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The Development of Superconducting Undulators for Diamond and the ILC. Tom Bradshaw Et al. Centennial Symposium on Superconducting Accelerators STFC, Daresbury Laboratory 8 th April 2011. Introduction. Helical Undulator for the ILC / EuCARD Programme Planar undulator for Diamond

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the development of superconducting undulators for diamond and the ilc

The Development of Superconducting Undulators for Diamond and the ILC

Tom Bradshaw

Et al....

Centennial Symposium on Superconducting Accelerators

STFC, Daresbury Laboratory

8th April 2011

introduction
Introduction
  • Helical Undulator for the ILC / EuCARD Programme
  • Planar undulator for Diamond
  • ColdDiag

Collaboration members

ASTEC:

JA Clarke, OB Malyshev, (DJ Scott, B Todd, N Ryder)

RAL:

T Bradshaw, A Brummit, G Burton, C Dabinett, A Lintern, Vicky Bayliss, S Watson, G Ellwood, S Canfer,

(E Baynham, J Rochford, S Carr, Y Ivanyushenkov)

University of Liverpool :

IR Bailey, JB Dainton, P Cooke, T Greenshaw, L Malysheva

DESY :

DP Barber

University of Durham :

GA Moortgat-Pick

(Moved on)

undulators

Undulators produce synchrotron radiation from a charged particle moving through a varying magnetic field

These can be made from permanent magnets – for high fields use superconducting devices

An undulator has a periodic structure of magnets – charged particles traversing the oscillating field radiate in the forward direction

Undulators

e

Ph

Ph

Ph

Ph

A device that produces coherent radiation is called an undulator – these have narrow well-defined wavelengths

A device that produces incoherent radiation is called a wiggler ...

slide4

International Linear Collider

The ILC requires 147m of 11.5mm period helical undulator

(2007 design)

slide5

International Linear Collider

+

-

  • Undulator :
  • To produce a circularly polarised positron beam
  • High energy electron beam through helical undulator
    • emission of polarised photons.
  • Downstream high Z target, pair production
  • Positrons stripped off to produce polarised positron beam.

Undulator Period 11.5 mm

Field on Axis 0.86 T

Peak field homogeneity <1%

Winding bore >6mm

Undulator Length 147 m

Nominal current 215A

Critical current ~270A

Manufacturing tolerances

winding concentricity 20µm

winding tolerances 100µm

straightness 100µm

NbTi wire Cu:Sc ratio 0.9

Winding block 9 layers

Ribbon 7 wire

design drivers
Design drivers
  • Initial specification
  • Electron Drive Beam Energy 150 GeV
  • Photon Energy (1st harmonic ) 10.06 MeV
  • Photon Beam Power 131 kW
  • Total undulator length 100-200m
  • Undulator Period 11.6mm
  • Field on Axis 0.84 T
  • Beam Stay clear 4.5mm dia

Graph of peak field against period for constant undulator K value.

design specification
Design specification

Undulator Period 11.5 mm

Field on Axis 0.86 T

Peak field homogeneity <1%

Winding bore >6mm

Undulator Length 147 m

Nominal current 215A

Critical current ~270A

Magnetic bore 6.35mm

K 0.92

Manufacturing tolerances

winding concentricity +/-20um

winding periodicity +/-50um

Axial straightness +/-50um

NbTi wire Cu:Sc ratio 0.9

Winding block 9 layers

7 wire ribbon

helical undulator
Helical Undulator

We made a number of short test pieces and ended up manufacturing wires into a cable to improve tolerance on windings

manufacture
Manufacture

One of the 2m sections after winding and potting

Detail of windings

View of the end superconducting connections

assembly
Assembly

Undulator in helium bath which is in cryostat main body

Two sections joined a the middle and mechanically anchored at that point.

assembly1
Assembly
  • Turret has:
  • Cryocooler
  • Recondenser
  • HTS current lead assembly
  • Fill and vent ports
2m module testing
2m Module testing
  • 2m module mounted vertically in liquid helium bath
  • 2m carbon fibre rod with two hall probes mounted orthogonally to each other and undulator axis
  • Logging system controls a stepper motor to move the probe through the undulator and then take voltage readings from the two hall probes
  • Probes can be orientated in 8 directions (0, 45, 90, 135, 180, 225, 270, 315 deg)
2m module testing1
2m Module testing
  • Each 2m module was tested in a cryostat
  • Field profile taken along the length every 0.1mm

Graph of field against position along undulator

Nick Ryder on top of cryostat

helical beam purity

R(um)

R(um)

Helical beam purity

Field profile Fourier analysed and plotted on a semi-logarithmic scale – sinewave is very pure – these are the same magnet with data taken on two different runs.

Peak corresponds to 11.5mm period

Particle trajectories using measured beam profile as calculated by SPECTRA as expected

slide15

Planar Undulator

  • Diamond light source can make use of a high performance planar undulator
  • Different geometry to the helical
  • Initial parameters are in table below
  • Aiming for good phase error in the external beam around 2-3°
slide16

Planar Undulator

Cryogenics:

Aim to run magnet at 1.8K

Beam tube at around 12K

planar undulator
Planar Undulator

Not good

Better

Winding trials within 10µm

nb 3 sn in helical undulator
Nb3Sn in Helical Undulator
  • We have an EuCARD Programme running to look at the use of Nb3Sn in helical undulators
  • Motivation:
  • Higher peak field
  • Possibly shorter undulator length
  • Temperature tolerance
  • “Simple” programme:
  • Source conductor
  • Use same period as for the NbTi undulator (11.5mm)
  • Wind test piece
  • Test
  • Report
nb 3 sn in helical undulator1
Nb3Sn in Helical Undulator

We have had the superconducting wire tested at Karlsuhe Institute of Technology and found (as we feared) that it is unstable at low fields:

We have two samples tested which have undergone different heat treatment to assess influence of stabilising copper RRR

nb 3 sn in helical undulator2
Nb3Sn in Helical Undulator

Modelling using extrapolated low field values

  • Field strength and Ic at 1 kA.
  • Winding ID: Ø6.35 mm.
  • Field on axis: 1.54 T. (0.7T higher than NbTi undulator)
  • Peak field in conductor: 4.42 T.
  • Operating at 82% of Ic.
nb 3 sn in helical undulator3
Nb3Sn in Helical Undulator
  • Challenges:
  • The wire suffers from “magneto thermal” instabilities:
  • Magnetisation instability – redistribution of persistent currents (depends on filament size)
  • Self Field instability – redistribution of the transport current within the conductor
  • Not clear that these problems can be overcome with current technology ...

It turns out that the stability is worse with high critical current so it is not clear that a stable wire can be procured for this programme.

colddiag
ColdDiag

One of the key issues surrounding undulators is the amount of heat deposited in the beam tube from “Wakefield Heating”

The beam passing through the beam tube is charged and this generates currents in the beam tube which generate Joule heating.

Hope to install this experiment on Diamond late this year.

summary
Summary
  • Where we are:
  • Results from the tests on the 4m helical look good
  • Working to address minor issues to achieve zero loss in cryostat
  • Planning tests to look at influence of wakefield heating on the magnet
  • Planar undulator development is challenging but if we can pull it off it will be a world beater
  • Nb3Sn development not looking too promising because of low field stability issues
  • Insulation system development continuing – important for a number of projects
  • Vital that it is thin for the use of Nb3Sn in the helical otherwise advantage over NbTi is quickly lost
  • Shows the advantage of working in close partnership over design and specification