The Superconducting Magnet of the Multipurpose Detector Evgeny Koshurnikov On behalf of the MPD...

The Superconducting Magnet of the Multipurpose Detector

Evgeny KoshurnikovOn behalf of the MPD (NICA) Collaboration

NovosibirskFebruary 25, 2014

Joint Institute for Nuclear Research (Dubna)

Superconducting MPD MagnetSuperconducting MPD Magnet

2February 25, 2014, Novosibirsk

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.

Main parameters of the MPD magnetMain parameters of the MPD magnet

Magnet aperture V=122 m3(D=4.596 m, L=7.35 m) Rated field of the magnet, Т 0.5Rated Ampere-turns of the sc coil, MA 3.0Rated current of the sc coil, кА 1.79Maximum design current of the sc coil, кА 2.39Stored energy at the design current, MJ 25.4Maximal Ampere-turns of the trim coil, kA 151Weight of the MPD detector (magnet +inner detectors), t 980


Magnetic Field RequirementsMagnetic Field Requirements

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• 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) :

|Int| <0.775mmz > 0, Zmax = +1700 mm403 mm < r < 1203 mm

|Int| <0.775mmz < 0, Zmin = -1700 mm403 mm < r < 1203 mm

minZ

z z

r dzB

BInt

• Magnetic field inhomogeneity in the tracker area

310

0

minmax

2

||||

B

BB

maxZ

z z

r dzB

BInt

Optimized geometry of the magnetic circuitOptimized geometry of the magnetic circuit


|Int|max = 0.08 mm < 0.775 mm

δ = 3 10∙ -4 < 10-3

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

TPCStability 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.

Main parameters of the SC cableMain parameters of the SC cable


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.

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 1.55 1.60

300600900

1.2 103

1.5 103

1.8 103

2.1 103

2.4 103

2.7 103

3 103

3.3 103

3.6 103

3.9 103

4.2 103

4.5 103

4.8 103

5.1 103

5.4 103

5.7 103

6 103

6.3 103

6.6 103

6.9 103

7.2 103

7.5 103

T=4.2 KT=4.68 KT=5.0 KT=5.5 KT=6.0 KT=6.5 KT=7 KI=k BIn=2388 A

B, T Ic

, A

I B 4.2( )

I B 4.68( )

I B 5( )

I B 5.5( )

I B 6( )

I B 6.5( )

I B 7( )

Knagr B

2388

B

Parameters of the sc wire ValueStrand diameter 1.4 ± 0.005 mmCu/SC ratio 0.9:1Filament diameter 20 µmNumber of filaments 2000Twist pitch 20 mmRRR of copper matrix > 100Critical current density at 4.2K&5T > 2700 A/mm2

Conductor: co-extruded high-purity aluminum (99.999%, RRR>1000) and a NbTi wire 1.4 mm in diameter

Transient processes after a quenchTransient processes after a quenchTransient 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

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FE model of the coil with the aluminium support cylinder

February 25, 2014, Novosibirsk

1/32 part

Power supply circuit of the magnet and protection circuit of the sc coil

Quench analysis Quench analysis

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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


The temperature distribution at the moment t = 300 sec after an unprotected quench at the design current 2.4 kA

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Outer diameter, mm 6583Inner diameter, mm 5883Length , mm 9010Interpole distance, mm 7390

Number of beams 24Yoke beam weight, t 18.5Support ring weight, t 41.8Pole 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

Main dimensions of the magnet yokeMain dimensions of the magnet yoke

February 25, 2014, NovosibirskSuper-nut

CryostatCryostat

10

Cryostat length, mm 7910Inner diameter, mm 4656Outer diameter, mm 5443Δi, Δe, mm 16; 25Weight of vacuum vessel, t 48.8Thermal shield weight, t 2.7Material of the suspension ties Inconel 718


Axial decentering force 61 kN/cmRadial decentering force 5.4 kN/cm

Superconducting WindingSuperconducting Winding


Cold mass (conductor mass) 13.3 (6.5) tonsNumber of turns 1674Length of the sc cable 27 km

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.

SC coil is indirectly cooled by two phase helium through the thermal contact with the aluminum cylinder.

Trim Coils on the Pole TipsTrim Coils on the Pole Tips


Aluminum conductor 42 × 42 mm2 Hole diameter 27 mm Radius of edges rounding 2 mm

Maximal Ampere-Turns 151 kA (2.06 A/mm2)Maximal current 4.44 kA (35 V)Cooling water flow rate 1.24 l/sec Pressure drop 7.7 bar

MPD Magnet in the In-Beam PositionMPD Magnet in the In-Beam Position


FE model, Main Load Cases, Results of AnalysisFE model, Main Load Cases, Results of Analysis


1 Assembled Detector rests on 6 stationary supports

2 Assembled Detector is reloaded on four roller skates.

3A roller skate runs over an obstacle on the rail until the loss of the contacts of rollers with the rails on one diagonal (magnet balances on two diagonal points - unstable equilibrium )

4Assembled Detector is installed on six supports and decentering magnetic forces are applied

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% and in a residual deformations of the support rings (up to 0.26 mm).

