0. REBCO magnet technology to enable next-generation magnetic-confinement fusion machines
X. Wang, S. A. Gourlay, S. O. Prestemon, G. L. Sabbi, LBNL
J. V. Minervini, PSFC/MIT
Virtual Laboratory for Technology for Fusion Energy Science
FESAC TEC Community Input Meeting, Rockville, MD, 5/31/2017

1. Outline Why we are here Our perspective
Strong synergy between HEP and FES high-field magnets
Our perspective
To ‘B’
And how to ‘B’
Synergistic REBCO technology development at LBNL
Summary

2. The LBNL magnet program is pushing the performance limit of high-field accelerator magnets
W. Barletta et al., NIMA, 764 (2014): 352–368
Nb3Sn technology
Challenges shared with high-field fusion magnets:
Lorentz force and stored energy

3. Renewed strong interest for high-field accelerator magnets led to the new US National Magnet Development Program
2016
2014
2015
Ebeam [TeV] ∼ 0.3 B R [T x km]
Significantly increase magnet performance/cost ratio
A community effort centered at LBNL (in collaboration with FNAL, FSU initially and conductor industry)

4. A key focus of MDP is to investigate the feasibility of HTS magnet technologyJe
Nb3Sn limits: ~ 16 T
P. Lee, ASC/FSU
V. Selvamanickam, U. Houston
Use HTS to push the dipole fields beyond 20 T
HTS’ high Je(B) also enables high-field fusion magnets

5. In addition to the maximum field, operation temperature determines the effectiveness of REBCO fusion magnets
Whyte et al., J. Fusion Energy (2016) 35:41–53
REBCO can work well beyond 4.2 K
Depend less on liquid He
Remove heat loads with less refrigeration penalty
Two critical variables: maximum field and operation temperature

6. Superconductor critical surface and magnet technology determine the magnet performance and cost
Develop magnet science and technology to retain conductor performance
Push the conductor critical surface

7. REBCO fusion magnet technology is at Technical Readiness Level 2 – 3 (feasibility research)
REBCO tape is sufficiently advanced to develop the magnet technology
Magnet community is embracing the conductor: solenoid magnets make multiple new field records
Fusion magnet technology is focusing on cable development
We can reach TRL3 – 4 level in the next few years, depending on the funding level
Collaboration among relevant programs will be critical

8. REBCO tape has the highest Je and is still improving
1700 A/mm2 at 4.2 K and 20 T (B perpendicular to tape surface)
DOE is supporting material development
HEP: Achieve engineering current densities of 3000 A/mm2 at 4.2 K, 20 T which can be readily transferable to pilot production
EERE: Optimize conductors for next-generation electric machines operating at liquid nitrogen temperatures

9. 15 worldwide vendors largely motivated by the anticipated utility applications
Vladimir Matias
CCA2016
Potential competition and market to drive cost down
Magnet applications should leverage and contribute to it

10. REBCO solenoids set multiple new field records
26 T, 4.2 K
11.3 T inside a 31.2-T resistive magnet
32 T user magnet
S. Yoon et al., Superconductor Science and Technology, 29 (2016) 04LT04
H. Weijers et al., IEEE TAS, 26 (2016)
Demonstrating REBCO performance and magnet technology

11. REBCO fusion magnet technology focuses on multi-tape cable development
MIT Twisted Stacked-Tape Cable
Swiss Plasma Center stack
ACT CORC® CICC
NIFS tape stack
ENEA slotted core CICC
KIT Roebel cable assembly
M. Takayasu et al., SuST, 25 (2012)
D. Uglietti et al., SuST, 28 (2015)
Y. Terazaki et al., IEEE TAS, 25(3), , 2015
G. De Marzi et al., IEEE TAS, 25(3) (2015)
A. Kario et al., SuST, 2013,
D C van der Laan et al., SuST, 24, , 2011

12. Initial characterization on cables demonstrates the potential of REBCO fusion cables
D. Uglietti et al., SuST, 28 (2015)
Y. Terazaki et al., IEEE TAS, 25(3), , 2015

13. Development magnet technology to address the uncertainties/risks
Magnet technology and conductor cost are two major uncertainties/risks
Key areas for development have been proposed in the past
5 components in the 2009 ReNeW report
9 technical elements in recent MIT paper (Whyte et al., J. Fusion Energy (2016) 35:41–53)
Most areas find overlap between FES and HEP applications
We highlight a few examples on the fundamental science and technology issues
Conductor cost can be reduced after device demonstration

14. Understand and manage the strain in REBCO conductor
REBCO is brittle ceramic – can crack due to excessive strain
REBCO is flat thin tape – how do we bend it with minimum strain induced in REBCO layer?
Cable/magnet design, fabrication and operation must properly manage the conductor strain
D. Uglietti et al., SuST, 28 (2015)

15. Develop innovative quench detection schemes
REBCO is highly stable due to the high heat capacity
Minimum quench energy 2 – 3 orders higher than LTS (J vs. mJ)
Normal zone does not propagate
2 – 3 orders slower than LTS (mm/s vs. m/s)
We only notice the hot spot when it burns up – how to detect a quench to avoid catastrophic damage?
Can become more challenge with higher current density in conductor

16. Understand and mitigate the impact of radiation
M. Eisterer, TU Wien, Recent neutron irradiation experiments on HTS coated conductors and Nb3Sn wires, 2015,

17. MDP is evaluating various cable architectures to determine the most viable conductor form for magnets
Round wire
Isotropic (mechanics, magnetics)
Challenge: achieve high Je (> 600 A/mm2) at small bending radius (< 15 mm) at 4.2 K, 20 T
CORC® by ACT
Twisted tape stack by MIT
Tape stack
High Je at small bending radius
Challenge: understand and control the bending strain
Roebel cable by Victoria University of Wellington
Compare conductors by making them into magnets

18. Successful tests in collaboration with industry demonstrate the conductor potential
Supported by DOE SBIR program
77 K
4.2 K
Current-carrying capacity x 11 from 77 K to 4.2 K.
Peak Je is 1000 – 1200 A/mm2

19. Demonstration of acoustic quench detection in REBCO tape stack (Maxim Marchevsky)
sender
receiver
“Acoustic thermometry for detecting quenches in superconducting coils and conductor stacks “, M. Marchevsky and S. A. Gourlay, Appl. Phys. Lett. 110, doi: /

20. A collaborative effort to push forward the REBCO fusion magnet technology
REBCO conductor can enable high magnetic field (> 10 T) at high temperature (> 20 K) – unprecedented opportunity for fusion
Magnet technology and conductor cost are major uncertainties and risks
Conductor/cable performance, magnet design, fabrication and protection, impact of radiation
We are at TRL2 – 3 level, demonstrating cable concepts and feasibility of fundamental magnet technologies with REBCO conductors
Collaborate to leverage other programs to reach TRL 3 – 4 within 5 years
Develop fundamental science and technology for REBCO magnets
The technology can lead to industrial competitions that drive down conductor cost and enable diverse HTS applications of broad impacts
HEP, power applications, medical applications, transportation, NMR, …

21. Backup slides

22. Strong overlap in REBCO conductor and cable technology for FES and HEP

23. Strong overlap on magnet issues too