Part 2 of 2 Parts – (Please read Part 1 first)
While fuel particles are much cooler when the reach the divertor, they still retain enough energy to knock atoms loose from the material of the divertor when they impact. Previously, JET’s divertor had a wall made of graphite. However, graphite absorbs and traps too many of the fuel particles for practical use.
About 2011, engineers at JET upgraded their divertor and inner containment vessel to tungsten. Tungsten was selected because it has the highest melting point of any metal. The inner vessel wall of the tokamak was changed to beryllium. Beryllium has excellent thermal and mechanical properties for a fusion reactor. It absorbs less fuel than graphite but can still survive high temperatures.
The energy JET produced made headlines. However, equally important is the use of the new wall materials. JET is a successful proof of concept for how to construct the next generation of fusion reactors.
The JET tokamak is the largest and most advanced nuclear fusion reactor currently operating. The next generation of reactors is already under construction. The biggest project is the ITER experiment which is scheduled to begin operations in 2027. ITER is the Latin word for “the way”. It is under construction in France and is funded and directed by an international organization of that includes the U.S. government.
ITER is going to utilize many of the material advances that the JET showed to be viable. While it does share some features of the JET, there are also some differences. First of all, ITER is huge. The fusion chamber is thirty-seven feet tall and sixty three feet in diameter. This is more than eight times larger than the JET. ITER will also utilize superconducting magnets able to produce stronger magnetic fields for longer periods of time compared to the ordinary magnets used in the JET. ITER is expected to surpass the performance of the JET in terms of energy output and how long the reaction will run.
ITER is also expected to do something central to the idea of a commercial nuclear fusion powerplant. This is the production of more power than required to operate the reactor. Computer models predict that ITER will generate about five hundred megawatts of power continuously for four hundred seconds while consuming only fifty megawatts of energy. This means that the reactor will be able to produce ten times as much power as it consumes. This is a huge improvement over the JET which required about three times as much energy than it produced for its breakthrough fifty-nine megajoule record.
The JET’s recent record has shown that years of research in plasma physics and materials sciences have paid off. They have brought scientists to the doorstep of harnessing fusion for power generation. ITER will provide a huge lead forward towards the ultimate goal of industrial scale nuclear fusion power plants.