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Magnet Design & Construction for EMMA. Ben Shepherd Magnetics and Radiation Sources Group ASTeC STFC Daresbury Laboratory. Overview. EMMA cell layout & magnet constraints Magnet design Results from prototyping Production magnet manufacturing progress Other magnets. ALICE and EMMA. - PowerPoint PPT Presentation
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FFAG 2008 - Manchester, 1-5 September 2008
Magnet Design & Construction for EMMA
Ben ShepherdMagnetics and Radiation Sources Group
ASTeCSTFC Daresbury Laboratory
Ben Shepherd 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
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
Ben Shepherd Magnet Design & Construction for EMMA
The EMMA Ring
42 cells, each has:
D magnetF magnet
84 magnets in main ring
+ injection
+ extraction
+ correctors
6m
Ben Shepherd Magnet Design & Construction for EMMA
EMMA Cell Layout
Cavity
ClockwiseBeam
Inside of ring
Outside of ringMagnet Reference OffsetsD = 34.048 mmF = 7.514 mm
Geometry consisting of 42 identical(ish) straight line segments of length 394.481 mm
Long drift 210.000 mm
F Quad 58.782 mm
Short drift 50.000 mm
D Quad 75.699 mm
Magnet Yoke LengthsD = 65 mmF = 55 mm
Circumference = 16.568m
FD D
low energy beam
high energy beam
Ben Shepherd 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!
Ben Shepherd Magnet Design & Construction for EMMA
Magnet Profiles
D magnetInscribed radius: 53mmLength: 65mm
F magnetInscribed radius: 37mmLength: 55mm
Ben Shepherd 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
hyperbolic region:y = ½r2 / x
tangent regiony = m x + c
poleprofile
inscribed radius r
Ben Shepherd 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 x / mm
normalised integrated gradient
clamp plateno clamp plate
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
Ben Shepherd 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
0.98
0.99
1.00
1.01
1.02
1.03
0 5 10 15 20 25 30 35
x / mm
model
measurements
0.990
0.992
0.994
0.996
0.998
1.000
0 5 10 15 20 25 30 35
x / mm
model
measurements
Prototype Test Results
Normalised integrated gradient
F
DGradient drops off quicker(in both cases) than for the model
For the F magnet, this improves the field quality…
Poor agreement with the model – tried using a different code (OPERA-3D)
Ben Shepherd Magnet Design & Construction for EMMA
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
Shimming
Shims added to D magnet to improve field quality
Vary width (in model) to optimise field quality
0 10 20 30 40 50 60 0 .05
0 .04
0 .03
0 .02
0 .01
0 .00
0 .01
0 .02
x mm
GG 01
no s h im28x2m m sh im27x2m m sh im26x2m m sh im31 .29x2m m sh im21 .29x2m m sh im11 .29x2m m sh im
31mm
28mm
27mm
26mm
21mm
11mmno shim
field quality vs. shim width
width
Ben Shepherd Magnet Design & Construction for EMMA
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 field quality
-5%
-4%
-3%
-2%
-1%
0%
+1%
-30 -20 -10 0 10 20 30 40 50
x / mm
G/G
0 -
1 before shimming
after shimming
D required good field region
Ben Shepherd Magnet Design & Construction for EMMA
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
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
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
new quads
reused SRS quads
new dipoles Magnet
manufacture has just started and should be complete by the end of October
Diagnostic line design is ongoing
Ben Shepherd Magnet Design & Construction for EMMA
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
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
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