It was the culmination of a decade’s work for a dedicated group of international scientists when German Chancellor Angela Merkel stepped up to a cube-shaped crystal button at the Max Planck Institute of Plasma Physics (IPP). The Chancellor, a former physicist with a PhD in hydrocarbon research, gave a short speech and pushed the button, setting in motion the first hydrogen plasma test of the Wendelstein 7-X stellarator nuclear fusion device.
The initial test of the world’s first large-scale stellarator design lasted 0.4 seconds and heated a small amount of hydrogen into plasma reaching 80,000,000°C. Crucially, a long enough time to study.
“This by far exceeds our expectations for the first operation phase of Wendelstein 7-X.”, says scientific director for the project, Professor Thomas Klinger.
The test was deemed a success, and significant steps have been made from the initial trials performed in December with helium gas. “At one million watts microwave heating power we could maintain the plasma for four seconds,” says Klinger. “We started in December with 0.04 seconds which means an improvement by 100 within only two months.”
The future of energy production
News of the test raised hopes of a clean, safe form of nuclear energy in the not-so-distant future, and of using fusion to replace current commercial nuclear fission power stations. Nuclear fission starts with heavy nuclei that are split to release energy. The nuclei used in fission reactors are normally uranium or plutonium isotopes, as their atoms have large nuclei that are easy to split.
Unfortunately, fission reactors also create radioactive waste and can cause devastation in the event of an accident. The most recent incident was the Fukushima plant in Japan which was hit by a tsunami in 2011. The disaster saw a 20km cordon put around the site and the clean-up operation is still in progress, five year on.
Nuclear fusion, on the other hand, works quite differently. The process is the same as the way the sun and stars create energy; the challenge is how to recreate these conditions on earth. Instead of making the nuclei lighter, as with fission, it works by fusing light atoms into heavier ones thereby converting mass into energy. The most common isotopes used in this process are deuterium and tritium, which are fused with eachother to create helium and a neutron. As the two atoms join, they lose a small amount of their mass in the form of energy, at a level greater than that required to create the fusion.
This is the embodiment of Einstein’s famous E=mc² formula; the lost mass, multiplied by the square of the speed of light equals a large amount of energy.
It sounds so simple; however, recreating this atomic process on earth has been the life’s work of many dedicated scientists. The sun is able to create so much energy because its gravitational force is so large. To replicate this on earth, scientists need to create an environment of 150,000,000°C to force the fusion of atoms. Reaching the temperature is not a problem, according to Professor Tony Donné, programme manager at EUROfusion, a body which co-ordinates and funds European fusion research activities, and is made up of research organisations and universities from 26 European states and Switzerland. “We are now trying to study how can we make hydrogen hot enough that we get fusion, how do we keep it stable, how do we extract the electricity from it,” he says.
The main problem to solve with nuclear fusion is how to keep the gas, which turns to plasma when heated to a high temperature, from touching the sides of the reactor. As the atoms fall apart into positive nuclei and negative electrons during the process, the plasma can be controlled by magnetic fields to keep it floating around the inside of the reactor. It is this magnetic process that is different in the two main reactor designs in this field, the tokamak and the stellarator.
To put it simply, the tokamak confines the plasma by running a magnetic current throughit to induce a magnetic field , whereas the stellarator has a complex group of external magnetic coils to control the plasma from the outside of the reactor.
Tokamak or stellarator?
Until recently, the tokomak design, invented in the 1960s, has been prevalent in experiments and studies in the field. However, the magnet design does cause issues preventing the system from running continuously without auxiliary assistance. “In a tokamak, plasma is prone to some instabilities, and we have some ways of dealing with this, but it would be better if we could have the magnetic field entirely external,” explains Donné, whose organisation co-ordinates nuclear fusion projects from JET, the world’s biggest tokamak design fusion reactor based in the UK, to ITER, a collaboration between 35 different countries to build an even larger tokamak machine based in France, to Wendelstein itself.
This is where developments in the stellarator come in. The design was first developed in 1950 by Lyman Spitzer at what would later become the Princeton Plasma Physics Laboratory. It was popular in the next two decades, but as the tokamak design began to show better results, the stellarator faded. Recent developments in technology have led to the return of the design. “It is only now we have very powerful computers that we can design this type of device” says Donné.
It is not as simple as replacing the tokamak design with the stellarator for future investigation, for one thing, the stellarator is generations behind the tokamak in terms of progressing toward energy production.
Comparing Wendelstein to the largest tokamak project in operation today, Donné thinks there is a way to go. “At JET we have all the nuclear licences. Wendelstein doesn’t have a nuclear licence, so they are only allowed to work with hydrogen, helium or deuterium,” he says. The team currently working on Wendelstein do not list proving energy production as one of their aims. This will come later for another group of scientists, or as a follow up to the Wenselstein 7-X study.
This doesn’t mean the stellarator has nothing to contribute. Its predicted ability to perform very long pulses will enable the team to study the plasma’s behaviour in the reactor over a period of thirty minutes, compared with just one minute in the tokamak. This knowledge will be shared with tokamak scientists around the world to freely incorporate into their own work.
Klinger remains positive about Wendelstein’s potential to contend with the tokamak. “Thanks to magnetic field optimisation Wendelstein 7-X has a good chance to catch up with the best performing tokamaks we have,” he says. “We have made the first steps, but already those look very promising.”
When will the lights be turned on by fusion?
The first hydrogen test was an auspicious day for the 500-strong WendelStein 7-X team, but there is still considerable work to do. The plasma vessel has just been reopened to install carbon tiles to protect the walls, with the aim of extending the plasma duration to 30 minutes, a first for a fusion reactor.
The team is working with industry partners rather than manufacturing the parts for the stellarator itself. This will ensure that when the device is ready to be used on a commercial scale, industry organisations will be ready to help.
According to Donné, fusion energy production could be in use as soon as the second half of this century. EUROfusion is currently in the pre-conceptual design phase of DEMO, a demonstration fusion reactor that will produce energy on a large scale and convert it to electricity. Presently, the idea is to use the tokamak design, but this could change, depending on a variety of factors.
ITER, the tokamak reactor being built in France, will come online around 2025 says Donné. It will begin to use the tritium and deuterium to create energy around 2035. The facility will be experimental, and lessons learned from it will be taken onward to build DEMO.
The DEMO team is taking an open view to the technologies it will use, although tokamak is currently the preferred design, with the Wendelstein stellarator serving as a back-up. “If we run into a problem with the Tokamak and we cannot make it work, then the stellarator can be a way out,” explains Donné. “It could also be that at one point we decide that DEMO will not be a device on the tokamak line but the stellarator line.”
Both Klinger and Donné are agreed that progress would be quicker with better funding. “With better funding the worldwide fusion community could make more progress just by working more in parallel than in series, like it is now the case,” says Klinger. “There are too many old fusion devices and too few new machines or machines under construction.”
It’s a long and bumpy road ahead for nuclear fusion scientists working to make fusion energy a reality, but recent developments and funding commitments mean they have a map, at least. X marks the spot – clean energy for all.