Strategic Framewo
Magnetic Confinement-Based Fusion Researchin the United States
High Field Superconducting Magnets- Promises and Challenges -Soren Prestemon
Director, US Magnet Development Program
Director, Berkeley Center for Magnet Technology
Lawrence Berkeley National Laboratory
A presentation to the National Academies of Sciences Committee
for a Strategic Plan for U.S. Burning Plasma ResearchOutline

Berkeley Center fo
Strategic Framewo• Current status and readiness of U.S. research that supports a strategy
to develop and use advanced high-temperature superconductors forfusion energy research• Technical and scientific research elements associated with high-field
superconducting magnets for fusion energy• The potential for partnerships with related science and technology
programs within the U.S. Department of Energy and other institutions• Strategic guidance for a long-term fusion energy research programthat might promote United States leadership in the field through theapplication of new superconducting magnets
Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018!2

Berkeley Center fo
Strategic Framewo
Primer - high temperature superconductors• We are primarily talking about Rare-earth Barium Copper-oxides (REBCO) andBismuth-Strontium Copper oxides
o REBCO is typically Yttrium-base: YBa2Cu3O7-x
o Bi2212: Bi2Sr2CaCu2O8-x• REBCO: anisotropic tapes (“coated conductors”); no heat treatment required• Bi2212: isotropic round wire; requires ~900C, O2, overpressure heat treatment
D. Larbalestier, A. Gurevich, and D.
Feldmann, Nature, 2001
D. C. Larbalestier et al., Nature Materials,
vol. 13, no. 4, pp. 375–381, Mar. 2014.

A Sundaram et al 2016 SUST 29 104007
Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018!3

Berkeley Center fo
HTS opens the possibility of magnets beyond
the Framewo
Strategic
realm of traditional low-temperature superconductors

Whole Wire Critical Current Density (A/mm², 4.2 K)

104

Nb-Ti

Maximal Je at 1.9 K for entire LHC NbTi
strand production (CERN-T. Boutboul '07).
Reducing the temperature from 4.2 K
produces a ~3 T shift in Je for Nb-Ti

4.2 K LHC insertion
quadrupole strand(Boutboul et al. 2006)

2212

REBCO B∥ Tape Plane
SuperPower tape, 50 μm
substrate, 50 μm Cu, 7.5% Zr,
measured at NHMFLPeter Lee,
ASC/NHMFL

55×18 filament B-OST strand with NHMFL
50 bar Over-Pressure HT. J. Jiang et al.

Nb-Ti

103

1.9 K

2223: B ∥ Tape Plane
Sumitomo Electric (NHMFL)

2223 "Carrier
Controlled"
MEM'13

2223: B⊥
Tape Plane
Sumitomo
Electric (2012prod.)

Nb-Ti
4.22 K High Field
MRI strand(Luvata)1022223: B⊥ Tape
Plane Sumitomo
Electric (NHMFL)

Nb3Sn: High Jc
Nb3Sn:
Bronze Process

MgB2: 2nd Gen. AIMI 18+1
Filaments , The OSU/ HTRI,
20134543 filament High Sn
Bronze-16wt.%Sn-0.3wt%Ti(Miyazaki-MT18-IEEE’04)

10
0

5

10

April 2018

Soren Prestemon

15

Compiled from
ASC'02 andICMC'03 papers(J. Parrell OI-ST)

20
25
30
Applied Magnetic Field (T)REBCO B⊥ Tape PlaneREBCO: B ∥ Tape plane
REBCO: B ⊥ Tape Plane
Bi-2212: 50 bar OP
Bi-2223: B ∥ Tape Plane
Bi-2223: B ⊥ Tape Place
Bi-2223: B ⊥ Tape plane (carr. cont.)
Bi-2223: B ⊥ Tape plane (prod.)Nb₃Sn: Internal Sn RRP®
Nb₃Sn: High Sn Bronze
Nb-Ti: LHC 1.9 K
Nb-Ti: LHC 4.2 K
Nb-Ti: High Field MRI 4.22 K
MgB₂: 18+1 Fil. 13 % Fill

35

40

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018

45!4

Berkeley Center fo
Recent progress in Bi2212 processing has Strategic
made the Framewo
conductor extremely attractive for high field applications
T. Shen EUCAS 2017

D. Larbalestier, FCC week 2018

• Some excellent characteristics…
o Round isotropic wire - easily
handled, cabled, etc
o Multi filamentary for low-losses

Nb-Ti• Offset by some real processing
difficulties…
o Requires reaction - at ~900C,
o O2 environmento 20+ bar to avoid leakage,enhance Jc

Nb3Sn

Bi-2212• Applications are being investigatedo Excellent candidate for high-field
NMR insert coilso Early investigations of magnet
application for HEP are very
promisingo Is there a route for its applicationin fusion, e.g. central solenoid?
React-and-wind? Overpressure in
conduit?

Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018!5

Berkeley Center fo
REBCO tape is becoming the HTS conductorof Framewo
Strategic
choice for fusion due to its perceived ease of use
SuperPower

CORC cable: 7 kA @ 17 T
D. Van der Laan et al. SuST 29(2016) 055009

http://www.superpower-inc.com/
system/files/
2015_SPI_New_Innovations.pdf• Continued potential for performanceenhancementso Improved pinning via Zr doping, etc
o Thicker REBCO layerso Thinner substrate
1000• But also has its issues…
o “single crystal” REBCO layer is fragile,
strain-sensitiveo tape configuration makes scalability formagnets complicatedo Large surface area implies large
magnetization⟹AC losses

4000

4.2 K data

3500

750

500

250

Jc, (non-Cu, 4.2 K), A/mm²

o No reaction requiredo Excellent performance at “higher”
temperatureo Many vendors - some level ofcompetition

Approx. 0.8 mm wire current, A• Important ease of use features…

Nb-Ti
5T

3000

30 µm + pins + thicker SC

Hi-Ho Production for
SSC R&D

2500

2212
20 T

$1 / kA-m
2000

38 µm

Over
Pressure
Processing

Tevatron

50 µm

MFTF

1500

Nb3Sn 12 T
1 bar

1000

$16 / kA-m
500
1975

1980

1985

1990

Plot courtesy D. Larbalestier
Soren Prestemon

Improved Powder
and Wire
Processing

LHC

Industry Compilation(SSC era)

1995

2000

2005

2010

Year

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018

!6

70 µm

2015

100 µm2020

REBCO 20 T
(also 65 K, ~2 T)Berkeley Center fo
Current status of US research towardsStrategic
the use of
Framewoadvanced HTS for fusion energy• The US has the expertise and facilities to make fast advances towards HTS for fusion The LBNL RC5 waso Industrial supplier of REBCO, Superpower, is leader in high-performance tapeso Bruker/OST is leading (and only…) supplier of Bi2212 round wireo Conductor testing facilities of various flavors

2212 powder develo• HEP-supported: LBNL, FNAL, ASC/NHMFL/FSU, Ohio State• FES-supported: PFSC

• Promising University-Industry connections in HTS materials exist:

o MIT/PSFC, ASC/NHMFL, U. of Houston, Ohio State, Tufts, Penn State;Co Superpower, Advanced Conductor Technologies (ACT), AMPeers LLC (REBCO)
RC5 is a product o
RC5 is a product of suco Bruker/OST, nGimat, MetaMateria… (Bi2212)• DOE labs are starting to look at HTS for fusion:national
national lab, uo PPPL, LBNL

• But efforts are not fully coordinated, and additional facilities needed:o Loosely organized groups• e.g. via the FES Virtual Laboratory (mainly MIT, LBNL)
o Programmatic goals for HTS not yet sufficiently focusedo Existing facilities are mainly modified from LTS approaches

Soren Prestemon– K. Z– K. Zhang,
M. TH

M. Turqueti

– E.

D.C

The LBNL RC5 was made fro
The LBNL
RC5
was madefrom by
thenGw
2212
powderdeveloped/2018
7!
NAS - Strategic Plan for U.S. Burning Plasma Research 4/122212
powder developed by nGimat LL

Berkeley Center fo
The good news: the next generation of magnet
scientists
Strategic
Framewoand engineers are eager to pursue HTS technology• A generation of scientists are coming from Universities with expertise in HTS
materials and there applicationo ASC/NHMFL/FSU, Tufts, MIT, NCSU…
o These scientists are actively engaged in fusion research and facilities, coordinating
with, or now scientists at, facilities:• PPPL, LBNL, MIT; NHMFL• A new generation can more readily question dogma and historical paradigms
o Is cable-in-conduit the right approach with HTS?
o Do we detect quenches with voltage taps? Do we need to provide ample
stabilizer for protection? Should we even assume the magnet will quench?
o Do we continue to use supercritical helium? Are new cryogenic solutions
possible with HTS?
o Are demountable joints realistic at the scale of a Tokamak?
o …

Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018!8

Berkeley Center fo
Strategic issues
Framewo
Current research efforts aimed at basic technology• Effort at a variety of levels:o high-level design work to demonstrate potential value of HTS to the Fusion community
o Early development of cable designs and prototypingo Various conductor characterization worko Fundamental and industrial efforts to enhance performance of REBCO tapes• First effort to develop a US strategy for HTS for fusion was a joint MIT/LBNL workshop held at
MIT in 2016o A prioritized set of near-term research elements was developedo Requires significant resources (but not unrealistic!)o Coordinate with industry on multiple fronts:• Technology development (e.g. well-coordinated SBIRs)• Focussed fusion attempts (e.g. Commonwealth Fusion Systems (CFS), GeneralFusion, Tri Alpha
Energy,…)Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018!9The LBNL-MIT workshop produced asignificant list of research areas

Berkeley Center fo
Participating Institutions
Strategic
Framewo
LBNL
MIT
Tufts

ASC/NHMFL/FSU

1. Develop conductor and magnet technology using High Temperature Superconductors (HTS)
1.1.Long lengths of YBCO tape suitable for operation at 20 K and 22 Tesla
1.2.Long conductor lengths capable of carrying ~50-100 kA at 20 K and 22 Tesla
1.3.Demountable joints using above conductors

2. Demonstrate HTS magnet performance in a suitable scale prototype magnet
2.1.Industrial development of conductor production and magnet fabrication processes and tooling
2.2.Development of experimental facilities capable of applying fusion reactor relevant operating
conditions for conductor and coils

3. Additional objectives
3.1.Improve radiation tolerance of magnet insulation systems
3.2.Advance HTS magnet design and analysis tools
3.3.Workforce education and training

High level goals identified•

Investigate fundamental aspects of HTS conductor and magnet design and technology that can lead to
substantial plasma performance improvements and magnet cost reduction.

•

Pursue HTS conductor R&D with clear targets to increase magnet performance and reduce the cost of
fusion reactors.
Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018!10

Berkeley Center fo
Conductor characterization is critical Strategic
to theFramewodevelopment of HTS for fusion• REBCO tapes need to be thoroughly studied:o Mechanics: brittle REBCO layer protected by substrate• Strain sensitivity of Ic (as function of field and temperature)• Degradation limits (cyclic forces, thermal cycles)o Magnetic: anisotropic lattice structure, inhomogeneity• large magnetization transverse to tape surface• strong Ic dependence on field angle• “single crystal” can have flaws, e.g. reduced transport
1.05
properties

0.95•Transport device invented by Yates Coulter, LANL, NHMFL•Further developed with magnetization at ASC, NHMFL
Purpose: quantify Ic variation, identify signatures of degradation

Iʘ

Voltage
taps

Hall
probe
array

Voltagetaps

εa = 0%ε = -0.3%
Cryogenic measurementswith the U-springa

A U-spring test rig was constructed
and optimized for the purpose of measuring the super60
conducting properties of Nb3 Sn bulk samples and thin films. With this test rig, cryogenic
measurements were performed by which the voltage drop over a sample was measured as a
50% In this way, thefunction of temperature, magnetic field, applied strain and current density.
criterium
normal state resistivity, critical 40
temperature, upper critical field and critical current density
under various conditions were determined. These measurements are discussed further in thenext chapters: chapter 3 focuses on the critical current density, chapter 4 on the relation be50 um substrate
tween composition, critical temperature
and20
15 T upper
12 Tcritical
10 T field,5andT chapter0 T5 on the effect30 um substratesample Iof strain on both the superconducting properties T c and µ0 H c2 as well as the normal state
30 um substratesample IIresistivity.

