The S uperconducting Magnet of the Multipurpose Detector

1. Joint Institute for Nuclear Research (Dubna) The Superconducting Magnet of the Multipurpose Detector Evgeny Koshurnikov On behalf of the MPD (NICA) Collaboration Novosibirsk February 25, 2014

2. Superconducting MPD Magnet The multipurpose detector (MPD) is a 4π spectrometer to be used for studying particles in heavy ion collisions at the NICA collider of the Joint Institute for Nuclear Research in Dubna. A constituent part of MPD is a solenoid magnet with a superconducting coil and a steel flux return yoke. The yoke consists of a barrel part and two end caps equipped with the trim coils. Two support rings provide general structural rigidity of the construction. The access to the inner detectors is provided by withdrawing the pole caps. February 25, 2014, Novosibirsk

3. Main parameters of the MPD magnet Magnet aperture V=122 m3(D=4.596 m, L=7.35 m) Rated field of the magnet, Т 0.5 Rated Ampere-turns of the sc coil, MA 3.0 Rated current of the sc coil, кА 1.79 Maximum design current of the sc coil, кА2.39 Stored energy at the design current, MJ 25.4 Maximal Ampere-turns of the trim coil, kA 151 Weight of the MPD detector (magnet +inner detectors), t 980 February 25, 2014, Novosibirsk

4. Magnetic Field Requirements • Rated axial component of induction in the tracker area - 0.5 T; • Integrals of the radial & azimuthal components of induction in the area of Charged Particle Tracker (TPC) : • Magnetic field inhomogeneity in the • tracker area February 25, 2014, Novosibirsk

5. Optimized geometry of the magnetic circuit The optimized geometry provides the better integral and the field homogeneity in the TPC area than it was specified: The optimized geometry (without corrective coils at the sc coil edges |Int|max = 0.08 mm < 0.775 mm δ = 3∙10-4< 10-3 TPC • Stability of the optimized geometry was verified with respect to technological deviations for the specified requirements to the field quality at the rated induction. • axial displacement of the SC coil 20 mm • axial displacement of the poles 5 mm • axial change of the linear current • density of the SC coil 2% • radial displacement of the sc coil 20 mm • radial displacement of a pole relative • to the opening of the support ring 1 mm. February 25, 2014, Novosibirsk

6. Main parameters of the SC cable Conductor: co-extruded high-purity aluminum (99.999%, RRR>1000) and a NbTi wire 1.4 mm in diameter The design current 2.39 kA provides safety margin ~45% along the load line to the conductor capability at the temperature 4.5 K and leaves a temperature margin ~2.3 K at the maximal induction 0.67 T in the coil. February 25, 2014, Novosibirsk

7. Transient processes after a quench Transient processes after a quench were computed taking into account eddy currents and heat capacity of the aluminum support cylinder, using the program QUENCH with an optional module TEMPO and program ELEKTRA, forming part of software Opera-3D 1/32 part FE model of the coil with the aluminium support cylinder Power supply circuit of the magnet and protection circuit of the sc coil February 25, 2014, Novosibirsk

8. Quench analysis The temperature distribution at the moment t = 300 sec after an unprotected quench at the design current 2.4 kA Maximal temperature, current and voltage across a normal zone for an unprotected quench (Initialization Points at the edge and at the center of the coil ). Tmax=108 K W=25.4 MJ February 25, 2014, Novosibirsk

9. Main dimensions of the magnet yoke Outer diameter, mm6583 Inner diameter, mm 5883 Length , mm 9010 Interpole distance, mm 7390 Number of beams 24 Yoke beam weight, t 18.5 Support ring weight, t 41.8 Pole weight, t 43.7 To fix the beams to the supports rings 96 x 2=192 studs M48x3 equipped by Super-Nuts will be used Super-nut February 25, 2014, Novosibirsk

10. Cryostat Cryostat length, mm7910 Inner diameter, mm4656 Outer diameter, mm5443 Δi, Δe, mm 16; 25 Weight of vacuum vessel, t 48.8 Thermal shield weight, t 2.7 Material of the suspension ties Inconel 718 Axial decentering force 61 kN/cm Radial decentering force 5.4 kN/cm February 25, 2014, Novosibirsk

11. Superconducting Winding Aluminium stabilized sc cable is internally wound into an aluminium mandrel (Al5083). Axial pre-stress of 10 MPa reduces the tensile stress between the turns to allowable level. Cold mass (conductor mass)13.3 (6.5)tons Number of turns 1674 Length of the sc cable27 km SC coil is indirectly cooled by two phase helium through the thermal contact with the aluminum cylinder. February 25, 2014, Novosibirsk

12. Trim Coils on the Pole Tips Aluminum conductor 42 × 42 mm2 Hole diameter 27 mm Radius of edges rounding 2 mm Maximal Ampere-Turns 151kA (2.06 A/mm2) Maximal current 4.44 kA(35 V) Cooling water flow rate 1.24 l/sec Pressure drop 7.7bar February 25, 2014, Novosibirsk

