ILC prototype undulator project

1. ILC prototype undulator project James Rochford For the HeLiCal Collaboration ILC positron source meeting 31stJan – 2rd feb 2007 @IHEP Beijing

2. 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

3. 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

4. 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

5. High mesh density Iron Conductor 3d model of undulator with iron poles Bore Modelling-predictions 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 - 11.5 mm Modelling predicts relationship between the bore and period

6. 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

7. Why operate at 80% 2 • 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%)

8. Why operate at 80% 3 • 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

9. Why operate at 80% 4 What does the operating point mean in terms of temperature margin? 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

10. 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 Operating point 80% to 90% halves the enthalpy dt 1.2k- 0.6K Variation in Cu:SC @80% dT reduced by 0.2K @90% dT reduced by 0.2K Variation in JC in NbTi @80% dT reduced by 0.4K @90% dT reduced by .5K Variation in operating temp @80% dT reduced by 0.3K @90% dT reduced by 0.3K

11. 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

12. Operating point – conclusion • 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

13. 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-

14. Prototypes programme 1 • Experimental programme at RAL: • To verify modelling and prove technology

15. Prototypes programme 2 1st 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): 0.822 T +/- 0.7 %

16. Prototypes programme 3 • Prototype V: • Did not go straight to full field before quenching • Magnet warmed between 23-25th 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

17. 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

18. Prototypes programme 5 Field is measured at 200A

19. 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 prototypeis now the priority and is well underway.