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Magnet Design & Construction for EMMA

Magnet Design & Construction for EMMA. Ben Shepherd Magnetics and Radiation Sources Group ASTeC STFC Daresbury Laboratory. Overview. EMMA cell layout Challenges in the magnet design Novel quadrupole design to improve field quality Results from magnet prototyping Next steps.

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Magnet Design & Construction for EMMA

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  1. Magnet Design & Construction for EMMA Ben Shepherd Magnetics and Radiation Sources Group ASTeC STFC Daresbury Laboratory FFAG 2007 - Osaka, 6-9 November 2007

  2. Overview • EMMA cell layout • Challenges in the magnet design • Novel quadrupole design to improve field quality • Results from magnet prototyping • Next steps Magnet Design & Construction for EMMA

  3. ERLP and EMMA • EMMA will be an FFAG addon to the Energy Recovery Linac Prototype (ERLP) project at Daresbury • EMMA: 10MeV  20MeV • Non-scaling FFAG • ERLP being commissioned at the moment • Ready by mid 2008…? Magnet Design & Construction for EMMA

  4. The EMMA Ring 6m 42 cells, each has: D magnetF magnet  84 magnets in main ring + injection + extraction + correctors Magnet Design & Construction for EMMA

  5. EMMA Cell Layout Geometry consisting of 42 identical(ish) straight line segments of length 394.481 mm D F D Inside of ring low energy beam high energy beam Circumference = 16.568m Clockwise Beam Outside of ring Cavity Magnet Reference Offsets D = 34.048 mm F = 7.514 mm Magnet Yoke Lengths D = 65 mm F = 55 mm Magnet Design & Construction for EMMA

  6. Magnet Challenges • ‘Combined function’ magnets • Dipole and quadrupole fields • Independent field and gradient adjustment • Movable off-centre quads used • Very thin magnets • Yoke length of same order as inscribed radius • ‘End effects’ dominate the field distribution • Full 3D modelling required from the outset • Large aperture + offset • Good field region (0.1%) must be very wide • Close to other components • Field leakage into long straight should be minimised • Close to each other • Extremely small gap between magnets • F & D fields interact • Full 3D modelling and prototyping essential! Magnet Design & Construction for EMMA

  7. Magnet Profiles D magnet Inscribed radius: 53mm Length: 65mm F magnet Inscribed radius: 37mm Length: 55mm Magnet Design & Construction for EMMA

  8. Field Clamps • Tracking studies suggest that field clamps are needed • Reduce field in the long straight (especially for kickers) • Decrease strength  increase power demand • Tried different profiles • Best is to match pole shape Magnet Design & Construction for EMMA

  9. Optimise in terms of normalised integrated gradient quality Maximise size of 0.1% region Minimise higher harmonics Shape Optimisation  integrate vertical field along z 0.1% region differentiate w.r.t x normalise to value at centre of vac chamber Magnet Design & Construction for EMMA

  10. Pole Shape Design • Standard quadrupole design: • hyperbolic pole face • finite pole width  add tangent • Choose tangent point to maximise good field region • Only 1 variable (in 2D) • Results not very good • Good field regions: • 14mm (F) • 26mm (D) • Try a new design pole profile hyperbolic region: y = ½r2 / x tangent region y = m x + c inscribed radius r Magnet Design & Construction for EMMA

  11. New Pole Shape Design • Remove the limitation of a hyperbolic pole face • Clearly any shape is possible – large parameter space • How to parametrise this? • Replace curved pole profile with straight lines – adjust vertex positions new old Magnet Design & Construction for EMMA

  12. Straight-Line Pole - Details • Start with a square pole – adjust d0 point to make two faces • Add d1 point for four faces, d2 for six – optimise with each additional point d0 d1 d2 Two Four Six Pole tip faces: Three Five d0 d1 • An odd number of faces produced better solutions Magnet Design & Construction for EMMA

  13. normalised integrated gradient clamp plate no clamp plate x / mm Straight-Line Poles: Results • Optimisation was carried out using the straight-line geometry for both magnets • 5 pole tip faces were used (2 variables) • Good field regions (0.1%): • 26mm (F) • 32mm (D) • Still rather short of the specified values • Better results when no clamp plates used F results Magnet Design & Construction for EMMA

  14. Magnet Prototypes • Two prototypes were built by Tesla to verify the design Magnet Design & Construction for EMMA

  15. Prototype Tests • Tested on a rotating coil bench at Tesla • Measure integrated field harmonics • quadrupole • 12-pole • 20-pole • 28-pole • … • Compare to model • Find magnetic centre (by minimising dipole component) Magnet Design & Construction for EMMA

  16. Extra Measurements • Carried out some extra measurements with the magnets on the bench • Clamp plate in different positions (and removed) • effect on magnet strength  fine adjustment • Steel buttons added to pole ends • effect on higher harmonics 5mm diameter steel buttons added in pairs Magnet Design & Construction for EMMA

  17. Parameter F model F spec F measured D model D spec D measured Units Current 350 364.0 350.0 -350 376 350 A Turns 10 10 10 15 15 15 turns Current turns 3500 3640 3500 -5250 5640 5250 At Gradient at magnetic centre -6.583 3.710 4.603 3.710 T/m Integrated central gradient 0.585 0.483 0.540 0.515 0.440 0.480 T Gradient / current turns -1.881 1.019 -0.877 0.658 mT/m/At Int. grad. / current turns 0.167 0.133 0.154 -0.098 0.078 0.091 mT/At Magnetic length -88.865 130.189 111.797 118.598 mm Good field region (±0.1%) 10.2 32.0 15.0 32.2 56.0 21.0 mm Field uniformity 2.80% 0.43% 0.11% 10.20% out to 36.0 30.5 32.2 56.0 mm 4-pole 0.585 0.540 0.515 0.476 T 12-pole -2.60E-09 3.14E-09 2.10E-10 -2.37E-10 T/mm4 20-pole 2.07E-15 -3.09E-15 -1.41E-15 -1.57E-16 T/mm8 Prototype Test Results Magnet Design & Construction for EMMA

  18. Prototype Test Results Normalised integrated gradient F Gradient drops off quicker(in both cases) than for the model For the F magnet, this improves the field quality… D Magnet Design & Construction for EMMA

  19. Prototype Tests – Clamp Plate Movement F: about 0.25% increase in strength per mm clamp plate movement D D: very slight reduction in strength central point is probably not correctly measured (hysteresis effect?) F Magnet Design & Construction for EMMA

  20. Prototype Tests – Buttons 12- and 20- pole components 1, 2, 3: buttons on open end 4, 5, 6: buttons on clamp plate end F Similar effects at both ends D Magnet Design & Construction for EMMA

  21. Model Comparisons • Measurements and model do not match up well • Further modelling should be carried out using a different code • Initial results from OPERA-3D model are more promising… 12-pole 28-pole skew harmonics 20-pole 36-pole normal harmonics Magnet Design & Construction for EMMA

  22. Next Steps • Measurement of both magnets together • Shimming? • OPERA modelling • Use of modelled field maps and measured data in tracking codes • Further tweaks to magnet designs • Tender exercise for production magnets (via OJEU) has started already Magnet Design & Construction for EMMA

  23. Conclusions • Very challenging magnets to design! • Old (hyperbolic + tangent) design insufficient • New design uses straight line pole profiles • Model results are much better • Prototypes have been built and tested • Test results show some differences to model – but prototypes still look reasonable • Improvement to field quality probably still possible Magnet Design & Construction for EMMA

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