0.90-0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.302.4.1
0.40 0.50
0.60 test
0.70 rig
U-spring

Strain, ε (%)

0
5

7.5

10

12.5

15

17.5

Temperature T [K]The U-spring test rig (figure 2.15) was originally developed by Ten Haken et al. [32, 71, 72]
for the purpose of measuring
the critical current of Nb3 Sn tapes
as a function of temperaFigure 2.17: Subset of the r(T ) measurements
performed on deposition 8-22-11, with 22.1
ture, magnetic field and strain,
alsoresistivity
allowswas
fordetermined
the measurement
samplesatwith
variousat.% but
Sn. Thevariousmagnetic
3as a function ofoftemperaturefieldsµH
andappliedstrainse.
Themeasurementsatea =74].
0.3%
and 0% aredescriprepresenteda0
geometries such as wires [32], thin films [46], and bulk samples [73,Detailed
with grey and open symbols respectively.
tions of the operation of the U-spring for the purpose of measuring wires, bulk samples andthin films are available elsewhere [32, 38, 46, 74].

Example of Nb Sn strain
sensitivity with temperature todemonstrate system capability;
The U-spring is made out of Ti-6Al-4V, a type of titanium alloy that maintains elastic besystemislevelscurrently
being
havior up to a strain limit ofthe±1.3%,
i.e. both highof compressive
and tensile strain
used to measure REBCO (Tufts &30
Chapter 2
LBNL)

Reel
#2

from Hooke’s law, with:

Rotating
permanent
magnetElectromagnet, H||c80

Resistivity ρ [μΩcm]

1.00

Ic/Ico• defect creation, impact on Ic

LN2 bath

F. Pierro, presented at
HTS4Fusion, 2018
2.4

o Impact of radiation

Reel
#1

PhD thesis, M. Mentink

Figure 2.15: Left: Schematic representation of the U-spring test rig. Right: Illustration oftemperature insulation with an ‘inverted cup’ system and strain application through a gearbox, after PhD thesis Godeke [32].

eop =

1

nsampleelong,ip,a + etrans,ip,a ,nsample(2.4)

where nsample is the Poisson’s ratio of the sample and eop is the out-of-plane strain resulting
from in-plane longitudinal and transverse strain. The resistivity r is related to the resistanceR, length l, width w, and thickness th as:IÄr=[1] Coulter, J.Y., et al., IEEE Trans. Appl. Supercond., 17, 3394-3397 (2007)[2] Coulter, J.Y., et al., IEEE Trans. Appl. Supercond., 19, 3609-3613 (2009)

Soren Prestemon

R · w · th
,
l

(2.5)

The relations between the dimensions l, w, and th on the one hand and the strains elong,ip,a ,
etr,ip,a and eop on the other depend on the direction of the current relative to the strain direction. In the case of the patterned samples, the resistivity is expressed with:

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018 !11Experimental Aspects

35

Berkeley
Centerfo
The scale of fusion magnets makes high-current cables
a necessity for LTS, and that characteristic Strategic
will likely Framewo
hold for HTS as well

• Cables likely needed for basic technology reasons, and require R&D:
o massive scale of fusion magnets implies large stored energy• need to manage system inductance for realistic ramping, protection

Pictures from N. Koizumi, Fusion
and Accelerator Magnet Workshop,
Brolo, 2008o commercial production of REBCO tapes limited in length ⟹ joints• cables should help in addressing tape length limitation• significant number of variables to study with cables:• fabrication variables (tension, transverse pressure, surface treatments, etc)
• cyclic behavior (thermal cycles, bending, transverse pressure, etc.)• interstrand/inter-tape resistance; current sharing• cable magnetization, persistent currents, AC losses• Need special facilities: high field, high current, variable temperature,tension/transverse pressure/torsion

Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018 !12Berkeley Center fo
The cable configuration is traditionallythe heart
Strategic
Framewoof fusion magnet technology• Almost all investigations into HTS for fusion assume
some variant of cable-in-conduit conductor (CICC)
o CICC has been the staple for LTS fusion since
introduced in the 1970’s (M.O. Hoenig, Y. Iwasa,
and D.B. Montgomery, Proc. MT-5 Roma (1975)• can provide cryo-stability - mitigate training• provides cooling power for dB/dt - generated heat• provides robust structure for mechanical support

o But CICC does have its issues…
• thermal strains can be large• friction and stress concentrations ⟹ potential
degradation• cost and complexity of cables

o Generally CICC places the “development load” on
the CICC, and less on the “magnet”• Very different from high-field NMR, where coils are
made from single wires• Different from HEP, where “simple” Rutherford
cable is used in “complex” magnets• Above typically use “adiabatic” (VPI’ed) coils L. Muzzi et al., SUST, vol. 28,
no. 5, p. 053001, May 2015.
Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018 !13

N. Koizumi, (JAEA)
FAM Workshop 2008

Berkeley Center fo
Strategic Framewo® cable winding
CORC
CICC cableconcepts
using HTS materials are underinvestigation worldwide

CORC®(wire(
Winding&of&long&CORC®&cables&with&custom&cable&machine:(
Accurate(control(of(cable(layout((tape(tension,(gaps(spacing,(etc.)(
Long(cable(lengths(possible((>100(meters)(
75(mm(mandrel(O.D.((bstrate(c YBCO wire!

