WG2 Proton FFAG Summary

1
WG2 (Proton FFAG) Summary

• G.H. Rees

2
Proton Driver Working Group

• Participants
• M. Yashimoto, S. Ohnuma, C.R. Prior, G.H. Rees,
  A.G. Ruggiero
• Topics
• FFAG or RCS proton driver for a Neutrino Factory
• 1 GeV, 10 MW Proton Driver
• 1 kHz H? Linac 1 kHz FFAG, or
• 50 Hz Proton Linac

3
Neutrino Factory Driver
RCS Designs 4 MW, 1 ns rms bunches

• Solutions found for
• H? injection at 180 MeV
• Collimation
• Bunch Compression to 1 ns rms

4
FFAG

• Short straights make difficulties for
• H? injection
• Collimation
• Spallation Neutron Sources favoured
• Linac/compressor ring over FFAG, or
• RCS over FFAG (old, out-of fashion)

5
Possible 50 Hz Neutrino Factory Driver

• 180 MeV H? Linac ? 3 GeV Booster (?2)
• ? 8 GeV FFAG (?1)
• (An 8 GeV FFAG replaces two 8 GeV RCS)
• If practical, would have some advantages
• More rugged
• Able to hold bunches until needed
• But
• May need separate compressor ring.

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10 MW Proton Driver
1 GeV, 1 kHz protons

• Comparison
• Capital cost 20 year operating cost
• Total power levels involved are important, and
• Number of operating staff

7
Comparison of R/T Linacs

• Proton Linac has advantage
• Structure power down by 1/3
• May use fewer, higher peak power klystrons
• Requires no chopper
• Chopper for H? linac is beyond state of art
• So, proton linac has head start over FFAG

8
10 MW, 1 kHz FFAG

• Will foil survive?
• Compare with other designs, for example
• 2.5 MW, 50 Hz (20 ms cooling time)
• ?T1000?C, T 1000 to 2000?C
• (State of art injection system with H? through
  foil and on average 2 later traversals/proton)

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H? Injection

• Needs to be studied very carefully
• State of art injection required
• Programmed H and V bumps
• Three free-edge corner foil
• High power electron collector
• Removal of unstripped beam from ring (Hº)
• To modify his design, A. Ruggiero has begun a
  study of insertions

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H? Injection (continued)

• May be forced to
• Or even
• More compressors to solve foil heating problem
• E.g. 3 rings of 1/3 circumference of FFAG

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FFAG Collimation/Protection

• Acceptable loss over most of ring 500 Watts
• Acceptable loss in dedicated collimators lt 5 kW
• (5 parts in 105, 5 parts in 104)
• Studies at SNS, ORNL suggest
• ?Qlt0.2 for 1 part in 104 loss
• Ruggiero design has ?Qlt0.35 at 200 MeV
• So injection energy 200?400 MeV?

12
Collimation

• No problem in designing collimators for the
  suggested compressor rings
• Insertions may be needed for the FFAG
• Note (also for an RCS)
• Bump magnets needed in the collimation straight
  insertions
• Vertical and horizontal bumpers needed
• Halo surviving to top energy may get lost on
  extraction elements
• Note for FFAG
• Beam lost longitudinally may survive at low
  energy
• ? kick out before next pulse?

13
Collimation

• Resonance crossing may be a problem
• Basic FFAG has high periodicity
• But if insertions are introduced, periodicity is
  reduced
• Major effect probably space charge induced
  coupling at lower energies
• Control of tunes likely to be needed over
  acceleration
• Radiation hard magnets in collimation regions

14
Other Thoughts

• Advisable to guard against e-p instability
• Coating of vacuum chamber
• Effect of shape of vacuum chamber
• Instabilities may be an issue at lower energies
• Effect of stray fields of injection/extraction
  septa and rf cavities

15
Summary

• The possible use of an FFAG in a Neutrino Factory
  Proton Driver has been outlined
• For a 1 GeV, 10 MW proton driver, a detailed cost
  comparison is suggested between the two scenarios
  discussed
• Note In a 25 MW, 1 GeV proton driver study, the
  following were considered
• 1 GeV proton linac, 50 Hz
• Three 8 MW cw cyclotrons
• Two 12.5 MW separated orbit cyclotrons
• It was found that a) was the cheapest option.
• The FFAG option was not considered.