Short answer, MIT discovered unobtanium and now fusion looks pretty good.
Longer answer, the crucial part in a fusion reactor is the magnetic confinement and with the field strength conventional superconductors can manage you need a large reactor. In the last 20 years two things happened, first high temperature super conduction was discovered and someone figured out how to build a compound material from them and stainless steel. The high temperature super conductors solve the problem that there is a critical magnetic field strength and the stainless steel solves the problem that the material has ugly mechanical properties. With that you can use much higher field strength in your fusion reactor and that means much smaller reactor and that means much cheaper experiments. (In another talk the speaker claimed the scale of the experiments drops from large experiment for the entire international community to large experiment for MIT.)
Last time I looked at that project, it looked that the MIT fusion group is competitive with ITER, and it should be mentioned that even if the path forward is high temperature super conductors, then ITER was still the right bet 15 years ago. The thing is 15 years ago you could not bet on everything magically working out and the entire ITER concept is guaranteed to work. The international community did decide that fusion is interesting enough even if the safe path forward is really really expensive.
Longer answer, the crucial part in a fusion reactor is the magnetic confinement and with the field strength conventional superconductors can manage you need a large reactor. In the last 20 years two things happened, first high temperature super conduction was discovered and someone figured out how to build a compound material from them and stainless steel. The high temperature super conductors solve the problem that there is a critical magnetic field strength and the stainless steel solves the problem that the material has ugly mechanical properties. With that you can use much higher field strength in your fusion reactor and that means much smaller reactor and that means much cheaper experiments. (In another talk the speaker claimed the scale of the experiments drops from large experiment for the entire international community to large experiment for MIT.)
Last time I looked at that project, it looked that the MIT fusion group is competitive with ITER, and it should be mentioned that even if the path forward is high temperature super conductors, then ITER was still the right bet 15 years ago. The thing is 15 years ago you could not bet on everything magically working out and the entire ITER concept is guaranteed to work. The international community did decide that fusion is interesting enough even if the safe path forward is really really expensive.