First Thoughts on IDS

1
First Thoughts on IDS

• G H Rees, RAL

2
Topics

• Two-way, µ injection chicane for the dog-bone
  RLA.
• Injection energy efficiency for a first
  dog-bone RLA.
• 3. Injection and extraction efficiency for an
  FFAG.

3
Evolution of NF Muon Acceleration

• Linac Energy RLA stages
  FFAG stages
• 3.0 GeV 2 Racetracks
  None
• (3-11 11-50 GeV)
• 1.5 GeV 1 Dog-bone (chicane) 2
  (5-10 10-20 GeV)
• 0.9 GeV 2 Dog-bones (chicane) 1
  (12.5 to 25 GeV)
• Q. How does 2-way chicane allow such a low
  injection energy?

4
Two-way, µ injection chicane

• .

µ D
l
µ µ
?1 5?/8
?
1.5 GeV 0.9 GeV
µ
5
Approximate Data for a Two-way Chicane

• Dipoles 2/3 m, sepns 2 m, ß 4 m, en 30
  mm, ? 7
• D (µ deflection shown) 2 tan ? 2 (1- cos
  ?)/3?
• 2 tan ?1 (1- cos ?1)/?1 1.8vße 2?(tan ?
  tan ?1 ?/3) l
• Central, two-way dipole (B) cannot be a septum
  magnet.
• Solutions then require D gt 4 m, ? gt 60 and B gt
  11 T.
• Practical solutions dont seem possible for the 6
  m chicane, nor
• for a longer chicane, with an added septum and x
  2 µ cooling.

6
Consequences of not using a Chicane

• 1. Injection of µ into upstream end of the
  RLA straight
• 2. A higher energy injector is required for
  the first RLA
• 3. There is a half-turn gain of acceleration
  in the RLA
• 4. Different µ injection and µ transfer
  lines required
• Reassessment of pros cons of dog-bones
  racetracks
• 6. There is no longer a base line NF design

7
Pros cons of dog-bones racetracks

• 5-pass Dog-bone RLA 4½-turn
  Racetrack RLA
• 2 x 2 droplets (4 x 360-420) 2 x 4 arcs
  (8 x 180)
• 1 long linac, energy E 2
  short linacs, energy E/2
• total energy gain 5 E total
  energy gain 4.5 E
• sepn 2E in arcs/spreaders sepn E
  in arcs/spreaders
• same µ beam focusing
  different µ beam focusing
• crossing of droplet orbits no
  crossing of orbits
• On balance, the dog-bone RLA is still the
  favoured choice

8
Energy Range of Revised Dog-bone RLAs

• An earlier, 3½ pass dog-bone RLA had energies 1½
  to 5 GeV.
• The first, full energy pass through linac was
  from 2 to 3 GeV.
• So, assume a first full energy linac pass from 2
  to 3 GeV
• and four further linac passes of 1 GeV to reach 7
  GeV.
• There are then many options, eg, RLA RLA, 2RLA
  FFAG
• A five pass, RLA with 3.6 GeV per pass could
  reach 25 GeV.
• Fast ejection (as in racetrack) prob. not needed
  for dog-bone.
• Q. If 50 GeV needs 2 RLAs, why does 25 GeV need 3
  accels?

9
Injection Energy for the First RLA

• Choice of the energy depends on the µ injection
  efficiency.
• Carol Johnstone required a racetrack at 3 GeV for
  en 15 mm.
• Chicane design assumes dog-bone at 0.9 GeV for en
  30 mm.
• No-chicane, dog-bone, ?f-s req. is 2.0 GeV for
  en 30 mm.
• No-chicane, dog-bone, efficient injection req.
  may be gt 2 GeV
• Spreader injection involves 3 (5) orbits for
  dogbone (racetrack).
• Spreader injection study is needed to decide
  injection energy.

10
Further Evolution of µ Acceleration?

• Linac Energy RLA stages
  FFAG stages
• 3.0 GeV 2 Racetrack
  None
• (3-11 11-50 GeV)
• 1.5 GeV 1 Dog-bone (chic) 2
  (5-10 10-20 GeV)
• 0.9 GeV 2 Dog-bones (chic) 1
  (12.5 to 25 GeV)
• 2.25 GeV? 2 Dog-bones (no chic)
  None, or
• (2.25-7 7-25 GeV)
  1 (25 to 50 GeV)

11
Injection Extraction for FFAGs

• Kicker-septum systems pulsed power scales
  approx. as (en)2.
• Kickers only pulsed power is F (en , w (cryostat
  dimension))
• and the extraction is more
  difficult than injection.
• At 25 GeV a 1.46 m, 1 T septum unit bends the
  beam by 1
• and displaces it lt w
  (septum, shield vac. wall).
• So, there is no advantage in
  such a septum unit.
• Decay ring 20 GeV, ?k 6.47 mr, 24 m kicker,
  44 m straights,
• 7, shorted, 3m, 10 O delay
  line, push pull K with
• 14 x (50 kV PFN, 5 kA pulsers
  10 O feeders)/ring
• FFAG ring 25 GeV, ?k 30 mr, 1.2 m kicker, B
  field x100

12
FFAG Injection and Extraction.

• Pulsed powers for kickers 20 x that of state of
  the art kickers.
• Deflecting fields in kickers 40 x that of state
  of the art kickers.
• Induction linac modulators are able to produce
  the pulse power,
• when driving cavities with toroidal B fields,
  longitudinal E fields.
• Different drive arrangements allow different
  impedance levels.
• Short, transverse deflection kickers do not have
  many options
• push-pull, 1-turn windings, each with a low Z,
  matched feeder.
• Difficult to transform from the low Z and the
  very high current.
• To see if such short kickers are feasible, R and
  D is needed
• in collaboration with an experienced, induction
  linac group.

13
Injection Extraction Efficiency

• Most, existing fast injection and extraction
  systems use
• zero dispersion straight sections, linear
  focusing regions,
• low beam emittances and a low beam momentum
  spread.
• None of these conditions apply to the 12.5-25 GeV
  FFAG.
• Linear, n-sc, FFAGs now consider adding sextupole
  comps.
• Special wide aperture magnets are needed for
  inj(ej) channels.
• Study needed of effect on in(out)put matching and
  efficiencies.
• Racetrack RLAs needed fast extraction, but not
  fast injection.
• Hopefully, the dog-bone RLAs will not need any
  fast system.

14
Summary

• A 2-way, 0.9 GeV injection chicane may not be
  feasible, so
• injection at 2 GeV may be needed for a
  first dog-bone RLA
• A possible, µ acceleration scenario could then
  consist of
• 5-pass, dog-bone RLAs at 2.25 to 7 GeV and 7
  to 25 GeV
• This would defer choice between a dog-bone and an
  FFAG
• accelerator to the higher energy range from
  25 to 50 GeV
• A 3 orbit, reverse beam spreader design is needed
  for dog-bone RLAs, and estimates made of the
  injection efficiencies