These are valid points. I was just responding to your statement that their time frame is "achievable if they don’t actually try and hit net energy gain." They a

These are valid points. I was just responding to your statement that their time frame is "achievable if they don’t actually try and hit net energy gain." They are trying, and are likely to accomplish net gain about as fast as they say they will. They actually have a fairly practical-looking design though. ARC will use FLiBe for tritium breeding and coolant. That will surround an inner reactor wall that's 3D-printed and replaced annually. MIT already demonstrated joints in the superconducting tape, allowing the reactor to be opened up to replace the core. Economic viability is an open question for all tokamaks. Some of the other designs would have a better chance of achieving low costs if things work out, but there's a much bigger question mark on the plasma physics.