1. Superconducting solenoid for MPD detector on heavy-ion collider NICA at JINR (Dubna) Presented by Evgeny K. Koshurnikov CERN September 27, 2011

2. Superconducting solenoid of Multi- Purpose Detector (MPD) The main component of the Multi-Purpose Detector (MPD) on heavy-ion collider NICA is a large 0.5 T superconducting solenoid. It has to provide resolution for transverse momenta over the range 0.1 ‑ 3 GeV/c. The magnet is designed as a superconducting solenoid with a flux return iron yoke and with aluminium stabilized coil implying an inner winding method and circulating indirect cooling. The magnet has to be commissioned in 2017. 2

3. General view of MPD 3 The magnet inner dimensions are chosen as a compromise between the time of flight requirements to length of tracks to be sufficient for good particle identification and track reconstruction precision on one side, and the needs in homogeneous magnetic field and reasonable cost of the magnet on the other side.

4. Interface requirements The solenoid aperture volume is determined by arrangement of the inner detectors ΔZ=5.24m; Ø=4m Requirement for cryostat radiation transparency is not considered It takes pole taper bores 14°- acceptance for two future forward spectrometers Important requirement! The installed electrical capacity in Dubna is very limited. So the decision was taken for benefit of superconducting winding 4

5. Magnetic field requirements Rated magnetic field in the aperture 0.5T High level homogeneity dictates requirements for the magnet geometry stability under action of the magnetic forces and after magnet transportation to assembly area and back 5 Magnetic field requirements are optimized for momentum resolution of particles. Requirement for integral of radial component of the magnetic field

6. MPDSolenoid Design MPD Solenoid Design Distinctive features of the magnet high field homogeneity in the tracker area, heavy weight and large dimensions of the system. Accepted concept is the well proved design Solenoid with a thin winding, pure aluminum stabilized NbTi superconductor, indirect cooling of the coil, and flux return iron yoke Yoke geometry stability is secured by the rigidity of two support rings joined by twelve flux return legs (this design is analogues to STAR magnet yoke design) Two correcting coils with higher linear current density at the ends of the main coil and trim coils on the poletips Other magnet features The magnet doesn’t have doors. The poles are being inserted in axial direction Inner detectors are fixated on the yoke support rings. So the inner shell of the cryostat is not loaded by addition weight of the detectors 6

7. Main solenoid parameters 7 Rated current, kA1.44 Rated induction, T0.5 Т Maximal designed current, kA1.59 Maximal flux density in the coil at maximal designed current [T]0.61 Current density in aluminium matrix of the corrective/main coil conductor for designed current, A/mm 2 50.2/46.6 Total current (Amp-turns) at the rated induction [ MA]2.18 Stored energy at the rated induction [ MJ]7.9 Decentering forces acted on the coil -axial force, kN/cm -radial force, kN/cm 37 1.07 Number of turns (main section of the SC coil and in the correcting sections)1512=758+2 x 377 Inductivity of the SC coil [H]7.3 Inductivity of the trim coil [H]0.0038 Rated/Maximal current density in the trim coil at the nominal induction [А/mm 2 ] 1.467/1.89 Total current (Amp-turns) in the trim coil at the nominal induction [kA]9797

8. MAGNETIC FIELD CALCULATIONS OPERA-3D and FE-2D software, original FORTRAN and Mathcad – based computer codes FE TOSCA model (1.8 ∙ 10 6 ÷ 5 ∙ 10 6 nodes)

9. MAGNET OPTIMIZATION The goal of optimization is minimization of the integral of the radial component of magnetic induction keeping minimal values of main and corrective coil current density difference and current density in the trim coil with help of Mathcad – based computer code Optimization parameters are:  Relation of current densities of corrective and main sc coils J CORR / J SC,  Trim coil current density J TRIM  SC coil current density J SC. Two first parameters are independent and the last parameter depends on the first two parameters trough the average magnetic induction in TPC area. 9 SC corrective coil center position dependence for radial component integral in the TPC area and relation of sc coils current densities Very high homogeneity of magnetic field and very low integral of radial component for the TPC area are achieved Int max = 0.17 mm< 0.775 mm |δ| < 0.12%

10. 10 SC solenoid coil One layer coil is wound on the inside of the structural aluminum alloy Al5083 cylinder Indirect cooling by force two-phase helium Two corrective coils with the current density about 6% higher than in central coil Radial conductor size and aluminium cylinder thickness provides acceptable temperature rise after a quench and keeping of the coil shape under gravity. Radial deformation of the coil loaded by gravity, magnetic pressure and radial decentering force <0.5mm Maximal radial magnetic pressure 0.12 MPa, maximal axial compression force 470 kN. Cooling tube length 80 m, diameter 18 mm

