1. Proposed FNSF Quench Studies and Structural Studies Using MIT Twisted Stacked Tape HTS Superconductors
P. Titus, February

2. Proposed HTS Model
Only geometry last time
Not much progress to report
Previous CICC Model
(Before Buck and Wedge

3. Jacket Stress Strain (Assumed)
Displacement Constraints on the Lower Face
Coupling on the Upper Face

4. Yellow current sticks model the TF current
Yellow current sticks model the TF current. A Biot Savart analysis is performed rotating the sticks 16 times
Thin slice models the inner leg by using coupling or CP commands on the surfaces – Allows tens1on loading as well

5. Field Vectors
Errors – Still fixing

6. Field Vectors

7. Winding Pack Compression (SIG3)
From US FNSF Study

8. Need to Understand This – Our Stacked Tape is 60MA/m^2
FNSF Sig3
(Titus)
Finite element investigation of the mechanical behaviour of a Twisted Stacked-Tape Cable exposed to large Lorentz loads Federica Pierro1, Zijia Zhao1, Luisa Chiesa1, Makoto Takayasu2 1 Tufts University, Mechanical Engineering Department, Medford, MA 02155, USA 2 MIT, PSFC, Cambridge, MA 02139, USA
Need to Understand This – Our Stacked Tape is 60MA/m^2

9. HTS Quench Problem:
Quench Propagation is slow
Heating is restricted to small area
Anecdotal: Tapes burn before quench detection can dump the coil
Possible solution:
Bitter Plate like TF coils with many parallel circuits
Similar to Sam Cohens Flux Concentrator with HTS Tape, only with one turn.
Concept also discussed in Joel Schultz
FIREscs

10. Inboard Leg Half Section
May need sequential persistent switches to force initial uniform currents in start up.
Also exploring overshoot and rampdown to force currents to the outer perimeter

12. Solution uses ANSYS Classic/EMAG
Solid 97 Vector Potential Solution
Air

13. Start of Flat Top
Ramp Up
Quench:
One current element is “turned off” by a step change in temperature. Currents immediately inductively switch
Later in the Quench. Current is inductively and resistively transferred to the next conductor

14. Reactor scale performance will be different than smaller scale magnets such as SPARC and Tokamak Energy. A reactor scale simulation is needed, benchmarked with the smaller examples.
Uniform currents at end of rampup have not been achieved. Some resistivity or persistent switch control may be needed. In copper Bitter plates resistance “pushes” current density away from the plasma side.
Currents readily transfer both inductively and resistively from the quenched conductor to neighboring conductors
The model is cyclic symmetric, modeling only one Bitter plate. In this model the currents in the neighboring conductor double – this might produce a chain of quenches but in a model with multiple Bitter Plates currents are expected to share with many neighboring Bitter Plates

15. December 2018 Slides

16. Bucked & Wedged Solution P. H. Titus, Jan 10, 2017
Dec – January 2017 – Buck and Wedge allows increasing the OH current center radius from .85 to .9. and Increasing the OH build from .4 to .6 m , OH OR= 1.2 m. OH Currents scaled down by .892 (Preserves Volt Seconds). OH Current Densities and Stresses drop by 50%
Bucked & Wedged Solution
P. H. Titus, Jan 10, 2017
Princeton Plasma Physics Laboratory
Gap Elements Added Between OH and TF Nose
EOP
Bucked and Wedged TF
600 Mpa Down from 990 MPa
B & W best implemented with Joints, Leads He Penetrations, and Preload mechanisms in the bore. May be difficult
EOP Free Standing , Original .4m Build, 1.9GPa
EOP Bucked and Wedged .6m build , 495 MPa

17. Buck and Wedge vs. Wedge Only All Results are For OH r=.9, dr=.6m
Allowable TF Stress =1GPa Peak,666 PM
OH Smeared Static Allowable =330 to 500 MPa Depending on the contribution from the conductor
Location IM
EOP
PF Free Standing Elastic (Smeared)
CS1 ID
540
720
Unacceptable Metal Stress
PF B&W Elastic (Smeared)
CS1 OD
495
Closer to Acceptable
TF Free Standing Elastic
Equator Nose
990
Acceptable
TF B&W Elastic
600
B & W Improves the stress state of both the OH and TF
OH can be improved by stealing a little more space from the TF
B & W best implemented with Joints, Leads He Penetrations, and preload mechanisms in the bore. May be difficult

18. 15.648T at 2.2m
T at 2.2m
7.5T at 4.8m Radius
7.5T at 4.8m Radius
1/r contribution should be 7.5*4.8/2.2=16.364T but the local ripple field increases this
8.86T at r=10.231
At the limit of Good LTS Nb3Sn?

