1. J.Yue, D. Doll, X. Peng, M.Rindfleisch, Mike Tomsic
Demonstration of Conduction Cooled MgB2 and Nb3Sn Coil Segments for Magnet Applications
Hyun Sung Kim, Chris Kovacs, Milan Majoros, Mike Sumption, E.W. Collings
Center for Superconducting and Magnetic Materials, MSE, The Ohio State University
J.Yue, D. Doll, X. Peng, M.Rindfleisch, Mike Tomsic
Hyper Tech Research
Funded by a National Institute of Biomedical Imaging and Bioengineering grant R01 grant, R01EB018363, and also an NIH bridge grant

2. Motivation
MRI systems based on MgB2 are of significant interest as one way to develop liquid-cryogen-free MRI systems
MgB2’s Tc of 39 K invites conduction cooling, and lower cost makes it an economically viable
The low-Tc-like coherence length allows for persistent joints
Intermediate Tc helpfully increases the minimum quench energy while not suppressing the normal zone velocity too much
Conductor performance is at the level needed for MRI application, and conductor designs appropriate for MRIs can be made -- the need is for developing conduction cooled coil technology

3. Outline Conductor/Coil specification Instrumentation
Facility and Cool down
Ic measurement vs T
Discussion and Conclusions
If Time
Nb3Sn Coil work
Initial Persistent joint development

4. Conductor Name 3364 In-situ 36 filament Nb barriers
# Mono
Barrier
Mono sheath
Multi sheath
Central fil(s)
powder material
Mg:B
dia (mm)
% powder 36 Nb Cu
Monel
MgB2_2%C
1:2
0.84
18.1
Name 3364
In-situ
36 filament
Nb barriers
Cu interfilamentay matrix
Monel outer matrix
SMI-2% C doped
S-glass insulated
Reacted at 675/90 min under Ar
Optical Micrograph of MgB2 conductor cross section, shown at wire OD = 0.84 mm.

5. Coil Design Specifics
Coil material
Former : 101 OFE copper
All fasteners : 316 stainless steel
Lead Insulator : Garolite G-10 or ceramic standoff
Lead connector : Alloy 101 OFE Copper
Coil Parameters
Winding pack OD : mm
Winding Pack ID : mm (18”)
Winding Pack Height : mm (0.775”)
WP cross sectional area : mm2
No. Turns : 225
Total Conductor L m (1078.7’)
Turns/layer : 19 (approx.)
No. Layers : 12
Final coil preparation
Solder for leads : Pb-Sn (40/60)
Epoxy CTD
Resistance measurements (after winding, after epoxy)
L1 to L2
41.9
Ohms
After winding
L1 to former OL
L2 to former
After CTD 528 Epoxy

6. FEM Simulation
Ic(B) curve of a typical strand with the calculated load line of the coil
Magnetic field map at the coil critical current.
Coil critical current
[A]
Max. on-axis field
at coil critical current [T]
Max. field in the winding
273
0.14
1.43
200
0.10
1.05

7. Experimental Set up (2) Two stage GM cryocoolers
(2) Cold heads attached to the copper ring
Copper ring and coil are thermally connected with high purity copper strips
4 BSCCO leads for each current tap
Heater attached in the copper ring to control the temperature of coil
Data acquisition system: Nanovoltmeters (Keithley), Thermometers (Lakeshore), Data acquisition (Labview)
Copper Ring
MgB2 Coil
Copper Strips

8. Voltage Taps Critical Current Measurement: I-V measurement
Resistance
@RT [Ω]
Estimated length
[cm]
CTI – C1
1.94
C1 – C2
0.135
105.6
C2 – C3
13.9
10849
C3 – C4
7.07
5522
C4 – C5
7.12
5559
C5 – C6
7.08
5526
C6 –C7
6.81
5313
C7 – CTO
3.73
Whole coil resistance: Ω,
Total conductor length: m
Critical Current Measurement: I-V measurement

9. Location/Description
Temperature Sensors
Location/Description
CTI 1
1st Type-E Thermo. On “IN” current tap
CTI 2
2nd Type-E Thermo. On “IN” current tap
CTO 1
1st Type-E Thermo. On “OUT” current tap
CTO 2
2nd Type-E Thermo. On “OUT” current tap C1
1st Type-E Thermo. On the top surface of coil C2
2nd Type-E Thermo. On the top surface of coil CS
Type-E Thermo. On the side surface of coil
CL1
1st Type-E Thermo. On BSCCO current lead
CL2
2nd Type-E Thermo. On BSCCO current lead
C1_cernox
CERNOX. On the top surface of coil
CR_cernox
CERNOX. On the top surface of cold ring
CTI_cernox
CERNOX. On “IN” current tap
CTO_cernox
CERNOX. On “OUT” current tap

