCS.
• Its a technical challenge to stably reduce the
  SEY below 1.1-1.2
• Redflag KEKB Annual Report 2005 The electron
  cloud effect still remains the major obstacle to
  a shorter bunch spacing, even with the solenoid
  windings 1.
• If the SEY can be reduced in magnets, the 6 km
  BRU and OCS can be feasible.
• Promising cures as microgrooves and clearing
  electrodes need further RD and full
  demonstration in accelerator.
• Larger wiggler apertures may be helpful to
  reducing the cloud density below threshold in 6km
  rings
• In the short bunch spacing 3 km DR,
  multipactoring arises even at low SEY1,
  developing the highest cloud densities (see
  Snowmass 05 talks) therefore should be discarded
  as possible candidates.

M.Pivi, K. Ohmi, R. Wanzenberg, Zimmermann,
SLAC, Nov 2005
23
Suppressing e- cloud in magnetic field regions

• Microgrooves.
• Groove spacing comparable with e- Larmor
  radius.
• RD status laboratory tests at SLAC very
  successful in magnetic free regions, measured
  reduction to SEY lt 0.7. Building chamber for
  installation in dipole region in PEP-II.
• Clearing electrodes simulations show that likely
  electrodes can suppress electron cloud in
  magnetic field regions, but need further RD and
  studies (Impedance, support ).
• RD at KEKb.
• Photon absorbers to reduce reflectivity

24
Rectangular grooves in BEND SEY
Parameters rectangular groove period 250 um
depth 250 um width 25 um
Simulated secondary yield of a rectangular
grooved surface in a dipole field compared with a
smooth surface (field free reference).
Groove dimensions in wiggler 10-100 um. 1cm wide
stripe with grooves.

• Possible solution need laboratory and
  accelerator tests in dipole field

25
(No Transcript)
26
ACCEPTANCE Dynamic Aperture with Multipole
Errors and Single-Mode Wigglers
MCH
OCS
16 km sz9mm
6 km sz6mm
DAS/PI
TESLA/S-Shape
17 km sz6mm
17 km sz6mm
Y. Cai, Y. Ohnishi, I. Reichel, J. Urban, A.
Wolski
27
Comparison of different wiggler models and
tracking codes
One-mode is an ideal, infinite pole width, wiggler
DA for TESLA DR with CESRc or one-mode wiggler
model
M. Venturini, ILC DR Meeting - CERN 10 Nov 05
28
Topics of Acceptance Study

• Dynamic aperture
• Items to be considered
• Ideal lattice, Multipole errors, Nonlinear
  wigglers, (Machine errors)
• Output
• g2Jy0-g2Jx0 plot, g2Jx0-d0 plot, Tune scan
• Physical aperture
• Aperture of wiggler section
• Frequency map analysis (already reported at
  Snowmass)
• Resonance structures
• Injection efficiency
• Input Positron distribution
• Output Survived particle distribution

29
Risks Associated the Acceptance Studies
Y. Cai

• Lack of margin in acceptance especially for the
  off-momentum particles
• Uncertainty of dynamic aperture in tracking
  compare to measurement, at best 20 agreement at
  SPS
• Wiggler model is the best could be achieved. This
  inexplicitly assumes that we need large aperture
  and super conducting wigglers
• Magnetic errors are also at the best can be
  achieved no room for any mistake
• No misalignments and linear optical errors in the
  simulations yet.
• Margin of acceptance is necessary for an adequate
  efficient collimation system in the damping ring.
• Uncertainty in the actual distribution for the
  positron source

30
Circumference recommendation Ion effects
Mini-gap can reduces the growth rate of FII and
tune-shift up to a factor of 1020 Ion-density
reduction factor (IRF) depends on fill-pattern,
optics and the time during the damping. IRF10
is guaranteed. The growth time with mini-gaps
will be longer than 1 turn. Detail study is under
the way to get a maximum IRF.
L. Wang, T. Raubenheimer, Y. Cai, E.-S. Kim
31
Conclusions - Space charge

