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Synchronization Issues in MEIC. Andrew Hutton, Slava Derbenev and Yuhong Zhang MEIC Ion Complex Design Mini-Workshop Jan. 27 & 28, 2011. The Problem. Electrons travel at the speed of light Protons and ions are slower There are three areas that need to be addressed

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synchronization issues in meic

Synchronization Issues in MEIC

Andrew Hutton, SlavaDerbenev

and Yuhong Zhang

MEIC Ion Complex Design Mini-Workshop

Jan. 27 & 28, 2011

the problem
The Problem
  • Electrons travel at the speed of light
  • Protons and ions are slower
  • There are three areas that need to be addressed
    • In collider ring  matching electron & ion beams at multiple IPs
    • During acceleration
    • Cooling  matching ion beam and cooling electron beam
  • Assumptions
    • MEIC collider ring circumference is around 1 km
    • Large booster (LEIC) is the same circumference as MEIC
    • Electron ring is the same circumference as MEIC
    • Superconducting RF systems have limited frequency swing
harmonic numbers
Harmonic Numbers
  • Assuming circumference of the MEIC collider ring is about 1 km
  • For an RF frequency of 1497 MHz
    • The best harmonic number is 4860 = 2x2x3x3x3x3x3x5
    • Corresponds to a circumference of 971.98 meter
  • For an RF Frequency of 748.5 MHz
    • The harmonic number is 2430
  • For an RF Frequency of 499 MHz
    • The harmonic number is 1620
orbit differences in meic
Orbit Differences in MEIC
  • MEIC design parameters

Proton energy 20 to 60 GeV Bunch repetition rate 748.5 MHz

Deuteron energy 10 to 30 GeV/uCollider ring circumference ~1000 m

Lead energy 7.9 to 23.8 GeV/u Harmonic number 2500

  • Orbit difference from 1000 m ring @ 60 GeV proton design point

proton 60 GeVdesign point

20 GeV -97.9 cm  2.44 bunch spacing  2 unit of HN

deuteron: 30 GeV/u  -36.7 cm  0.92 bunch spacing  1 unit of HN

10 GeV/u  -429 cm  10.7 bunch spacing  11 unit of HN

Lead: 23.8 GeV/u  -65.7 cm  1.64 bunch spacing  2 unit of HN

7.9 GeV/u  -692cm  17.3 bunch spacing  17 unit of HN

  • MEIC Circulator Cooler

Energy range 4.3 to 32.7 MeVBunch repetition rate 748.5 MHz

γ 8.4 to 63.9 Circulator ring circumference ~ 50 m

β 0.9929 to 0.9999 Harmonic number 125

Orbit difference

cooling [email protected] GeV/u -4.9 cm  0.1 wavelength  no change of HN

cooling [email protected] GeV/u -35 cm  0.86 wavelength  1 unit of HN

harmonic number vs proton energy
Harmonic Number vs. Proton Energy
  • The proton energy that corresponds to a harmonic number of 1 less than the nominal is
    • 43.32 GeV for 1497 MHz
    • 31.77 GeV for 748.5 MHz
    • 25.77 GeV for 499 MHz
  • For 750 MHz, change of harmonic numbers is not a viable solution for the 20 – 60 GeV energy range
    • It is a viable solution at lower energies
two interaction regions
Two Interaction Regions
  • The two Interaction Regions are 180°apart for both beams in the present configuration
    • Arcs are equal and straight sections are equal
      • Offsetting the beam in the Arcs would work
    • Putting two Interaction Regions in a single straight will not work without an additional variable chicane
      • Chicane is complicated in this region
        • Magnet offset ~1 meter for 2 mm path length change
  • MEIC can have up to two interaction regions
    • Must be equidistant in ring
  • There can be one more interaction region in LEIC
change ion ring path length
Change Ion Ring Path Length
  • It is possible to change the path length in the ion ring
    • For one Interaction Point, need +/- 20 cm
    • For two Interaction Points, need +/- 40 cm
  • If path length is created in the arcs
    • 20 cm corresponds to an offset of about ±25 mm
    • 40 cm corresponds to an offset of about ±50 mm
  • Increasing the bore of a 6 Tesla magnet by 30 mm is expensive!
    • 60 mm may be prohibitive
  • Need to mount all the magnets on movers
    • Unpleasant, but possibly affordable
three ring collider proposal
Three Ring Collider Proposal
  • The MEIC ring should be used to cover the higher energies
    • RF frequency will be fixed
    • Electron ring and ion ring will use SRF cavities
    • Ion ring magnets will be on movers to accommodate velocity change
  • The LEIC ring will be used to cover lower energies
    • The LEIC ring will need variable RF frequency
      • Ion ring will require RF cavities that can span a wide frequency range
      • Could be a sub-harmonic of MEIC ring
        • Injected bunch trains would be interleaved using an RF separator
alternate solution change of electron path rf frequency
Alternate Solution: Change of Electron Path & RF Frequency

