Magnet R&D for Muon Beam Cooling at FNAL

1. Magnet R&D for Muon Beam Cooling at FNAL Alexander Zlobin Fermilab Muon Collider Design Workshop, BNL December 1-3, 2009

2. Contributors TD MSD N. Andreev, E. Barzi, V.S. Kashikhin, V.V. Kashikhin, M. Lamm, V. Lombardo, M. Lopes, A. Makarov, D. Orris, A. Rusy, M. Tartaglia, D. Turrioni, G. Velev, M. Yu APC Yu. Alexahin, V. Balbekov, A. Janssen, K. Yonehara Muons Inc. R. Johnson, S. Kahn, M. Turrene et al. JLab V. Derbenev

3. Intro • Requirements for a Muon Collider magnet systems pose significant challenges beyond the existing SC magnet technology. • The magnets require innovative design approaches, new superconductors and structural materials, advanced fabrication processes and quality control methods, etc. • Strong focused magnet R&D is absolutely necessary to support the MC feasibility study • During last few years Fermilab magnet group actively contribute to different MC/NF R&D focusing on magnets for muon beam cooling • This year we are also joining the efforts related to MC ring and IR magnets brining the experience gained during the development and production of NbTi IR quads for LHC, and successful HFM program developed Nb3Sn accelerator magnet technologies • This presentation will focused on magnet R&D results and plans at Fermilab for muon beam cooling including • SC solenoids for 6D muon beam cooling • ultra-high field HTS solenoids for final cooling

4. 6D cooling: Helical Cooling Channel K. Yonehara, S. Kahn, R. Johnson et al. Multi-section HCC • Wide range of fields, helical periods, apertures • Room for RF system and absorber • Field tuning more complicate at high fields HS concept (FNAL/Muons Inc.) • Ring coils follow the helical beam orbit producing all required field components • Straight solenoid concept does not work for high-field/small-aperture sections V.S. Kashikhin et al. M. Lopes et al.

5. HS Technology R&D • Design studies show that it is very complex magnet • significant magnetic forces and stored energy • must eventually incorporate RF system => large heat depositions • 4-coil Helical Solenoid Model Program • Large-aperture HS for the first stage • High-field HS for the final stage • The program is partially supported by Muons Inc. • Goals: • Select conductor • Develop and validate mechanical structure including cryostat • Develop fabrication methods • Study and optimize the quench performance and margins, field quality, coil cooling scheme, quench protection

6. 4 single-layer SC coils with support structures and end flanges. Model OD is limited by the VMTF ID. Rutherford-type SC cable (NbTi, SSC). Inner and outer stainless steel rings provide the coil support and intercept the radial Lorentz forces. At currents ~14 kA the fields, forces, and stresses in the 4-coil model are close to the long HS parameters. 4-Coil Model HSM01

7. HSM01 Quench Performance The first 4-coil HS model HSM01 reached 85 % of its short sample limit => close to the design operation current. No temperature dependence => mechanically limited – why?

8. HSM01 Field Measurements • Measured longitudinal and transverse field distributions agree well with predictions. • Some differences in transverse field distributions are due to the uncertainty in coil position wrt coordinate system => further care will be taken on subsequent magnets to fiducialize the coil to facilitate field comparisons.

9. HSM01 was cut in several cross-sections to evaluate the model design and the quality of fabrication Findings: Irregular turn position Different turn number Poor epoxy impregnation – voids Thick epoxy layers Insufficient coil and splice ground insulation Coil 4 9turns Coil 3 9 turns Voids Coil 2 10 turns Thick epoxy Coil 1 9 turns HSM01 Autopsy

10. HSM02 NbTi 4-coil model 2 HSM02 baseline magnetic and mechanical design is the sameas for HSM01. Improved: • mechanical structure and insulation • cable geometry and insulation • coil winding and impregnation procedures SSC cable re-sized: • Thick side 1.600mm =>1.416mm • Thin side 1.375mm =>1.271mm • Avg. 1.413mm =>1.343mm • Width 12.36mm =>12.945mm Cable test => no degradation HSM02 fabrication status: • Preparing for winding • Test in January 2010

