1. Budker Institute of Nuclear Physics,
Thin solenoid for the CTF detector placed in front of the identification system (option)
Alexey Bragin
Budker Institute of Nuclear Physics,
Novosibirsk, Russia
May 2018
October 2010

2. OUTLINE
1. The placement of the thin superconducting solenoid in front of the identification system of the detector.
2. Main parameters of the solenoid
3. Design of the solenoid.
4. Radiation thickness of the solenoid.
5. Potential risks of such design of the thin solenoid.

3. Possible placement of the solenoid
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.

4. The field uniformity is  4% around the center.
Magnetic field
The field uniformity is  4% around the center.

5. Main parameters of the thin solenoid and SC winding (not approved)
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

6. 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.

7. Solenoid design approaches 1 – aluminum stabilizer
PANDA solenoid
to be manufactured in BINP
CERN existing solenoids

8. Solenoid design approaches 2 – the winding is uniformly shunted
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.

9. Design of the 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.

10. 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

11. 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.

12. Advantages and disadvantages of the proposed design
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.
3. Eddy currents on neighbor structural elements should be estimated.
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.

13. Results The design of the thin superconducting solenoid is presented.
It has extremely low value of the thickness in terms of radiation length.
New technology of thin solenoid manufacturing should be realized.
Dummy solenoid should be manufactured and tested.
The CTF detector team should make a decision upon using such solenoid.