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EMMA: Pulsed magnets Kiril Marinov MaRS group, ASTeC, Daresbury Laboratory 1
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2. Outline Septum magnet Geometry and positioning Modelling Stray fields Field quality Kicker Delay-line vs. inductive design Modelling
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3. Septum – formulation of the problem Movable septum, translation in one direction + rotation Vacuum vessel geometry is fixed Large bending angle – 70 o extraction, 65 o injection Limited space available (w=10 cm) The available space needs to be used efficiently. Positioning and geometry need to be carefully optimized.
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4. Septum geometry w a Determine optimum values for w and a based on “real” injection/extraction data. Magnetic “steel” Coil Eddy-current screen
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5. Geometry II Simple shape: coaxial arcs and lines Rotation center Translation
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6. Hard edge model β δ α
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7. Thick septum with a small aperture Incoming beam parallel to the polygon side 17.14 mm away; w=102 mm, a=35mm c Advantage: Smaller field (current): smaller stray field Disadvantages Negative rotation angle Poor beam clearance C=2.5 mm Septum wall and wing too close to the vacuum vessel
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8. Thick septum with large aperture Incoming beam parallel to the polygon side 17.14 mm away; w=102 mm, a=70 mm Improved clearance C≈15 mm c Negative rotation angle, bigger in absolute value; Septum wall and wing too close to the vacuum vessel Larger pole area requires higher voltage; Using the largest possible magnet “that still fits in the box” is not the solution.
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9. “Thin” septum will “small” aperture Incoming beam parallel to the polygon side 17.14 mm away; w=80mm, a=35mm Positive rotation angle c Good beam clearance C>15 mm Longer wing can be used. Requires stronger field (current); stronger stray field Advantages: Disadvantage
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10. Vertical position The same incoming beam requires different “horizontal” position, rotation and magnetic field, depending on the septum “vertical” position.
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11. Results 200 injection/extraction scenarios considered for consistence with the septum geometry. Both “phase-space painting” and “closed orbits” modes of operation B max =0.85 T 0<δ<7 o -7 <Translation<15 mm I max =16.5 kA L=0.19 μH V max =403 V
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12. Coil position
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13. Coil position II
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14. Field quality t=10 μs t=12.5 μs t=15 μs t=17.5 μs
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15. Eddy currents distribution Eddy currents Little or no current here
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16. Eddy currents distribution II Will go into the beam pipe, if necessary Beam pipe + wing “box”; extra shielding
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17. Kickers Which type is suitable for EMMA? Kicker magnets Inductive magnets Delay-line magnets Easier to design and build. Faster, but structurally and electrically complex.
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18. Transmission-line model of a magnet Voltage source l h d ZL(ω)ZL(ω) Load impedance “Magnet” Distributed inductance L [H/m] and capacitance C [F/m].
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19. Transmission-line model: inductive magnet Impedance 1) Inductive magnet Suitable for EMMA ( ω l is small, fortunately…) Limited to small ω l values. “Ringing” (oscillations in the trailing edge of the current pulse). E=0, no electric field in this magnet.
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20. Transmission-line model: delay-line magnet Impedance Impedance matching: All frequencies “see” the same impedance: frequency independent behaviour; “high” frequency. Travelling voltage-current wave (Z 0 is real); E and B are both non-zero! Z 0 needs to be as low as possible: E needs to be taken into account.
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21. Delay-line magnet: power supply Initial voltage distribution. An impedance-matched line (PFN) is charged to a high voltage. A voltage-current wave is then “launched” by closing the switch.
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22. Voltage evolution with time Time=1 Time=100 Time=250 Time=400 PFNMagnet PFN Magnet PFN Magnet
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23. Impedance Voltage 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 mm R. B. Armenta et al, PAC’05 (2005) Ferrite
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24. Inductive kicker: window frame design Max length 100 mm Ferrite frame Shims are important.
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25. Kickers: geometry and ferrite material HV source connected here 70 ns current pulses! f=7 MHz Ferrite data: Type NiZn, Bs=0.35 T; Hc=400A/m, ρ=10 5 Ωm, f<100 MHz (“4E2”, page 142, Ferroxcube Data Handbook 2005) Ferrite material available B max =0.07 T
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26. Kickers: magnetizing coil Conductor spacing. Conductor cross- section. The shims are important.
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27. Role of the shims 0.2 % 0.2 % flux density variation in the presence of the shims.
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28. Role of the shims 12 % flux density variation in the absence of the shims. 12 %
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29. Vertical plane White areas B 0.075 T Saturation End effects
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30. Kicker: parameters
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