1. 1. Overview of the mu2e magnet system 2. Collaboration mu2e-COMET R. Ostojic Based on presentation of M. Lamm in ASC2010. All credit goes to the members of the mu2e magnet design team.

2. Measure the Rare Process:  - + N  e- + N → It will be world class experiment in the “Intensity Frontier”… 4 orders of magnitude improvement over existing measurements Judged by the US Department of Energy and the High Energy Physics Community to be a high priority for Fermilab → …either with or without a signal…. WITH: Indicate new physics beyond the “standard model” WITHOUT: Put severe limits on theories beyond the standard model It will compliment Large Hadron Collider (LHC) Experiments 2 What is mu2e?

3. 3 Plan View of Solenoid System 8 GeV P Production Solenoid 8 GeV P hit target. Reflect and focus  /  ’s into muon transport Strong Axial Gradient Solenoid Field Sign/momentum Selection Negative Axial Gradient in S.S. to suppress trapped particles Transport Solenoid Graded field to collect conv. e - Uniform field for e - Spectrometer Detector Solenoid 24 meters

4. 4 Tentative schedule Start of Magnet Construction2013 CD-2/3Mid-2012 CD-1 ReviewMarch 1, 2011 CDR completeJan. 15, 2011 Final cost & schedule and associated documentation. Jan. 15, 2011 Director’s Design ReviewNov. 1, 2010 CD-0Nov, 2009 Time

5. Fermilab will act as a “General Contractor”: PS and DS will likely be built in industry Need to develop a strong conceptual design and technical specifications for vendors Final engineering design done by industry Similar strategy for most detector solenoids TS will likely be designed/built “in house” Cryostat, mechanical supports built by outside vendors Coils wound in-house or industry depending on technology choice Final assemble and test at Fermilab Solenoid task has co-responsibility for all interfaces Significant magnet coupling between PS-TS and TS-DS Tight mechanical interfaces Cryoplant, power supplies, instrumentation… 5 Procurement strategy

6. 6 Detector solenoid

7. Two functions: 1. Axial Gradient Field for particle collection (2T  1T) Uniformity of axial gradient along axis: 5% 2. Uniform field for spectrometer and calorimeter Most like a HEP detector magnet but stricter field specs! ~3 meter high uniform field 0.2% request Significant Axial Forces between Iron, DS and TS 7 DS Challenges

8. Coils wound on separate mandrels, bussed in series, Iop ~5kA Cold mass in “single cryostat” Use Al stabilized NbTi conductor More experience with detector solenoid vendors Considerably less weight Two layer coils throughout Achieve axial gradient by effectively changing winding density by introducing spacers and varying conductor thickness. 8 DS Design Concept

9. 9 DS 5-Coil Design MECO(blue) field is overlapped on the field of this design(red)

10. Unusual field requirements “S”-shaped to reduce line of sight PS to DS; momentum selection negative axial gradient in SS to prevent trapped/out of time particles Effect of magnetic coupling between TSn and PS/DS and S shape: significant non-axial excitation forces complicated stresses during cooldown Removable TS3 to service collimator and vacuum break 10 Transport Solenoid Challenges

11. 11 TS Design Concept 15 0 20 0 TS2/4 assembled using 3-coil modules Conductor in copper channel Sections welded or bolted together Coils bussed in series I op ~1000 Amperes

12. 12 Production Solenoid

13. Axially Graded Field: 5 T  2.5 T ~5.7 T on conductor Wide aperture 1.5 m, 4 m long Large stored energy (~100MJ) There’s a target in the aperture… 25 kW off target, 25-50W into coils…depending on absorber design and beam intensity Heat load and Radiation issues on conductor, insulator and stabilizers Strong Magnetically Coupled with Iron and TS Unlike typical detector solenoid significant axial forces >100 T of axial force 13 PS Challenges

14. Gradient made by 3 axial coils same turn density but increase # of layers (2,3,4 layers) Wound on individual bobbins Aluminum stabilized NbTi reduce weight and nuclear heating Indirect cooling High Current/low inductance Efficient energy extraction Less layers: simplify winding, minimize thermal barriers from conductor to cooling channels. I operation ~10 kA 14 PS Design Decisions

