HTS Magnet

General Information – Big Picture

What is being demonstrated?

The magnet we are testing is a large-bore, full-scale high-temperature superconducting magnet that is suitable for fusion devices. It is the most powerful superconducting magnet ever built for fusion applications. It proves out key technology for SPARC – which will be the first machine to create and confine a plasma that makes net fusion power. We already have much of what needs to come together to build SPARC – the physics basis, site, machine design, etc. – the magnet is the last piece of the puzzle. With this success, we’re ready to go with SPARC.

Why are magnets so important?

To make fusion work, the fuel must be heated to temperatures above 100 million degrees. At those temperatures, matter is in a state called a plasma – where the particles have net electric charge. To be kept hot, this plasma must be very well insulated from ordinary matter. Fusion devices use magnetic fields to provide the thermal insulation that is required. The stronger the magnetic field, the stronger the confining force on the charged particles in the plasma, the better the insulation, which enables a much smaller, better performing fusion device.

What is special about this magnet?

Unlike existing fusion magnets our magnet is built using a new conductor – HTS (high temperature superconductors). Compared to conventional superconductors (LTS Low temperature superconductors) HTS can carry more current even when embedded in a strong magnetic field. The magnet incorporates important innovations in design, the use of HTS will allow us to build smaller magnets that are more powerful.

What would it mean for fusion?

Using HTS magnets means that we can build smaller tokamaks which can produce as much fusion power as larger, lower field devices. Fusion power systems need magnets to provide the thermal insulation that is required to isolate the super-hot plasma from ordinary matter. Superconducting magnets which are stronger than conventional copper magnets prevent heat loss and provide higher quality thermal insulation for the plasma. Fusion devices built with this new class of magnets will be smaller, and as a result can be built faster and cheaper, which in turn puts us on a faster path to commercializing fusion energy in time to impact global warming.

Is this the magnet that will be used in SPARC?

Not quite: it is close in scale to magnets that will be used in SPARC. It is designed to address technical and engineering questions surrounding the manufacture and operation of SPARC toroidal field magnets; and to prove out the SPARC design.

What are the differences between this demo magnet and the SPARC magnets?

The TFMC is a single coil and a little smaller – SPARC will have 18 similar magnets arranged into a toroidal solenoid. In addition, SPARC tokamak has other, smaller coils, which lead to different mechanical loads than would occur in a single coil. These differences are well understood and can be modeled by standard engineering codes.

Who worked on it?

Designing and building the magnet was a collaborative effort between MIT and Commonwealth Fusion Systems which began in the fall of 2018. MIT focusing on design and analysis; CFS on manufacturing and supply chain.

What is the significance and relevance of this work to MIT and the PSFC?

MIT has been a leader in developing high-field magnets for fusion since the early 1970s, pioneering developments for copper magnets based on even earlier work at the (then) Francis Bitter Magnet Laboratory. MIT researchers developed the “cable in conduit” design for low-temperature superconductors – the basis for the magnets of all superconducting fusion devices (up to now) – and for other applications. We have built and operated a series of compact high-field tokamaks that demonstrated the advantages of this configuration and have set a number of world records for fusion plasma performance along the way. Out team at the PSFC carried out early R&D that led to high-performance HTS magnets. The TFMC is a logical step in this progression for MIT. It allows us to maintain intellectual leadership for development of large-scale HTS magnets, for both fusion and non-fusion applications. In addition, this body of work around the development of the magnet

  • Supports science and technology development needed to commercialize fusion
  • Opens up other applications for high-field magnets for science experiments and industry
  • Will enable our ground-floor participation in the most important fusion experiments on the most capable fusion device ever built.
  • Will lead to demonstration of net power from a confined plasma – a goal of international research for more than 60 years
  • Enables crucial studies of the physics of a self-heated plasma
  • Will provide a gateway to what should be a burgeoning field of fusion technology

More About the Magnet

  • Reached a peak field of 20 T (MIT News article) – 12 times stronger than a traditional MRI, 400, 000 times stronger than the earth’s magnetic field
  • Stored energy: 110 MJ
  • Mass: 9265 kg (20425 lb)
  • HTS tape in coil: 267 km (166 mi) / Boston to Albany, NY
  • At the time that the magnet was built it contained close to 10% of the world’s supply of commercially available HTS
  • Maximum helium coolant pressure: 28 bar (405 psi)
  • Each of the 16 layers is the largest HTS magnet in the world

About HTS

What is a superconductor?

Superconductors are unique materials that, under the right conditions, can carry electricity with no loss. In contrast, ordinary materials and metals – even the best conductors like copper, silver, and gold offer some resistance to the flow of current. This resistance means that electrical energy is converted to heat. While this okay in a toaster, it is not good for a fusion power plant, where the goal is to generate not consume electricity.

In order to be function as superconductors superconducting materials need to be cooled to cryogenic temperatures – how cold they need to be depends on the material.

What is HTS?

High temperature superconductors are a new, commercially available, material with a unique property – they can carry a lot of current even when embedded in strong magnetic fields. Until now, all fusion magnets have been made with copper conductors or Low Temperature Superconductors (LTS) which limit the strength of magnetic field that can be produced.

Why hasn’t it been used to make magnets before?

HTS became commercially available only 8 years ago as a result of a technology breakthrough unrelated to fusion. The international fusion program hasn’t yet looked to exploit this capability. With its long history and deep expertise on using high-field magnets for fusion, it was a natural next step for our team to work on developing an HTS magnet for fusion.

Looking ahead

What is next?
  • Device design has passed through an important conceptual design milestone
  • Construction at the site will begin soon, with a goal to complete in 2025
  • Commissioning and operation of SPARC would follow
  • We would proceed to “fusion power” operations rapidly, but deliberately
What about the overall timeline?

We are still on track – our goal is to begin operations in 2025.

Other Efforts

How does the MIT-CFS approach differ from other fusion approaches, Particularly ITER?

SPARC will be parallel and complementary to other international fusion efforts, including ITER, as well as other ongoing private-sector fusion endeavors. Decades of research worldwide in fusion science and technology, including that carried out in support of ITER, have already paved the way for much of the SPARC work. The science behind the two projects is different in that ITER is a moderate-field, moderate-density device, while SPARC is a high-field, high-density device.

Focusing on new high-field magnet technology is an alternate approach: Ultimately, fusion is far too important for scientists to allow its pursuit to have us putting all of our eggs in one basket, limiting ourselves to one approach or one experiment

The SPARC plan is driven by a focus on short-term commercialization, while U.S. interest in ITER lies in basic science. Right now, the U.S. government funds a fusion science program, but it does not have a fusion energy program.