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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 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 For energy variable extraction, large kicker aperture or movable extraction system is required.(It requires complicated system) Extraction orbit largely changed in energy.
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
EMMA(Electron Model for Many Applications) • Proof of Principle machine of NS-FFAG(especially for NF) • NS-FFAG (FD lattice) • Electron(1020MeV) • Variable energy injection and extraction • 5 years project
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.
Requirement for extraction (injection) scheme • Energy Range : 10MeV~20MeV(variable) (orbit shift: ~11mm(10MeV20MeV) • Beam Emittance: 3000mm·mrad(normalized) (if possible, 6000mm·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.
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
Tracking studies • Tracking code : ZGOUBI(Sacley Group,F.Meot) • Magnet Parameter: From S.Berg • Fringing field : Enge type fall off 2in 2out C0=0.1455, C1=2.2670, C2=-0.6395 C3=1.1558, C4=C5=0.
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
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
Influence of fringing field 10MeV 10MeV in=out=0.5 aperture in=out=0.75 aperture 10MeV 10MeV in=out=1 aperture in=2out= aperture
Configuration of extraction system Tracking with realistic 3D modeling is indispensable in studying the extraction orbit downward of the septum
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
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
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
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
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
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