Twin Solenoid Twin Solenoid - conceptual design for FCC-hh detector magnet - Matthias GT Mentink Alexey Dudarev Helder Pais Da Silva Leonardo Erik Gerritse Herman ten Kate FCC Detectors CERN, 3 Feb

Overview  Introduction / general concept  Mechanical analysis of the cold mass  Quench protection  Magnetic properties and field integrals 2

Introduction CMS system: 4 T solenoid, iron yoke Cold mass: 0.23 kt Iron mass: ~ 11.6 kt Stored energy: 2.6 GJ Stored energy density: 12.2 kJ/kg CMS+ option Twin Solenoid option ~8x increase in volume ~1.5x increase in magnetic field 3

Cold Mass Concept Stored energy: 70 GJ (  B 2 V), conductor stored energy density: 12.6 kJ/kg  Conductor mass: ~6 kt (Total cold mass: ~10 kt) Large forces resulting from minor misalignments between the coils  Support cylinders and spokes are essential parts of the cold mass Large forces and high stored energy  high-strength aluminum stabilized conductor 3.5 meters for muon detectors between solenoids (B = 3.3 T, almost empty) 5 mT line at 38 meters away from center Superconducting coils Support structure 4

Structural Support Concept Warm bore tube (1.5 kt) Space for muon chambers Inner detector and calorimeters resting on the bore tube (~15 kt ?) Twin Solenoid (10 kt) Vacuum vessel Fixed point Outer support frame Tie rods 5

Overview  Introduction / general concept  Mechanical analysis of the cold mass  Quench protection  Magnetic properties and field integrals 6

Lorentz Forces Coil is pressed into support structure due to radial Lorentz force. Both the inner and outer solenoids are under net compression (on purpose to avoid local tensile stress). Formation of a gap would result in a larger compressive force in the support structure relative to the coil  No gaps between coils and support structure Radial forces (MN) Axial forces (MN)

Mechanical Analysis of Six Different Scenarios Combined magnetic and mechanical calculations. Two bonding scenarios: fully bonded and frictionless contacts between coil windings and support structure. Six scenarios: Normal operation, misalignment along axial / off-axis orientations, rotational misalignment, and seismic activity along axial direction and off-axis directions. Modeling assumption: twin solenoid is hanging on inner support rings. 8

Von Mises Stress in the structure (case 1) Case 1. Gravity + Lorentz force (Normal operation) Fully bonded (frictionless) Coils: ≤ 80 (80) MPa Spokes: ≤ 90 (95) MPa Support structure: ≤ 75 (85) MPa 9

Von Mises Stress in the structure (case 2) Case 2. Gravity + Lorentz force + 20 mm axial misalignment (  8 MN repulsion) Fully bonded (frictionless) Coils: ≤ 80 (80) MPa Spokes: ≤ 100 (105) MPa Support structure: ≤ 75 (85) MPa 10

Von Mises Stress in the structure (case 3) Case 3. Gravity + Lorentz force + 20 mm off-axis misalignment (  4 MN repulsion) Fully bonded (frictionless) Coils: ≤ 80 (80) MPa Spokes: ≤ 90 (95) MPa Support structure: ≤ 75 (85) MPa 11

Von Mises Stress in the structure (case 4) Case 4. Gravity + Lorentz force + 2 degree rotation (1 GNm torque) Coils: ≤ 85 (85) MPa Spokes: ≤ 125 (100) MPa Support structure: ≤ 85 (100) MPa 12

Von Mises Stress in the structure (case 5) Case 5. Gravity + Lorentz force + Seismic along gravity direction (1.2g along off-axis direction) Coils: ≤ 80 (80) MPa Spokes: ≤ 70 (75) MPa Support structure: ≤ 75 (75) MPa 1g + 1.2g 13

Von Mises Stress in the structure (case 6) Case 6. Gravity + Lorentz force + Seismic activity (1.2g along axial direction)  Both solenoids are supported by stops Coils: ≤ 80 (80) MPa Spokes: ≤ 90 (95) MPa Support structure: ≤ 75 (85) MPa 1.2g 14

Von Mises Stress - Summary Superconducting coils have to withstand 80 MPa. For example: ATLAS solenoid conductor yield strength at 4.2 K = 146 MPa. Forces on spokes and support structure depend on level of misalignment, but can all be handled safely considering realistic misalignments! ScenarioMaximum Von Mises Stress CoilsSpokes Support structure Normal Axial misalignment Off-axial misalignment Rotational misalignment Seismic (off-axis) 8075 Seismic (axial)

Overview  Introduction / general concept  Mechanical analysis of the cold mass  Quench protection  Magnetic properties and field integrals 16

Quench Protection PropertyValue Conductor current [kA]100 Current density [A/mm 2 ]6.0 Number of turns2430 Inductance [H]14.2 Maximum voltage [V]1000 Dump resistance [Ω]0.01 Magnetic energy per kg conductor [kJ/kg] 12.6 Assumed RRR200 Outer solenoid Inner solenoid 17

Quench Protection Scenarios Simplified assumption: Instantaneous quench propagation The cold mass temperature at quench remains safe at 87 and 62 K without and with energy extraction, respectively. No dump resistor: 87 K With dump resistor: 62 K (66% extraction) 18

Overview  Introduction / general concept  Mechanical analysis of the cold mass  Quench protection  Magnetic properties and field integrals 19

Peak Field on the Superconductor Peak field: 6.7 T Peak field on the superconductor: 6.7 T (uniform current distribution) NbTi: B c2 at 5 K = 9.4 T For safe operation with maximum of temperature margin cooling channels inside the conductor are preferential. 20

Field Integrals: Current Design η=0: 35 Tm inside inner solenoid, 12 Tm between solenoids. Field integral drops off at high η. Pseudorapidity η R [m] 21

Field Integrals: Longer Outer Solenoid Longer outer solenoid, with higher outer radius. η=0: 35 Tm inside inner solenoid, 13 Tm between solenoids. 85 GJ stored magnetic energy instead of 71 GJ

Field Integrals: With Iron Regular design, but with two 1.6 kt iron blocks in forward direction to shape locally the magnetic field. Minor increase in field integral (8 Tm  9 Tm) inside iron. Stored magnetic energy remains 71 GJ

Field Integrals: Current Design η=0: 35 Tm inside inner solenoid, 12 Tm between solenoids. Field integral drops off at high η  an additional magnet may be needed. Pseudorapidity η ? R [m] 24

Conclusion Twin Solenoid Design The mechanical and thermal behaviour of the system is challenging but certainly doable. NbTi can be used as a superconducting material, but with limited temperature margin  Direct cooling of conductor is preferable. Field integral at η = 0: 35 Tm inside the solenoid and 12 Tm in between the solenoids. 25