1. INTER UNIVERSITY ACCELERATOR CENTER, INDIA
Analysis of Quench initiation & its effect in the Superconducting Quadrupole Doublet at IUAC
Santosh Kumar Sahu
INTER UNIVERSITY ACCELERATOR CENTER, INDIA
Cryogenics & Applied Superconductivity Lab

2. CONTENTS
Short description of Superconducting Quadrupole magnet cryostat at IUAC.
Operation In Details.
Quench. How & Why ??
Problem with the design & analysis.
New design & experiment.
Result
Conclusion

3. Cryocooler
1st Stage
2nd Stage
Helium Vessel
300mm
250mm
250mm

4. Superconducting Quadrupole Magnet at IUAC

5. Superconducting Quadrupole Magnet at IUAC

6. Failure sequence of Quadrupole magnet
Cryocooler
1st Stage
2nd Stage
45K
Helium Vessel
300mm
250mm
250mm

7. BURNT HTS Lead

8. Initial Design Cryocooler HTS-LTS Joint Cu base plate
Point of Heat Generation
Aluminum Nitride
Cu Braid
To Magnet
SCHEMATIC DIAGRAM

9. Initial Design During magnet charging & at hold position T1 was rising
Heat Flow
Electrical Analogy T1 T2 R1 R2 R3 R4 R5 T1 T2
Magnet Quenched after some time
SCHEMATIC DIAGRAM

10. Analysis
The thermal resistance of the path from HTS-LTS joint to the copper base plate was found to be ~ 30 K/Watt.
To transfer 1 watt of heat it has to maintain a temperature difference of 30 Kelvin.
In our case the heat load is something around ~ 100 mW at 70 ampere.
To transfer this heat load ΔT between T1 & T2 increased.
T1 went up to ~ 8 K which is the critical temperature of NbTi wire (LTS) at 70 Ampere operating current & its self field.
So the superconducting wire became normal & the magnet Quenched.

11. New Design
To avoid this heat transfer issue we redesigned the structure from HTS-LTS joint to the Copper base plate & experimented with different electrical isolator to find out the least thermal resistance & best heat transfer.
Cryocooler Place
Cu Base plate
Electrical Isolator

12. Experimental set up for New Design
Heat load applied from 0 to 300mW at T1
Temperature rise in T1 & T2 measured with different electrical isolator
HTS-LTS is Placed
Different electrical isolator used were:-
AlN + Indium
AlN + Apiezo-N grease
Kapton Tape (50 micron)
Kapton tape + Apiezo-N grease
Quartz Crystal
Top View T1
Electrical isolator T2

13. Experimental Set up

14. Results

15. Result
After the experiment with the new design, kapton tape ( 50 micron thick) with Apiezo-N grease is found out to be the least resistive path from HTS-LTS joint to the Copper base plate
The thermal resistance of the path is found out to be ~ 8 K/W.
After implementing it to the main cryostat the base temperature which was previously 4.8 K was come down to 3.55 K.

16. Installation in the Quadrupole Cryostat
HTS Lead
Cryocooler
Cu base plate
HTS-LTS joint
NbTi wire

18. New Design Of Quadrupole Cryostat

19. Thank You For Your Attention
Visit to IUAC on 11th March, 2016