ILC prototype undulator project ILC positron source meeting 31 st Jan – 2 rd feb Beijing James Rochford For the HeLiCal Collaboration

CCLRC Technology Rutherford Appleton Laboratory: D.E. Baynham, T.W. Bradshaw, A.J. Brummitt, F.S. Carr, Y. Ivanyushenkov, A.J. Lintern, J.H. Rochford CCLRC ASTeC Daresbury Laboratory and Cockcroft Institute: A. Birch, J.A. Clarke, O.B. Malyshev, D.J. Scott University of Liverpool and Cockcroft Institute: I.R. Bailey, P. Cooke, J.B. Dainton, L.J. Jenner, L.I. Malysheva University of Durham, CERN and Cockcroft Institute : G.A. Moortgat-Pick DESY: D.P. Barber, P. Schmid

Talk outline Specification of an undulator for the ILC 3d modelling of the undulator –Defines period and bore for operating point 80% Why operate at 80% short sample Benefits of operating at 90% Latest test results from experimental prototypes Summary

Undulator specification Undulator period: as close as possible to 10 mm Field on axis: to produce 10 MeV photons (first harmonic) Field homogeneity: ≤1% Vacuum bore: to have beam stay clear of 4 mm => about 5 mm for vacuum bore and about 6 mm for magnetic bore Superconductor (NbTi) working point : about 80% of short sample critical current. Modular design -module length: 4 m

Modelling-predictions 3d model of undulator with iron poles High mesh density Iron Conductor Bore Conclusion for NbTi a period of 10 mm means very small bore -unpractical! Realistic figures: Beam stay clear – 4 mm Vacuum bore - 5 mm Winding bore - 6 mm Period mm Modelling predicts relationship between the bore and period

Why operate at 80% 1 The RAL design is based on operation the magnet at 80% along the magnet peak field load line This choice is one of the factors which limits the minimum period that can be obtained for a given bore A design based on operation at 90% could allow some reduction in period or an increase in the bore The justification for operation at 80% is now given The gains from operation at 90% are quantified

Factors defining operating point/margin Variation in operating temperature Local variations within the magnet Global due to operation from a refrigerator at higher To or higher pressure Variation in Jc superconductor value ? 1-2% mabye as much as 5% Variation in Cu:Sc Figure typically quoted (+/-10%) Why operate at 80% 2

Magnet quenching Enthalpy margin simplest criterion – energy to raise winding from Top to Tc (critical temperature ) Minimum propagating zone (MPZ) – minimum quench energy (MQE) Defines the size of normal (non-superconducting) zone which can exist without developing into a magnet quench Characteristic length L~((2k(Tc-To))/(Jc^2xrho))^0.5 k=thermal conductivity,Tc= critical temp, To= Op temp,Jc= critical current density, rho =resistivity For the undulator typically – MPZ length ~ 10mm Energy to Quench ~ 50microjoules Reliable operation is the balance between energy releases in the winding (wire movement-resin cracks) and stability margin In the undulator the energy releases will probably be small ( stresses are small) – very difficult to estimate energy release spectrum Why operate at 80% 3

This is calculated for Prototype 4 operating at 80% at 4.2k It equates to a temperature margin of 1.2K i.e it equivalent to operating at 100% at 5.4K Why operate at 80% 4 What does the operating point mean in terms of temperature margin?

Operating point 80% to 90% halves the enthalpy dt 1.2k- 0.6K Why operate at 80% 5 Sensitivity analysis Aim here is to quantify effect of parameter variation on temperature margin and enthalpy margin. Note the enthalpy margin is a relative value Variation in dT reduced by dT reduced by 0.2K Variation in operating dT reduced by dT reduced by 0.3K Variation in JC in dT reduced by dT reduced by.5K

Benefit operating at 90% 1 Gains Reduction in magnet period estimated for operation at 90% of short sample rather than 80% ~ 0.25mm Increase in bore ~ 0.5mm Only one of these is available Reduction in manufacturing cost is insignificant

Magnets should operate in a long string without quenching Mass production in industry – variations in fabrication quality Need allowances for variations in operating temperature (pressure) variations in wire properties Jc(NbTi) and Cu:Sc ratio for enthalpy margin/stability All the effects have been quantified in previous slide If these effects are assumed to be additive – which they can be – An operating point at 90%of short sample wire performance leaves magnet operation vulnerable to very small variations in fabrication and operating parameters. Whilst the benefits of increasing the operating point to 90% are marginal So we consider 80% to be the correct design choice for the undulator Operating point – conclusion

Prototypes programme 1 Experimental programme at RAL: To verify modelling and prove technology Series of five prototypes Last one has just been tested Final 500mm long prototype-

Prototypes programme 1 Experimental programme at RAL: To verify modelling and prove technology IIIIIIIVV Former materialAl Iron Pitch, mm Groove shaperectangulartrapezoidal rectangular Winding bore, mm Vac bore, mm (St Steel tube) 5.23* (Cu tube) Winding8-wire ribbon, 8 layers 9-wire ribbon, 8 layers 7-wire ribbon, 8 layers 7-wire ribbon, 8 layers 7-wire ribbon, 8 layers Sc wireCu:Sc 1.35:1 Cu:Sc 0.9:1 StatusCompleted and tested Completed, tested and sectioned Completed and tested Test is in progress

1 st results from prototype V Prototype V details Period : 11.5 mm Magnetic bore: 6.35 mm Configuration: Iron poles and yoke Measured field at 200A (RAL PSU): T +/- 0.7 % Prototypes programme 2

Prototypes programme 3 Prototype V: Did not go straight to full field before quenching Magnet warmed between th to ~150K before testing recommenced Reason for training is not known may be due to impregnation problem Quench current 316A Equates to a field of 1.1T in bore

Prototypes programme 4 Prototype V: Achieved a higher critical field than that predicted from manufacturer nominal values The implication is the wire we are using is at pretty good in terms of super conductor content. If we assume the upper limit then the observed quench current agrees exactly with the calculated value

Field is measured at 200A Prototypes programme 5

Conclusions Experimental programme at RAL: Modelling of a undulator capable of satisfying the ILC requirements has been completed The chosen the technology is to use NbTi ribbon operating at 80% of short sample The testing of the series of five prototypes has been completed Work on the design and manufacture of a full scale 4m prototype is now the priority and is well underway.