T Bradshaw

On behalf of the SCU group

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Status of the Superconducting Undulator Development in the UK

Superconducting Undulator Workshop, Rutherford Appleton Laboratory 28th April 2014

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Introduction

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Outline of the current UK developments in Superconducting Undulator Technology

• Start with a brief retrospective of the Helical Undulator• Planar undulator specification• Major concerns and how we are handling those concerns• Status

Many people have contributed to the developments

RAL Technology Department on Harwell CampusASTec at Daresbury LaboratoryDiamond Light Source on Harwell Campus

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Helical Undulator

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Design principles have grown from the work on Helical Undulator for the International Linear Collider:

Undulator Period 11.5 mm Field on Axis 0.86 TPeak field homogeneity <1%Winding bore >6mmUndulator Length 147 mNominal current 215ACritical current ~270A Manufacturing tolerances

winding concentricity 20µmwinding tolerances 100µmstraightness 100µm

NbTi wire Cu:Sc ratio 0.9 Winding block 9 layers Ribbon 7 wire

+ -

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Helical Undulator

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Helical Undulator

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Fourier transform:Very pure sine wavePeak corresponds to 11.5mm period

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Integration into Cryostat

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Magnet was integrated into cryostat and tested with currentField measurements in full cryostat were not attempted

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Planar Undulator

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Development of a Superconducting Undulator for the Diamond Light Source

Magnetic length~2 Metres TBD by the physical length

of gap and modellingTotal length

2486 Millimetres Confirmed by Diamond 22/9/11

Period at Room Temp.15.5 Millimetres Confirmed by Diamond

12/12/12Period at 4.2K >15.45 Millimetres  Field on axis >1.25 Tesla At Operating TempK (undulator parameter) >1.804    

Minimum Physical Aperture

5.4 Millimetres (Vertical)Including bore tube

64 Millimetres (Horizontal)RMS phase error <3 Degrees Required

<2 Degrees DesirableTrajectory straightness +/- 1 Microns Both planes, after average

angle removal, 3.0147 GeV +/-5 MicroradiansFirst Field Integral (H+V)

<+/-0.5 Gauss*Metres Within +/-10mm H, V on axis<+/-1 Gauss*Metres Within +/-20mm H, V on axis

Second Field Integral (H+V)

+/-1 Gauss*Metre2 Within +/-10mm H, V on axis+/-2 Gauss*Metre2 Within +/-20mm H, V on axis

Normal and skew multipoles (integrated over +/-10mm in H)

<50 Gauss Quadrupole<50 Gauss/Centimetre Sextupole<50 Gauss/Centimetre2 Octupole

       

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Major Concerns

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Tolerances Very tight ~10µm (Ben Shepherd and Tim Hayler talks)

Quench protection Thermal issues – one coil should not be a problem but 2m module is. (Vicky Bayliss talk)

Cooling and thermal issues Need temperature margin on the conductor – run at 2K (T Bradshaw later talk)Wakefield/beam/cavity heating beam tube design

Field Measurement Accuracy ..

Mechanical (Tim Hayler talk)

Insulation and potting

Forces

Joints and interconnects Large number of these

Mounting of units Bolt together or leave a gap?

Everything really, this is a tough project ………….

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Implementation

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The specification means that the tolerances on the manufacture are very tight (Ben Shepherd talk).Typically we are looking at ~10µm tolerances or of that order

Magnetic length: 2 m Period : 15.5 mmField on axis: 1.266 T-> K =1.8Beam stay clear: 5.4 mm (Vert.) x 60 mm (Horiz.)rms phase error: < 3 degrees (target 2 degrees)Trajectory straightness: +/- 0.5 micron

Implementation

• The end poles are stepped to ensure that the beam trajectory is straight. (Note that the trajectory can effect the phase error).

• End windings have odd numbers of layers to make winding easier

5 7 9 ············Coil layers =

2.35 4.8 3.83 ············Pole heights =

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4.8

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Early Prototype tests

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Accurate translational stage

Top Plate

Carbon fibre rod supporting Hall probe

Test Undulator

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Prototype tests

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• Highest field magnetic measurement at 260A Maximum magnet quench at 287A –need

407A Issues with cracking on potting material Peak fields on back of winding – need to

improve spacing

• Periodicity from sin fit at all currents is 14.995mm +/-0.001mm at RT (10-100mA) 14.963mm +/-0.001mm at 4K (10-260A)

Re-evaluation on how it is made

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Test Pieces

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Winding trials and test pieces showing good winding technique:

Section from straight, showing wires level with poles. Coil height measures 4.03 to 4.05mm.

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Test Pieces

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Profile of former has undergone many revisions to ease the winding process

Metrology is key to understanding the machining processes

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Wire Quality

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Wire found to have voids:

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Voltage Breakdown tests

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Wire quality has been found to be an issue and details of winding has caused problems with electrical breakdown.

• Looked at winding issues to reduce abrasion• Looked at insulation layer position and thickness• Looked at potting issues

Now achieved good results:

Location Max calculated voltage (VB)

Achieved Notes Safety factor

Coil to ground (end winding to ground)

3000V 4500V On steel testpiece, 0.5mm isopon (no vacuum impregnation)

1.5

Turn-to-turn 120V 1000V (pass) Three short samples, Vacuum Impregnated at 60C with RAL230 (note 1)

8 (minimum)

Coil-to-crossover wire

430V 1200V On 4cf #2 with wire on Araldite 2014. Expected to improve with addition of isopon.

2.8

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Forces

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Forces are enough to cause problems with alignment and positioning (Tim Hayler talk)

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Interconnects

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Using crimps for the joints and interconnects – we have a large number of these so they need to be reliable and fully superconducting.

Looking at finding a more compact crimp tool

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Testing

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“Guillotine” approach to Hall probe carriageArrangement made to minimise “crabbing”

Carriage and railsGRP construction

Concentric guidewheel and axel Eccentric guide

wheel and axel

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Testing

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Formers sit on beam inside test cryostatWe will be testing at 4K only

Summary

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• Large number of difficult technologies in this build – ticking off all of the technological challenges

• Status:• Just about ready to build end magnet pieces• Prototype “straight” formers – have a drawing

and a design• Building up test cryostat for magnetic

measurements/training prior to build• Possible to build the magnet but difficult!

Other talks will be dealing with the details of the technical challenges

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END