19. Winding Pack Effective Current Density
500 a/mm^2*36.0=18kA
70.3MA/m^2
Maybe MA/m^2 for Design?
MIT Twisted Stacked Tapes
ITER CS
Total area=16mm square=.016^2=2.56e-4
Yuhu and Tom get 36 MA/m^2
~42kA
=42000/ =
15.8MA/m^2
Total area=51.5mm square=.0515^2=

20. MIT TSTC Conductor – Achieved at NHMFL
Base cable: 40 tapes, 4 mm width, 0.1 mm YBCO Tape Ic (4.2K, 20T) = 170 A
MIT TSTC Conductor – Achieved at NHMFL
10 mm
6 kA TSTC x 0.01 m = 1e-4 m2
1000 turns -> A = 0.1 m2
Overall Je = 60 A/mm2
7.4 mm
10 mm

21. How Much Help Can we Expect from the Nitronic Tape
How Much Help Can we Expect from the Nitronic Tape? ~150 Mpa on the Case
HTS for DC Operation
Or Very Long Pulse Tokamak?
LTS with He for AC Stability
Winding Pack modulus estimated to be 175 Gpa from the mixture rule. Essentially all metal
Winding pack modulus estimated to be 70 Gpa for ITER-Like CICC , No credit for reacted, cabled strand

22. The first inner corner radius was chosen as 3.7309231-2.8833=.8476m
FNSF
TF and PF Structural Analysis Results
Peter H. Titus,Princeton Plasma Physics Laboratory
:36:45
FNSF has 16 TF Coils, with 1 turns per coil
FNSF has a major radius of 4.8 m with a toroidal field of at Ro
FNSF has a minor radius of m
Case Radius set to 3 Case Width set to
OIS Radius set to 3 Case Width set to 3
Section filename=wba4 divx,divy=
Case Radius set to Case Width set to
Nose radius set to 1.1
FNSF Path has 7 Points in the TF Path
FNSF has 33 Poloidal Field (PF) Coils
FNSF has 2 Poloidal Field (PF) Currents in the Scenario
Scenario 2 is being analyzed
Each TF sector is degrees
The current per TF coil is: amps
PF R,Z,ND,DZ,NX,NY
1 , .85 , .2 , .4 , .39 , 4 , 4
2 , .85 , .6 , .4 , .39 , 4 , 4
3 , .85 , 1 , .4 , .39 , 4 , 4
4 , .85 , 1.4 , .4 , .39 , 4 , 4
5 , .85 , 1.8 , .4 , .39 , 4 , 4
6 , .85 , 2.2 , .4 , .39 , 4 , 4
7 , .85 , 2.6 , .4 , .39 , 4 , 4
8 , .85 , 3 , .4 , .39 , 4 , 4
9 , .85 , 3.4 , .4 , .39 , 4 , 4
10 , 1.25 , 5.35 , .3 , .4 , 4 , 4
11 , 1.95 , 5.85 , .5 , .4 , 4 , 4
12 , 2.65 , 6 , .3 , .4 , 4 , 4
13 , 4.4 , 6.3 , .6 , .3 , 4 , 4
14 , 5.15 , 6.25 , .4 , .3 , 4 , 4
15 , 7.25 , 5.8 , .6 , .3 , 4 , 4
16 , 8.75 , 5 , .8 , .6 , 4 , 4
PF, Cur 1,Cur2
1 , 0 ,-4.42 , 0 , 0 , 0 , 0 , 0
2 , 0 ,-4.42 , 0 , 0 , 0 , 0 , 0
3 , 0 ,-4.42 , 0 , 0 , 0 , 0 , 0
4 , 0 ,-4.42 , 0 , 0 , 0 , 0 , 0
5 , 0 , 4.67 , 0 , 0 , 0 , 0 , 0
6 , 0 , 4.67 , 0 , 0 , 0 , 0 , 0
7 , 0 , 4.67 , 0 , 0 , 0 , 0 , 0
8 , 0 , 4.67 , 0 , 0 , 0 , 0 , 0
9 , 0 , 4.67 , 0 , 0 , 0 , 0 , 0
10 , 0 , 4.04 , 0 , 0 , 0 , 0 , 0
11 , 0 , 5.98 , 0 , 0 , 0 , 0 , 0
12 , 0 , 6.91 , 0 , 0 , 0 , 0 , 0
13 , 0 , 1.33 , 0 , 0 , 0 , 0 , 0
14 , 0 , 2.32 , 0 , 0 , 0 , 0 , 0
15 , 0 , 7.23 , 0 , 0 , 0 , 0 , 0
16 , 0 , , 0 , 0 , 0 , 0 , 0
The first inner corner radius was chosen as =.8476m
!Pr Pz Pang FNSF Path Specs
PATH 7
s, , 0 , 2 , 0
t,0 , , 0 , 20
r, , , 20 , 5
r, , , 20 , 10
r, , , 50 , 20
r, , , 15 , 20
r, , e-10 , 75 , 20

