Fusion Magnets using HTS R. Mumgaard for J. Minervini and B. … · 2017-06-16 · 26 Tesla small bore non-insulated HTS solenoid (SUNAM) 10 Tesla intermediate bore non-insulated

FESAC TEC presentation

Fusion Magnets using HTS

R. Mumgaard for J. Minervini and B. Sorbom


Superconductors in 1 slide

• NbTi and Nb3Sn (known as “low-temperature superconductors” or LTS) were discovered in the 1960’s

• Still required extremely low (~4 K) temperatures to operate but could tolerate moderate currents and fields

• Development of NbTi and Nb3Sn in the 1970’s and 80’s led to use in MRI machines (NbTi) and in ITER coil development (Nb3Sn)

• Developed for routine use in large-scale science facilities such as the particle accelerators, light sources, detectors, and

• magnet fusion devices [1]

Current density

[A/mm2]

Temperature[K]B-field [T]

Critical surface for NbTi(superconducts only when

J, B, T below surface)

[1] https://arxiv.org/abs/1501.07169

Superconductivity only occurs below a

critical surface:Magnet-grade superconductors are rare

Of >100,000 known superconductors only

4 have been commercialized

https://arxiv.org/abs/1501.07169


HTS: What is it?

• 1986: New family of copper oxide ceramic superconductors were discovered in (“High temperature superconductors”or HTS) Led to Nobel prize

• In addition to high temperature operation, this new material could also tolerate high currents and high magnetic fields unlike previous LTS materials

• Unfortunately, fabrication process difficult for samples larger than a single crystal, requiring extremely precise grain boundary alignment via “texturing” of substrate

• Thus, high-temperature superconductors existed mostly as a bench-top scientific curiosity for two decades

• 1990s: People learned to fabricate it into tapes

• 2000s: Companies started making reproducible tapes

• 2010s: Companies started making reproducible tapes in quantity and length that mattered

Single

crystals

of YBCO


Why do we care?

[1] J.P. Freidberg, Plasma Physics and Fusion Energy.

“Magnetic fusion, as its name implies, requires high magnetic fields.”

1950-1960s:

Copper wire and bars

The pioneers

Most copper machines

1990s-2010s:

Nb3Sn for higher field

Reactor-class devices

1980-2000s:

NbTi superconductors

First superconducting devices

1960-1980s:

Cryogenic Bitter plate magnets

The Alcators at MIT

ITER 2015

Bcoil = 13 TTore Supra 1988

Bcoil = 9 T

Alcator A

1968

Bcoil = 17 T

Stellarator A 1953

Bcoil = 0.1 T

2010-2020s:

REBCO for very high field

???

????

Bcoil > 20 T


HTS properties and what they mean for fusion magnets(it is a whole new world)


Tolerance to high magnetic field

Why it matters:• Constraint on magnetic field is now a structural issue, not a quantum mechanical issue• Can conceive of designs to arbitrarily high magnetic fields

HTS is nearly field-agnostic whereas LTS had a hard field limit Very high magnetic field solenoids are being constructed, 50T is within reach, 100T is not inconceivable

42.5T insert coil at KBSI (2017) 100T solenoid design


High engineering current density

Why it matters:• More space for structure and other components• More compact, higher-field magnets

HTS carries a ~5x higher engineering current density than LTS in a toroidal field magnet.(100A/mm2 designs vs ~20A/mm2 for ITER)

Current density keeps improving due to innovations in processes and engineering

~10x improvementin last ~5 years

Tape performance continues to improve as processes are refined

Cables concepts improving.

Now at 400A/mm2 @ 20T, 20K

Headed to 600A/mm2 @20T, 20K

Recent 42.5T: Je > 1000A/mm2

LTS 20T NMR vs HTS 26T NMR


Higher operating temperature

Why it matters:• Wider flexibility in design of cooling system, including cryogen free, or large heat loads (nuclear, joints)• Much more stable design and much larger margins• Reduced cryogenic system (factors of 5-20)

As its name implies HTS can go to higher temperature, but it performs better when sub-cooled.

Changing the operating temperature changes all the material properties, particularly heat capacity and thermal conductivity

Can now tolerate large heat loads

Can use new cryogens (Hydrogen, Neon)

Can use conduction cooling techniques

More stable to off-normal events


Different form factor with stronger materials

Why it matters:• Superconductor can become part of structure and can design to higher stress and thus smaller magnets• Have to design the magnets and cables differently than LTS

HTS is incorporated into a tape with a strong hastelloy substrate instead of brittle tiny wires

Can design up to 700MPa and 0.4% strainFactors of 2 and 1.3 above LTS respectively


No heat treatment and more robust characteristics

Why it matters:• Much easier to work with, particularly when prototyping, lower cost magnets• Lack of heat treatment opens possibilities to higher strength materials (composites, alloys)• Robustness can open path to fault tolerant magnets

Nb3Sn requires heat treatment to react the components, HTS is ready to go off the reel

HTS’s thermal properties make it robust to errors and enable winding without insulation

ITER wind and react process: High temp heat

treatment prior to insulation prior to impregnation 26T All REBCO non-insulated no epoxy


Adequate performance under neutron irradiation

Why it matters:• Fusion magnets are unique in this category• Limits the ultimate lifetime of the magnet (and thus of the fusion device)• But is no worse than LTS

>10 studies with REBCO under neutron irradiation inside reactors simulating spectrum at the magnet in a fusion reactor

Experiments underway at MIT to compare to proton irradiation under cryogenic conditions


Process and Production length

Why it matters:• Process is still evolving and getting better, lots of potential for improving yield and throughput• Piece lengths are recently (last 3 yrs) sufficient to make practical magnets• No bottlenecks foreseen to go to very long lengths (now up to 4km reels at some manufacturers)

The process of making HTS is a thin-film deposition process. Similar in many ways to chip fab. It is highly dependent on process control which sets the piece length and yields.