13. MPD Magnet in the In-Beam Position February 25, 2014, Novosibirsk

14. FE model, Main Load Cases, Results of Analysis Stress in all magnet parts are within allowable level. Safety margins are sufficient If a roller skate runs over on-path irregularity (until the loss of contacts on a diagonal) it could result in the subsequent change ​​of reactions in the stationary supports up to 25% andin a residual deformations of the support rings (up to 0.26 mm). February 25, 2014, Novosibirsk

15. FE model of the sc coils.Loading steps Al 99.999 Loading Steps in the Design Model Simulating of axial pre-stress 10 MPaof the coil turns. Modeling of the state after epoxy curing and removal pre-stress load. Cooling down from 20°C to -269°C. Cooling down plus magnetic forces. Warming up and magnetic loads removal. Repetition of the loading steps 3-4-5-3… Accepted values of allowable stress for insulation at 4.5K : tens=6,6MPa; =7,0MPa February 25, 2014, Novosibirsk

16. Results of stress-strain analysis of the coil • Mean tensile and shear stress in the coil insulation ​​do not exceed the allowable values. Nevertheless cracks can be expected in small local areas of side turns where the permissible value of the tensile and shear stresses significantly exceeded. • Cycling (→ cooling → magnetic force → heating →cooling →….) has the maximum impact on the radial stress. The local radial stress on the outer surface of the side turns increases by 20-75% after the eight cycles. However, for adjacent turns this effect is almost negligible. • Maximal equivalent stress over the support cylinder for the combined load (temperature and magnetic) is 18.9 MPa <[92MPa] (central part). • Maximal local stress in the support cylinder and in the pressure rings is 117 MPa< [120 MPa] for the combined load (temperature and magnetic). • The maximal elastoplastic equivalent stress in the conductor matrix reaches 21 MPain small area around the superconducting wire for the side turns of the coil. February 25, 2014, Novosibirsk

17. Cryogenic System. Forced two-phase Helium Cooling and thermosyphon regimes Refrigerator: «Linde» LR 140 with cooling capacity up to 400 W at the temperature level of 4.5 K. • 1. Operating pressure of the • refrigerator • 2. 3bar, 5.5К • 2’. 3 bar, 5.65 K • 3.3 bar, 4.7 K • 4.1.35 bar, 4.55 K, 5 % • 5.1.3 bar, 4.5 K, 30 % • 6. 1.3 bar, 4.5 K, saturated • vapor Main parameters of the cooling system February 25, 2014, Novosibirsk

18. Distinctive Features of the MPD Magnet • Large dimensions and weight; • Strict requirements to the field quality and as a consequence: • restriction on mutual displacements of the magnet parts; • disuse of correction coils at the ends of the superconducting coil. February 25, 2014, Novosibirsk

19. Status of work • Technical design of the MPD magnet was finished in 2013 • The project has passed Independent expertise • The project was presented at two meetings with CERN experts • Preliminary discussions with potential manufacturers are in progress • There may be some design changes due to further amendments of the inner detectors... • The magnet has to be commissioned to the beginning of 2018 in accordance with the current time table February 25, 2014, Novosibirsk

20. Thank you for your attention February 25, 2014, Novosibirsk

21. Comparison of solenoids similar to the MPD solenoid February 25, 2014, Novosibirsk

22. Layout of the inner detectors • Interface restrictions which define the magnet geometry: • Outer diameter of the inner detectors – 4596 mm • Axial length occupied by the inner detectors – 7350 mm • Axial limitation of the magnet length - 9010 mm • Opening in the end cap -14° February 25, 2014, Novosibirsk

23. Magnet assembly To increase the overall rigidity of the magnet and to reduce stresses in the studs M48x3 it takes to provide maximally tight conjugation of the mating surfaces of the support rings and the beams (especially on the 3-5 lower beams) February 25, 2014, Novosibirsk

24. Coil cooling • The sc coil is indirectly cooled by two phase helium through the thermal contact with the aluminum cylinder. • The heat losses are taken by a vapor-liquid helium mixture circulated in the shaped aluminum tube welded to the external surface of the cylinder. • Total length of the tube - 107 m • After a quench the evaporating helium will be expelled from the tube through the relief valves to collection and storage system for the gaseous helium . • Liquid helium volume in the tube - 40 L. • Maximal pressure up to - 136 bar February 25, 2014, Novosibirsk

25. Hydraulic drive for the magnet movement • Tentatively twice a year the MPD detector will be moved for repair or upgrade (one way distance is ≈ 12 m). • Two hydraulic cylinders of bidirectional action will be used for it. Each of the cylinders produce a pushing/pulling force up to 35 t. • The movement will be fulfilled by transferring cylinder stops at a step of piston length ≈1500 mm. The fixing points of the relocatable stops are placed on the baseplates at a certain distance apart. • The detector cruising speed is 2–3 mm/s. For precise positioning at the final step it will be decreased to 0.4–0.5 mm/s. It will take about couple shifts for one way movement considering the time for transferring the stops and withdrawal/insertion of the poles. 1 – hydraulic cylinder; 2 – cylinder rod; 3 – stop February 25, 2014, Novosibirsk

26. Thermal load of the cold mass and the radiation screen. Main parameters of the cooling system February 25, 2014, Novosibirsk