Mu2e Magnet Design Changes Michael Lamm for the Mu2e Collaboration and TD/Magnet Systems Dept. March 26, 2012 All Experimenters Meeting 1 Contributors to the Mu2e Solenoid Design: N. Andreev, G. Ambrosio, R. Bossert, J. Brandt, M. Buehler, R. Coleman, D. Evbota, W. Jaskierny, V.V. Kashikhin, M. Lopes, J. Miller, T. Nicol, D. Orris, R. Ostojic, T. Page, T. Peterson, J. Popp, V, Pronskikh, Z. Tang, M. Tartaglia, Z. Tang, M. Wake, R. Wands and R. Yamada

2 Production Solenoid Transport Solenoid Detector Solenoid Production Target Collimators Stopping Target TrackerCalorimeter protons 2.5T 4.6 T 2.0T 1.0T ee     Mu2e experiment consists of 3 solenoid systems: Measure the Rare Process:  - + N  e- + N Muon timing is important. Negative axial field gradients prevent unwanted trapped particles from entering “Search Window”

March 26, 2012 All Experimenters Meeting 3 Reason for Design Changes Recommendations from May 2011 Independent Design Review –More operating margin for PS –Simplify DS –Better mechanical support for PS coils Value Management exercise in Fall 2011 –Reduce cost of Solenoid project by ~$20M Change in requirements –Field requirements have become less stringent with detailed beam studies  Simplify magnet designs

L2 Solenoid Power Supply/Quench Protection Cryoplant PS IRON DS IRON Field Mapping Ancillary Equipment Insulating vacuum Installation and commissioning Production Solenoid (PS) Transport Solenoid (TS) Detector Solenoid (DS) Cryogenic Distribution OFF PROJECT Single Layer-shorter Spectrometer 4.6 T peak field Less layers for PS DOWN SCALED Changes Since May 2011 IDR 4

PS Baseline Design Changes All Experimenters Meeting 5 Peak field 5T- I operation ~10kA NbTi Rutherford cable + Ni doped aluminum stabilizer (like ATLAS CS) Indirect Cooling (Thermal Siphon) Hadron absorber intercepts beam secondaries –~20 Watts deposited in coils Nominal peak field 4.6T –5T still possible with reduced margin Reduce number of layers Thinner conductor (lower current) Remove iron yoke   Gradient made by 3 axial coils same turn density but change # of layers Wound on individual bobbins

PS Field vs. Tolerance Bands All Experimenters Meeting March 26, Meets 5% field uniformity spec

March 26, 2012 All Experimenters Meeting 7 Collaboration with Japan Fabrication of practice PS coil at Toshiba (4 Layer/8 Turns) Uses aluminum stabilized NbTi conductor from Hitachi Cable Coil will be later tested at Fermilab

New baseline Transport Solenoid TS1 TS2 TS4 TS5 Three  Two cryostats: TSU, TSD TS3:  TS3U, TS3D. Wider coils to compensate for gap Rotatable Collimator, P-bar window G. Ambrosio TS Leader New coil fabrication proposed for better mechanical support. All Experimenters Meeting March 26, TS1,TS3,TS5: Straight sections with axial gradient TS2/TS4: approximate toroidal field Accomplished by many thin solenoid rings of different amp-turns

Coil Fabrication 9 Bolted connections Conductor Al Outer Supports March 26, 2012 Original plan: use SS inner bobbins  mechanical support complications. New plan: fabrication unit consists of two coils with outer support aluminum structure Coils wound on collapsible mandrel-then fit into outer aluminum ring Placement of coil in transport is determined by outer shell geometry All Experimenters Meeting

TS Field Requirements All sections meet all requirements Large margin wrt gradient requirement March 26, 2012 All Experimenters Meeting 10 Axial field distribution in the center of TS3 (left), axial gradient along TS3 (right).

Simplify DS Baseline March 26, 2012 OLD base line –Two coils: gradient + spectrometer bussed in series in a single cryostat –Two layer spectrometer, single mandrel  field uniformity –Two layer gradient on single mandrel with aluminum spacers –Iron return yoke (not shown) 11 All Experimenters Meeting Spectrometer Section Gradient Section

Simplify DS Baseline March 26, 2012 Spectrometer Section Gradient Section New base line driven by relaxed field requirements –Modular coil design  reduced cost/coil –Spectrometer: 3 Single Layer Coils  shorter coils, greatly reduced conductor volume, reduced field uniformity OK –Original conductor cost estimate based on expensive PS conductor, smaller field DS requires smaller cross section, no need for special reinforced aluminum –Relaxed calorimeter field requirements  shorten spectrometer 12 All Experimenters Meeting

DS Field vs. Tolerance Bands March 26, All Experimenters Meeting Gradient Section Spectrometer Section

March 26, 2012 All Experimenters Meeting 14 Conclusion Significant amount of work done prior to CD1 –Conceptual design of solenoids –Technology development with Japan Near term schedule –CD1 directors review April 3-5, Lehman review in June –June Test Toshiba coil/built prototype TS module/prototype conductor –CD2 sometime in 2014 Order conductor/ Contract final design with industry –Begin fabrication in 2016