Magnet FAQ
General information — The big picture
What is being demonstrated?
We have designed and built a large-bore, full-scale high-temperature superconducting magnet suitable for fusion devices. It will be the most powerful superconducting magnet ever built for fusion applications. The magnet is a key technology for SPARC, which will be the first machine to create and confine a plasma that makes net fusion power. The successful magnet demonstration is the last piece of the puzzle — it will mean that we have all the pieces to build SPARC
Why are magnets so important?
To make fusion work, the fuel must be heated to temperatures above 100 million degrees. Matter in that state is 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?
It incorporates important innovations in design. Unlike existing fusion magnets it is built using a new conductor HTS (high temperature superconductors). Compared to conventional superconductors (LTS Low temperature superconductors) our magnet can carry more current even when embedded in a strong magnetic field. It incorporates important innovations in design which together with the use of HTS allows us to build smaller more powerful magnets.
What would it mean for fusion?
- Means that we can build smaller tokamaks which can produce as much fusion power as larger, lower-field devices.
- Fusion power systems needs magnets. They provide the thermal insulation that is required to isolate the super-hot plasma from ordinary matter.
- Magnets for fusion must be superconducting, otherwise too much power would be lost as heat in a magnet wound with copper conductors.
- Stronger magnets provide higher quality thermal insulation for the plasma.
Why is this important?
Allows fusion devices to be made smaller, faster, cheaper. 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 approximately 80% the size of the magnets that will be used in SPARC. Designed to prove out the SPARC design.
What are the differences?
- The TFMC is a single coil and somewhat smaller – SPARC will have 18 similar magnets arranged into a toroidal solenoid
- The SPARC tokamak has other, smaller coils, which lead to more complicated mechanical loads than in a single coil
- The differences are well understood and can be modeled by standard engineering codes
More about the magnet
- Build to reach peak field of 20 T — 12 times stronger than a traditional MRI
- Stored energy: 110 MJ
- Mass: 9265 kg (20425 lb)
- HTS tape in coil: 267 km (166 mi) / Boston to Albany, NY
- 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.
- Compare to ordinary materials/metals – even the best materials (copper, silver, gold) offer some resistance to the flow of current.
- This resistance means that electrical energy is converted to heat – OK in a toaster, not good for a fusion plant, where you want to generate not consume electricity.
- Superconductors need to be cooled to cryogenic temperatures in order to work – how cold depends on the material.
What is HTS?
- High temperature superconductors are a new, commercially available, material with a unique property — it 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) — limits the magnetic field that can be produced.
Why hasn’t it been used to make magnets before?
- Commercially available only 8 years ago due to a tech breakthrough.
- The international fusion program hasn’t really looked to exploit this capability.