23. FNSF needs 11.25 Mat per TF coil – with 16 coils for 7.5 Bo
Last evolution of the FNSF had .327m^2 in the winding pack
HTS is good for ~ 35 MA/m^2
So with HTS conductor the potential current per TF is .327*35 =11.4 Mat or
11.4/11.25*7.5=7.6 T - About the same
We will need better than 35 MA/m^2 to improve the FNSF Bo at Ro
Remember the peak field at the TF is 17.1 for 7.5T at .48m
Next Steps
Evaluate Tensile Stiffness and strength of the winding pack. Determine if it helps structure enough to be able to increase the field
Quantify transverse compression in the tape stacks, Literature search on transvers compression allowables
Quantify %Copper for stability – Acceptability of Plastic Copper Strains – Use CuCrZr?

25. Local Lorentz Forces Higher in Conductor that picks up the extra current

26. CORC Conductor – Achieved now
Base cable: 50 tapes YBCO Tapes with 38 um substrate (Van Der Laan, HTS4Fusion, 2015)
10 mm
6 mm
10 mm
7 kA CORC (4.2K, 19 T) cable
0.01 x 0.01 m = 1e-4 m2
Current density in CORC cables now at 247 A/mm2 at 4.2 K and 17 T (Van Der Laan, HTS4Fusion, 2015)
1000 turns -> A = 0.1 m2
Overall Je = 70 A/mm2
Je in CORC cables expected to increase
30 mm thick substrates: Je > 300 A/mm2
better pinning (15 % Zr): Je > 450 A/mm2
thicker REBCO films: Je > 600 A/mm2
Run at 7 kA - 16 T and 20°K

27. MIT TSTC Conductor – Achieved at NHMFL
Base cable: 40 tapes, 4 mm width, 0.1 mm YBCO Tape Ic (4.2K, 20T) = 170 A
10 mm
7.4 mm
10 mm
6 kA TSTC x 0.01 m = 1e-4 m2
1000 turns -> A = 0.1 m2
Overall Je = 60 A/mm2

28. MIT TSTC Conductor
Base cable: 40 tapes, 4 mm width, 0.1 mm YBCO Tape Ic (4.2K, 20T) = 170 A
20 mm
16 mm
20 kA TSTC

29. MIT Large TSTC Conductor highlighting the 12 sub-cable arrangement
32.6 mm square conductor
81.6 kA
74 turns
12-sub-cable conductor picture taken from Ziad Melhem presentation

30. US FNSF (Chuck Kessel’s Study)
Inner leg is over-stressed
Radial Maintenance Scheme makes OOP Support Challenging
“Caps” added to try to engage more of the extended metal in the outer leg