by Ryan Ridden-Harper
Fusion, the ability to create near limitless power is always a decade away. Or so the joke goes. This summer I got the opportunity to join the quest for fusion, with a Summer Research Scholarship at the Australian National University. For my project I was supervised by Associate Professor Matthew Hole as I worked on simulating plasma models.
This gave me a great opportunity to learn more about the complexities of plasma physics and where humanity is in their long decade to fusion.
The short answer is that fusion is hard. Recreating the core of a star with plasma heated to around 15 million degrees Celsius and crushing pressure, 250 times that of Earth’s atmosphere is a challenge. Stars use their immense mass to do this but that’s not possible for us to do on Earth. Instead physicists turned to using magnetic fields to create a magnetic bottle that holds the electrically charged plasma. With carefully constructed magnetic fields, the plasma can be packed together into high pressure. However, this technique is unable to reach the core pressure of a star, so to compensate the plasma is heated to around 150 million degrees Celsius—10 times hotter than the Sun’s core.
The first magnetic bottle was designed in the early 1950s, proposed independently by Soviet physicist Gersh Budker and the American physicist Richard F. Post. Their design was a cylindrical magnetic bottle, which held the plasma in the centre by varying the magnetic field at the ends, to create what are known as magnetic mirrors. In the 1960s experiments to achieve fusion began with this design and although it worked well to hold the plasma, it never succeeded in producing energy from fusion. By the 1980s the last fusion experiment with this design called the Tandem Mirror Experiment was shut down.
An interesting side note: Lockheed Martin’s (LM) recent announcement that they will have developed fusion reactors in the next ten years appears to use this abandoned design. With the lack of detail and no solid design specifications most plasma physicists are highly sceptical of LM’s announcement. That said, they would all be overjoyed if LM does succeed.
For an in depth review on LM’s claim check out Matthew Hole’s article.
Following shortly on from the work of Gersh Budker, another design of a magnetic bottle was developed in the 1950s by Soviet physicists, Igor Tamm and Andrei Sakharov. Known as a tokamak their design connects the ends of the cylinder together making a torus. Using both magnetic and electric fields, the plasma can then be guided to continuously flow around the torus avoiding issues arising from the cylindrical design. After decades of both theoretical and experimental research this design came closer to producing energy with fusion, at a rate similar to Moore’s Law for electronics.
In 1991 that growth reached a milestone at the Joint European Torus (JET). For the first time physicists achieved a steady energy release through fusion, getting more energy out than was put in. Then in 1997 JET set a new record producing 40% more energy than was used to heat the plasma for 6 seconds, a remarkable step for humanity, but not nearly enough for a power plant. From the experimental data gathered the problem was obvious—JET was simply too small. To produce enough power the tokamak must be massive.
The solution to this problem is called ITER. This enormous tokamak will have a major radius of 6 meters, making it two times larger than JET. With this enormous size comes an enormous price tag, of around 13 billion Euros, so it wasn’t until 2006 that an international funding agreement was reached between 35 countries. Following this, the construction of ITER has begun during 2008 in the south of France and politics willing, it will be completed early 2020s, with plans to attempt fusion in 2027.
That is still over 10 years away, but physicists are confident that ITER will produce 100MW for every 10MW used to heat the plasma. That’s an enormous improvement on JET’s record, but it is still not enough for a fusion power plant.
With our current understanding a fusion power plant will need to be bigger than ITER still.
This presents some serious challenges, one of which is designing materials for the walls of monster tokamaks that could survive the extreme conditions. Another is pretty fundamental; what is the best way to get energy out of the plasma? With these issues in consideration leading physicists predict that fusion power plants might begin appearing around 2050. 45 years from now.
So it looks like fusion is still some decades away from us still. Fusion power is an immensely difficult problem, it has taken the efforts of thousands of men and women to get us this far and there is still a long way to go. Arthur Eddington speculated fusion power was only a decade away in 1920 and many that came after him thought from their time too, that fusion was only a decade away. Perhaps now for the first time we can catch a glimpse of the goal and it lies 45 years from now. So maybe the 2050s will draw to a close the 130 year decade.
Ryan Ridden-Harper is a University of Canterbury physics student and member of the Canterbury Astronomical Society