The max available piece length has increased above what is required for a fusion magnet cable (200-800m) at high performance

All Rights Reserved. Copyright SuperPower® Inc. 2016

X-ray

inspection Payoffs

Alignment & pre-clean Post clean

Bonding station

Take-up

Critical

curr

ent

of

tape (

A)

Length of tape (m)


Market drive beyond fusion

Why it matters:• Fusion is a bit player, others are pushing this forward, we can ride coattails in regards to tape• Price and quantity are going to be influenced by a large suite of possible applications• Actual market dynamics are likely to be important, never occurred for Nb3Sn

Compact NMR

High-efficiency power transmission High-efficiency motors

High-fieldparticle

acceleratormagnets

High-efficiency, high currentmagnet leads Advanced MRI

machines


Many companies entering market

Why it matters:• Competition for best process, best price, best application• Different strategies for approaching the market for HTS, industry groups formed• Driving prices down, production up year by year


Cost and production amounts

Why it matters:• Cost is currently too high and production too low to build a device• Projects show that in the next 5 years production and cost will be low enough to build a small tokamak• Market dynamics at play

Current HTS production is insufficient. Single manufacturers produce 1/50th of a fusion reactor per year.Industry-wide this is similar to what Nb3Sn was at the start of ITER procurement (15 tons/yr)

Will need to scale up but this is already happening.

Now at a sufficient scale to start making serious test magnets.

At current production cost is ~100$/kAm which would mean ~$0.5B superconductor for ARC (ITER was $0.6B), but at scale cost is expected to drop factor of 4-10

1000 km/y with$7M investment

15,000 km/y and 4x pricereduction with $20M investment


Where are we in building magnets and where do we need to go?


HTS tape now being incorporated into cutting edge magnets across disciplines

26 Tesla small borenon-insulated

HTS solenoid (SUNAM)

10 Tesla intermediate borenon-insulated HTS pancake

coil (MIT PSFC)

32 Tesla small boreHTS solenoid (NHFML)

SMES in Russia

Dipole at BNL

Dipole in Europe


Need to start putting HTS into realistic fusion magnet designs

=Manufacturingfor traditional

superconductingfusion magnets

New highperformance

superconductors

Fusion magnets at high field and

novel operating ranges

+ +

The challenge for HTS in fusion magnets is to marry what we know from LTS to the unique aspects of HTS while taking advantage of the advantageous aspects of the underlying conductor

Almost all MFE concepts will benefit from the development since they share many similarities What needs to be done:

Integrated devices design, cabling of HTS, managing quench at large stored energy, handling structural forces

Decades ofexperienceengineering

fusion magnet


Advances for incorporating HTS into fusion magnets:Cabling the REBCO in high strength CICC looks feasible

CRPP HTS CICC 60kA class cable Tested at EDIPO : >60kA @ 12T Only ~10% Lorentz force degradation despite over 2000 up/down cycles

“6-around-1” CORC-CICC 60kAclass HTS cable design [1] 7mm diameter To be tested in EDIPO in 2016 Expected performance:

6x10 kA = 60 kA @ 4.2 K, 12 T

Steel jacket

IndividualCORCcables

Coolantchannels

Copperstabilizer

“TSTC” 10kA class HTS cable qualified 17T with no degradation


Large-scale test facilities from LTS development are being convertedto test high current HTS cables in high B fields: more work required

EDIPO (CRPP, CH) [1]Bmax = 12.5TImax = 100 kAT = 4 – 50 K

SULTAN (CRPP, CH)Bmax = 11.0 TImax= 100 kAT = 4 K

SC Test Facility (NIFS, JP)[2]Bmax = 13.0 TImax = 50 kAT = 4 – 50 K

FBI Facility (KIT, DE)[3]Bmax = 12.0 TImax = 10 kAT = 4 – 80 K

“We have built up a lot of experience and know-how in working for ITER and I can only hope that there won't be too long a gap before the DEMO-phase machines are under construction. Otherwise, we risk losing the human expertise and the industrial know-how that we are accumulating now.”

- Pierluigi Bruzzone, head of CRPP's Superconductivity sectionhttp://dx.doi.org/10.1016/j.phpro.2015.06.129[1]

[2][3]

http://www.jspf.or.jp/PFR/PDF/pfr2015_10-3405020.pdfhttp://dx.doi.org/10.1109/TASC.2013.2287710

http://dx.doi.org/10.1016/j.phpro.2015.06.129

http://www.jspf.or.jp/PFR/PDF/pfr2015_10-3405020.pdf

http://dx.doi.org/10.1109/TASC.2013.2287710


Recommendations for further development

Explore how HTS changes the types of devices we design and plan from reactors to experiments

Particularly how HTS can make for more compact and more robust designs

Support and integrate with the HTS manufacturing industry to ensure they develop conductors that are compatible with fusion on an appropriate timescale (more likely adapt to industry demands)

Partner with other HTS magnet developers where appropriate to share knowledge

Ensure adequate test facilities are available (currently not the case)

Continue and accelerate work into unique and required aspects for HTS magnets

Cable development

Quench detection and dump

Higher strength structural designs

Alternate coolants and magnet layouts

Non-insulated designs

Demountable joints

Documents

Fusion Magnets using HTS R. Mumgaard for J. Minervini and B. … · 2017-06-16 · 26 Tesla small bore non-insulated HTS solenoid (SUNAM) 10 Tesla intermediate bore non-insulated