15. 15 Conductor and Coil Support Doped Al NbTi/Cu Cable cross-section Outer support shell Pure Al sheets (RRR>500 ) Coil Configuration 4 Layer Coil “Hardway bend” Epoxy impregnated

16. 5.7 T peak field in the coil; >5 T peak field on the axis; ~2.5 T at the TS interface; <1.5 T field in the yoke body; <2.4 T in the yoke end caps. 16 Flux densities

17. 17 Axial gradient

18. No heat load: Operating point is at 68% of the SSL along load line or at 25% of the SSL at the constant field; Under heat load: The temperature increment of 5.32 K-4.50 K = 0.82 K allows to operate at 80 % of the SSL along the load line or at 40 % of the SSL at the constant field. 18 Critical current

19. 19 3D field distribution

20. The second end cap was added to the iron yoke (vs. MECO) to eliminate the net axial self-Lorentz force (TS=off); When all magnets are powered, the net axial force is +116/-124 tons, depending of the current direction; MECO axial force of 140 tons was used for the design of axial supports; Due to the force directions, the coil to coil interfaces are always under compression. 20 Axial forces 22.46 MN 10.65 MN

21. The Lorentz forces are reacted by the outer shells made or Al 6061-T6; The shells are assembled around the coils with no prestress; All gaps are filled with epoxy. Coil support concept 21 The Lorentz forces are reacted by the outer shells made or Al 6061-T6; The shells are assembled around the coils with no prestress; All gaps are filled with epoxy.

22. 22 Cryostat design Thermal syphon cooling Suspension system

23. 8 GeV proton beam, Au target (r=0.3 cm, H 2 0, Ti), 25 kW, I=2E13, σ x = σ y = 1 mm 23 Baseline absorber configuration

24. 24 Neutron flux >100 keV and power deposition Absorbed dose (Gy/s) = Power density (mW/g), i.e., peak in the coils ~ 100 kGy/yr

25. 25 DPA (displacements/atom) Peak DPA in Al ~2x10 -5 /yr

26. 26 NbTi degradation (Al Zeller, 2003) http://supercon.lbl.gov/WAAM/ 5% degr. 15-20 years to accumulate 5 % of I c degradation (w/o annealing)

27. Under the expected dose of 2÷6·10 -5 DPA/year, Al resistivity degrades by a factor of:  5÷10 at B = 0 T  2.5÷5 at B = 5 T 27 Al resistivity degradation

28. Al resistivity recovers during the thermal cycle:  by 60 % at 80 K;  by 100 % at 300 K. 28 Al resistivity recovery

29. 29 Quench protection

30. Pion Capture Solenoid Muon Transport Solenoid Spectrometer Solenoid Detector Solenoid proton beam pion production target radiation shield iron yoke CS MS1 MS2 COMET SC Magnets

31. R&D Program Model coils of Al- stabilized superconductor with high yield strength  Development of conductor  Model coil in the COMET- Mu2e collaboration Neutron irradiation test  Expect 10 21 n/m2 for 30 day operation in COMET  Need to check degradation of high yield strength aluminum “Isochronal recovery of fast neutron irradiated metals,” J.A. Horak and T.H. Blewitt, Journal of Nuclear Materials, Volume 49, Issue 2, December 1973, Pages 161-180

32. Neutron irradiation facility Check degradation of stabilizer up to 10 21 neutrons/m 2  degradation of resistivity  recovery by annealing to RT Kyoto Univ. Research Reactor （ KUR ）  5MW at maximum  Low temperature facility available  10K-20K  9.8 x 10 11 n/cm²/s 32

33. The design of the mu2e experiment and its magnet system is vigorously proceeding with the goal of obtaining the DOE CD-1 approval in Spring 2011. The mu2e magnet design uses many of the features developed for the latest generation of detector magnets. Its specific issues are: high field gradient, tight field tolerances and high radiation level. The magnets will be built in industry and at Fermilab and should be operational by 2016. Their construction could be regarded as a technological bridge between the solenoids built for ATLAS and CMS and those proposed for the LC experiments. A collaboration has been established between mu2e and COMET in view of resolving joint concerns, in particular obtaining improved data on properties of superconductors and stabilizers after irradiation. 33 Summary