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Energy Variable Extraction in NS- FFAG

Energy Variable Extraction in NS- FFAG. Takeichiro Yokoi(Oxford Univ.). Accelerators for practical applications require to change the extraction energy flexibly.  How about in FFAG ??. Extraction in Scaling FFAG. Tune variation: constant, beam excursion: large

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Energy Variable Extraction in NS- FFAG

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  1. Energy Variable Extraction in NS- FFAG Takeichiro Yokoi(Oxford Univ.)

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

  3. 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.

  4. 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

  5. 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

  6. 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 10MeV~20MeV. • To investigate the dynamics in various amplitude, it is desirable to inject beam into various position in the phase space.

  7. Requirement for extraction (injection) scheme • Energy Range : 10MeV~20MeV(variable) (orbit shift: ~11mm(10MeV20MeV) • Beam Emittance: 3000mm·mrad(normalized) (if possible, 6000mm·mrad for margin) • Aperture :>45mm(Horizontal and vertical) • Fast extraction(Kicker +Septum) • Kicker rise time :<20ns(revolution period: ~55ns) The requirements are quite similar in injection and extraction If possible, the same scheme should be adopted.

  8. Scheme & Specifications • Kicker aperture: 45(H)  45mm(V) :window frame type • Kicker length:100mm 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: 0.38~0.18/cell 20cm

  9. Tracking studies • Tracking code : ZGOUBI(Sacley Group,F.Meot) • Magnet Parameter: From S.Berg • Fringing field : Enge type fall off 2in 2out C0=0.1455, C1=2.2670, C2=-0.6395 C3=1.1558, C4=C5=0.

  10. 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 Emittance:6000πmm·mrad(norm.) Physical aperture Kicked beam Observed here Circulating beam 20MeV

  11. Tracking(with Fringing field) Physical aperture Physical aperture Ciruclating beam Kicked beam Kicked beam 15MeV 10MeV Ciruclating beam Kicker field: 1kgauss (30kV) Beam Emittance:6000πmm·mrad(norm.) Physical aperture Non-linnear fringing field causes deformation of beam shape (deformation has strong amplitude dependence ) Kicked beam Ciruclating beam 20MeV

  12. Influence of fringing field 10MeV 10MeV in=out=0.5  aperture in=out=0.75  aperture 10MeV 10MeV in=out=1  aperture in=2out= aperture

  13. Configuration of extraction system Tracking with realistic 3D modeling is indispensable in studying the extraction orbit downward of the septum

  14. 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

  15. Tracking study(How is the reality ?) Kicker Filed: 0.3k gauss (9kV) Beam Emittance:6000πmm·mrad(norm.) Circulating beam Kicked beam Circulating 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

  16. Influence of fringing field 15MeV 15MeV in=out=0.5  aperture in=out=0.375  aperture 15MeV 15MeV in=out=0.62 aperture in=out= 0.75  aperture Beam is more sensitive to the distribution of fringing field compared to the case of horizontal injection

  17. 4D tracking(horizontal extraction) Initial emittance: 6000 mm·mrad.(normalized) Physical aperture 10MeV(H) 15MeV(H) 20MeV(H) 10MeV(V) 15MeV(V) 20MeV(V) Kicker: 1kgauss Kicker: 0.6kgauss Kicker: 0.6kgauss

  18. 4D tracking(horizontal extraction) Initial emittance: 3000 mm·mrad.(normalized) Physical aperture 10MeV(H) 20MeV(H) 15MeV(H) 15MeV(V) 20MeV(V) 10MeV(V) Kicker: 1kgauss Kicker: 0.6kgauss Kicker: 0.6kgauss

  19. 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

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