FE model of the sc coils.FE model of the sc coils. Loading steps Loading steps

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Accepted values of allowable stress for insulation at 4.5K :

tens = 6,6 MPa; = 7,0 MPa

Al 99.999


Loading Steps in the Design Model

1.Simulating of axial pre-stress 10 MPa of the coil turns. 2.Modeling of the state after epoxy curing and removal pre-stress load. 3.Cooling down from 20°C to -269°C. 4.Cooling down plus magnetic forces.5.Warming up and magnetic loads removal. 6.Repetition of the loading steps 3-4-5-3…

Results of stress-strain analysis of the coilResults 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 MPa in small area around the superconducting wire for the side turns of the coil.


Cryogenic System. Forced two-phase Helium Cooling and Cryogenic System. Forced two-phase Helium Cooling and thermosyphon regimes thermosyphon regimes

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1. Operating pressure of the refrigerator2. 3 bar, 5.5 К2’. 3 bar, 5.65 K3. 3 bar, 4.7 K4. 1.35 bar, 4.55 K, 5 % 5. 1.3 bar, 4.5 K, 30 % 6. 1.3 bar, 4.5 K, saturated vapor


Refrigerator: «Linde» LR 140 with cooling capacity up to 400 W at the temperature level of 4.5 K.

Heat load on the heat exchanger of the control Dewar, W 164

Cooling capacity of the refrigerator, W 315Helium consumed by the current leads, g/s 0.38Helium direct flow for cooling the coil, g/s 13.9Helium flow for cooling the thermal shields, g/s 4.4Temperature (inlet/outl.) of thermal screen Helium flow , K 40/80

Time of full cooling down the coil, hour 190

Main parameters of the cooling system

Distinctive Features of the MPD Distinctive Features of the MPD MagnetMagnet

• 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.


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


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Thank you for your attentionThank you for your attention


Comparison of solenoids similar to Comparison of solenoids similar to the MPD solenoid the MPD solenoid


DELPHI (CERN) ALEPH (CERN) BABAR [4] (SLAC)

CDF (Fermilab)

MPD detector (JINR)

Year of complection 1985 1986 1997 1984 2017

Central field, T 1.2 1.5 1.5 1.5 0.5

Field inhomogeneity in the

tracker area, % 0.1 0.4 2 1 0.1

Stored Energy, MJ 110 137 25 30 14.6

Total Amp.Turns, MA 7.6 8.56 5.12 5.75 3

Current density, A/mm2 46.3 40 47 64 19.5

Current, kA 5.0 5.0 4.6 5.0 1.79

Aluminum stabilized conductor

cross section, mm24.5 x 24 3.6 x 35 4.9x20 3.89x20 4.1 x 20

Inner Bore, m 5.2 4.96 2.8 2.86 4.596

Coil length, m 6.8 7 3.46 5 7.598

Yoke incircle outer diameter, m 9.36 5.84 9.5 6.583

Yoke length, m 10.6 6 7 9.01

Total magnet weight, t 2640 580 2000 794

Cold mass, kg 25000 4900 5570 1330

Thermal load at 4.5 K, W 150 W+1.25 g/sec 100 W+1.25 g/sec 52 35 68W+0.38 g/sec

Layout of the inner detectorsLayout 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°

Magnet assemblyMagnet 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)

Coil coolingCoil 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

Hydraulic drive for the magnet movementHydraulic drive for the magnet movement

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1 – hydraulic cylinder; 2 – cylinder rod; 3 – stop

• 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.


Thermal load of the cold mass and the radiation screenThermal load of the cold mass and the radiation screen. . Main parameters Main parameters of the cooling systemof the cooling system

T=4.5 K (safety factor 2) Thermal load, W

Radiation 33.6Support conduction 22.3Cryogenic chimney and Control Dewar 10

Conductor joints and wires 2Eddy current losses in the Al cylinder (input mode - 60 minutes) 4.2

Total (normal/transit regime): 67.9/72.1T=4.5 K (without safety factor) Current leads

without current 4.2

with current 7 T=60 K (safety factor 2) Radiation 657.3

Shield supports conduction 138.6Heat intercepts of the coil supports 116.8

Total: 912.7


Heat load on the heat exchanger of the control Dewar, W

164

Cooling capacity of the refrigerator (including thermal screens), W

315

Helium consumed by the current leads, g/s 0.38

Helium direct flow for cooling the coil, g/s 13.9Helium flow for cooling the thermal shields, g/s 4.4Helium flow temperature at the inlet/outlet of the thermal screens, K

40/80

Time of full cooling down the coil, hour 190

The Superconducting Magnet of the Multipurpose Detector Evgeny Koshurnikov On behalf of the MPD...

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