Overview s ummary of Nb 3 Sn SCU

1. Overview summary of Nb3Sn SCU S. Prestemon for the LBNLLCLS SCU team Mar. 3, 2016

2. Outline • History and Motivation • The LBNL SCU Team • Technical facilities at LBNL • LBNL SCU Scope and associated R&D • Summary of major results • Conclusions

3. LBNL has pioneered the use of Nb3Sn for SCUs • Initially proposed the use of Nb3Sn for SCUs in late 2001: first effort funded by LDRD in FY2002, with follow-on funding in FY2003 (6-period prototypes, λ=30mm) • Nb3Sn SCU single yoke R&D funded by ANL 2005-2006 (6 period, λ=14.8mm) • LBNL support for FEL development 2011-2013 included development of Nb3Sn SCUs; investment in winding and testing infrastructure • 2016: ANL/LBNL/SLAC collaboration resulted in first 1.5m, λ=19mm Nb3Sn SCU prototype

4. Nb3Sn has significant performance advantages for SCUs • Much higher Jc(5T,4.5K) • Translates into potentially ~30% higher field than NbTi • Much higher Tc (18K vs 9.5K) • Translates into reduced temp. sensitivity / more temp. “margin” JE [A/mm2] JE [A/mm2] T [K] T [K]

5. The LBNL SCU team covers a spectrum of expertise • Diego ArbelaezProject lead: design & analysis, fab., testing • Etienne Rochepault* Field quality analysis • Ross SchlueterMentor: magnet design & analysis • Marcos TurquetiElectrical Engineer: magnet protection • Xiaorong Wang Magnet testing • Dan DietderichMaterials expertise • Scott Myers Project designer • MatthaeusLeitnerConceptual design of scale-up • Tom Lipton Technical lead: fabrication oversight • Ron OortLead technician: winding and general fab. • Jim Swanson Technician: vacuum impregnation • Hugh HigleyTechnician: coil reaction • Tom Johnson Technician: impregnation of tuning system • Ken Wilson Technician: impregnation of tuning system • Mike Barry Cost & schedule *Now at CERN

6. LBNL Facilities in support ofSCU development • Short-sample test facilities • Specially-designed winding table • Heat treatment facilities • Vacuum impregnation facilities • Magnet test facilities ~4m Potting vessel ~4m reaction furnace

7. LCLS-II SCU R&D Project Scope • LBNL deliverables • Fabrication of a 1.5 m long Nb3Sn undulator • Development and fabrication of field correction scheme • Development and transfer of pulsed wire setup for magnetic measurements (complementary to ANL measurement system) • Final magnetic measurements performed in ANL cryostat

8. Undulator Layout • Undulator period = 19.0 mm, gap = 8.0 mm • Peak field requirement Beff = 1.86 T • Single wire winding • 0.6 mm diameter wire • 60 μm thick s-glass braid insulation • Wire turns around at the end of the pole • Nb3Sn to NbTi joints at the end of the undulator Joint Section Single Wire Winding Electron Beam

9. LBNL End Design Principles 2 Independent Correctors • Correction of global field effects • Correction of local end kick • Field clamps are included for this corrector in order to avoid interference with nearby magnetic components

10. Tuning for internal trajectory and phase errors • Concept of in-situ tuning of undulators • Selectable correction locations • Corrections at all locations have the same strength • Strength can be varied with a single power supply as a function of the undulator field strength

11. Pulsed wire system developed, compatible with small-gap undulators such as SCUs NIMS 716 (2013)

12. Important results • Cryogenics worked very well – stable with low heat-load • End-correctors work well; interesting hysteresis effects seen with both NbTi and Nb3Sn devices • Looking into possible (presumably small) persistent-current contributions • Field quality appears good; noticeable taper contributes to measured ~10∘ phase errors, but could be removed • Novel magnet protection circuit was developed for high-Je devices • works well, implemented at LBNL and at ANL for Nb3Sn SCU testing • Field 2nd integral without correction is already quite good

13. Mixed high-field results • Each core was tested separately at LBNL in a LHedewar – goal 800A • First core trained quickly; stopped at 766A (protection circuit was still being improved) • Second core showed significant training • Training was not localized to one spot • Obtained >720A before training was stopped • Reason for difference not known; • previous short practice device (4-period) had fast training to 960A, similar to first core • fabrication QA identifies difference in temp. gradient during VPI • Complete system training at ANL: • First quench at 345; next at 525A, followed by numerous quenches from 525-540A • Reason for low quench current not known; appears to be conductor-limited, and occurs in the 1st core

14. Conclusions • We have made significant progress in developing Nb3Sn undulator technology for real applications: • Developed ︎and demonstrated scalable winding tooling ✔ • Developed compatible fabrication processes of scale ✔ • Demonstrated solid performance of each undulator-half ✔ • Developed and tested an active tuning system ✔ • Developed the pulsed-wire measurement system with ✔ dispersion-correction, applicable to small-gap SCUs • Demonstrated good intrinsic field quality of Nb3Sn SCUs ✔ • Demonstrated undulator performance to 536A ✗ • Goal was ~800A; need to improve this Many thanks to the ANL team for their support in cryostating and testing the Nb3Sn undulator, and to Paul Emma for keeping us all focused throughout the project!