Unexpected energy barrier for uptake of hydrogen in tungsten wall of fusion reactor

November 27, 2013
The European fusion reactor JET near Oxford was given a tungsten internal wall in 2010. Credit: CCFE / JET

The reactor walls of future fusion reactors will absorb fusion fuel one million times slower than previous research had indicated. A layer of bound hydrogen on the surface of the tungsten wall seems to protect the deeper metal layers. An international team led by FOM PhD researcher Rianne 't Hoen has published this finding in Physical Review Letters. 't Hoen did her research using the plasma generator Pilot-PSI of FOM Institute DIFFER.

In a fusion reactor, heavy isotopes of hydrogen (deuterium and tritium) fuse into helium. As a result of this clean energy in the form of heat is released. The exhaust of a fusion reactor must be able to withstand large quantities of heat and particles. Nevertheless the reactor walls always absorb some of the fusion fuel. As for safety reasons only a limited quantity of fuel may be present in the reactor, physicists are trying to minimise the amount of hydrogen absorbed by the wall material. Therefore the advanced future reactor ITER will be fitted with an exhaust made from the metal tungsten. Tungsten has a high melting point, is a good conductor of heat and absorbs little hydrogen, although this absorption can rise by several orders of magnitude under the influence of neutrons from the fusion reaction.

Unexpected shielding

PhD researcher Rianne 't Hoen and her colleague Dr Pedro Zeijlmans van Emmichoven from DIFFER did their experiments together with colleagues from the University of Amsterdam and the Max Planck Institute for Plasma Physics in Garching, Germany. They discovered that the chances of hydrogen particles being absorbed by tungsten drops by a factor of one million under the extremely high flow of particles expected in ITER. The team simulated the intense conditions in the exhaust of a fusion reactor using DIFFER's device Pilot-PSI. When they compared how much hydrogen hit the walls of the reactor and how much actually penetrated the metal, they discovered an unexpected shielding effect.

DIFFER's devices Pilot-PSI and Magnum-PSI can test materials under the hot, dense plasma conditions of future fusion reactors. Credit: DIFFER

Protective layer

"It would appear that a protective hydrogen layer one atom thick arises on the metal surface," says 't Hoen. "That would give a perfect explanation for the energy barrier we measured." The that arrive at the tungsten surface collide with the atoms in the protective layer, as a result of which they lose a large amount of their energy. Consequently only one in one million hydrogen atoms penetrate into the deeper metal layers.

Although the conditions in the experiments performed are very similar to those in a reactor exhaust, they are not identical. For example, the particles in the large-scale fusion reactor might collide with the tungsten with a greater energy. Future research will examine the effect of the particles' energy and the surface temperature on the uptake in .

Explore further: Wanted: the right wall material for ITER

More information: Strongly reduced penetration of atomic deuterium in radiation damaged tungsten, Physical Review Letters, 111, 225001 (27 November 2013). prl.aps.org/abstract/PRL/v111/i22/e225001

Related Stories

Wanted: the right wall material for ITER

October 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. The results ...

A new clean nuclear fusion reactor has been designed

January 14, 2013

A researcher at the Universidad politécnica de Madrid (UPM, Spain) has patented a nuclear fusion reactor by inertial confinement that, apart from be used to generate electric power in plants, can be applied to propel ships.

Scientific vandalism helps ITER

August 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 acts of scientific ...

Plasma experiment demonstrates admirable self-control

November 13, 2013

A team of Chinese and American scientists has learned how to maintain high fusion performance under steady conditions by exploiting a characteristic of the plasma itself: the plasma self-generates much of the electrical current ...

Hot lithium vapors shield fusion facility walls

November 13, 2013

Recent experiments provide the first assessment of the toughness of a novel lithium coating in the face of intense bombardment by very hot plasma in the divertor region of fusion devices. The results show that this coating ...

Recommended for you

Fusion reactors 'economically viable' say experts

October 2, 2015

Fusion reactors could become an economically viable means of generating electricity within a few decades, and policy makers should start planning to build them as a replacement for conventional nuclear power stations, according ...

Iron-gallium alloy shows promise as a power-generation device

September 29, 2015

An alloy first made nearly two decades ago by the U. S. Navy could provide an efficient new way to produce electricity. The material, dubbed Galfenol, consists of iron doped with the metal gallium. In new experiments, researchers ...

Invisibility cloak might enhance efficiency of solar cells

September 30, 2015

Success of the energy turnaround will depend decisively on the extended use of renewable energy sources. However, their efficiency partly is much smaller than that of conventional energy sources. The efficiency of commercially ...

Extending a battery's lifetime with heat

October 1, 2015

Don't go sticking your electronic devices in a toaster oven just yet, but for a longer-lasting battery, you might someday heat them up when not in use. Over time, the electrodes inside a rechargeable battery cell can grow ...


Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Nov 27, 2013
I enjoyed this article for people interested in fusion. Interesting comment bit on the money distribution for various types of fusion research.

not rated yet Nov 27, 2013
In the opening sentence "of future fusion reactors" makes me chuckle. If tomorrow never comes, will twenty years in the future ever arrive?
1 / 5 (1) Nov 28, 2013
It's surprising that governments are blindly wasting so many billion euros on a unique outdated project instead of investing few millions on promising concepts based on aneutronic fusion.

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.