# Presentation: 108217

## 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

- Present

- Past

- Future

- VEPP-2000

- PEP-N

- DAFNE

- VEPP-4M

- BEPC-II

- BEPC

- 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 nonlinearities
- Beam 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 2
- e+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

## 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

## 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!

## 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

## 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-1 | LER:0.95
HER:0.78 |
| PEP-II | 3.3/3.0 | 4.1fb-1 | LER: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...”

- DAFNE
- L = 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-II
- L=3.3x1033 cm-2 sec-1 (design 3.0x1033)
- 4.1 fb-1/month
- Overcoming e- cloud effect with solenoid
- KEK-B
- L=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 Issues
- Orbit drift from thermal effects
- Understanding beams at IP
- Achieving 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 SummaryStuart 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 Design
- Even 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 Rings
- e- cloud mitigation
- RF systems and very heavy beam-loading
- Vacuum system design (no-bake / no bellows low-impedance chambers)
- Limits to bunch length
- Round Beam Collisions
- Potential for higher specific luminosity
- Tests at CESR and VEPP-2000