General Fusion : the Technical challenge of Precisely Timed Spheromaks Compressions

Power pistons: General Fusion’s reactor is a metal sphere with 220 pneumatic pistons designed to ram its surface simultaneously. The ramming creates an acoustic wave that travels through a lead-lithium liquid and eventually accelerates toward the center into a shock wave. The shock wave compresses a plasma target, called a spheromak, to trigger a fusion burst. The thermal energy is extracted with a heat exchanger and used to create steam for electricity generation. To produce power, the process would be repeated every second. Credit: General Fusion

MIT Technology Review (Tyler Hamilton) covers General Fusion. General fusion has raised between $9-13.5 million and gotten C$13.5 million in government funding for the latest round.

The prototype reactor will be composed of a metal sphere about three meters in diameter containing a liquid mixture of lithium and lead. The liquid is spun to create a vortex inside the sphere that forms a vertical cavity in the middle. At this point, two donut-shaped plasma rings held together by self-generated magnetic fields, called spheromaks, are injected into the cavity from the top and bottom of the sphere and come together to create a target in the center. “Think about it as blowing smoke rings at each other,” says Doug Richardson, chief executive of General Fusion.

On the outside of the metal sphere are 220 pneumatically controlled pistons, each programmed to simultaneously ram the surface of the sphere at 100 meters a second. The force of the pistons sends an acoustic wave through the lead-lithium mixture, and that accelerates into a shock wave as it reaches the plasma, which is made of the hydrogen isotopes deuterium and tritium.

If everything works as planned, the plasma will compress instantly and the isotopes will fuse into helium, releasing a burst of energy-packed neutrons that are captured by the lead-lithium liquid. The rapid heat buildup in the liquid will be extracted through a heat exchanger, with half used to create steam that spins a turbine for power generation, and the rest used to recharge the pistons for the next “shot.”

The ultimate goal is to inject a new plasma target and fire the pistons every second, creating pulses of fusion reactions as part of a self-sustaining process. “One of the big risks to the project is nobody has compressed spheromaks to fusion-relevant conditions before,” says Richardson. “There’s no reason why it won’t work, but nobody has ever proven it.”

General Fusion says it can achieve “net gain”–that is, create a fusion reaction that gives off more energy than is needed to trigger it–using relatively low-tech, mechanical brute force and advanced digital control technologies that scientists could only dream of 30 years ago.

It may seem implausible, but some top U.S. fusion experts say General Fusion’s approach, which is a variation on what the industry calls magnetized target fusion, is scientifically sound and could actually work. It’s a long shot, they say, but well worth a try.

“I’m rooting for them,” says Ken Fowler, professor emeritus of nuclear engineering and plasma physics at the University of California, Berkeley, and a leading authority on fusion-reactor designs. He’s analyzed the approach and found no technical showstoppers. “Maybe these guys can do it. It’s really luck of the draw.”

The company can now start the first phase of building the test reactor, including the development of 3-D simulations and the technical verification of components. General Fusion aims to complete the reactor and demonstrate net gain within five years, assuming it can raise another $37 million.

If successful, it believes it can build a grid-capable fusion reactor rated at 100 megawatts four years later for about $500 million, beating ITER by about 20 years and at a fraction of the cost.

General Fusion’s basic approach isn’t entirely new. It builds on work done during the 1980s by the U.S. Naval Research Laboratory, based on a concept called Linus. The problem was that scientists couldn’t figure out a fast-enough way to compress the plasma before it lost its donut-shaped magnetic confinement, a window of opportunity measured in milliseconds. Just like smoke rings, the plasma rings maintain their shape only momentarily before dispersing.

Nuclear-research giant General Atomics later came up with the idea of rapidly compressing the plasma using a mechanical ramming process that creates acoustic waves. But the company never followed through–likely because the technology to precisely control the speed and simultaneous triggering of the compressed-air pistons simply didn’t exist two decades ago.

Richardson says that high-speed digital processing is readily available today, and General Fusion’s mission over the next two to four years is to prove it can do the job. Before building a fully functional reactor with 220 pistons on a metal sphere, the company will first verify that smaller rings of 24 pistons can be synchronized to strike an outer metal shell.

Summarizing the Nuclear Fusion Projects that could Commericialize before 2020

Nuclear fusion projects that have been funded and have some chance of successful commercial fusion before 2020 are:

1. IEC (Inertial electrostatic confinement) fusion work by EMC2 Fusion. This is building upon the work of the late Robert Bussard. In a personal interview the project lead Dr Richard Nebel stated:

The project that we hope to have out within the next six years will probably be a demo, which won’t have the attendant secondary equipment necessary for electricity generation. Hopefully the demo will demonstrate everything that is needed to put a full-scale working plant into commercial production. So if the concept works we could have a commercial plant operating as early as 2020.

In a separate comment in May, 2009 Dr Nebel stated that commercial viability of this technology should be known in 18-24 months from this Navy and US government funded project.

2. Tri-Alpha Energy which has received over $50 million in funding and is developing colliding beam fusion. This is building upon the work of fusion researcher Norman Rostoker and is using a field reversed configuration. The project is highly secretive but has mentioned 2015-2018 target dates.

3. General Fusion is working on magnetized target fusion. They have private funding and funds from the Canadian government. General Fusion is likely to get the full $50 million for a net energy gain device with a target date of 2013. If the current validation and early stage efforts are successful then the first commercial scale unit could be in 2016-2018.

4. Lawrenceville Plasma Physics is working on controversial dense plasma focus fusion. This has also received sufficient funding for a currently ongoing technology validation effort.

Helion Energy is also working on a version of colliding beam fusion, but they do not appear to be funded yet.

There is the Laser fusion-fission hybrid but it is unlikely to commercialize before 2030.

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