summary of the working group on electron-positron circular colliders (m2)

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)


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, ….


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 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


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


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


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


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


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


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


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


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


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


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


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


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


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.


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



• 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



• 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!



• 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


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


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


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)


“…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


“…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


• “…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:


“…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


“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 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 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 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

summary of the working group on electron-positron circular colliders (m2)

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