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

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

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

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)

A key focus of MDP is to investigate the feasibility of HTS magnet technology Je 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

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

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

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

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

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

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 http://news.fsu.edu/tag/seungyong-hahn/ S. Yoon et al., Superconductor Science and Technology, 29 (2016) 04LT04 H. Weijers et al., IEEE TAS, 26 (2016) 4300807 Demonstrating REBCO performance and magnet technology

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) 014011 D. Uglietti et al., SuST, 28 (2015) 124005 Y. Terazaki et al., IEEE TAS, 25(3), 6977909, 2015 G. De Marzi et al., IEEE TAS, 25(3) (2015) A. Kario et al., SuST, 2013, 26 085019 D C van der Laan et al., SuST, 24, 042001, 2011

Initial characterization on cables demonstrates the potential of REBCO fusion cables D. Uglietti et al., SuST, 28 (2015) 124005 Y. Terazaki et al., IEEE TAS, 25(3), 6977909, 2015

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

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) 124005

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

Understand and mitigate the impact of radiation M. Eisterer, TU Wien, Recent neutron irradiation experiments on HTS coated conductors and Nb3Sn wires, 2015, https://indico.fnal.gov/conferenceDisplay.py?confId=8709

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

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

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, 2017 doi:10.1063/1.4973466

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, …

Backup slides

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

Strong overlap on magnet issues too