summary of the working group on electron-positron circular colliders (m2)
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Summary of the Working Group on Electron-Positron Circular Colliders (M2). Stuart Henderson Spallation Neutron Source Convenors: S. Henderson (SNS), K. Oide (KEK), J. Seeman (SLAC). Working Group Participants. - PowerPoint PPT PresentationTRANSCRIPT
Electron-Positron Circular Collider Working Group – S. Henderson
Summary of the Working Group on Electron-Positron Circular Colliders (M2)
Stuart Henderson
Spallation Neutron Source
Convenors: S. Henderson (SNS), K. Oide (KEK), J. Seeman (SLAC)
Electron-Positron Circular Collider Working Group – S. Henderson
Working Group Participants
M. Sullivan, C. Biscari, K. Oide, S. Henderson, M. Tigner, J. Seeman, U. Wienands, S. Ecklund, A. Fisher, D. Sagan, F.J. Decker, R. Assmann, T. Sen, A. Skrinsky, D. Rubin, P. Colestock, J. Norem, Y. Cai, G. Hoffstaetter, A. Burov, H. Yamamoto, M. Sokoloff, A. Bogacz, Y. Derbenev, S.Y. Lee, A. Chao, M. Palmer, J. Rogers, J. Shi, J. Ellison, Y. Ohnishi, M. Liepe, A. Hutton, K. Hubner, ….
Electron-Positron Circular Collider Working Group – S. Henderson
Working Group Charge
1) “…perform a survey of the present status as well as future promises of e+e- circular colliders.”
2) “…emphasis on clear identification of the beam physics and accelerator technology limits…”
3) “…identify new and promising ideas even though they may need additional work.”
4) “…summarize the highest priority research topics…”
Electron-Positron Circular Collider Working Group – S. Henderson
Electron-Positron Collider Landscape
VEPP-2M
PresentPast Future
VEPP-2000
PEP-N
DAFNE
VEPP-4M
BEPC-IIBEPC
KEK-B Super-KEK-B
PEP-II 1035 PEP-II Super-B-Factory
CESR CESR-C
LEP VLLC
VEPP-5
Electron-Positron Circular Collider Working Group – S. Henderson
PEP-II Status
Performance Issues:• e- cloud Instability (e+ LER)
Effects: e+ beam blowup with I
rapid pressure with I
increase along train
lum reduction along train
Mitigation:TiN coated vac chamber
wind solenoids (800m)
tailor bunch pattern
• HOM heating in Vertex beampipe
• Orbit/Dispersion/Coupling
Achieved/Design
L(1033/cm2/s) 3.3 / 3.0
L/day (pb-1) 220 /135
L/month (fb-
1)4.1 / 3.3
IHER (A) 0.88/0.75
ILER (A) 1.55/2.14
Nbunch 692/1658
.03-.05/.03
y* (cm) 1.3/1.5
Electron-Positron Circular Collider Working Group – S. Henderson
PEP-II Plans
• 2x1034: More RF, more solenoids (ECI), optimize working point, improved IP chambers, better feedback kickers
• 1x1035: More RF, IR upgrade: reduced *, l
with IR quad modifications, crossing-angle, vac chamber upgrades for HOM reduction.
Lum When Nbunch IHER/ILER *,l
3x1033 Now 692 0.9/1.5 1.25 0.03-0.05
2x1034 2006 1658 1.4/4.0 0.7 0.07
1x1035 2010? 1658 2.0/7.4 0.45 0.10
Electron-Positron Circular Collider Working Group – S. Henderson
KEK-B Status
Performance Issues:• ECI: 1300m of solenoid• Operating point at
CESR tunes (qh=0.51, qv=0.58)
• Good beta/coupling correction
• Movable masks heating from HOM
• Heating of IR chambers
Achieved/Design
L(1033/cm2/s) 4.5 / 10.0
L/day (pb-1) 224
L/month (fb-
1)4.7
IHER (A) 0.78/1.1
ILER (A) 0.95/2.6
Nbunch 1153/5000
0.03-0.05 /0.05
y* (cm) 0.65/1.0
Electron-Positron Circular Collider Working Group – S. Henderson
KEK-B Plans
• 1x1034: more solenoids, 2 bunch e+ injection, IR vac chamber replacement, param search
• 1x1035: Super KEK-B: Exchange e+/e-, upgrade injector, antechamber vac system, SR absorbers, Crab cavity, More RF, HOM Dampers
Lum When? Nbunch IHER/ILER *,l
4.5x1033 Now 1153 0.78/0.95 0.65 0.03-0.05
1x1035 2007 5120 3.0/10.0 0.30 0.05
Electron-Positron Circular Collider Working Group – S. Henderson
CESR Status
Performance Issues:• CESR operated in “Factory
Mode” since Nov. 2000– Injection improvements– Shortened run length– “Pedal to the Metal”
• Continue to push the limits of single-ring collider approach
• Beam-beam tuneshift increased x2 in 9 yrs
• Confronting Long-range parasitic B-B effects
Vertical separation at IP
Differential H, V tunes
L(1033/cm2/s) 1.3
L/day (pb-1) 73
L/month (fb-
1)1.5
ITot (A) 0.75
Nbunch/beam 45
0.07
y* (cm) 2.0
Electron-Positron Circular Collider Working Group – S. Henderson
CESR Plans: CESR-C
• Extend operating range of CESR to 1.55 < E < 5.6 GeV with damping wigglers
• Luminosity scaling:– Assume limiting Ib E– Assume v 1/1/3
• Issues:Reduced *:
Superconducting Quad IR installation in progress
Combat parasitic beam-beam with bunch-by-bunch orbit and tune adjustments
Wiggler nonlinearitiesBeam stability, lifetimes and
backgrounds look fine.