11. Main parameters of the conductor 11 Aluminium stabilized conductor with central sc wire Ø1.2 mm The critical parameters of the conductor for low inductions were chosen on the base of approximation expressions L. Bottura. “A practical fit for the critical surface of NbTi”. CERN, LHC Project Report, MT-16, 1999. The design current 1.59kA is ~40% along the load line to the conductor capability at the temperature 4.5 K. The maximal current corresponds to a temperature 7.2 K leaving a temperature margin of greater than 2.7 K at the maximal induction 0.61 T at the coil end. MQE ~1 J/cm 3

12. Influence of technological deviations on the magnet parameters Nature of deviation Change of the integral of radial component [mm] Axial/radial force on the shifted unit [kN] Current density in the trim 1 / trim 2 coils [А/mm 2 ] Axial shift of SC coil by 10 mm 0.1636/01.39/1.59 Radial shift of SC coil by 10 mm 0.010/2.71.467/1.467 Symmetric axial shift of the poles by +5 mm each 0.04890/01.536/1.536 Radial shift of the pole by 5 mm 0.02940/1371.467/1.467 Radial deformation of the coil Δ = 10 mm 0.020/01.467/1.467 Axial shortening of the SC coil by 1% 0.310/01.753/1.753 Complex axial deviation * 0.5234.3/0 (SC coil)1.68/1.89 * Cumulative effect of all axial deviations given in the previous lines of the table 12

13. 13 Cryostat design Stainless steel cryostat: t o =16mm/t i =13mm. Maximal overpressure– 0.7 Bar. Cryostat supports Control Dewar 2x12 radial ties 6 axial ties Inner radius, m2.02 Outer radius, m2.36 Length, m5.7 Inner radius, m2.02 Outer radius, m2.36 Length, m5.7

14. Cryogenic system 14 Heat load at T=4.5 K, W46 Heat load on the Control Dewar heat exchanger, W 123 Refrigerating capacity (including thermal screen), W 220 Forward flow, g/s9.8 Return flow, g/s9.58 The flow trough the current leads, g/s 0.22 Steam-content in the inlet/outlet of heat exchanger, %5/ 23 Pressure drop in the cooling tube, kPa4.7 Gaseous Helium flow for thermal screen, g/s2.9 «Linde» Refrigerator LR 140, 210 - 255 W at 4.5K Forced Two-Phase cooling system Helium circuit parameters Cryostatting cycle in T-S diagram

15. Yoke Assembly at the factory and in the Experimental building 15 Part count WeightSum Iron Yoke Support ring, ton220.941.8 Barrel beam, ton1217.2206.4 Pole tip inner ring, ton 21428 Pole tip outer ring, ton 214.428.8 Yoke support, ton217.535 Pole support, ton231.763.4 Trim coil, ton20.751.51.5 Total (weight of the yoke): 405 Cryostat & coil Vacuum vessel, ton126.426.426.4 Thermal shield, ton11.31.31.31.3 Coil+Support cylinder, ton 16.36.36.36.3 Total (cryostat+coil) 3434 Grand total (magnet weight) 440 Weights of the magnet main parts Incircle radius of the yoke, m2.4 Circumcircle radius of the yoke, m2.67 Interpole distance, m5.24 Length of the yoke, m6.4

16. 16 Assembly/Operation conditions Parking Position Operation Position Rails for magnet and platform transportations Platforms for equipment and electronics Magnet poles on their rails Assembled magnet Accelerator ring Iron yoke and cryostat with assembled inner detectors

17. Moving and Supports Systems 17 Yoke movement – 2 hydraulic cylinders Pole insertion – 2+2 cylinders Yoke supports – 6 cylinders The magnet has:  Two hydraulic horizontal drive cylinders for translation of the detector, which have positional feedback gages of the pistons.  Controller which allows operation of each cylinder either independently or synchronously. At every stage of movement the free ends of the cylinders are fixed on the floor. The detector is translated of 1.5m and after that the pistons repositioned in new positions on the floor for the next step of translation. Hilman Rollers

18. Solenoid Coil Quench Protection 18 symmetry: 1 / 2 in axial and 1 / 32 in azimuthal direction QUENCH model of electric circuit R1 = 1.3 ∙ 10 -3 Ohm R2 = 0.3145 Ohm S1 opens when V nz >1 Volt QUENCH FE design model Quench processes were modeled by means of Vector Fields Software Protection Circuit

19. MODELLING OF THE COIL PROTECTION QUENCH, TEMPO and ELEKTRA modules of the OPERA-3D software Detail of FE QUENCH model (2.5 ∙ 10 6 nodes) Al cylinder Insulation Yoke pole Air SC coil Quench-back effect is seen (60 sec after quench starts) Temperature distribution: 40 sec after quench starts 19

20. RESULTS OF THE QUENCH TRANSIENT ANALYSIS Energy extraction to the external dump resistor Energy extraction without active protection ParameterWith protectionWithout protection Maximal temperature (design current 1590 A), T max [K]24112 (100 for Al6061) Maximal temperature difference in the coil, ΔT max [K]1493 Maximal radial temperature difference in insulation, ΔTr max [K]430 Maximal voltage on the normal zone, V max [Volt]19230 Energy dissipated in the coil, W [MJ]0.438.98 20

