Fusion reactor wall manages unexpected shielding against extreme heat loads

Mar 24, 2014
Hydrogen plasma in DIFFER's linear plasma generator Pilot-PSI. Credit: Fundamental Research on Matter (FOM)

Researchers of the FOM Institute DIFFER[ have discovered that the wall material of a fusion reactor can shield itself from high energy plasma bursts. The wall material tungsten seems to expel a cloud of cooling hydrogen particles that serves as a protective layer. The research team publishes their results on 24 March 2014 in the journal Applied Physics Letters.

Currently, an international collaboration building the ITER, designed to be the first in the world to produce net power from fusion. The heart of a fusion reactor like ITER contains an extremely hot plasma, from which short, intense bursts rain down on the reactor wall. In ITER, the tungsten wall will face powerful discharges of several gigawatts per square meter, several times per second.  However, researchers at FOM Institute DIFFER discovered that under some conditions less than half of that incoming energy actually hits the surface.

Pilot-PSI

The physicists used their linear plasma experiment Pilot-PSI to show that the tungsten surface shields itself from the blast by expelling a cloud of cooling hydrogen particles. This is the first time that fusion researchers see the energy pulses and the wall react to each other at this level of detail.

Physicist Dr. Greg De Temmerman heads the plasma surface interactions-research at DIFFER. Using the laboratory setup Pilot-PSI, his team of physicists from DIFFER and Eindhoven University of Technology were the first in the world to mimic the extreme energy bursts (ELMs - Edge Localized Modes) that the wall materials of future fusion power plants will have to endure. "Of course such ELM eruptions already happen in existing fusion reactors", says De Temmerman, "but their energy is much smaller than that expected in ITER. Our laboratory setups offer conditions very similar to those in ITER, with much better diagnostics access and controllability of the system."

Edge Localized Mode-eruptions in the MAST tokamak, CCFE, UK. Credit: Fundamental Research on Matter (FOM)

Counterintuitive

"During the simulated ELM pulses, we saw a completely counterintuitive behaviour", says de Temmerman: "The more power we sent to the wall material, the less energy actually reached the surface. The temperature of the tungsten samples already peaked part-way through the energy pulse and then started to drop. At the same time, our fast camera saw Hα-light coming from near the surface." Hα-light is a spectral line that indicates that cool hydrogen gas has escaped from the tungsten wall surface. De Temmerman: "We already know that the metal tungsten can absorb limited amounts of hydrogen, like a sponge. It looks like the incoming energy pulse frees a cloud of this absorbed hydrogen from the tungsten. The gas blanket then sucks energy from the incoming power pulse and distributes it evenly, protecting the surface directly below it." Simulations of the hydrogen stored in the tungsten before and after a plasma pulse support this analysis.

Energy pulses in ITER

Fusion researchers try to recreate nuclear fusion, the power source at the heart of the sun,  as a sustainable energy source on Earth in tokamak reactors like ITER. In a fusion reactor, hydrogen nuclei collide at hundreds of millions degrees Celsius, then fuse together to form helium and release prodigious amounts of energy. ITER has been designed to demonstrate the technical feasibility of fusion as an energy source, and will be online in the early 2020s. At peak performance, ITER will produce 500 megawatts of power, while the heating power will only be 50 megawatts. Much research is focused on dealing with the ELM energy bursts, which strike spots on the reactor wall with energies up to gigawatts per square meter - and could lead to uncontrolled melting of the wall. ITER is currently under construction in the south of France and will come online at the start of the next decade.

Artist's concept of tungsten shielding itself via outgassing of hydrogen (bottom) against the impact of a sudden energy burst from the plasma beam in Pilot-PSI (top). Image credits: ICMS. Credit: Fundamental Research on Matter (FOM)

The results in Applied Physics Letters might be good news for ITER: under certain conditions, its planned wall material appears to be able to shield itself from the worst of the ELM strikes. It is still not completely clear whether this effect will also occur in the more complex geometry of the ITER exhaust. Follow-up research needs to further investigate the mechanism behind the self-shielding process, so that researchers can design the optimal wall for future power plants.

Explore further: New technique for sustaining high-performance fusion plasmas

More information: Self-shielding of a plasma-exposed surface during extreme transient heat loads, Applied Physics Letters, 24 March 2014.

add to favorites email to friend print save as pdf

Related Stories

Scientific vandalism helps ITER

Aug 23, 2013

Scientists at JET, the world's largest fusion energy research facility, have been deliberately melting parts of their own machine as they test materials for the fusion reactors of the future. These apparent ...