E (GeV) 5.3 1.88
v*(cm) 2.1 1.0
Ib (mA) 8.5 3.0
x,y (ms) 23 50
v 0.07 0.055
Nbunch 9x5 9x5
L (1032
/cm2/s)
13.0 2.7
Electron-Positron Circular Collider Working Group – S. Henderson
DAFNE Status and Plans
Performance Issues:• Strong Solenoid Coupling
(40 rotation) achieved 0.2% coupling (1% design)
• Nonlinearities in wigglers, sextupoles, correctors
• Touschek limits lifetime: top-up operation
• 2nd IR -> chromaticity – strong sextupoles
• Plans: reduce coupling, detune 2nd IP, working point, octupole compensation, work up current
Achieved/Design
L(1032/cm2/s) 0.32 /1-5
L/day (pb-1) 1.5
L/month (pb-1) 20
I+ (A) 1.0/1-5
I- (A) 1.0/1-5
Nbunch 50/120
0.018/0.04
y* (cm) 4.5/4.5
Electron-Positron Circular Collider Working Group – S. Henderson
Recent Successes
Think about what has been accomplished!• > 1 Amp beams can be stored• Bunch-by-bunch transverse and longitudinal
feedback controls coupled-bunch instabilities• RF systems can handle large beam-loading• Asymmetric energy collisions work (energy
transparency requirement is weak)• Higher than expected beam-beam tuneshifts• Detectors can handle beam backgrounds• Large crossing-angles are OK• PEP-II has reached design luminosity, KEK-B within
a factor of 2e+e- colliders can reach design luminosity in a
reasonable time in the original machine configuration
Electron-Positron Circular Collider Working Group – S. Henderson
BINP Plans
• VEPP-4M: in operation at (1-6 GeV)– Expect L=2x1031 at 5 GeV (higher with
more wigglers)– Present operation at +-
• VEPP-2000: (replacing VEPP-2M) is being constructed at BINP.– Ecm = 1-2 GeV, Lum = 1032 /cm2/s – High from round colliding beams.
• VEPP-5: tau/charm collider – L = 1034/cm2/s with round beams– Injector complex is constructed
Electron-Positron Circular Collider Working Group – S. Henderson
PEP-N Collider
• Collide PEP-II e+ LER with100-800 MeV e-:– Linac– Storage ring– Linac with energy-recovery
• Ecm= 1-3 GeV.
• Beam-beam tuneshift low so that LER unaffected
• L = 2x1031 /cm2/s at E= 800 MeV.• IR Separation with large dipole field at IP
Electron-Positron Circular Collider Working Group – S. Henderson
e+e- Collider in the VLHC Tunnel
• Outfit VLHC tunnel with 90<ECM<400 GeV e+e- collider
• Conservative extrapolation of LEP technology
• Use Nb/Cu LEP cavities• Considering Z-factory
injector for VLLC• Many issues:
TMCI at injection
Arcs (one or two rings)
Achievable polarization
Low field
Cost
E (GeV) 185
C (km) 233
L (/cm2/s) 1033
*(cm) 5.0
v 0.1
B185/B45 (G) 240/57
SR Power 100 MW
RF Volts 4.6 GV
Nbunch 126
Ibeam (mA) 12.6
Electron-Positron Circular Collider Working Group – S. Henderson
1036 Super-B-Factory
• J. Seeman has put forth parameters for a 1036 Super-B-Factory
• Beyond the upgrade path of existing B-factories.
• A new machine based on new technologies is required.
• Every parameter pushed to limit: many accelerator physics and technology issues (more later)
• Great launching point!
