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

2. SCU R&D Review, Jan. 31, 2014 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 – Nb 3 Sn SCU prototyping – SCU testing Cost estimate: LBNL contribution Project schedule: LBNL contribution Infrastructure and resource availability Conclusions

3. SCU R&D Review, Jan. 31, 2014 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 NbTi helical SCUs for SLAC FEL – 2002-: Development of Nb 3 Sn SCUs *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. SCU R&D Review, Jan. 31, 2014 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 Nb 3 Sn 1.5m prototype – 18.5mm period, end corrections – Potential for significant performance enhancement or significantly increased performance margin (e.g. temperature) vs NbTi Testing – Participate in testing and tuning of SCU prototype in the ANL Test Cryostat

5. SCU R&D Review, Jan. 31, 2014 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 +I cor,0,-I cor are allowed – Optimize distribution of active correctors to minimize trajectory and phase-shake errors.

6. SCU R&D Review, Jan. 31, 2014 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 ±I cor – I cor can be varied with main coil current I 0 – N varies from undulator to undulator selected based on measurements

7. SCU R&D Review, Jan. 31, 2014 Tuning concept: basics

8. SCU R&D Review, Jan. 31, 2014 Tuning concept - improvements

9. SCU R&D Review, Jan. 31, 2014 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 Nb 3 Sn undulator readiness Develop algorithms to optimize corrections based on measured field and/or first and second integrals

10. SCU R&D Review, Jan. 31, 2014 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. SCU R&D Review, Jan. 31, 2014 Test cryostat: details

12. SCU R&D Review, Jan. 31, 2014 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. SCU R&D Review, Jan. 31, 2014 Nb 3 Sn SCU development at LBNL: background Motivated by performance potential

14. SCU R&D Review, Jan. 31, 2014 Nb 3 Sn superconductor options

15. SCU R&D Review, Jan. 31, 2014 Nb 3 Sn prototyping: history (1) Prototype 1 (2003): – Demonstrated that superconducting undulators operating at very high current densities (J E >1500A/mm 2, resulting in J cu >6000 A/mm 2 during a quench) can be passively protected without damage

16. SCU R&D Review, Jan. 31, 2014 Nb 3 Sn 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. SCU R&D Review, Jan. 31, 2014 Nb 3 Sn prototyping: history (3) Prototype 3 (ANL funded; 2006) one- yoke only Demonstrated field performance consistent with predicted B(λ,g m ) curves, as used by Paul Emma

18. SCU R&D Review, Jan. 31, 2014 SCU development for FELs - 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. SCU R&D Review, Jan. 31, 2014 Nb 3 Sn prototyping: ongoing… Nb3Sn prototype for FEL applications: – λ=20mm, g m =7.5mm, 50cm device – Optimized end design – Tight fabrication tolerances Detailed tolerance and tuning analysis

20. SCU R&D Review, Jan. 31, 2014 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. SCU R&D Review, Jan. 31, 2014 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. SCU R&D Review, Jan. 31, 2014 Nb 3 Sn prototyping: ongoing - fabrication

23. SCU R&D Review, Jan. 31, 2014 Status

24. SCU R&D Review, Jan. 31, 2014 Nb3Sn prototype: proposed R&D Design and fabricate a Nb 3 Sn prototype – λ=18.5mm, g m =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 R&D Review, Jan. 31, 2014 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 R&D Review, Jan. 31, 2014 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 Nb 3 Sn undulator in ANL test cryostat

27. SCU R&D Review, Jan. 31, 2014 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. Nb 3 Sn SCU design and fabrication. The Nb 3 Sn SCU prototype will have a period λ=18.5mm. Contribute to prototype testing in the ANL test cryostat

28. SCU R&D Review, Jan. 31, 2014 Schedule and Cost for LBNL effort NOTE: This estimate does not include contingency

29. SCU R&D Review, Jan. 31, 2014 Infrastructure

30. SCU R&D Review, Jan. 31, 2014 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. SCU R&D Review, Jan. 31, 2014 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 Nb 3 Sn 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