New jet results tick all the boxes for ITER

Oct 08, 2012

Latest results from the Joint European Torus (JET) fusion device are giving researchers increasing confidence in prospects for the next-generation ITER project, the international experiment that is expected ...

ELISE investigating new type of heating for ITER

Nov 29, 2012

(Phys.org)—Tests for the heating that is to bring the plasma of the ITER international fusion test reactor to a temperature of many million degrees can go ahead from today: After three years of construction, ...

Wanted: the right wall material for ITER

Oct 12, 2007

ASDEX Upgrade at Max Planck Institute of Plasma Physics (IPP) in Garching, Germany, recently became the world's first and only device allowing experiments with a wall completely clad with metal, viz. tungsten. ...

New technique for sustaining high-performance fusion plasmas

Dec 04, 2013

(Phys.org) —A multinational team led by Chinese researchers in collaboration with U.S. and European partners has successfully demonstrated a novel technique for suppressing instabilities that can cut short the life of controlled ...

Recommended for you

Particles, waves and ants

Nov 26, 2014

Animals looking for food or light waves moving through turbid media – astonishing similarities have now been found between completely different phenomena.

User comments : 7

Adjust slider to filter visible comments by rank

Display comments: newest first

Scottingham
5 / 5 (3) Mar 24, 2014
Sweeet. Notice the level of detail in this article. Cold fusion is always 'mumble mumble...energy!'
baudrunner
5 / 5 (1) Mar 24, 2014
In a fusion reactor, hydrogen nuclei collide at hundreds of millions degrees Celsius, then fuse together to form helium and release prodigious amounts of energy.
Okay, so Hydrogen has a boiling point of 20.28°K, and Tungsten has a boiling point of 5828°K. I might be able to wrap my head around the fusion process, with Hydrogen nuclei colliding at 800 million kelvin , but not quite how a bound Hydrogen layer can keep the Tungsten cool enough to not break down in the first second of operation. What kind of magic is at work here?
WillieWard
5 / 5 (2) Mar 24, 2014
When a design is ill-conceived, all that remains is to believe in enchantments in a hope that this behemoth (ITER) works.
GSwift7
3.7 / 5 (3) Mar 25, 2014
What kind of magic is at work here?


The fusion reaction is not supposed to actually touch the wall of the reactor. If I'm reading it correctly, they are experiencing something like static shocks against the wall, and they really don't want them. Again, if I'm reading it right, there's something happening on the tungsten surface when these "sparks" contact it, which makes it release tiny amounts of hydrogen around the point of contact, and this is actually reducing the damage that the sparks would otherwise cause to the wall.

I wonder what happens when the tungsten has used up all of the hydrogen inside it? Or does it replenish it's supply?
TheGhostofOtto1923
3.7 / 5 (3) Mar 25, 2014
Sweeet. Notice the level of detail in this article. Cold fusion is always 'mumble mumble...energy!'
Well it is for people who stop at a pr news article and don't bother to research any further. Guess you're not that interested.
Jizby
Mar 25, 2014
This comment has been removed by a moderator.
TheGhostofOtto1923
3 / 5 (2) Mar 25, 2014
f I'm reading it correctly, they are experiencing something like static shocks against the wall, and they really don't want them
But only a little research saves us from brainless guessing:

"(H-mode). This confinement mode is characterized by the formation of very steep plasma pressure profiles at the edge of the plasma that lead to periodic bursts of energy being expelled by the plasma (typically a small percentage of the total plasma energy) called ELMs (Edge Localized Modes)."

-Which is different from a much more severe problem:

"This device where a large toroidal current is established (15 Mega-amps in ITER) suffers from a fundamental problem of stability. The nonlinear evolution of magnetohydrodynamical instabilities leads to a dramatic quench of the plasma current on a very short time scale, of the order of the millisecond. Very energetic electrons are created... A very high energy is deposited on small areas. This phenomenon is called a major disruption."
GSwift7
4.2 / 5 (5) Mar 25, 2014
This is just the point...We aren't paying the scientists for more research requiring MORE scientists, but for more effective research, which is requiring LESS scientists.


I think I see your point, but I don't agree with you. The theory says that should be possible to build a fusion reactor and that it would be great if we figure it out. So, we supply public funding to experimentalists, who's job it is to try to build it. It's not a trivial task. It's expensive and it might take a long time to figure it out, and there's even the possibility that it won't work, or that someone else will figure out a better process and make it obsolete. That makes it difficult to get private companies to do this sort of thing. This kind of high risk (but potentially high reward) work is exactly the type of thing that government research is meant for. If/when they figure it out, or at least get close, then it can be turned over to private companies for implementation. It's done in agriculture too.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.