• The winner is the OCS lattice medium-size
  circumference (6.1Km), good symmetry properties
• The lattices shorter than 6km have not been
  analyzed in detail but they should be as good or
  better
• The dogbone lattices are more vulnerable to space
  charge (as expected) but they still seem to offer
  patches of usable tunespace
• Choice of working point may get in conflict with
  other requirements
• Risk is higher
• Augmented symmetry helps (S-shaped TESLA DR is
  better than the C-shaped version)
• Coupling bumps come at a cost as they excite new
  resonances and restrict region of usable
  tunespace
• Effectiveness of coupling bumps seems dependent
  on lattice design
• In general, they do not necessarily offer a
  decisive advantage
• Still, installation may be recommended to add
  flexibility

M. Venturini
32
Circumference recommendation Space-charge effects
Vertical (left) and horizontal (right) emittance
growth from tracking MCH (16 km lattice) using
Marylie-Impact. TopParticles/bunch
0 Middle Particles/bunch 21010 Coupling
bumps OFF BottomParticles/bunch
21010 Coupling bumps ON Errors will further
reduceusable area of tune space
K. Oide and M. Venturini
33
Preliminary Cost estimates
A 3 km ring would have rather a lower cost than 6
km or 17 km rings. The additional tunnel in the
6 km rings makes the costs comparable to the 17
km rings. Two 6 km rings in a single tunnel is a
higher cost than a 17 km ring.
34
An example from the Summary Report the
Circumference (4)
The significance of each issue and the risk
associated with each option are based on results
from the configuration studies, which will be
presented in the Detailed Report.
35
Recommendation for the circumference (baseline
configuration)

• Positrons two rings of 6 km circumference in a
  single tunnel.
• Two rings are needed to reduce e-cloud effects
  unless significant progress can be made with
  mitigation techniques.
• Preferred to 17 km due to
• Space-charge effects
• Acceptance
• Tunnel layout (commissioning time, stray fields)
• Electrons one 6 km ring.
• Preferred to 3 km due to
• Larger gaps between minitrains for clearing ions.
  
• Injection and extraction kickers low risk
• Estimated cost for 3x6 km rings is lower than
  2x17 km.

36
Recommendations for the circumference
(alternative configurations)

• 1. If techniques are found that are sufficiently
  effective at suppressing the electron cloud, a
  single 6 km, or possibly smaller, ring can be
  used for the positron damping ring. This will
  save costs.
• 2. If electron cloud mitigation techniques are
  not found that are sufficient for the baseline
  positron ring, then a 17 km ring is a possible
  alternative this would require addressing
  space-charge, acceptance and stray fields issues.
  This will increase costs.

37
Recommendations summarized
38
Energy recommendation

• Options 3.7 GeV, 5 GeV, 6.8 GeV
• Issues

Baseline recommendation 5 Gev Lower energy
increases risk for collective effects, higher
energy makes more difficult to tune for low
emittance
39
Wigglers for ILC DR

• Parameters
• Bpeak 1.6 T
• lw 0.4 m
• Total length 165 m
• Radiated energy 9.3 MeV
• A high quality field is needed to achieve the
  dynamic aperture necessary for good injection
  efficiency
• Physical aperture A large gap is needed to
  achieve the necessary acceptance for the large
  injected positron beam
• a full aperture of at least 32 mm is highly
  desirable for injection efficiency
• a full aperture of at least 46 mm is highly
  desirable to mitigate e-cloud effects

40
Technology Options

• Field requirements have led to 3 suggested
  options
• Hybrid Permanent Magnet Wiggler
• Superferric Wiggler
• Normal Conducting Wiggler
• Design Status
• Hybrid PM based on modified TESLA design
• Basic modified TESLA design (Tischer, etal, TESLA
  2000-20)
• 6 cm wide poles
• Tracking simulations in hand
• Next generation design (see note from Babayan,
  etal)
• New shimming design
• Improved field quality field maps available at
  end of last week
• Field fitting now underway, but no tracking
  studies yet
• Superferric design based on CESR-c wiggler (Rice,
  etal, PAC03, TOAB007)
• Tracking simulations in hand
• No active design for normal conducting option
• Will scale from TESLA (TESLA TDR) and NLC
  (Corlett, etal, LCC-0031) proposed designs