21. Yoke deflected mode under action of gravity and magnetic forces 21 Maximal pole to pole approach distance < 2 х 0.5 mm for rated solenoid current and for ANY combination of the magnet support reactions The magnetic force applied to the pole = 960kN. Maximal vertical deflection of the support cradles when magnet is rested on two supports <1mm Maximal stresses (membrane+bending) are located in the Yoke cradles Normal operative condition, MPa [169] 43 Violation of Normal operative Conditions, MPa [234] 56

22. Stress in the CryostatShells Stress in the Cryostat Shells 22 Operative magnet on two diagonal supports. Equivalent stress in the cryostat shell Magnet transportation. Two diagonal supports Vertical deformation of the cryostat shell

23. Conclusion The most critical features of the magnet of Multi- Purpose Detector (MPD) :  low value of integral of radial component of magnetic induction  large overall dimensions and heavy weight The solenoid design provides very rigid fixation of the yoke and cryostat parts. The mutual positions of the solenoid parts are secured against action of gravity and magnetic forces after multiple magnet transportations to beam/parking position and removing/insertion of the poles.

24. 24 THANK YOU FOR YOUR ATTENTION!

25. Comparison of solenoids similar to the MPD solenoid 25

26. RESULTS OF OPTIMIZATION 26

27. T=4.5 K (safety factor 2) Load, Watt Radiation 20.5 Support conduction 9 Chimney and Control Dewar 10 Conductor joints and wires 2 Eddy current losses in the Al cylinder 12 Total (normal/transient regime): 41.5/53.5 T=77 K (safety factor 2) Radiation 398 Shield supports conduction 73 Heat intercepts of the coil supports 140 Total:611 Current leads (safety factor 1.5) Operation current 0.22 g/sec Zero current 0.094 g/sec Heat Loads 27

28. Deformation of the coil loaded by gravity, magnetic pressure and radial decentering force Radial displacements The maximal radial deviation of the coil shape doesn't exceed 0.5 mm Coil space fixation by 2 x 12 radial ties Two 45 mm thickenings on both ends of the support cylinder 28 The origin of decentering force: 20 mm vertical off-center coil displacement

29. Maximal stresses (membrane+bending) Yoke beams Magnet transportation, MPa[169] 5,5 Normal operative condition, MPa [169]3,6 Violation of Normal operative Conditions, MPa [234]7,5 Cryostat outer shell and flanges/ Cryostat supports Magnet transportation, MPa[169] 30,6/64,1 Normal operative condition, MPa [169] 9,7/24,4 Violation of Normal operative Conditions, MPa [234] 36,3/97,5 Yoke Support Rings & Poles Normal operative condition, MPa [169] 10,3 Violation of Normal operative Conditions, MPa [234] 11,0 Yoke cradles Normal operative condition, MPa [169] 43,4 Violation of Normal operative Conditions, MPa [234] 55,5 29

30. Maximal axial deformation of the yoke under action of gravity and magnetic forces Maximal pole to pole approach distance < 2 х 0.5 mm for rated solenoid current and for ANY combination of the magnet support reactions 30 U z1 <0.36mm

31. Yoke footprint vertical deflection 31 Maximal vertical deflection of ANY combination of the support point lost <0.94mm

32. Stresses in the coil 32 Tensile stress in aluminium 5083 support cylinder under action of differential thermal contraction and magnetic pressure  =26 MPa <  al  =92MPa Local axial tensile stress conductor/insulation because of differential thermal contraction  =6 MPa (Axial prestress = 10MPa/162 ton) Local shear stress conductor/insulation because of differential thermal contraction τ=12 MPa Equivalent stress in the aluminium matrix of the conductor  =11 MPa (plastic deformation is considered)

33. Thermomechanical stresses in the coil on the conductor/insulation boundaries 33 Local radial tensile stress up to  =13 MPa >  ins  =10MPa Local shear stress τ max =12 MPa >  τ  =7MPa Local axial tensile stress  max =16 MPa >  ins  =10MPa

34. Axial and Radial Passages for Cabling and Tubing 34

35. Yoke Deflected Mode FE Computations 35 Step-by-step load application in the process of FE computation: Gravity load. The poles are not mounted Gravity load. The poles are mounted Gravity load. The poles are mounted. Magnet is rested on two diagonal support points Gravity load. The poles are mounted. Magnet is rested on two diagonal support points. Magnetic forces. Six magnet support points. Operative regime - Normal Conditions The pressure in two diagonal hydraulic mountings is 20% higher than in all other mountings. Operative regime - Normal Conditions Two diagonal magnet supports. Operative regime – Violation of Normal Conditions M48 studs 2 x 72 pcs. Initial M48 stud tightening force 295 kN Two critical Studs M48 M24/M42/M48 (magnet is in the beam position) Normal operative conditions, MPa [708] 388/571/533 Emergency conditions, MPa [ 1000 ] 1200/580/1110 Action M24 → M27 At least 2x3 beam/ring radial contacts