ffag 2008 - manchester, 1-5 september 2008 magnet design & construction for emma ben shepherd...

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


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


The EMMA Ring

42 cells, each has:

D magnetF magnet

84 magnets in main ring

+ injection

+ extraction

+ correctors

6m


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


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 Profiles

D magnetInscribed radius: 53mmLength: 65mm

F magnetInscribed radius: 37mmLength: 55mm


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


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


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)


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)


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


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


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


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


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


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


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


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

ffag 2008 - manchester, 1-5 september 2008 magnet design & construction for emma ben shepherd...

Documents

d magnet f magnet

field distributionfull

good field regiononly

variablesgood field

field qualitypoor agreement

d modelling

magnet design construction

mmf magnetinscribed