For a long time one of the hardest problems in fusion reactor design is what the hell you make it out of. The big win here is that they replaced the walls of the reactor with a new alloy, and it worked according to what theory predicted, which gives them the green light for using that material in ITER.
To simplify a little (ok, a lot) there are two big materials problems inside the reactor. The first is the walls: you need something that's going to survive the temperatures, not disturb the reaction, and not get too radioactive in the process. They previously used carbon, which isn't great: it gets radioactive because it absorbs tritium, which is in the fuel. This experiment used a beryllium alloy, which doesn't absorb nearly as much, and worked, validating the material choice for ITER.
The second problem is to do with the exhaust. You need to get hot plasma out of the chamber without disturbing the ongoing reaction, and with a tokamak that means ridiculously energetic particles hitting a solid divertor. Again, the problem here is what materials you might come up with that stand a chance of surviving useful operational periods. ITER is currently planned to use beryllium walls and a tungsten divertor, but I don't know what JET's divertor is made of at the moment to know whether this experiment will have informed whether tungsten is a good enough choice.
What all this means is that there's one less thing on the "ITER might fail because of..." list.
For a long time one of the hardest problems in fusion reactor design is what the hell you make it out of. The big win here is that they replaced the walls of the reactor with a new alloy, and it worked according to what theory predicted, which gives them the green light for using that material in ITER.
To simplify a little (ok, a lot) there are two big materials problems inside the reactor. The first is the walls: you need something that's going to survive the temperatures, not disturb the reaction, and not get too radioactive in the process. They previously used carbon, which isn't great: it gets radioactive because it absorbs tritium, which is in the fuel. This experiment used a beryllium alloy, which doesn't absorb nearly as much, and worked, validating the material choice for ITER.
The second problem is to do with the exhaust. You need to get hot plasma out of the chamber without disturbing the ongoing reaction, and with a tokamak that means ridiculously energetic particles hitting a solid divertor. Again, the problem here is what materials you might come up with that stand a chance of surviving useful operational periods. ITER is currently planned to use beryllium walls and a tungsten divertor, but I don't know what JET's divertor is made of at the moment to know whether this experiment will have informed whether tungsten is a good enough choice.
What all this means is that there's one less thing on the "ITER might fail because of..." list.