Energy Variable Extraction in NS- FFAG

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Energy Variable Extraction in NS- FFAG

• Takeichiro Yokoi(Oxford Univ.)

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• Accelerators for practical applications
  require to change the extraction energy flexibly.
  
• ?? How about in FFAG ??

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Extraction in Scaling FFAG

• Tune variation constant, beam excursion large
• ? For energy variable extraction, large
  kicker aperture or movable extraction system is
  required.(It requires complicated system)
• Extraction orbit largely changed in
  energy.

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Extraction in Non-Scaling FFAG

• Tune variation large, beam excursion small
• ? Kicker aperture and change of extraction
  orbit are relatively small.(vertical extraction
  is also an option)
• It makes flexible extraction energy
  change possible.
• Large tune variation put restriction to the
  lattice and configuration of kicker system.
• As an example of NS-FFAG case, energy variable
  extraction from EMMA NS-FFAG is shown

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EMMA(Electron Model for Many Applications)

• Proof of Principle machine of NS-FFAG(especially
  for NF)
• NS-FFAG (FD lattice)
• Electron(10?20MeV)
• Variable energy injection
• and extraction
• 5 years project

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Beam extraction in EMMA ring

• In EMMA, to study the beam dynamics of
  non-scaling FFAG and resonance crossing
  acceleration, the injection and extraction energy
  should be varied to arbitrary energy (if
  possible) in the range of 10MeV20MeV.
• To investigate the dynamics in various amplitude,
  it is desirable to inject beam into various
  position in the phase space.

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Requirement for extraction (injection) scheme

• Energy Range 10MeV20MeV(variable)
• (orbit shift 11mm(10MeV?20MeV)
• Beam Emittance 3000?mmmrad(normalized)
• (if possible, 6000?mmmrad for margin)
• Aperture gt45mm(Horizontal and vertical)
• Fast extraction(Kicker Septum)
• Kicker rise time lt20ns(revolution period 55ns)
• The requirements are quite similar in injection
  and extraction ?If possible, the same scheme
  should be adopted.

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Scheme Specifications

• Kicker aperture 45(H) ? 45mm(V)
• window frame type
• Kicker length100mm
• ?Bare inductance 130nH
• Kicker field strength 730gauss/20kV
• (20ns rise time, 150nH
  inductance)
• Direction horizontal, from outside
• Serial straight sections for kicker and
• septum ?Tune variation 0.380.18/cell

20cm
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Tracking studies

• Tracking code ZGOUBI(Sacley Group,F.Meot)
• Magnet Parameter From S.Berg
• Fringing field Enge type fall off

2??in
2??out
C00.1455, C12.2670, C2-0.6395 C31.1558,
C4C50.
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Tracking(without fringing field)
Kicked beam
Physical aperture
Physical aperture
Kicked beam
Circulating beam
Septum can be installed here
Circulating beam
15MeV
10MeV
Kicker Filed 1k gauss (30kV) Beam
Emittance6000pmmmrad(norm.)
Physical aperture
Kicked beam
Observed here
Circulating beam
20MeV
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Tracking(with Fringing field)
Physical aperture
Physical aperture
Ciruclating beam
Kicked beam
Kicked beam
15MeV
10MeV
Ciruclating beam
Kicker field 1kgauss (30kV) Beam
Emittance6000pmmmrad(norm.)
Physical aperture
Non-linnear fringing field causes deformation
of beam shape (deformation has strong amplitude
dependence )
Kicked beam
Ciruclating beam
20MeV
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Influence of fringing field
10MeV
10MeV
?in?out0.5 ? aperture
?in?out0.75 ? aperture
10MeV
10MeV
?in?out1 ? aperture
?in2?out aperture
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Configuration of extraction system
Tracking with realistic 3D modeling is
indispensable in studying the extraction orbit
downward of the septum
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Vertical injection option

• The distance to the boundary of the physical
  aperture is independent of the energy.
• ?kicker spec. might be reduced, and
  deformation of phase space also might be less
  severe compared to horizontal injection
• In EMMA ring, magnet position is varied
• to adjust the lattice. ?Extraction system
• including chamber and duct should take
• into account the shift to avoid geometrical
• interferences.

w/o fringing field
with fringing field
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Tracking study(How is the reality ?)
Kicker Filed 0.3k gauss (9kV) Beam
Emittance6000pmmmrad(norm.)
Circulating beam
Circulating beam
Kicked beam
Kicked beam
15MeV
10MeV
Even with a small kick, the phase space is
strongly deformed by the non-linear fringing field
Circulating beam
Kicked beam
Observed here
20MeV
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Influence of fringing field
15MeV
15MeV
?in?out0.5 ? aperture
?in?out0.375 ? aperture
15MeV
15MeV
?in?out0.62? aperture
?in?out 0.75 ? aperture
Beam is more sensitive to the distribution of
fringing field compared to the case of
horizontal injection
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4D tracking(horizontal extraction)
Initial emittance 6000? mmmrad.(normalized)
Physical aperture
15MeV(H)
20MeV(H)
10MeV(H)
15MeV(V)
10MeV(V)
20MeV(V)
Kicker 1kgauss
Kicker 0.6kgauss
Kicker 0.6kgauss
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4D tracking(horizontal extraction)
Initial emittance 3000? mmmrad.(normalized)
Physical aperture
10MeV(H)
20MeV(H)
15MeV(H)
15MeV(V)
20MeV(V)
10MeV(V)
Kicker 1kgauss
Kicker 0.6kgauss
Kicker 0.6kgauss
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Summary

• For practical applications, energy variable
  extraction is a must.
• For EMMA NS-FFAG, energy variable extraction with
  a moderate kicker specification seems possible.
• Beam shape is very sensitive to the distribution
  of fringing field. ?Realisitic field
  distribution with 3D modeling is crucially
  important.
• Vertical injection option looks unrealistic at
  the moment with the present lattice.
• Influence of fringing field needs detailed
  studies