E+/E- (GeV) 9.0/3.1
I+/I- (A) 6.2/18
Nbunch 5600
cross (mrad) +/- 4.5
0.11
Lifetime 4 min
y* (cm) 0.12
Mom comp. 9x10-5
Electron-Positron Circular Collider Working Group – S. Henderson
R&D Issues for Operating Colliders
• All machines struggling with– Coupling correction (solenoid compensation)– Bunch-by-bunch effects (orbit, tunes, beamsize)– Day-to-day and hour-to-hour drifts in
orbit/coupling/dispersion that affect luminosity• Need real-time monitoring/correction of fundamental
optics parameters: • Our diagnostics and corrections are not up to the task!• Getting a handle on these effects will allow true factory
operation, and free up much needed personpower.
Electron-Positron Circular Collider Working Group – S. Henderson
R&D for Future Machines
• Increasing I: Present 1.5 A to 20A
– What does the vacuum system look like?
Requires low-impedance welded no-bellows chambers (need to keep temp constant)
Can the SR power be brought outside? (natural for VLLC)
Chamber materials and SR absorber geometries
– RF systems: Large RF plants, higher impedance and instability growth rates, very high beam loading
– Feedback systems: Does scale-up of existing systems work? Need higher-power and bandwidth and lower impedance transducers
– Machine Protection
– Combat ECI – solenoids are partial cure – other cures needed
),()1( *
* zyy
y FrI
L
Electron-Positron Circular Collider Working Group – S. Henderson
R&D for Future Machines
• Reducing * – Stronger quads closer to IP (CESR:40cm)– IR Chromaticity k stronger sext dynamic
aperture– Bunch length must follow to avoid hourglass:
• Increase RF voltage• Low-momentum compaction optics (need real tests of
low- optics in a colliding beam machine)• Short-bunch limitations (Ohmic heating of vac chamber,
Coherent SR). Looks ok at 2mm, bunch lengthening?• Intrabeam scattering?• HOM loss in RF, feedback kickers, crotches
Electron-Positron Circular Collider Working Group – S. Henderson
R&D for Future Machines
• Increase beam-beam tuneshift parameter– We don’t understand what sets limits:– Experience at CESR shows “clean-living” and active
parameter exploration increased v x2 in 9 years– Experience at LEP shows strong dependence on
damping– Can the B-B tunespread be tailored favorably with
beam-beam compensation methods?– Round Beam collisions at CESR demonstrated v =
0.09. Can we harness for real luminosity production? Important tests at CESR and VEPP-2000
– We seem to be entering a new era in strong-strong B-B simulations. We have the opportunity to learn!
Electron-Positron Circular Collider Working Group – S. Henderson
R&D for Future Machines
• Interaction Region Issues– Separation Issues: crossing-angles, parasitic
crossings– Real Estate: Quads closer to IP, smaller vertex
beampipes– Detector backgrounds: (lost-particle and SR,
injection, luminosity) Detector technology must develop to handle radiation levels and occupancy
– Impact of short beam lifetime and continuous injection on detector
– Can SR from round beams be shielded?– Heating, HOM (Be beampipe ok). We need
reliable HOM calculational tools
Electron-Positron Circular Collider Working Group – S. Henderson
Summary and Outlook
• Tremendous progress has been made in e+e- collider design, engineering and performance in recent years
• Luminosity is being delivered at unprecedented rates
• The demonstrated success of e+e- factories gives confidence that higher luminosities can be achieved over a wide range in energies.
