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

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

3. Magnet Design & Construction for EMMA
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
go through ERLP energies: 350keV – 8MeV – 35MeV, FEL, dump
commissioning in progress now; very slow due to gun problems
Ben Shepherd
Magnet Design & Construction for EMMA

4. Magnet Design & Construction for EMMA
The EMMA Ring 6m
42 cells, each has:
D magnet F magnet
 84 magnets in main ring
+ injection
+ extraction
+ correctors
short magnets – do the job of bending and focusing the beam
very little room – need to fit in inj/ext, cavities, vacuum equipment and diagnostics too!
Ben Shepherd
Magnet Design & Construction for EMMA

5. Magnet Design & Construction for EMMA
EMMA Cell Layout
Geometry consisting of 42 identical(ish) straight line segments of length  mm D D F
Long drift mm
F Quad mm
Short drift mm
D Quad mm
Inside of ring
low energy beam
high energy beam
Circumference = m
Clockwise
Beam
explain about offsets – beam is bent one way then the other
independent adjustment of B & G
Outside of ring
Cavity
Magnet Reference Offsets
D = mm
F = mm
Magnet Yoke Lengths
D = 65 mm
F = 55 mm
Ben Shepherd
Magnet Design & Construction for EMMA

6. Magnet Design & Construction for EMMA
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!
used two codes since magnets are very novel
‘good field region’ determined in terms of strength – integrated gradient
prototypes to check agreement with model
Ben Shepherd
Magnet Design & Construction for EMMA

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

8. Magnet Design & Construction for EMMA
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
Ben Shepherd
Magnet Design & Construction for EMMA

9. Magnet Design & Construction for EMMA
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)
Ben Shepherd
Magnet Design & Construction for EMMA

10. 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
x / mm
normalised integrated gradient
clamp plate
no clamp plate
F results
Ben Shepherd
Magnet Design & Construction for EMMA

11. Magnet Design & Construction for EMMA
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)
Ben Shepherd
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
Ben Shepherd
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
Ben Shepherd
Magnet Design & Construction for EMMA

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

15. 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
D required good field region
Ben Shepherd
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
Ben Shepherd
Magnet Design & Construction for EMMA

17. Magnet Design & Construction for EMMA
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
Ben Shepherd
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
Ben Shepherd
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
Ben Shepherd
Magnet Design & Construction for EMMA

20. Magnet Design & Construction for EMMA
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
Ben Shepherd
Magnet Design & Construction for EMMA