EMMA: Pulsed magnets
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DESCRIPTIONEMMA: Pulsed magnets. Kiril Marinov MaRS group, ASTeC, Daresbury Laboratory. 1. 2. Outline. Septum magnet Geometry and positioning Modelling Stray fields Field quality Kicker Delay-line vs. inductive design Modelling. 3. Septum formulation of the problem. - PowerPoint PPT Presentation
EMMA: Pulsed magnetsKiril Marinov
MaRS group, ASTeC, Daresbury Laboratory1
2. OutlineSeptum magnet Geometry and positioningModellingStray fieldsField qualityKickerDelay-line vs. inductive design Modelling
3. Septum formulation of the problemMovable septum, translation in one direction + rotationVacuum vessel geometry is fixedLarge bending angle 70o extraction , 65o injectionLimited space available (w=10 cm)The available space needs to be used efficiently.Positioning and geometry need to be carefully optimized.
4. Septum geometrywaDetermine optimum values for w and a based on real injection/extraction data.Magnetic steelCoilEddy-current screen
5. Geometry IISimple shape: coaxial arcs and linesRotation center
6. Hard edge model
7. Thick septum with a small apertureIncoming beam parallel to the polygon side 17.14 mm away; w=102 mm, a=35mm cAdvantage: Smaller field (current): smaller stray field Disadvantages Negative rotation anglePoor beam clearance C=2.5 mmSeptum wall and wing too close to the vacuum vessel
8. Thick septum with large apertureIncoming beam parallel to the polygon side 17.14 mm away; w=102 mm, a=70 mm Improved clearance C15 mm cNegative rotation angle, bigger in absolute value;Septum wall and wing too close to the vacuum vesselLarger pole area requires higher voltage;Using the largest possible magnet that still fits in the box is not the solution.
9. Thin septum will small apertureIncoming beam parallel to the polygon side 17.14 mm away; w=80mm, a=35mm Positive rotation angle cGood beam clearance C>15 mm Longer wing can be used. Requires stronger field (current); stronger stray fieldAdvantages: Disadvantage
10. Vertical positionThe same incoming beam requires different horizontal position, rotation and magnetic field, depending on the septum vertical position.
- 11. Results200 injection/extraction scenarios considered for consistence with the septum geometry.Both phase-space painting and closed orbits modes of operationBmax=0.85 T0
12. Coil position
13. Coil position II
14. Field qualityt=10 st=12.5 st=15 st=17.5 s
15. Eddy currents distributionEddy currents Little or no current here
16. Eddy currents distribution IIWill go into the beam pipe, if necessary Beam pipe + wing box; extra shielding
17. KickersWhich type is suitable for EMMA? Kicker magnetsInductivemagnetsDelay-linemagnetsEasier to design and build.Faster, but structurally and electrically complex.
18. Transmission-line model of a magnetVoltage sourcelhdZL()Load impedanceMagnetDistributed inductance L [H/m] and capacitance C [F/m].
19. Transmission-line model: inductive magnetImpedance 1) Inductive magnet Suitable for EMMA (l is small, fortunately)Limited to small l values. Ringing (oscillations in the trailing edge of the current pulse). E=0, no electric field in this magnet.
20. Transmission-line model: delay-line magnetImpedance Impedance matching: All frequencies see the same impedance: frequency independent behaviour; high frequency.Travelling voltage-current wave (Z0 is real); E and B are both non-zero!Z0 needs to be as low as possible: E needs to be taken into account.
21. Delay-line magnet: power supplyInitial voltage distribution.An impedance-matched line (PFN) is charged to a high voltage.A voltage-current wave is then launched by closing the switch.
22. Voltage evolution with timeTime=1Time=100Time=250Time=400PFNMagnetMagnetPFNPFNMagnetPFNMagnet
23. ImpedanceVoltage on the magnet is only a half of the source voltage. Both forward and backward waves of equal amplitude.Backward wave reflected upon reaching the open end of the circuit.w=58 mm, h=22 mm, D=26.5 mmR. B. Armenta et al, PAC05 (2005)Ferrite
24. Inductive kicker: window frame designMax length 100 mm Ferrite frameShims are important.
- 25. Kickers: geometry and ferrite materialHV source connected here70 ns current pulses! f=7 MHzFerrite data: Type NiZn, Bs=0.35 T; Hc=400A/m, =105 m, f
26. Kickers: magnetizing coilConductor spacing. Conductor cross-section.The shims are important.
27. Role of the shims0.2 %0.2 % flux density variation in the presence of the shims.
28. Role of the shims12 % flux density variation in the absence of the shims.12 %
29. Vertical planeWhite areas B< 0.065 T or B> 0.075 T Saturation End effects
30. Kicker: parameters