SCU Development at LBNL

1. SCU Development at LBNL Soren Prestemon Lawrence Berkeley National Laboratory Superconducting Undulator R&D Review Jan. 31, 2014

2. Outline • Background • Areas of contribution to the proposal • Status of technology in each area and proposed R&D • Test cryostat for tuning development • Tuning concepts • Nb3Sn SCU prototyping • SCU testing • Cost estimate: LBNL contribution • Project schedule: LBNL contribution • Infrastructure and resource availability • Conclusions

3. Background • Long history in undulator development at LBNL • ~1985: Halbach initiated development of PM technology • ~1991-: Development, fabrication, and implementation of large number of plane-polarizing and elliptically-polarizing undulators for the ALS • ~1995-1996: Studies of NbTihelical SCU’s for SLAC FEL • 2002-: Development of Nb3Sn SCU’s • *First LDRD, ALS-motivated: 2003 – Prototype 1 • *Continuation LDRD, ALS-motivated: 2004 – Prototype 2 • *WFO funding from ANL: 2006 – Prototype 3 • LDRD, Variable-polarizing undulator, NGLS-motivated: 2011 • *NGLS R&D funds: 2011-2012 • *Continued funding via LDRD:mid-2013, 2014 • 2012-: Responsible for the LCLS-II hybrid PM baseline undulators

4. Areas of contribution • Tuning system scale-up • Scale-up existing tuning concept and test off-line • Tuning test cryostat • “Simple” extension of existing cryogen free cryostat: 1m => 1.5m • Primary purpose: will allow testing of tuning system in parallel with main cryostat fabrication ⇒avoid risk of commissioning tuning system late in project • Nb3Sn 1.5m prototype • 18.5mm period, end corrections • Potential for significant performance enhancement or significantly increased performance margin (e.g. temperature) vsNbTi • Testing • Participate in testing and tuning of SCU prototype in the ANL Test Cryostat

5. Tuning concepts • Guidelines: • Want method that provides sufficient degree-of-freedom correction • Want to minimize cool-down => warm-up cycles • Want minimal complexity • Approach: • Single active electrical circuit drives multiple correctors in series • Initially large selection of possible corrector locations • At each location +Icor,0,-Icor are allowed • Optimize distribution of active correctors to minimize trajectory and phase-shake errors.

6. Tuning concept scale-up • General approach to field-errors: • Minimize errors via tight machining tolerances, assembly • Eliminate “global” steering and displacement via end correction coils • But… also provide a mechanism for local field error correction • Use detailed error analysis to develop algorithm for tuning concept scale-up • Many poles (N) can have correction loop carrying current ±Icor • Icorcan be varied with main coil current I0 • N varies from undulator to undulator • selected based on measurements

7. Tuning concept: basics

8. Tuning concept - improvements

9. Tuning concept scale-up: proposed R&D • Scale up tuning concept for application to 1.5m undulators • Demonstrate concept off-line (no undulator) in advance of NbTi and Nb3Sn undulator readiness • Develop algorithms to optimize corrections based on measured field and/or first and second integrals

10. Existing Test Cryostat: features • A cryogen-free test cryostat has been fabricated • Currently compatible with 1m prototypes • Uses 2 pulsed-tube cryocoolers • 500A HTS leads for main coil • 250A HTS leads for end correctors • 250A HTS leads for tuning system • Large number of possible diagnostics (thermal, voltage,…)

11. Test cryostat: details

12. Test cryostat modifications for tuning development: proposed R&D • Extend existing cryostat ends to allow 1.5m testing • Need additional spools with flanges • Need appropriate cryogenic shielding • Modify existing pulsed wire system to accommodate new length • Commission modifications via demonstration of cryogenic performance • Use test cryostat to demonstrate scale-up of tuning concept in advance of undulator prototype readiness ⇒ minimize schedule risk

