is there somewhere a summary of “basic science” problems that need to be solved to make fusion feasible?
And - would throwing more money at the problem?
The maybe-tldr version: we can make fusion occur, but it currently (well, until today) takes more energy to make it happen than we get out. We have good models that predict this relationship, and it mostly boils down to maximizing the "triple product": temperature times plasma density times confinement time. The two most popular broad approaches are "magnetic confinement" (holding a plasma for awhile with magnetic fields) and "inertial confinement" (taking a capsule and rapidly mechanically compressing it, with lasers or a railgun or something, which is what this NIF thing is), and each chooses to maximize the triple product by leaning on different multiplicands -- inertial confinement is much shorter time, but higher density as compared to magnetic. For both, the other factor is plasma instabilities: plasmas don't like to behave, and like to leak out of their enclosures or not maintain the shapes you want them to, and lots of research seems to be about controlling those.
Beyond that, what the challenges are depend on the approach you choose. For inertial, bumping up the triple product seems to be mostly about building bigger and more powerful systems, and managing plasma instabilities. NIF also uses an "indirect" approach where the lasers get (inefficiently) turned into X-rays which then compress the plasma, and "direct" inertial fusion has even bigger plasma instability problems to solve.
For magnetic, the most mature technologies, tokamaks, have well-understood properties in terms of plasma management, and the main still-to-do work had been thought to just be making the machines bigger, which is what ITER is doing, but the recent change is the development of high-temperature superconducting magnets, which might allow for much higher-strength magnetic fields, which would allow for success with smaller machines (that's what, e.g., Commonwealth Fusion, is pursuing). In either case, the goal is just bumping up the triple product until we get to net gain. Other magnetic approaches (stellarators, etc.) are probably at a somewhat-earlier stage of understanding plasma behavior.
For both inertial and magnetic, there will also be development needed after net energy gain to get enough of a gain factor that the economics actually make sense and things can be mass-produced (current thinking is that to actually be economical, we need to get to ~30x energy out compared to what went in), and also likely some materials-science innovations needed to keep the reactor from wearing out due to high neutron flux, and possibly some work producing tritium, the likely fuel, from lithium.
Beyond those MCF and ICF, there are also a bunch of other less-mature technologies that startups are exploring that might also produce good results, and (the founders think) might do so more efficiently than the big approaches, but they're not as far along, and the work still to do is more basic-science-ish. This would be things like Z-pinch, fuel cycles other than deuterium-tritium, etc. etc.
Also, realizing I didn't answer the "money" question. Fusion enthusiasts definitely think so, and personally (just random interested lay-person) it seems like for tokamaks in particular, the physics are now well-enough understand that it's probably just a matter of money/time, but it's hard to say for sure.
apendleton|4 years ago
The maybe-tldr version: we can make fusion occur, but it currently (well, until today) takes more energy to make it happen than we get out. We have good models that predict this relationship, and it mostly boils down to maximizing the "triple product": temperature times plasma density times confinement time. The two most popular broad approaches are "magnetic confinement" (holding a plasma for awhile with magnetic fields) and "inertial confinement" (taking a capsule and rapidly mechanically compressing it, with lasers or a railgun or something, which is what this NIF thing is), and each chooses to maximize the triple product by leaning on different multiplicands -- inertial confinement is much shorter time, but higher density as compared to magnetic. For both, the other factor is plasma instabilities: plasmas don't like to behave, and like to leak out of their enclosures or not maintain the shapes you want them to, and lots of research seems to be about controlling those.
Beyond that, what the challenges are depend on the approach you choose. For inertial, bumping up the triple product seems to be mostly about building bigger and more powerful systems, and managing plasma instabilities. NIF also uses an "indirect" approach where the lasers get (inefficiently) turned into X-rays which then compress the plasma, and "direct" inertial fusion has even bigger plasma instability problems to solve.
For magnetic, the most mature technologies, tokamaks, have well-understood properties in terms of plasma management, and the main still-to-do work had been thought to just be making the machines bigger, which is what ITER is doing, but the recent change is the development of high-temperature superconducting magnets, which might allow for much higher-strength magnetic fields, which would allow for success with smaller machines (that's what, e.g., Commonwealth Fusion, is pursuing). In either case, the goal is just bumping up the triple product until we get to net gain. Other magnetic approaches (stellarators, etc.) are probably at a somewhat-earlier stage of understanding plasma behavior.
For both inertial and magnetic, there will also be development needed after net energy gain to get enough of a gain factor that the economics actually make sense and things can be mass-produced (current thinking is that to actually be economical, we need to get to ~30x energy out compared to what went in), and also likely some materials-science innovations needed to keep the reactor from wearing out due to high neutron flux, and possibly some work producing tritium, the likely fuel, from lithium.
Beyond those MCF and ICF, there are also a bunch of other less-mature technologies that startups are exploring that might also produce good results, and (the founders think) might do so more efficiently than the big approaches, but they're not as far along, and the work still to do is more basic-science-ish. This would be things like Z-pinch, fuel cycles other than deuterium-tritium, etc. etc.
apendleton|4 years ago