ﬂexibility&will&likely&
bending&diameter&
ember(2015)(

M. Takayasu, L. Chiesa, L. Bromberg, and J. V. Minervini,
SUST, vol. 25, no. 1, Jan. 2012.

D. van der Laan, Advanced Conductor Technologies LLC

proved&accuracy&now&allows&winding&of&CORC®&cables&from&tapes&with&30&µm&substrate&
pe&Ic&retenGon&increased&from&70&%&to&over&85&%&during&last&3&months

W. Goldacker et al.,TAS 17 3396–401

D. Uglietti, R.
Wesche, and P.
Bruzzone, TAS, vol.
24, no. 3, pp. 1–4.

G. Celentano et al., TAS,
vol. 24, no. 3, pp. 1–5.

Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018!14

Berkeley Center fo
The Swiss CRPP facility exemplifies the state of the art
in high-field
cable
Strategic
Framewo• 580 mm Ø solenoid bore (1% in a 300 mm Ø sphere)• DC current for testing samples up to 100 kA• Supercritical Helium at 10 bar and 4.5–10 K, up to 20 g/s• Superimposed steady state ac field: up to 0.8 T, 0.01 to 6 Hz
testing - critical capability to develop HTS fusion
magnet technology• Superimposed pulsed field: up to 3 T amplitude, 140 ms period

EDIPO – dipole magnet
In the US, the large
bore 20T at NHMFL
was used until
recently, but is nolonger operational.

es - SULTAN

100 kA superconducting
transformer• Superimposed steady state ac field, up to 0.4 T, 0.01 to 6 HzN

online in a few
months at the NHMFL

Is being erected next to SULTAN. Operation will start in2012 to expand the test capabilities of SULTAN. The
racetrack dipole generates 12.5 T over 1.1 m.
Except for the magnet, supplied by F4E and recently
delivered, CRPP designed, procured and assembled all theparts of the facility, e.g. 100 kA transformer, thermal shield,
vacuum vessel, etc.

A proposal is underconsideration at DOE
for the US tocollaborate with
CERN and CRPP on
the design andfabrication of a new
dipole for the EDIPO
facilityb3Sn long cables (up to 4 m) are available.

umentation installation (high precision thermometers,
train gauges) are carried out at CRPP-SC; we have gained
ent contacts and joints preparation.

2

e

bl
a
l
i
va
a
r
e

• Supercritical Helium at 10 bar and 4.5–10 K, up to 20 g/s

A new magnet (14.5T,

ility for ITER superconductors. The
other fusion magnets (Wendelstein 7-X, HT7U,
ts (high field hybrid) are also tested in SULTANll• DC current for testing samples up to 100 kA

Test facilities- EDIPO
160mm
bore) will be

wide magnet facility to test forced flow, high580ofmmors up to 11 T. It consists
six Ø
noids cooled by forced
flow of supercriticalsolenoid
bore

ng
o
l
o

The EDIPO facility
prior to damage

Test facilities - Current leads

A large cryostat for testing current leads up to 25 kA with v
temperature and variable mass flow rate is available.
A pair of 18 kA HTS current leads, needed for the EDIPO facility, hasdesigned, manufactured and successfully tested at CRPP-SC.

