Status of CEPC Detector magnet

Zhao Ling, Zhu Zian, Wang Meifen, Hou Zhilong, Zhang Guoqing, Ning Feipeng, Yang Huan, Liu

Zhongxiu, Zhao Wei, Yao Weichao

CEPC-SPPC Study Group Meeting

2015.9.11

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Outline

Magnetic field design Superconducting cable R&D in next five years R&D Budget

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The CEPC detector magnet system is designed to provide an axial magnetic field of about 3.5 T, homogeneous over the tracking volume (TV).

The superconducting solenoid has a warm bore of 6.8 m in diameter and 8.05 m in length.

The iron yoke consists of the barrel with 3 rings (11 layers each) and the end-caps (11 layers each).

CEPC detector magnet _ Pre-CDR

2015/9/11

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Field distribution of the Magnet

The calculated magnetic field Bz along the detector

axisField map of the magnet (T)

• The 7.4 m long CEPC detector coil is composed of 5 modules; Each module has 4 layers.

• The nominal current is 18.575 kA for the design central field of 3.5T, and the maximum filed on the coil is 3.85T.2015/9/11

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The 50 G line is at 14.8 m radial distance and 17.2 m axial distance with a total thickness of iron of 2.44 m both in the barrel and the two end-caps with the 3.5 T central field.

Magnetic flux line distribution of the magnet

Stray field distribution outside the magnet (the field is given in T)

Stray Field Distribution outside the Magnet

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3.5m×3.5m central area in a quadrant Different radius along the detector axis R = 0m, 0.5m, 1.0m, 1.5m, 2.0m, 2.5m, 3.0m,

3.5m with Z from 0 to 3.5m

Magnetic field distribution in the

3.5m×3.5m central area

Different radius path along the detector axis

Magnetic field distribution of the central area

R = 500mm, with Z from 0 to 3.5m

BZ Br

R = 1500mm, with Z from 0 to 3.5m

BZ Br

R = 3000mm, with Z from 0 to 3.5m

BZ Br

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Magnetic field optimization

current ： 16600A

current ： 28500A Two supply

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Magnetic field optimizationField homogeneity （ Diameter 3.45m ， Z length 4.7m ）： 10% 3.85% （ CMS: 3.99% ）

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Superconducting cable

Cross section of Superconducting cable: BESIII 、 CMS 、 ILD

Superconducting strand in virgin state

Strand diameter 1.28 mm

Cu/NbTi 1.1

SC strand critical current density

3300A/mm2 @4.2K,5T

Rutherford cable

Number of strand 36

Cable transposition pitch

185 mm

Final conductor

Bare dimensions 75*23 mm2

SC strand critical current density

>2970A/mm2 @4.2K,5T

Ic degradation during manufacturing

<10%

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Progress in the Rutherford cable

2015.1 ～ 2015.5, Rutherford Cables with 30 pure copper strands. They have Good surface quality.

2015.6 ～ 2015.8 ， Rutherford Cables with 17 NbTi strands and with 24 NbTi strands. The critical current is in the testing.

Some problems:1)Bad surface flatness of the cable caused by inconsistent tension of each strands.2) Lack of traction and straightening equipment. 3)Dimension control should be strengthened. 4) Online quality monitoring equipment should be added.

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Number of strands ： 17Strand diameter ： 0.727mmMateriel :Nb/Ti Complete time:2015.7

Number of strands ： 20Strand diameter ： 1.0mmMateriel: CopperComplete time:2015.5

Number of strands ： 24Strand diameter ： 0.727mmMateriel :Nb/Ti Complete time:2015.8

Progress in the Rutherford cable

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R&D: Field design

The effects of the final focus magnets on the field uniformity and stability of the detector magnet.

Field optimization: Two directions: 1)Reasonable field homogeneity in the tracking volume;

2)lower cost.

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R&D: Superconducting cable Stranding process of the

Rutherford type cable: Coextrusion process of the

high purity aluminum: Mechanical reinforcement

Electron beam welding? Cable performance tests:

Critical current/mechanical performance/RRR value/ etc.

Conductor joints

Soft soldering technique?

Measurement of critical current by induction method

2015/9/11

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R&D: Inner winding and impregnating

2015/9/11

Inner winding machine:

Conductor preparation: De-Spooling and straightening; Cleaning ; Bending ; Insulation wrapping .

winding machine: winding table;

conductor driving unit;

conductor positioning system.

Prototype coil:

Test the inner winding machine;

Simulation of winding process;

Simulation of impregnating process;

Low temperature test.

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R&D: Cooling system

2015/9/11

• Thermosyphon cooling circuit: indirect cooling used for superconducting coils.

• Forced flow helium gas cooling circuit: indirect cooling for thermal shield.

• Calculation of the heat loads and temperature distribution for the coil and for the shield .

• 1/10 model and prototype coil of thermosyphon cooling to vertification the parameters.

• Thermosyphon cooling line design.

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R&D: Power supply and quench protection

2015/9/11

Goals:Power supply: 20KA, 20VDC, used for direct Ic measurement and dummy coil test.Quench protection: Analysis of the quench propagation; Protection circuit design.

Electrical circuit of magnet with power supply and quench protection

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R&D: Power lines with HTS

2015/9/11

Length: about 50mCooling method: LN2Conductor: HTS

Joint between HTS and Copper

Goals: One meter HTS with joints between HTS and copper and between HTS and NbTi.

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R&D: Iron Yoke

Influence on the field homogeneity by the different B-H curves of the yoke.

Influence on the forces of the coil by the different B-H curves of the yoke.

Design and test of the connection structure of the yokes.

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R&D costRMB Details

1 Superconducting cable 6,600,000 Material 1,880,000Processing 2,000,000Test equipment 2,500,000Travel +Test 120,000

2 Winding equipment &Prototype coil

4,900,000 Cable 1100m, about2,200,000Winding machine 800,000Support Cylinder for prototype coil and

Epoxy adhesive 1,900,0003 Inner Cooling system 3,600,000 small model (1/10)?

Prototype model

4 Power supply 1,800,000 Power supply for direct Ic test

5 Power lines 500,000 One meter 20KA HTS linesJoint between copper and HTS and NbTi

6 Iron yoke 2,100,000 Equipment 1100,000Material 800,000Travel & Test 200,000

7 Cryogenic system for prototype coil test

13,500,000 Liquefaction system Test Dewar

Total 33,000,0002015/9/11

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Summary

Field optimization for homogeneity and lower cost is in the progress;

R&D of the superconducting cable has a good beginning, but more need to be done.

In the next five years, R&D of inner winding/cooling system/power supply/HTS power line/iron yoke will be started gradually.

Looking forward to your joining!2015/9/11