Using large cryogenic pellets, US ITER advances new fusion technology

US ITER three-barrel prototype unit for massive pellet injection
A three-barrel pellet injector developed at Oak Ridge National Laboratory for the ITER disruption mitigation system. Credit: US ITER/ORNL

The international ITER fusion project is building "a sun on earth" that will produce a self-heated, burning plasma—a key step toward industrial-scale fusion energy production. Controlling that plasma can be tricky, though, because disruptions may occur that cool and collapse the plasma. Sudden losses of plasma energy and current have the potential to erode plasma-facing components inside the ITER vacuum vessel. US ITER researchers based at the Department of Energy's Oak Ridge National Laboratory are leading the development of a disruption mitigation system to reduce the effects of plasma disruptions. The United States Domestic Agency for ITER, one of seven international partners, signed a formal arrangement with the ITER Organization on July 29 for the work.

"We have a very conservative and flexible approach to disruption mitigation on ITER," said Larry Baylor, a distinguished scientist in technologies and applications at ORNL, "with different locations for material to be injected, different types of material, and different response times. We are also designing the system in a way that will allow for evolution of the mitigation technology."

Two approaches have been developed to help reduce the effects of plasma : Massive gas injection and shattered pellet injection. Both deliver material to the plasma within milliseconds. By injecting material to the plasma, ITER operators will be able to manage plasma energy in a way that lessens thermal loads and mechanical stresses on the plasma-facing components of the machine. The injected material can also inhibit the formation of runaway electrons, which occur when electrons are accelerated by the electric field in the plasma during a disruption.

The gas will be neon, argon, deuterium or helium; the pellets will typically be composed of neon with a deuterium outer layer. The pellets are shattered against a plate as they enter the vacuum vessel in order to better disperse the material into the plasma.

First-of-a-kind achievements have already emerged from the US ITER and ORNL team, including the largest cryogenic frozen hydrogen pellet ever formed and fired by a pellet injector "gun" (25 mm in diameter) and a novel three-barrel pellet injector for delivering the pellets to the plasma. The pellet guns use a gas propellant to fire pellets at 300 meters per second, or about 670 miles per hour. The team is now at work making even larger cryogenic pellets—up to 41 mm in diameter—that can still maintain the necessary speed to deliver material to the plasma within milliseconds of a disruption.

A combination neon-deuterium pellet being tested at ORNL
A 16 mm neon–deuterium pellet, indicated by an arrow, captured with a high speed camera as it travels from left to right at about 300 meters per second in a test stand at the Oak Ridge National Laboratory Pellet Lab. Credit: ORNL

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Disruption mitigation researchers investigate design options

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User comments

Sep 30, 2014
There needs to be a modern day 'Manhattan'esque Project' for fundamental energy research, nuclear, fusion, hydrogen, etc.... $30 billion in 57 years is not very much for fusion.

Let the free market and economic conditions be the arbiter of which defeats CO2 energy and scale the technology autonomously. The solution to AGW is a technological one, NOT a political ideological one. No social engineering, no government investment-speculating in companies (the gov has no profit motive and does not care if it loses money rendering it eminently unqualified to do this), no mudding the issue with threats of out of an context socialistic agenda.

Sep 30, 2014
Re: " The team is now at work making even larger cryogenic pellets—up to 41 mm in diameter"

41mm, that is the size of a new regulation ping pong ball, hardly the size of a pellet anymore.

Sep 30, 2014
Nothing like playing with fire.

Sep 30, 2014
Shooting pellets at plasma - not very elegant. Hopefully there are more fundamental fixes for instability. Or perhaps the configuration itself is fundamentally flawed.

Oct 04, 2014
You want a manhattan-esque project but don't want the goverment involved? Just who do you think created and ran the Manhattan project?

Free market forces will devour fushion technology if/when it gets out of the lab.

The market rarely, if ever, invests in fundamental science. And the obstacles to fusion are not all technological. We don't even know if we got a deployable strategy yet. The answer could be something utterly different from anything on the bench right now.

Only the goverment can and will takes multi-billion risks like that.

Oct 04, 2014
Yes, of course, I thought it was clear that by using the Manhattan Project analogy that it is indeed the government that I would expect to fund such fundamental research in a concerted manner. I specified where the government should NOT get involved and the role of the free makret.

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