13. Nb3Sn SCU development at LBNL: background • Motivated by performance potential

14. Nb3Sn superconductor options

15. Nb3Sn prototyping: history (1) • Prototype 1 (2003): • Demonstrated that superconducting undulators operating at very high current densities (JE>1500A/mm2, resulting in Jcu>6000 A/mm2during a quench) can be passively protected without damage

16. Nb3Sn prototyping: history (2) • Prototype 2 (2004): • Demonstrated that simple current loop on a pole can provide adequate field perturbation to serve as tuning mechanism

17. Nb3Sn prototyping: history (3) • Prototype 3 (ANL funded; 2006) • one- yoke only Demonstrated field performance consistent with predicted B(λ,gm) curves, as used by Paul Emma

18. SCU development for FEL’s - ongoing • Systematic R&D undertaken to address key technological issues with high-performance superconducting undulators • Development of an SCU short model to => demonstrate field performance • Development of a magnet measurement system to => evaluate field quality • Development of a shimming concept to => correct trajectory and phase-shake errors

19. Nb3Sn prototyping: ongoing… • Nb3Sn prototype for FEL applications: • λ=20mm, gm=7.5mm, 50cm device • Optimized end design • Tight fabrication tolerances • Detailed tolerance and tuning analysis

20. End design (1) • Odd number of poles chosen for prototype • Non-ideal effects due to finite permeability and differential saturation of end poles • End kick is dependent on the undulator field • Dipole field is generated by unbalanced yoke field As field is ramped: Pole 2 saturates before 1

21. End design (2) • Odd number of poles • Ideal end design is used for the main coil (1/8, 1/2, 7/8) • Kick corrector + field clamps placed at each end (only generates a kick) • Dipole corrector is co-wound with the main coil in the first pocket (generates both kick and dipole) • Strength of both correctors is varied as a function of the undulator field (look-up table)

22. Nb3Sn prototyping: ongoing - fabrication

23. Status

24. Nb3Sn prototype: proposed R&D • Design and fabricate a Nb3Sn prototype • λ=18.5mm, gm=7.5mm, 1.5m • Document all design choices • Document all fabrication tolerances • Identify issues associated with future scale-up to industrial fabrication level

25. SCU testing: capabilities • Pulsed wire development • Demonstrated accuracy on SLAC ECHO undulator • Will be incorporated in tuning test cryostat for use during tuning scale-up testing at LBNL • Will be incorporated into ANL test cryostat for SCU testing and tuning

26. SCU testing: proposed R&D • Implement pulsed-wire in tuning cryostat for tuning scale-up testing • Implement pulsed-wire system in ANL test cryostat • Demonstrate tuning on NbTi undulator in ANL test cryostat • Demonstrate tuning on Nb3Sn undulator in ANL test cryostat

27. Summary: proposed LBNL contributions • Modifications of an existing cryocooler-based, cryogen-free test cryostat to allow development of a tuning system commensurate with the 1.5m SCU prototypes • Development of a 1.5m scale tuning system, based on concepts already tested and proven in previous work at LBNL. • Nb3Sn SCU design and fabrication. The Nb3Sn SCU prototype will have a period λ=18.5mm. • Contribute to prototype testing in the ANL test cryostat

28. Schedule and Cost for LBNL effort NOTE: This estimate does not include contingency

29. Infrastructure

30. Resources • Engineering Division: • Magnetic Systems group • Accelerator and Fusion Research Division: • Superconducting Magnet Group • Together we have a strong team with expertise in: • Magnetics and magnetic systems • Undulators: design, fabrication, and implementation • Superconducting magnets • Cryogenics Ample resources are available to perform the proposed R&D Work will not be limited by resource availability

31. Summary • We have designed, fabricated and tested multiple prototypes that provide credibility to the proposed design point, and have invested in significant analysis to support the tuning concept. • We have infrastructure and resources available to perform the proposed work. • The proposed LBNL contributions: tuning system development and 1.5m Nb3Sn design and fabrication, complement the ANL part of the proposal and are critical to minimize risk for the project so as to achieve LCLS-II undulator specifications