1. 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

2. Outline Magnetic field design Superconducting cable
R&D in next five years
R&D Budget
2015/9/11

3. CEPC detector magnet _ Pre-CDR
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).
2015/9/11

4. The calculated magnetic field Bz along the detector axis
Field distribution of the Magnet
The calculated magnetic field Bz along the detector axis
Field 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 kA for the design central field of 3.5T, and the maximum filed on the coil is 3.85T.
2015/9/11

5. Stray Field Distribution outside the Magnet
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)
2015/9/11

6. Magnetic field distribution of the central area
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

7. R = 500mm, with Z from 0 to 3.5m BZ Br

8. R = 1500mm, with Z from 0 to 3.5m BZ Br

9. R = 3000mm, with Z from 0 to 3.5m BZ Br

10. Magnetic field optimization
current：16600A
current：28500A
Two supply
2015/9/11

11. Magnetic field optimization
Field homogeneity（Diameter 3.45m，Z length 4.7m）：10% %（CMS: 3.99%）
2015/9/11

12. Superconducting cable
Superconducting strand in virgin state
Strand diameter
1.28 mm
Cu/NbTi
1.1
SC strand critical current density
Rutherford cable
Number of strand 36
Cable transposition pitch
185 mm
Final conductor
Bare dimensions
75*23 mm2
Ic degradation during manufacturing
<10%
Cross section of Superconducting cable:
BESIII、 CMS、 ILD
2015/9/11

13. 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.
2015/9/11

14. Progress in the Rutherford cable
Number of strands：20
Strand diameter：1.0mm
Materiel: Copper
Complete time:2015.5
Number of strands ：17
Strand diameter ：0.727mm
Materiel :Nb/Ti
Complete time:2015.7
Number of strands ：24
Strand diameter ：0.727mm
Materiel :Nb/Ti
Complete time:2015.8
2015/9/11

15. 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.
2015/9/11

16. 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

17. R&D: Inner winding and impregnating
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.
2015/9/11

18. R&D: Cooling system
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.
2015/9/11

19. R&D: Power supply and quench protection
Electrical circuit of magnet with power supply and quench protection
Goals:
Power supply: 20KA, 20VDC, used for direct Ic measurement and dummy coil test.
Quench protection:
Analysis of the quench propagation;
Protection circuit design.
2015/9/11

20. R&D: Power lines with HTS
Joint between HTS and Copper
Length: about 50m
Cooling method: LN2
Conductor: HTS
Goals: One meter HTS with joints between HTS and copper and between HTS and NbTi.
2015/9/11

21. 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.
2015/9/11

22. R&D cost RMB Details 1 Superconducting cable 6,600,000
Material 1,880,000
Processing 2,000,000
Test equipment 2,500,000
Travel +Test 120,000 2
Winding equipment &
Prototype coil
4,900,000
Cable 1100m, about2,200,000
Winding machine 800,000
Support Cylinder for prototype coil and Epoxy adhesive 1,900,000 3
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 lines
Joint between copper and HTS and NbTi 6
Iron yoke
2,100,000
Equipment 1100,000
Material 800,000
Travel & Test 200,000 7
Cryogenic system for prototype coil test
13,500,000
Liquefaction system
Test Dewar
Total
33,000,000
2015/9/11

23. 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