• Much R&D to be done ranging from engineering for high power deposition to fundamental beam dynamics to computational physics
Electron-Positron Circular Collider Working Group – S. Henderson
Performance of the Factories
Collider
Peak L Achieved/
Design
Integrated Luminosity/month
Beam Current Achieved/Design
KEK-B 4.49/10.0 4.7fb-1LER:0.95
HER:0.78
PEP-II 3.3/3.0 4.1fb-1LER:1.55/2.1
HER:0.82/0.75
CESR 1.3 1.5fb-1 0.75A
DAFNE 3.2x1031/10 20pb-1 1.0 + 1.0
Electron-Positron Circular Collider Working Group – S. Henderson
Outline• WG Charge (1)• E+e- collider landscape (1)• Status of the operating e+e- colliders (11)
– PEP-II (status and upgrades) (2)• Status (Lum, I, Optics…)• Performance Issues (e- cloud, lum vs. bunch…)• Upgrade plans (10^35 upgrade plan)
– KEK-B (status and upgrades; super KEK-B) (2)– CESR (status and upgrades) (2)– DAFNE (status) (2)– BEPC (status and upgrades) (…2…)– VEPP-2M and VEPP-4– LEP– Summary of Present Status (1)
• Perspective/Outlook (1)• New Machines (4)
– Upgrades– VEPP-2000, PEP-N– Super-B-factory– VLLC
• Electron-Positron Collider Issues and Research (4)– IR Issues– Beam-beam interaction– Very high current beams– Fundamental accelerator physics problems
• Perspective and Summary (1)
Electron-Positron Circular Collider Working Group – S. Henderson
“…perform a survey of the present status…”
• DAFNEL = 3.2x1031 cm-2 sec-1 (design 1x1032) Progress in understanding coupling/solenoid compensation
and non-linearities• CESR
L=1.3x1033 cm-2 sec-1
Pushing limit of single-ring collider with 45 bunches/beam. Confronting limitations of parasitic beam-beam
• PEP-IIL=3.3x1033 cm-2 sec-1 (design 3.0x1033)4.1 fb-1/monthOvercoming e- cloud effect with solenoid
• KEK-BL=4.4x1033 cm-2 sec-1 (design 1.0x1034)Higher currents, more solenoids for e- cloud, working point
Electron-Positron Circular Collider Working Group – S. Henderson
“…vision of the future promises of e+e-
colliders…”• Upgrades of existing facilities:KEK-B:
PEP-II:
CESR:(BEPC – not represented)
• New Machines:PEP-N:
VLLC:
VEPP-2000:
1036 B-factory
Electron-Positron Circular Collider Working Group – S. Henderson
• “…perform a survey of the present status…..”• New factories are performing very well.• Rapid turn-on and luminosity ramp-up sets a
new standard in performance• 2: “….the vision of the future promises….”• Upgrade paths for PEP-II and KEK-B are
relatively straightforward:– Higher Current
• CESR-B:• PEP-N:• VLLC:• VEPP-2000:
Electron-Positron Circular Collider Working Group – S. Henderson
“…identification of beam physics and technology limits…”
• Single-ring Colliders: Destructive parasitic beam-beam effects
• Two-ring colliders:E- cloud mitigation
• All colliders:Solenoid compensation and coupling in e+e- colliders
(diagnostics and understanding)Lacking diagnostics: Operational IssuesOrbit drift from thermal effectsUnderstanding beams at IPAchieving design lattice..IR issues at high-current rings: Detector interface, SR and HOM heating, beam
separation, strong quads near IP
Electron-Positron Circular Collider Working Group – S. Henderson
“Identify new and promising ideas”
• Round beams (not new but promising)
Important tests at VEPP-2000 and CESR are forthcoming
• High-current storage ring design:
No weld - no bellows chambers to minimize impedance
Absorb SR power outside vac chamber (natural for VLLC, thin windows required for B-factory)
• Very short bunches (1-2mm)
Need to understand limits from vacuum chamber, Coherent SR, bunch lengthening effects
• Short lifetime, continuous filling operation of a collider
Electron-Positron Circular Collider Working Group – S. Henderson
Electron-Positron Circular Collider Working Group SummaryStuart Henderson
Spallation Neutron Source• Where we are:
– Can store 1A currents– Can provide beam stability in 3 d.o.f. with feedback
systems– Can compensate large beam-loading– Can achieve high tuneshift parameters 0.06-0.07at B-
factory energies– Can bring two high-current beams into collision with
acceptable backgrounds– Can achieve L > 4x1033 cm-2 sec-1 and 4.7 fb-1/month
• Rapid turn-on and luminosity ramp-up of PEP-II and KEK-B demonstrates that design luminosities can be achieved!
• This marks a new era in e+e- collider performance!
Electron-Positron Circular Collider Working Group – S. Henderson
Electron-Positron Circular Colliders – Where We’re
Going• Machines under consideration range in energy from 1
< s < 400 GeV with luminosities up to 1036 cm-2 sec-1 • Upgrades:
– Plans are forming for PEP-II and KEK-B to reach L = 1035 cm-2 sec-1 (Aggressive but achievable)
– Plans to extend CESR energy range with wigglers to cover 1.5 < E < 5.6 GeV
• New machines:– VLLC (Z-factory, ttbar)– PEP-N (1-3 GeV)– VEPP-2000 (1-2 GeV)– Super-B-factory with L = 1036 cm-2sec-1 and 20A +
5A
Electron-Positron Circular Collider Working Group – S. Henderson
Electron-Positron Circular Colliders -
How do we get there?A Sampling of R&D issues under discussion:
Interaction Region DesignEven higher currents (backgrounds, SR and HOM power)
Smaller V* (Superconducting Quads inside detector, IR
chromaticity)Beam separation (closely spaced bunches)Smaller beampipes
High-Current Storage Ringse- cloud mitigationRF systems and very heavy beam-loadingVacuum system design (no-bake / no bellows low-impedance
chambers)Limits to bunch length
Round Beam CollisionsPotential for higher specific luminosityTests at CESR and VEPP-2000