1. The superconducting solenoids for the Super Charm-Tau Factory detector
Alexey Bragin, Evgeny Pyata
Budker Institute of Nuclear Physics,
Novosibirsk, Russia
December 2018
October 2010

2. OUTLINE
1. Two designs of the solenoid is considered to be. In the first design the solenoid will be placed outside all systems of the detector. In the second design, the thin solenoid would be placed between the DC and the identification system.
2. The superconducting solenoid placed outside of calorimeter – traditional design.
3. Main parameters of such solenoid.
4. Demands to have a thin solenoid placed inside the calorimeter – very low radiation thickness.
5. Various design approaches in making thin solenoids for detectors .
6. Design proposal for ultra-thin solenoid for the Super Charm-Tau factory detector
October 2010

3. Outer solenoid – first design
Originally, the design of the outer superconducting solenoid was discussed in 2011.
Length, m
3.8
Inner diameter, m
3.2
Number of layers (considered to be)
1 (2)
Number of turns
940
Current at 1.2 Т, А
4300
Inductance 2Е/I2, H
2.3
Ratio Iop/Icr, %
≤ 30
Cold mass, tons
5.1
Ratio Е/М, kJ/kg
3.6
Magnetic field in the center, Т
1.2
Stored energy, MJ
18.4
Cost, 0.56[E(MJ)]0.69, М$
4.2
Ramping rate, h
< 4

4. Outer solenoid – coil design on traditional technology
The coil design is based on using a superconducting cable with high purity aluminum stabilizer. The presented design is similar to the ATLAS solenoid (CERN).
Quench protection is based in the using of Al stabilizer and aluminum strips for fast quench propagation. The hot spot temperature is very low.
Temperature distribution after 1.6 s start of a quench

5. Outer solenoid – magnetic field in the detector
The uniformity area is 3% with respect to the center of the detector.
The uniformity is not high because the solenoid is short.

6. Outer solenoid – traditional technology will be used
CERN existing solenoids

7. BINP is getting experience from PANDA solenoid manufacturing to make the outer solenoid for the SCT detector

8. Ultra thin superconducting solenoid – second design
The thin superconducting solenoid is placed in front of the identification system of the detector.
Improvement in the system performance!
Minimal radiation length of the solenoid materials, ~ 0.1 X0 – main parameter.
The magnetic field is ~ 1 T
(up to 1.5 T may be discussed).
The solenoid sizes should be determined. All space between the poles may be taken by the solenoid.
October 2010

9. Main basic parameters of the thin solenoid and SC winding
Values
Length, m
~ 3
Inner diameter, m
~ 1.66
Radial thickness, mm
~ 80
Number of turns
1500
Number of layers 1
Current, kA
1.8
Diameter of the NbTi/Cu wire, mm
1.2
Icr at 5 Т and 4.2 K, kA
1.7
Iop/Icr ratio, %
< 50
Cold mass, kg
173
Magnetic field, Т
~ 1
Stored energy, MJ
3.0
Powering time, h
< 4

10. Cryogenics
The cryogenics will be based on a refrigerator station a kind of Linde L70 (may be another) for both designs of the solenoids.
Superconducting magnets of the collider should be also cooled by this refrigerator.
Its cost is ~ 1.5 M€.

11. Solenoid design basics
1. Low magnetic field, <5-6 T, the NbTi superconductor is used.
It has Jc = 3 kA/mm2 @ 4.2 K and 5 T field.
Lowest cost among all superconductors.
2. The thickness of the solenoid materials is linked with magnetic field value.
The magnetic field acts as pressure
on the solenoid B2 ~ p; 1 T ~ 0.4 MPa.
The thickness is t = p*R/s , s – material stress.
s – has limits (typically around 100 MPa).
3. Cryogenics demands to solenoid:
- cryostabilization at K
- radiation shields at K (demands some thickness of metal materials)
- vacuum vessel (buckling atmosphere pressure)
4. Solenoid protection from premature transition to normal state (quench) should be realized.

12. Not traditional solenoid designs for detectors
Solenoid of KEDR detector (1999 – now)
The SC wire is soldered to the SUS cylinder.
CMD-3 solenoid (2008 – now)
The winding is shunted with separated brass shunts.
CMD-2 solenoid (1990 – 2000)
The SC wire is soldered to the SUS cylinder.

13. Design of the ultra thin solenoid for CTF detector
Design peculiarity – is application of the carbon fibres composite for the solenoid support cylinder.
That is the same design approach as for solenoid for the CMD-2 and KEDR detectors.
The Al strips are for temperature stabilizing at ~ 4.2 K. They should be insulated from the coil!
The SC wire is not insulated!
The carbon fibres should be chosen with specific electrical resistivity which is in the range
10-5105 *m.
Stainless steel has 5.1*10-7 *m.

14. Magnetic system design with thin solenoid
Possible magnetic system design with the thin solenoid.
Correcting coils are to improve uniformity of the magnetic field.
The identification system and the calorimeter may be placed almost around all space of the solenoid.
The magnetic field uniformity is 3% by the center of the detector.
The uniformity in the outer solenoid design – for comparison

15. Thickness in radiation lengths
Materials
Thickness
X, mm
Radiation length
X0 мм X/X0
Material ratio, %
SC wire, NbTi/Cu = 1/1
0.56
17.7
0.032
31.0
Carbon fibre (1.5 g/cm3)
1.5
251
0.006
5.8
Epoxy compound (NB as filler)
150*
0.010
9.7
Aluminum strips (2 x 0.5 mm)
1.0
88.9
0.011
10.7
Radiation shields, Al
2.0
0.022
21.4
Vacuum vessel, Al
Total, Xtot
0.103
100

16. Typical parameters of the carbon material
Carbon content, %
99 – 99.9
Tensile strength of single fibre, GPa
0.5 – 1.2
Young modulus, GPa
40 – 100
Density, g/cm3
1.4 – 1.5
Diameter of single fibre, um
6 – 10
Resistance in acid free conditions, oС
Up to 3000
Resistance in oxidizing conditions (air), oС
Up to 450
Ash content, %
0.1 – 1
The electrical resistivity can be customized in the range 10-5105 *m.
The electrical resistivity of specific carbon plastic should be measured at low temperatures. Especially below 30 K where it can be too high. This effect is not considered as a problem because the energy dissipation occurs at temperatures higher than 40 K.

17. Advantages and disadvantages of the proposed design of the thin solenoid
1. This is new technology of thin superconducting solenoid based on carbon fibres composite. It allows to make transparent solenoid for particle physics detectors.
2. Quench behavior of the system should be analyzed taking into account carbon plastic properties at low temperatures. If the carbon plastic has too high electrical resistivity at T < 30 K it would be the best design because the quench propagation could be realized as in the CMD-3 design.
3. Eddy currents on neighbor structural elements should be estimated. They would absorb the significant part of the stored energy.
4. The supports should be strong enough as the current in the solenoid will be not uniform.
5. The thickness of the radiation shields may be decreased by ~ a factor of 2 if they will be cooled at lower temperatures and if pure aluminum would be used.
6. Corrugated outer cylinder of the vacuum vessel should be made.

18. Conclusions
1. The design of the outer superconducting solenoid can be realized on the base of the gained experience of the PANDA solenoid manufacturing.
2. Ultra thin superconducting solenoid is considered to be used in the SCT factory detector. Such solenoid should be designed using non traditional technology such as in solenoids of the CMD-2 and CMD-3 detectors.
3. SCT factory detector team should establish main parameters of the magnet system in the following months.
4. In case of ultra thin solenoid decision a lot of R&D works should be done especially in modelling of the magnetic system of the detector and the collider.