The Accumulator/Pre-Booster

1
The Accumulator/Pre-Booster

• Bela Erdelyi
• Department of Physics, Northern Illinois
  University,
• and Physics Division, Argonne National Laboratory

2
Acknowledgements

• Joint Work with
• Shashikant Manikonda (ANL)
• Peter Ostroumov (ANL)
• Sumana Abeyratne (NIU student)
• With assistance from JLab staff (Y. Derbenev, Y.
  Zhang, G. Krafft, etc.)

3
ELIC Conceptual Layout
4
Accumulator/Pre-Booster Concept

• Purpose
• Inject from linac
• Accumulate ions
• Accelerate them
• Extract and send to large booster
• Concepts
• Figure-8 shape for ease of spin transport,
  manipulation and preservation
• Modular design, with (quasi)independent module
  design optimization
• FODO arcs for simplicity and ease of
  implementation of optics correction schemes
• No dispersion suppressors
• Matched injection insertion
• Triplet straights for long dispersion-less drifts
  and round beam
• Matching/tuning modules in between

5
Constraints

• Figure-8 shaped circumference 200-300 m
• Maximum bending field 1.5 T
• Maximum quadrupole gradient 20 T/m
• Momentum compaction smaller than 1/25
• Maximum beta functions less than 35 m
• Maximum full beam size less than 2.5 cm, and 1 cm
  vertically in dipoles
• 5m m long dispersion-less sections for RF
  cavities, electron cooling, collimation,
  extraction, and possibly decoupling
• Sizable (normalized) dispersion for/at injection
• Working point chosen such that tune footprint
  does not cross low order resonances (tunability)

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Injection

• Protons (and possibly light ions)
• Stripping injection
• Heavy ions
• Repeated multi-turn injection
• Transverse (horizontal and possibly also
  vertical) and longitudinal painting
• Electron cooling for stacking/accumulation

7
Heavy-Ion Injection and Accumulation
8
Electron Cooling
9
Accumulated Beam

• Intensities needed to achieve design luminosity,
  with some safety factors included for possible
  losses during
• Stripping
• Capturing, re-capturing
• Transfers
• Proton current 1A (6x1012 total particles in
  the ring)
• Heavy-ion current 0.5 A (1x1011 total particles
  in the ring) gt 10 linac pulses of 250 µs
  length (subject to optimization)

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Acceleration

• h1
• RF swing necessary is 0.4,2 MHz
• 4 kV per cavity
• 50kV/turn gt 12-13 cavities
• Synchronous phase -30
• 65000 turns for 200MeV -gt 3 GeV
• 100 ms acceleration time
• Allows acceleration with h2 with the same
  cavities, if needed

11
LEIR-Type Cavities

• Finemet cavities
• 0.5 m long
• 4kV/cavity
• 0.35,5 MHz frequency swing
• Practically no maintenance needed

12
Extraction and stripping

• Conventional single-turn fast extraction
• To minimize heavy-ion loss, strip once in linac
  and once after the pre-booster to maximize fully
  stripped fraction
• Advantages
• Less beam-loss to reach fully stripped state
• Less severe space charge in pre-booster
• Drawback lose some energy gain

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Layout
To Large Booster
ARC 1
Collimation
Electron Cooling
Extraction
Non dispersive section 1
Injection Insertion section
ARC 3
Non dispersive section 2
ARC 2
RF Cavities
Beam from LINAC
Solenoids for Electron Cooling and Decoupling
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Circumference
Total length of the long drifts in the straights
20m
15
Linear Optics
Arc 2
Arc 1
Straight 2
Arc 3
Injection
Straight 1
16
Optical modules
ARC3 FODO
ARC12 FODO
INJECTION INSERT
STRAIGHT TRIPLET
17
Matching/Tuning modules
18
Tunability
19
Main Parameters
Units Value
1 Circumference m 302
2 Angle at crossing deg 44
3 Number of dispersive FODO cells (Type I) 6
4 Number of dispersive FODO cells (Type II) 8
5 Number of triplet cells 18
6 Number of matching cells (2 types) 4
7 Minimum drift length between magnets cm 50
8 Drift length in the injection insertion m 5.0
9 Drift lengths between triplets (for RF, extraction, collimation and electron cooling) m 5.3
10 Beta maximum in X m 33
11 Beta maximum in Y m 36
12 Maximum beam size cm 2.3
12 Maximum vertical beam size in the dipole magnets cm 0.6
13 Maximum dispersion (xdelta_KE) m 3.3
14 Normalized dispersion value at injection insert m½ 2.1
15 Tune in X 7.92
16 Tune in Y 7.24
17 Gamma of particle 4.22
18 Gamma at transition energy 5.6
19 Momentum compaction 3.2E-2
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Magnets
Quantity Parameters Units Value
1 Quadrupole Magnets 113
Length cm 40
Half aperture cm 5
Maximum pole tip field T 1.5
Minimum pole tip field T 0.15
2 Dipole Magnets (Type I) 16
Strength T 1.41
Radius m 9.0
Vertical aperture cm 3.0
Angle deg 11.6
Length m 1.83
3 Dipole Magnets (Type II) 18
Strength T 1.41
Radius m 9.0
Vertical aperture cm 3.0
Angle deg 14.0
Length m 2.19
20
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Beam Parameters at the End of the Pre-Booster
Cycle
Proton Lead
Beam energy GeV 3 1.18
Particles number 1012 6 0.1
Beam Current A 1 0.5
Polarization gt90 (est.) N/A
Energy spread 10-4 ? ?
Bunch length m 63 63
Horizontal acceptance, normalized µm rad 55 28
Vertical acceptance, normalized µm rad 37 12
Laslett tune shift (after injection) 0.071 0.015
22
Pre-Booster Cycle Time