The scheme does not require change of the ion orbit which is considered far more difficult to realize for SC magnets. It rather varies

  • RF frequency (less than ±10-3)
  • Ion ring harmonic number
  • Electron orbit (less than half wavelength for one IP

and one wavelength for two IPs)

  • Circulator cooler ring circumference (less than half bunch spacing)
slide11

MEIC with 2 IPs (Half Ring Apart)

Harmonic number has to be changed by unit of 2

electron cooling
Electron Cooling
  • Electron cooling requires exact matching of the electron and ion velocities
  • The time between adjacent buckets is 1/frequency
    • Therefore RF frequencies must also be matched
  • In the MEIC ring, if the RF frequency is constant (749.5 MHz) so the same electron cooling system will work at all energies
    • Fixed frequency SRF cavities will work for energy recovery of the electron beam used for cooling
circulator ring circumference
Circulator Ring Circumference
  • The length of the circulator ring will need to be changed to accommodate different electron velocities
    • The maximum change will be 1/hion
    • The circumference change in the circulator ring is heλ/hion
  • Numerical example
    • MEIC is ~900 metres long, hion = 4500
    • Circulator ring is ~20 meters long, he = 100
    • Circulator ring must change circumference by 4.5 mm for a one wavelength change in MEIC circumference
    • This is a radius change of ~0.7 mm
  • This is a small number so it can easily be accommodated within the circulator ring magnet bore
leic electron cooling
LEIC Electron Cooling
  • The RF frequency in the LEIC ion ring has to change
    • The circumference change in the circulator ring can be accommodated within the magnet bore
  • The RF frequency in the electron cooling system has to change
  • The RF frequency of the electron linac must change
    • SRF cavities will not work
  • Electron energy is low
    • Propose no energy recovery for the electron beam
    • Extend the number of turns that the electron beam is in the circulator ring
  • Electron cooling would then be available throughout the acceleration cycle
circulator ring
Circulator Ring
  • Assume racetrack layout as proposed in the ZDR
    • Electron cooling occurs on one straight section
    • Electron beam injected/extracted on opposite straight section
  • Straight sections must have zero dispersion
    • If injected beam is on axis, it will be on axis for cooling
    • Injection orbit is independent of beam energy
  • However, correct longitudinal position is not guaranteed by good injection orbit
    • Requires Arcs to be achromatic, but not isochronous
    • Arc energy setting must lead beam energy during ramp so path length shortens to maintain correct timing
clearing gaps
Clearing Gaps
  • Colliders usually have one (or more) gaps in the bunch train
    • Ion clearing in electron beams
    • Electron cloud clearing in proton or positive ion beams
    • Required for aborting high power beams
  • MEIC will have gaps, probably ~10% of the circumference
    • Will reduce MEIC luminosity by ~10%
      • RF frequencies are the same so gaps are synchronous
  • LEIC will have gaps, also about 10% of the circumference
    • Will reduce LEIC luminosity by at least 20%
      • Gaps are asynchronous
      • Could increase beam-beam effects
        • Needs study
impact of clearing gaps
Impact of Clearing Gaps
  • The clearing gaps impact the RF systems
  • Stored energy in the cavities changes along the bunch train
    • Bunch energy changes along the bunch train
    • Transverse position in regions of non-zero dispersion changes along the bunch train
    • Polarization precession changes along the bunch train
  • Effect minimized with RF systems with high stored energy
    • SRF cavities
    • Copper cavities with storage cavities
      • It is difficult to vary the frequency of both types of cavity
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