In a Swiss Federal project, CRPP-SC supports the WEKA AG
development of HTS current leads (3-30 kA) suitable for an ind
EPFL
manufacturing process.
CRPP - Superconductivity

Applied Superconductivity at CRPP
CH-5232 Villigen PSISULTAN – split coil solenoid• 11 T –• 12.5 T (92x142 mm2 test well), 1% homogeneity over 1 meter

An upgrade of the tests facility is presently under way at CRPP-SC.
Switzerlandphone, fax, email, web page

94x144 mm2 split coil test well (1% over 300 mm)
September 2011

• 580 mm Ø solenoid bore (1% in a 300 mm Ø sphere)• DC current for testing samples up to 100 kA• Supercritical Helium at 10 bar and 4.5–10 K, up to 20 g/s• Superimposed steady state ac field: up to 0.8 T, 0.01 to 6 Hz

Access to reliable high field,
high current cable testing
facility is critical for HTS fusion
magnet development• Superimposed
pulsedfield: up to 3 T amplitude, 140 ms period
580 mmØsolenoid bore

EDIPO – dipole magnet

Soren Prestemon

The Superconductivity Section, SC, of CRPP(Centre de Recherches en Physique du Plasma,
Swiss Federal Institute of Technology of
Test Lausanne,facilities- isCurrent
EPFL)
located at theleads
Paul Scherrer
NAS - Strategic Planfor U.S.
Burning
Plasma Research 4/12/2018
A large Institutecryostat inforVilligen,testing Switzerland.
current leads up to 25 kA with variable• 12.5 T (92x142 mm2 test well), 1% homogeneity over 1 meter

temperature and variable mass flow rate is available.

The 20 people strong team, active since more than!15

Berkeley Center fo
Magnet protection considerations with HTS Strategic
is an activeFramewo
areaof research - detection and energy extraction are concerns• Traditional protection paradigms are challenged by HTS materialso Large temperature margin results in slow quench propagation• impacts detection: slow voltage growth implies difficulty in detecting onset of quench• increases hot-spot temperature and strong thermal gradients that can cause mechanical damageo Higher-field, more compact magnets ⟹ higher JE ⟹ higher stabilizer current density ⟹ aggravates the hotspot issueo Measuring small normal voltage signals (<<100mΩ) in a background terminal voltage of >10 kV is a challenge!"# (%)'% = )*+(,)2 ',!

Soren Prestemon

M.K. Wilson,
Superconducting Magnets

J. H. Schultz, “Protection of superconducting
magnets,” IEEE Trans. Appl. Supercond, vol.
12, no. 1, pp. 1390–1395, Mar. 2002.

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018!16

Berkeley Center fo
Advanced magnet diagnostics are critical for the application of HTS to fusion
Strategicparadigms
Framewo- provide design flexibility and enable new design and operational• Fiber-optics promise minimally invasive measurement of temperature/strain⟹ quench
diagnostic that avoids the signal to noise issue associated with voltage taps
F. Scurti, S. Ishmael, G. Flanagan, and J. Schwartz, SUST, vol. 29, no. 3, p. 03LT01, Mar. 2016.

• Acoustic signals (both passive and active) are proving to be extremely valuable in identifying
and locating quench events in HTS - non-invasive and independent of voltage
M. Marchevsky and S. A. Gourlay, Appl. Phys. Lett.,
vol. 110, p. 012601, (2017), doi:10.1063/1.4973466
M. Marchevsky et al., IEEE Trans Appl. Supercond. vol28, issue 4 (2018), doi:10.1109/TASC.2018.2817218

Bi-2212 coil RC3(K. Zhang, T. Shen)

ReBCO CORC coil(X. Wang)

Soren Prestemon

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Berkeley Center fo
Current research efforts aimed primarily atStrategic
basic technical
Framewoissues - the early building blocks of the technology• Effort at a variety of levels:o High-level design work to demonstrate potential value of HTS to the Fusion community• e.g. F. Mangiarotti, Ph.D. Thesis, MIT, 2016, “Design of Demountable Toroidal Field Coils with
REBCO Superconductors for a Fusion Reactor”

o Early development of cable designs and prototyping (M. Takayasu, MIT and L. Chiesa, Tufts)
o Various conductor characterization work
• Radiation damage to REBCO (B. Sorbom, MIT)
• Understand conductor and cable performance and its impact on magnet design andperformance (X. Wang, LBNL)o First look at joint technologies (MIT group)o Produce subscale coils that have magnetic and mechanical features of relevance to fusion
coils, and understand their behavior (mainly NHMFL and LBNL)o Fundamental and industrial efforts to enhance performance of REBCO tapes• Feedback to conductor and cable manufacturers on parameters that will improve magnet
performance (X. Wang, LBNL)

Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018 !18

Berkeley Center fo
Technical and scientific research elementsStrategic
associatedFramewo
with high-field superconducting magnets for fusion energy• There are three primary elements required to rapidly develop HTS for fusion:o A clear driving scientific need that provides motivation and context
o Expertise, i.e. the right people with the right skills and driveo Facilities, i.e. equipment tailored to the R&D needso (And of course, the funding to support them…)• The US has excellent examples of such research groups
o HEP: FNAL, LBNL, ASC/NHMFL ⟹ Now US MDPo NSF: the NHMFL
o Fusion: MIT-PSFC• Industry plays a central role, symbiotic relationship with government:o A healthy level of DOE-SC support for conductor development is critical• provides “steady” support for critical conductor research• provides stream of conductor for magnet programs• Core technical elements that need to be addressed are:o Conductor development (close collaboration with industry)o Cable development (industry or lab)o Magnet technology development (e.g. components, sub-scale magnets,
etc)• Test facilities
o wire, cable, sub-scale magnets

35 years of exceptional service to the community

Ultimately a systems engineering approach will be needed, with all components designed in an integrated manner
Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018 !19

Berkeley
Centerfo
There is strong potential for partnerships with related
Strategic
Framewoscience and technology programs within theU.S.
Department of Energy and other institutions• Strong synergy between FES and HEPo in superconductor R&D and industrialization• The Low Temperature Superconductor Workshop has been extremely successful in mapping scienceneeds to industry developments - 35 years of work demonstrating value• Continue to leverage “LTSW” for common HEP/FES goals for HTS

o in high field superconducting magnet technology• HEP has initiated the US Magnet Development Program with clear goals and a roadmap to achieve them
• A similar programmatic roadmap for FES magnet development would clarify areas of unique investment
and areas of overlap (synergy)• Strong synergy with the (largely NSF-funded) National High Magnetic Field Laboratoryo Leading the development of HTS for high field in a solenoid configurationo Deep expertise in conductor development and characterizationo significant expertise and infrastructure to support HTS technology developmento Coordination/integration of DOE/NSF HTS technology capabilities and development roadmaps would
lead to enhanced efficiency and speed up technology development• The international community has growing interest in exploring HTS for fusiono Many areas where facilities and expertise can be leveraged/coordinatedo Collaboration with the international community is essential - access to expertise, facilities

Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018 !20

Berkeley Center fo
A perspective on how to position the US
for longFramewo
Strategic
range leadership in magnet technology for fusion• A long term DOE-SC research program in HTS magnets will provide critical value to thefusion community on a number of fronts:
o Build expertise and a pipeline of future scientists and engineerso Invest in critical infrastructure whose investment in time and cost may be beyond the scopeof any specific project or experimento Provide leadership in identifying and acting on future promising fusion technologies/projects
o Provide continuity and focus to US industry in technology development for fusion• Basic R&D serves as the catalyst for future projects
o When a potential project is seen on the horizon, the basic R&D program provides the“technology toolbox” that can then be downselected/improved upon through a technology
readiness program, ultimately culminating in a formal project

Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018!21

Berkeley Center fo
Strategic guidance for a long-term fusion energy research
Strategic
program that might promote United States leadershipin theFramewo
field through the application of new superconducting magnets• An key strength of the US is the innovative spirit we foster in our
Universities and Laboratories - leadership comes from intense
curiosity and the willingness and confidence to pursue high-risk,
high-reward avenues of research• A long-term program should be built on two pillars
o Developing and maintaining Expertiseo Identifying and investing in Critical Facilities• Forming a national program for HTS magnets for fusion thatprovides coherence and focus to the various research groups
should be considered• Fusion energy should leverage other parts of DOE (HEP in
particular, but also NP, BES, …) with common interest in magnet
technology
o The US MDP (HEP accelerator magnets) and the NHFML(primarily high-field solenoids) are examples where coordination
should occur with fusion energy interests in magnet technology• Industry/private investments should be welcomed, andcoordination should occur where possible - but the fusion energy
program should be steadfast in its core mission• Fusion energy research has an excellent history of fruitfulinternational collaborations - this should be maintained as much as
possible

MDP
Cable test
facilities

High-JE cables

CICC
concepts

Transverse loads~10kA cables

HybridLTS/HTSmagnets

Materials
development
Conductor
test facilities
Modeling~100kA cables
DemountablejointsSuperconducting
jointsSingle-strand
magnets

