Magnet Design & Construction for EMMA

1. Magnet Design & Construction for EMMA Ben Shepherd Magnetics and Radiation Sources Group ASTeC STFC Daresbury Laboratory FFAG 2008 - Manchester, 1-5 September 2008

2. Overview • EMMA cell layout & magnet constraints • Magnet design • Results from prototyping • Production magnet manufacturing progress • Other magnets Magnet Design & Construction for EMMA

3. ALICE and EMMA • EMMA will be an FFAG addon to the ALICE (was ERLP)accelerator at Daresbury • EMMA: 10MeV  20MeV • Non-scaling FFAG • ALICE being commissioned at the moment • Energy Recovery expected very soon 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. 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 – integrated profiles quite different to 2D predictions • 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

9. Straight-Line Poles • Replace hyperbolic curved pole face with series of straight lines • Adjust positions of vertices to optimise field distribution (determined by inscribed radius) (determined by symmetry) Magnet Design & Construction for EMMA

10. 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 with no clamp plates F results Magnet Design & Construction for EMMA

11. Prototypes • Two prototypes were built by Tesla Engineering to verify the design • 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

12. Prototype Test Results Normalised integrated gradient F Poor agreement with the model – tried using a different code (OPERA-3D) 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

13. Prototype Tests – Clamp Plate Movement • A clamp plate on each magnet reduces the field in the long straights • The position of the clamp plates can be adjusted at the factory to equalise the strength across all magnets • For the prototypes: • 0.25% change per mm for the F - okay • No change for the D - bad • Saturation in the clamp plate was reducing its effectiveness • Clamp plate thickness increased to 8mm Magnet Design & Construction for EMMA

14. 31mm 28mm 27mm field quality vs. shim width 26mm 21mm 11mm no shim Shimming • Shims added to D magnet to improve field quality • Vary width (in model) to optimise field quality width Magnet Design & Construction for EMMA

15. D required good field region Measured results with shims • Following shimming, the D was re-measured with the F present on the bench too (at an offset) • The field quality is greatly improved • The shim edges were rounded off in the model and incorporated into the pole profile Magnet Design & Construction for EMMA

16. Extraction Region Magnets • The extracted beam pipe goes through a clamp plate • For the D magnet in this region, a special clamp plate had to be designed to go around the beam pipe • A ‘bridge’ provides an additional flux return path • The flux density is not too high • Field quality is identical to the other magnets • The strength is slightly different – can use a separate power supply Magnet Design & Construction for EMMA

17. Timetable • Assembly of the production magnets is taking place now at Tesla Engineering • Magnetic measurement begins this week • Magnets will be delivered to DL in batches from September to November • Meanwhile at DL, the prototype magnets will be mapped using a Hall probe • This data could feed into tracking studies for improved accuracy Magnet Design & Construction for EMMA

18. Injection/Extraction Line Magnets • For the EMMA injection line, 13 new quadrupoles and 4 new dipoles are required • Contract was placed with Scanditronix (Sweden) in early July 2008 • Magnet manufacture has just started and should be complete by the end of October • Diagnostic line design is ongoing new quads new dipoles reused SRS quads Magnet Design & Construction for EMMA

19. Vertical Steering Magnets • The specification (number and strength) for the vertical correctors is being completed at the moment • Space is VERY tight! • Try to squeeze as much strength as possible into the available space Magnet Design & Construction for EMMA

20. Conclusions • Very challenging magnets to design! • Pole profile based on straight lines (not hyperbola) • Prototypes have been built and tested • Field quality for D improved by shimming • All production magnets will be delivered by November 2008 • Other magnets are being designed and procured in parallel Magnet Design & Construction for EMMA