Mu2e Superconducting Solenoids

1. Mu2e Superconducting Solenoids Michael Lamm Fermilab TD/Magnet Systems Dept. Mu2e/Comet Joint Workshop January 24, 2009

2. Talk Outline • Mu2e Magnet System Description • Present State of Magnet Design for Mu2e • Design Issues • Possible collaboration with COMET collaboration Mu2E/COMET Joint Workshop

3. History of Muon System Design • Mu2e baseline is the the MECO solenoid system • Conceptual Design completed in 2002 • Cost and schedule as well as technical details • Several incremental improvements to design 2002-2005 • Documented in reviews and internal notes • But CDR was never updated • CDR and subsequent design improvements were favorably reviewed several times Mu2E/COMET Joint Workshop

4. Magnet System by Cryostat and Powering • Production Solenoid • Single Cryostat: pool-boiling • Single power supply • Transport Solenoid • Two cryostats: Indirect cooling • Four power supplies • No iron shielding envisioned • Kapton window • Detector Solenoid • Single Cryostat: Indirect cooling • Single Power supply Designed for independent cooling and powering Mu2E/COMET Joint Workshop

5. Mu2e Coil Design • System consists of 96 coil units (~80km of SSC cable) • Fields 1-5 T, Aperture 1-2 meters, 1.5-4 kA excitation • Very large operating margin in current density, field and temperature • Conductor • SSC cable soldered into a half hardened copper bar • Insulated with glass tape and Kapton • Stabilizer is sized for Production, Transport and Capture target requirements • Structure • epoxy vacuum impregnated • outer mandrel for hoop stress • Coils series-connected through soldered splice joints LDX Coil SSC cable Copper Bar Mu2E/COMET Joint Workshop

6. Mu2e Quench Protection • Digital Quench Protection with analog backup • Input • Calculated Inductance Matrix and Splice Resistance • Monitor voltage across each coil, power supply current I(t) • Upon quench (deviation from expect voltage over long integration time) • Extract current from quenched magnet through external dump resistor • Other magnets brought down in orderly fashion • Design peak voltage to ground (1kV) • Design peak spot temperature ~150K Mu2E/COMET Joint Workshop

7. Mu2e and the MECO Magnet System • Mu2e is studying the Meco design • Face to face meeting with magnet designers(MITGA) • Developing proposal with General Atomics (GA) to assemble and documents to produce an updated CDR • Time frame: 4 months • We will use this time to investigate ways to make the Mu2E solenoid system more efficient i.e.: • Produce more “capturable” muons/incident proton, less background • For less money and as quickly as possible (since the magnet system seems to be the cost and schedule driver for the experiment) Mu2E/COMET Joint Workshop

8. Areas of Investigation from Baseline Mu2e • Punt on the reflected pions/muons in the production solenoid • Eliminate highest field solenoid • Forward production is swept from the magnets: less nuclear heating • Indirect cooling then may be possible • Go away from SSC conductor to wider cable • Higher current, but less turns, lower inductance • May be easier to build • Sub-divide magnet system into smaller units for powering • More effective extraction, reduce the amount of stabilizer • With HTS leads, helium consumption penalty is substantially reduced • Have to weigh against added cost of HTS leads, extraction circuits, PS etc. • Use of other conductors • For e.g., use of Aluminum stabilized conductor. Related to this.. • Look for synergies with COMET experiment Mu2E/COMET Joint Workshop

9. Possible Areas of Mu2e/Comet Magnet Collaboration Conductor development • While there are several commonalities in the magnetic design…. • Common goal of maximizing clean “capturable muons” • …there are significant differences in the actual magnet designs • A large driver is the conductor choice which greatly influences mechanical and quench designs • Conductor development (Aluminum stabilized conductor) is a logical place to consider collaboration • Could have significant benefits for Mu2e design • But need to make clear case for moving away from baseline • COMET has some concerns that need to addressed about the availability and affordability of the aluminum stabilized conductor on the market today… • Vendors who will bid on magnet fabrication may have a preference towards a particular technology • Most detector solenoids in recent times built with stabilizer Al • Should be prepared to consider all reasonable proposals Mu2E/COMET Joint Workshop

10. Areas of Collaboration II • Under discussion is a proposal under the US-Japan agreement to study muon beamline magnets • In particular, the parts of the proposal addressing Al stabilized NbTi, are very well aligned with the near term interests of both Mu2E and Comet. • Hopefully this program, if approved, will produce conductor in the 2010 that would be timely for Mu2e/Comet tests and prototypes. • The immediate need for a realistic detailed conductor specification • In the case of Mu2e, conceptual design studies with Al stabilizer should be performed in parallel with the Meco CDR updates (i.e. in the next 6 months) • Therefore, we should develop as soon as possible a conductor specification with realistic attainable Jc and good structural properties • Aligned with US-Japan agreement • Near term need for practice conductor • We would ask that in the very near future, some conductor is identified, either from surplus or available from industry that could be used to practice winding coils in the near future. If possible this conductor should be as close as possible to the future base line conductor. Mu2E/COMET Joint Workshop

11. Focus on Design of Pion-Production Solenoid • Recognizing similarities in function of Pion-Production Solenoids for Mu2e/COMET… • Using common conductor design… • Select a few design studies of mutual interests • Possible topics: • Quench protection of coupled solenoids under various power schemes • Heat load studies on production solenoids from particle production under various shielding scenarios. This would require coordination with particle production models, particle interaction models like MARS as well as the magnet quench codes, which would be a good cross check on the two experiments. • Agree on sensible thermal and quench margins, safe differential thermal contractions due to quenches, based on previous detector practices. • There are probably other studies that could be proposed. Mu2E/COMET Joint Workshop