NHMFL
Examples of programmatic coordinationthat should be considered within US
research programs

Leadership is staying in front, forging the path forward!
Soren Prestemon

FusionNAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018 !22

Conclusions

Berkeley Center fo
Strategic Framewo• The time is ripe for the US to support a strategy to develop and use advanced
high-temperature superconductors for fusion energy research - excellent
opportunity for leadership as well as coordination across the DOE-SC• A first look at critical technical and scientific research elements associatedwith high-field superconducting magnets for fusion energy was made with the
LBNL-MIT workshop - a more in depth and systematic analysis should be done
• There is excellent potential for partnerships with related science andtechnology programs within the U.S. Department of Energy and otherinstitutions - primarily MDP and the NHMFL• We have provided some thoughts on strategic guidance for a long-term fusionenergy research program that would promote United States leadership in thefield through the focused development of HTS superconducting magnet
technology
Soren Prestemon

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Berkeley
Centerfo
Backup: How the DOE-OHEP US Magnet Development
Program was initiated and structured: first Strategic
identify theFramewo
questions of interest…
1.

What is the nature of accelerator magnet training? Can we reduce or eliminate it?

2.

What are the drivers and required operation margin for Nb3Sn and HTS accelerator magnets?

3.

What are the mechanical limits and possible stress management approaches for Nb3Sn and 20 T LTS/HTS magnets?

4.

What are the limitations on means to safely protect Nb3Sn and HTS magnets?

5.

Can we provide accelerator quality Nb3Sn magnets in the range of 16 T?

6.

Is operation at 16 T economically justified? What is the optimal operational field for Nb3Sn dipoles?

7.

What is the optimal operating temperature for Nb3Sn and HTS magnets?

8.

Can we build practical and affordable accelerator magnets with HTS conductor(s)?

9.

Are there innovative approaches to magnet design that address the key cost drivers for Nb3Sn and HTS magnets thatwill shift the cost optimum to higher fields?

⑩

What are the near and long-term goals for Nb3Sn and HTS conductor development? What performance parameters in
Nb3Sn and HTS conductors are most critical for high field accelerator magnets?
Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018!24

Berkeley Center fo…Then develop a program with a clear
set of Framewo
Strategic
goals to maintain focus…

Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018 !25

Berkeley Center fo…And finally sketch a roadmap with milestones
Strategic Framewo
to judge progress

Soren Prestemon

NAS - Strategic Plan for U.S. Burning Plasma Research 4/12/2018 !26

Berkeley Center fo
The management structure is designed
to foster
Strategic
Framewocollaboration and integration of teams
DOE Office of HEP
Research & Technology Div. – G. Crawford
Program Manager – K. Marken

MDP Steering
Council

Lawrence Berkeley National Laboratory
Associate Lab Director, Physical Sciences
T.J. Symons
ATAP Division Director
W.P. Leemans

Magnet Development Program
S. Prestemon, Director
G. Velev, Deputy

Nb3Sn
magnets

HTS magnets

Technology
development

Technical Advisory
Committeee

Conductor procurement
and R&D

ASC/NHMFL

LBNL

Technical Advisory Committee
Andrew Lankford, UC Irvine – ChairDavide Tommasini, CERN
Akira Yamamoto, KEK
Joe Minervini, MIT
Giorgio Apollinari, FNAL (LARP/Hi-Lumi)
Mark Palmer, BNL
MDP Management Group
S. Prestemon, LBNL
G. Velev, FNAL (Deputy)
L. Cooley, FSU
S. Gourlay, LBNL
D. Larbalestier, FSU
A. Zlobin, FNAL

FNAL

Program management
and oversightSoren Prestemon

Technical leads
Cond Proc and R&D

Lance Cooley

Magnets

Lead

Cosine-theta 4-layer

Sasha Zlobin

Canted Cosine theta

Diego Arbelaez

Bi2212 dipoles

Tengming ShenREBCO dipoles

Xiaorong Wang

Technology area

LBNL lead

FNAL lead

Modeling & Simulation

Diego Arbelaez

Vadim Kashikhin

Training and diagnostics

Maxim Martchevsky

Stoyan Stoynev

Instrumentation and quench protection

Emmanuele Ravaioli

Thomas Strauss

Material studies – superconductor andstructural materials properties

Ian Pong

Steve Krave

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