Mark Palmer, ILCDR Meeting - CERN - 11 Nov 05
41
Field Quality

• Significance A
• Primary Issue is Dynamic Aperture
• 3 pole designs in hand
• Superferric with
• DB/B 7.7 x 10-5 _at_ Dx 10 mm (CESR-c)
• Shows acceptable dynamic aperture!
• However, most designs approaching DA limit for
  Dp/p1!
• Modified TESLA design (60 mm pole width)
• DB/B 5.9 x 10-3 _at_ Dx 10 mm (TESLA A)
• Dynamic aperture unacceptable!
• Note that normal conducting designs (as is) are
  in this ballpark
• Shimmed TESLA design (60 mm pole width)
• DB/B 5.5 x 10-4 _at_ Dx 10 mm (TESLA B)
• Detailed field map has just become available
• Field fits and tracking studies not yet available
• Concerned about potential impact on DA near Dp/p
  1

Mark Palmer, ILCDR Meeting - CERN - 11 Nov 05
42
ILC DR Wiggler Technology

• Baseline
• The CESR-c wigglers have demonstrated the basic
  requirements for the ILC damping ring wigglers.
  Designs for a superconducting wiggler for the
  damping rings need to be optimized.
• Alternatives
• Designs with acceptable costs for
  normal-conducting (including power consumption)
  and hybrid wigglers need to be developed, that
  meet specifications for aperture and field
  quality.

43
List of RD

• International Linear Collider Damping Ring
  Research and Development Projects web site
  (Thanks to G. Gollin)
• http//www.hep.uiuc.edu/LCRD/ILCDR.html
• Start discussion to create a global RD plan for
  the Damping Ring
• "Strawperson" list of design and engineering
  tasks
• Table of comments, interests and planned
  activities
• Categories
• Fast Kickers (HV pulsers, stripline kickers)
• Feedback systems
• Wiggler (design, beam dynamics)
• High resolution BPMs
• Fast Ion instability
• Electron cloud (grooved metal surface, clearing
  electrodes)
• Beam dynamics issues
• Beam size monitors (X-SR, ODR, Laser wire)
• Beam Based Alignment RD
• Feedforward system for the stabilisation of the
  extracted
• superconducting RF cavity

44
List of RD

• International Linear Collider Damping Ring
  Research and Development Projects web site
  (Thanks to G. Gollin)
• http//www.hep.uiuc.edu/LCRD/ILCDR.html
• Laboratories, universities and industries
• Diversified Technologies, Inc. (USA), University
  of Illinois (USA), KEK-ATF (Japan), LBNL (USA),
  CERN (EU), Cornell/CESR (USA), SLAC (USA), ANL
  (USA), DESY (EU), INFN-LNF (EU)
• Infrastructures
• ATF (KEK), SPS (CERN), DAFNE (LNF), ALS (BNL),
  PEP-II (SLAC), KEKb, APS (ANL), CESR (Cornell)

45
Final Remarks

• The configuration recommendations presented here
  represent a consensus amongst the participants at
  the CERN damping rings meeting.
• The damping rings community has demonstrated the
  ability for highly collaborative and well
  co-ordinated effort.
• Next step is to continue to work in close
  collaboration to coordinate the required RD
  activity and to prepare the RDR.

46
END
47
Risk associated with electron cloud simulations
(..disclaimer)

• Build-up simulation codes give satisfactory
  agreement with experimental observation in
  existing accelerators.
• Codes benchmarking agreement.
• Single-bunch threshold simulation codes agree
  qualitatively with some observations
  (chromaticity,..). Single-bunch simulation codes
  under development.
• One should take a margin factor when comparing
  build-up and threshold.
• For comparative ILC DR studies, train gaps not
  introduced (yet). Gaps likely reduce cloud
  density by certain extent.
• Cloud space charge 2D limit for wiggler
  simulations.

48
ILC DR Parameters