• Assuming 1x1011 lead ions need to be accumulated
• One 250 µs long linac pulse (subject to
  optimization) delivers 0.5 mA
• Assume 50 injection efficiency (CERN
  experience)
• gt 9 linac pulses
• Cooling time estimated to be 130ms
• gt Total time
• 9x 250 µs (injection)
• 9x130 ms (cooling)
• 2x100 ms (acceleration and de-ramping)
• 1.4 s
• Assuming factor of 4 ratio between circumferences
  between pre-booster and large booster, and
  acceleration with -30 gt 16 cycling times needed
  to fill the large booster gt 22s (3s for p)
• Large booster starts with coasting beam

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Summary and Work in Progress

• Design of the accumulator/pre-booster is well
  underway
• Satisfies the constraints while providing
  superior performance
• Fine tuning first order optics
• Space charge simulations limits on current and
  emittance
• Spin tracking, polarization preservation studies
• Dynamic aperture estimation

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BACKUP SLIDES
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Cooling times

• Assuming
• 3 m long cooling section
• 300 mA electron current
• 2.5 cm beam radius
• 5 mrad beam divergence
• 0.004 momentum dispersion
• Cooling for 3 time constants
• Transverse cooling time 130 ms
• Longitudinal cooling time 67 ms
• Cooling electron energies
• _at_ injection 0.55394 MeV, ?2.0840
• _at_ extraction 1.15511 MeV, ?3.2605

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Lead Charge Distributions

• _at_ injection
• Q (0) Q (1) Q (2) Q (3) Q (4)
• 0 4 70 22 3
• _at_ extraction
• Q (0) Q (1)
• 80 20

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Shorter Version (C250m)
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Linear Optics
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Optical Modules
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Main Parameters
Units Value
1 Total length m 254
2 Angle at crossing deg 62
3 Number of dispersive FODO cells (Type I) 6
4 Number of dispersive FODO cells (Type II) 9
5 Number of triplet cells 10
6 Number of matching cells 4
7 Minimum drift length between magnets cm 50
8 Drift lengths in the insertion region m 5.0
9 Drift lengths between triplets (for RF, collimation and electron cooling) m 5.0
10 Beta maximum in X m 19
11 Beta maximum in Y m 34
12 Maximum beam size cm 2.0
12 Maximum beam size in the dipole magnets cm 0.6
13 Maximum Dispersion (xdelta_KE) 2.5
14 Normalized dispersion value at injection (xd_KE)/vß 1.41
15 Tune in X 8.33
16 Tune in Y 7.43
17 Gamma of particle 4.22
18 Gamma at Transition Energy 5.62
19 Momentum compaction factor 0.031
31
Magnets
    Quantity Parameters Units Value
1 Quadrupole Magnet 95      
      Length cm 40
      Half aperture cm 5
      Maximum pole tip field T 1.5
      Minimum pole tip field T 0.16
2 Dipole Magnet (Type I) 6      
      Strength T 1.41
      Radius m 9
      Vertical aperture cm 3
      Angle deg 14
      Length m 2.19
3 Dipole Magnet (Type II) 12      
      Strength T 1.41
      Radius m 9
      Vertical aperture cm 3
      Angle deg 13.17
      Length m 2.06
4 Dipole Magnet (Type III) 18      
      Strength T 1.41
      Radius m 9
      Vertical aperture cm 3
      Angle deg 13.44
      Length m 2.11
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Laslett Tune Shift (protons)

• Beta0.57
• Gamma1.21
• Nt(total)5.36E12
• rc  1.53E-18m
• EN(normalized)BetaGamma9E-6 m.rad
• BF1 (Peak to average current radio)
• laslett_tune_shift-(NtrcBf)/(4piENbetagamma
  2)
• laslett_tune_shift-0.071.

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Laslett Tune Shift (Lead)

• Beta0.37
• Gamma1.08
• Nt(total)4.33E10
• rc  1.53E-18m
• EN(normalized)BetaGamma17.5E-6 m.rad
• BF1 (Peak to average current radio)
• laslett_tune_shift-(NtrcBfQ2)/(4piENMbeta
  gamma2)
• laslett_tune_shift-0.015.