11. Next steps Next models will address the issues in preparation to the 6D HCC demo model: Conductor: • MgB2 => low-field higher-temperature margin or operation temperature • Nb3Sn/Nb3Al => higher fields higher-temperature margin • Conductor stabilization => quench protection Coil winding: • hard-bend vs. easy-bend => operation margin Cryostat and coil cooling: • Indirect coil cooling => simple cryostat • Cable-in-conduit – better cooling, simple cryostat P. Lee, NHMFL MgB2 6-on-1 cable (FNAL/HyperTech)

12. Hybrid HS Model • Conceptual design study shows that a Hybrid HS may be needed for HCC • The goal - develop mechanical design and technology for HTS section based on G2 tape/cable and its assembly with RF and Nb3Sn section • The work is partially funded and performed in collaboration with Muons Inc.

13. Modeling HTS section with RF

14. HS rapid prototyping

15. Updated HCC parameters Bz_max~4-14T => NbTi/MgB2 and Nb3Sn

16. Yu. Alexahin et al., PAC2009, PAC2007 HFOFO = Helical FOFO channel of alternating solenoids (ASOL) FOFO-xyz = FOFO with xyz resonance phase advance per cell and one solenoid HFOFO-60 (6 cell period, Q1) HFOFO-120 (6 cell period, Q2) - smaller beta @ absorbers FOFO-180 (2 cell period, Q1) - really low-beta FOFO: HFOFO-270 (4 cell period, Q3) 6D cooling: HFOFO Snake alternating solenoids absorbers RF cavities Similar conductor and technologies as for HS

17. Provide input on solenoid design and parameters for cooling channel based on HFOFO structure • Coordinated specifications of magnet system for 6D cooling demo unit

18. B Coil radius, m 50 T Solenoid Conceptual Design Basic Parameters • Inner bore diameter 50 mm • Length 1 meter • Fields 30 T or higher  • HTS materials Key design issues: • superconductor type • Jc, effect of field direction in case of HTS tapes • stress management • quench protection • cost Conceptual design: • hybrid coil design • coil sections NbTi Nb3Sn BSCCO

19. Strand and Tape Samples

20. HTS/HFS Conductor R&D Monitoring industry progress to provide input to magnet design. This includes studies of the engineering current density (Je) as a function of: • magnetic field => up to 28 T (FNAL-NIMS); • temperature => from superfluid He to LN; • field orientation (for tapes) • bending strain; • longitudinal strain => new fixture being commissioned; • transverse pressure => setup is available.

21. HTS cable R&D G1 cable: • In FY07-08 fabricated and tested several Rutherford cable designs based on Bi-2212 strand (OST) • cabling technology • effect of cable PF • Starting from FY2009 continue this work as part of National HTS program G2 cable: • In FY09 started G2 Roebel cable studies

22. Insert Coil R&D Present focus on single and double-layer pancake coils based on HTS tapes. ~20 single and double-layer pancake coils made of YBCO and Bi-2223 were built and tested in self-field and external solenoid • tape splicing techniques, effect of coil impregnation, coil preload A modular HTS Insert Test Facility to test up to 14 double-layer pancake coils inside the 14T/16T solenoid (B>20 T) For the second phase of the coil program, larger multi-section HTS coils will be designed, fabricated and tested to achieve higher magnetic field and force levels.

23. Summary • The midterm goal of the Fermilab’s accelerator magnet R&D program is to support the Fermilab’s and national efforts towards the demonstration of feasibility of a Muon Collider, with the long term goal of building this machine on Fermilab site. • Fermilab’s magnet program is making progress in all key directions • Magnet design studies • Technology development • HTS material R&D • We collaborate with DOE labs, industries and Universities through National HTS Conductor program, SBIR and other programs. • Our efforts are coordinated with National MAP R&D plan • Adequate and stable funding is critical for the successful magnet R&D • at the present time the program funding is provided by MCTF and HFM Program with contribution from Muons Inc. • after MAP approval by DOE we will still need substantial contribution from core program and other sources