10. Cooldown
Voltage signals
Temperature signals

11. I – V curves: 20 K, 0.1 A/s
A bit of coil heating

12. I – V curves: 20 K, 2A/s
Less coil heating

13. I – V curves: 20 K, 5A/s
Very little coil heating

14. Temp @ Current Tap IN (∆T) [K] Temp @ Current Tap OUT (∆T) [K]
Ic vs T
Temp
Test #
Ramping Rate
Ic [A]
Coil (∆T) [K]
Current Tap IN (∆T) [K]
Current Tap OUT (∆T) [K]
30 K
# 14 2
23.3
29.4 ~ 29.4 (0.0)
29.9 ~29.9 (0.0)
30.6 ~ 30.6 (0.0)
# 15
0.1
17.6
29.6 ~ 9.9 (0.3)
30.1 ~ 30.4 (0.3)
30.8 ~ 31.0 (0.2)
27 K
# 16
50.5
27.1 ~ 27.1 (0)
27.3 ~ 27.4 (0.1)
27.7 ~ 27.8 (0.1)
# 17
50.1
27.3 ~ 27.8 (0.5)
27.9 ~28.2 (0.3)
22.5 K
# 20 5
116
22.5 ~ 22.7 (0.2)
23.0 ~ 24.0 (1.0)
23.5 ~ 23.7 (0.2)
# 18
116.5
22.6 ~ 22.8 (0.2)
22.6 ~ 24.2 (1.6)
23.1 ~ 23.9 (0.8)
# 19
111.7
22.5 ~ 23.1 (0.6)
22.9 ~ 25.3 (2.4)
23.4 ~ 24.9 (1.5)
20 K
# 23
152.4
20.0 ~ 20.5 (0.5)
20.6 ~ 23.1 (2.5)
21.0 ~ 22.3 (1.3)
# 24
20.1 ~ 20.6 (0.5)
21.0 ~ 24.0 (3)
21.4 ~ 22.9 (1.5)
# 26
140.6
20.1 ~ 21.4 (1.3)
20.5 ~ 24.2 (3.7)
20.9 ~ 23.1 (2.2)
17 K
# 27
187.0
17.1 ~ 18.1 (1.0)
18.0 ~22.3 (4.3)
18.6 ~ 20.9 (2.3)
# 28
183.8
17.4 ~ 18.6 (1.2)
16.7 ~ 22.6 (5.9)
16.9 ~ 20.7 (3.8)
# 29
173.6
17.2 ~ 18.9 (1.7)
16.9 ~ 23.3 (6.4)
17.3 ~ 21.6 (4.3)
15 K
# 34
204.6
15.1 ~ 16.8 (1.7)
16.6 ~ 22.7 (6.1)
17.3 ~ 20.9 (3.6)
# 35
196.7
15.1 ~ 17.2 (2.1)
16.6 ~ 23.5 (6.9)
17.2 ~ 21.7 (4.5)
# 36
191.7
16.5 ~ 23.5 (7.0)
17.2 ~ 21.4 (4.2)
A key aspect -- to test the end transitions, thus no preferentially cooling
Thus some current tap heating at lower T (where I higher) and for slower ramps.
However, we could observe that the coil, as well as the current in and out junctions, were good.
The coil transitioned by quench, and no resistive baseline was seen.

15. Summary
An MgB2-based react and wind coil was made and tested as part of a technology development effort for MgB2-based, cryogen-free, MRI.
A 36 filament MgB2 conductor was used to wind a small MRI- segment-like coil using a react and wind protocol. The coil was 457 mm ID and used a total length of conductor of 330 m.
The coil was then epoxy impregnated, instrumented, and tested. After initial cool down the coil Ic was measured as a function of temperature.
Both the coil itself and the terminations were seen to perform well -- A load line was generated – full analysis awaits 15 K measurement of this particular strand.
The coil transitioned by quench, and no resistive baseline was seen. A coil Ic of 200 A was seen at 15 K.

16. Nb3Sn FEM Simulation_Magnetic
Ic(B) curve of the strand measured at 4.2 K with the calculated load line of the coil
Magnetic field map at the coil critical current.
Coil critical current
[A]
Max. on-axis filed
at coil critical current [T]
Max. field in the winding
871
0.73
6.818
Physical parameters of the coil at 4.2 K

17. Nb3Sn FEM Simulation_Temp, Strain.
Coil temperature distribution. No current in the coil. Maximum temperature in the winding = K.
Volumetric strain distribution in the winding cross-section.

18. Other Coil Measurements – Future Reporting
MgB2 Coil
Nb3Sn Coil

19. New 1.7 M cryostat to be in place this fall!
8 in port for instrumentation
Feedthroughs. About 8 – 18pin
connectors will fit on one port
and there’s 4 of these.
Radiation shield
for feedthrough (4)
Swinging door
cover to block
shine but allow
current leads to be
pulled through
Through-bolts;
should be tapped
holes
3 inch clearance w/o MLI
New 1.7 M cryostat to be in place this fall!

20. Development of Persistent Joints
Two styles of joints
Superconducting solder type
Direct MgB2-MgB2
In both cases, used already reacted wire
Preliminary testing to date using direct I-V, R < 
Decay Testing rig and samples in preparation for increased R sensitivity and decay test
Working now to improve performance and measure to high sensitivity
Superconducting Solder Type 4 K
MgB2-MgB2Type 4 K

21. Moving from screening test to decay test
While further improvement in critical current of joints is still in process, it is important to measure R at values below ohm
Thus, a decay rig was needed, as well as some initial testing and verification

22. New test arrangement for decay measurements – machine drawing

23. Test rig for decay measurements – with test NbTi joint mounted

24. Expansion of decay region NbTi test joint
Results for a NbTi persistent joint
(at the time of stage III, IV in overview result).
Superconducting solder type.

25. Test of first persistent decay MgB2 sample
Results for a MgB2 persistent joint
(at the time of step III  IV along the lines of NbTi overview figure).
Superconducting solder type.

26. Conclusions (II)
Various MgB2 and Nb3Sn coil segments are being tested by conduction cooling
For joints
Initial screening results show good results R < ohm, indicate that it is time to move to decay measurements
The design of a new PJ decay rig is shown
Initial tests with NbTi and MgB2 joints are shown, and the results where described
Joint Testing and development (HTR-OSU) is in full swing, moving now to larger conductor joints for image guided system