Commonwealth Fusion Systems’ second breakthrough superconducting technology handles mammoth pulses of power
PIT VIPER cable technology enables powerful magnets needed to make fusion machines commercially viable at scale.
DEVENS, Mass., Oct. 30, 2024 — Commonwealth Fusion Systems, the world’s largest fusion company, has for the first time detailed its PIT VIPER superconducting cable technology. It’s the second foundational electromagnet technology the company developed for its effort to build compact, powerful, and economical fusion energy power plants.
The journal Superconductor Science and Technology in October published CFS’ peer-reviewed PIT VIPER superconducting cable paper. The research shows that the company’s high-temperature superconductor (HTS) cables work under arduous conditions and, importantly, can be manufactured at scale.
CFS proved the merits of its first superconducting magnet technology — a novel, no-insulation approach called NINT — in a 2021 test called TFMC that the company detailed in earlier research papers. NINT is appropriate for steady-state magnets driven by an unvarying electrical current, a design needed for some CFS magnets.
But CFS fusion machines, called tokamaks, also need traditional insulated magnet designs that enable pulses of electrical currents to ramp up and down. NINT can’t handle fast pulses, so the company developed a second novel HTS-based cable technology called PIT VIPER.
The paper describes how PIT VIPER cables:
- can carry strong pulsed electrical currents without heating problems;
- can withstand the powerful physical and electromagnetic forces inside a tokamak; and
- use fiber optics to rapidly detect hot spots that can cause magnet-damaging “quench” events.
CFS developed PIT VIPER on the aggressive schedule needed to meet the company’s plans for commercial fusion energy. The company expects its first power plant, called ARC, to deliver power into the electrical grid in the early 2030s.
“We did this at an incredibly fast pace. The idea was conceived four years ago. Now we have a functioning magnet, manufactured at full scale,” said Charlie Sanabria, Principal Magnet Test Engineer at CFS and the paper’s lead author. “Similar earlier technological arcs in the magnet world have taken decades.”
PIT VIPER beats competing technologies in three key ways.
First, the magnet can handle strong electromagnetic forces that in effect try to unravel the loops of cable that make up the magnet. PIT VIPER can withstand 1000 kilonewtons of force per meter of looped cable. That’s like each turn of the magnet standing up to the thrust of a SpaceX Raptor rocket engine trying to pull it apart. Second, a single PIT VIPER cable can carry an extraordinary 50 kiloamps of electrical current — about what 250 American homes would use at their maximum power consumption. Third, PIT VIPER can operate under a pressure of 300 megapascals. That’s nearly triple the pressure of ocean water 36,000 feet down at the bottom of the Mariana Trench, the deepest spot in the planet’s oceans.
“PIT VIPER exceeded all of our expectations,” Sanabria said.
PIT VIPER in production today
With many questions about the technology answered, CFS has fabricated more than 4 kilometers of PIT VIPER cable. Some of that is part of a CFS magnet test program called the Central Solenoid Model Coil (CSMC). PIT VIPER is also in other magnets CFS is building for its first tokamak, called SPARC, which is under construction now at company headquarters in Devens, Massachusetts.
SPARC and its successor, the power plant called ARC, use PIT VIPER cables for two types of pulsed-power magnets, the circular poloidal field (PF) magnets ringing the outside of the tokamak and the column-like central solenoid (CS) magnet that stands vertically in the middle.
The other CFS magnet approach, NINT (non-insulating, non-twisted), houses HTS tape in steel plates instead of in cables. Those plates are stacked to form the steady-state D-shaped toroidal field (TF) magnets that CFS is now building at full throttle in its magnet factory.
Peer-reviewed research
The PIT VIPER paper exemplifies the CFS commitment to sharing research with independent experts who can spot problems and confirm successes. CFS encourages companies similarly involved in fusion energy to build trust in this emerging industry by publishing their progress past six milestones on the path to commercial fusion energy.
“Peer-reviewed research is the gold standard for ensuring that we’re not fooling ourselves or anyone else,” said Chief Science Officer and Co-Founder Brandon Sorbom. “The PIT VIPER paper is the newest example showing that CFS research, development, and manufacturing teams can innovate fast enough to tackle climate change and the world’s growing demand for energy.”
Awards from two US Department of Energy efforts, Advanced Research Projects Agency–Energy (ARPA–E) and Fusion Energy Sciences (FES), helped to fund PIT VIPER development.
Making superconductors work
Superconductors are materials that carry electrical current with no resistance once cooled to a low enough temperature, a property that makes them perfect for building powerful electromagnets.
A newer class of high-temperature superconductors — called REBCO, after their rare-earth element, barium, and copper oxide ingredients — don’t need to be cooled as much. They also carry more current, and, crucially for fusion, withstand much higher magnetic fields.
But REBCO superconductors have formidable engineering challenges. It took researchers more than two decades to find a way to package REBCO’s crystalline structure into thin tapes that are flexible and practical enough for machinery. After that, CFS had to figure out how to make REBCO work in its pulsed and steady-state magnets.
Superconducting cables that beat the heat
PIT VIPER advances the VIPER superconducting cable design that CFS and MIT developed in earlier tokamak research. VIPER houses multiple stacks of HTS tape in channels within a copper cable. PIT VIPER improves that approach with internal electrical insulation that partitions each stack of HTS tape.
The upgrade lets PIT VIPER better handle rapidly increasing currents whose side effects otherwise would heat up the cable more and limit performance.
Each HTS stack also gets its own fiber optic cable. Light signals traversing the fiber can rapidly raise the alert that a hot spot is forming. If left unaddressed, the heat would otherwise spread, halt superconduction, and cause a quench that could damage the magnet.
That quench detection system can find hot spots so the tokamak can react in less than a second to head off problems.
The name PIT VIPER refers to the cable’s construction. The earlier VIPER name is short for vacuum pressure impregnated, insulated, partially transposed, extruded, and roll-formed. The PIT addition stands for partitionally insulated and transposed.
About Commonwealth Fusion Systems
Commonwealth Fusion Systems is the world’s leading and largest private fusion company. The company’s marquee fusion project, SPARC, will generate net energy, paving the way for limitless carbon-free energy. The company has raised more than $2 billion in capital since it was founded in 2018.
Contact: press@cfs.energy