4 MW, 50 Hz, 10 GeV, 1 ns rms, FFAG Proton Driver Study

1
4 MW, 50 Hz, 10 GeV, 1 ns (rms), FFAG Proton
Driver Study

• G H Rees, RAL

2
4 MW Proton Driver Arrangement

• Muon yields optimal for 6 - 10 GeV (S Brooks)
• Choose 10 GeV, 50 Hz to ease target shocks
• Choose 3 GeV booster for a 3 10 GeV FFAG
• Choose between 1, 50 Hz or 2, 25 Hz boosters
• Choose 0.18 GeV H? linac for low bunch areas
• Choose 5 bunches at h 5 for RCS booster(s)
• Transfer all 5 (1013 protons/bunch) to the FFAG
• Compress adiabatically (h 30 180, R 2Rb)

3
Longitudinal bunch area

• A, the longitudinal bunch area (in eV sec),
• (8Ra/(ch))((2 V(I-?sc)Eo?)/(h??))½
• For a small longitudinal bunch area, choose
• a low value of injection energy and ring radius
• Choose Eo (? - 1) 0.18 GeV and R ? 50.0 m
• Choose the bunch harmonic number (h) 5
• Compressed bunch area needed ? 0.66 eV sec

4
4 MW, Proton Driver Layout
0.18 GeV H ? Linac
0.18 GeV H ? Achromat
3 GeV, 50 Hz, h 5, RCS (1 at 50 Hz, or 2 at 25
Hz)
10 GeV, 50 Hz, N 5, FFAG with 1013 protons per
bunch
5
FFAG Design Criteria

• For compression of the 5 bunches at 10 GeV
• Design for a gamma-t value at 10 GeV ? 18.5
• Design for longitudinal bunch areas ? 0.66 eV s
• Adiabatic acceleration comp. with h 30, 180
• Design the FFAG ring with lattice insertions, to
• ease injection, ejection beam loss collection
• Use two insertions to allow most flexibility, eg
• 21 normal and 13 insertion cells per insertion

6
Lattice Cell Options

• Normal cell Insertion cell
  Magnet types
• Doublet D D1 T0 D2
  2 7
• Triplet T T1 T2 T1
  2 4
• Pumplet P1 P2
  3 3
• Easiest solution is to match the two, pumplet
  cells
• P1 has a smaller ß-range than either D or T
• The insertion has only one type of cell, P2
• P2 has the smallest closed orbit lever arm
• Dispersion suppressors (2?) are not included in
• the insertions as too many of them are needed

7
10 GeV, Normal Insertion Cell Layouts

• bd(-) BF() BD ()
  BF() bd(-)
• O 0.5 0.5
  0.5 0.5 O
  
• 0.45 1.0 1.6
  1.0 0.45
• 0.77 Normal cell (5.294º,
  8.037 m) 0.77
• 2.25 Insertion cell (5.294º,
  11.0 m) 2.25
• There are two superperiods of 21 normal 13
  insertion cells
• Betatron tunes at 10 GeV are 19.2 (Qh)
  and 13.7 (Qv)
• Ring circumference 2? (99.24125)
  m

8
FFAG Lattice Design

• Use the five-unit cell of the isochronous, muon
  ring
• Arrange matching for a normal and insertion
  cell
• Arrange integer, insertion tunes eg Qh 4 Qv
  3
• The normal cells in an insertion are then matched
• Seek unchanged closed orbits on adding insertions
• by varying the normal cell field gradients and
  tunes
• Then, dispersion match is almost exact for
  insertions
• Small ripple remains in ßh and ßv (max) in
  insertions

9
Study Progress

• Orbits evaluated at 10.0, 9.6, 9.2 and 8.8 GeV
• Satisfactory matching found at these energies
• P- driver bends bd BF BD - 0.23 1.0
  0.23
• (Muon ring bends bd BF BD - 1.0 1.0
  1.0)
• Dispersion match requires lower Qh in normal
  cells
• Qh 19.2, 19.16,19.08 at 10.0, 9.6,8.8 GeV
• Next, switch integer tunes from the insertion to
  the
• normal cells so tunes may be raised again to 19.2

10
10 GeV FFAG versus RCS

• Required is one FFAG ring, but two RCS(s)
• Operation is allowed at 50 Hz instead of 25 Hz
• with 5 1013 ppp at target, instead of 1014 ppp
• Shock per pulse on the target is thus halved
• FFAG allows acceleration over more of cycle
• FFAG is more flexible for holding of bunches
• FFAG has a more rugged vacuum chamber
• FFAG does not need ac magnet power supply