Respectfully,
Frank Sanders
Green Energy Labs

Re conventional tokamaks I agree*, but this is the point I am making. The focus on the science, which demands comparison on different scales with as much kept similar as possible, and focus on scale rather than design improvements leads to the first main problems you talk about: large magnetic volumes, superconducting coils, huge cryostats and vacuum vessels.

On the other hand, the Spherical Tokamak power plant concept designs suggest you could get to a GW power plant on a machine that was approximately JET sized… (e.g. aspect ratio 1.6, major radius about 3m). For comparison ITER’s major radius is over 6m, DEMO even larger.

http://www.docstoc.com/docs/28084384/Development-of-the-Spherical-Tokamak-Power-Plant/

If the next big programme is building a bigger stellarator, a bigger tokamak, or a tokamak about the size of JET but differently shaped, guess which one the scientists (predominantly plasma physicists) driving the field are going to pick? Plus, in practice, you couldn’t just build a JET sized ST, you have to build the intermediate sized machines to check that power degredation scales as in conventional machines to get the funding: “show us it works in chunks of a 1bn over ten years”.

Ever since people trumpeted Fusion on Zeta, there has been a lot of conservatism in the field, the whole thing has gone down a rabbit hole of proving we can get MCF ignition without regard to whether we can do so usefully. We will probably get ignition, but in the least useful way imaginable.

R.e. Radioactive components is true of a fission device and less of an issue than people make out. Remote handling works ok, and while the activity is high, it does mean you are talking a 50-100 year problem according to colleagues in neturonics, rather than thousands of years. Of course the issues of neutronics and irradiation needs a lot more thought on blanket design, which not much work has been done on as we are all still chasing ever bigger plasmas…

The obsession with fusion being clean means the programme has skipped past hybrid fission fusion machines (actinide burners or fuel breeders) as an intermediate step. We could have done that with JET technology… whether this is better or worse than accelerators and whether you need it if you have a thorium cycle is also a valid question.

We can play the opportunity cost game on everything of course (depending on the assumptions and preferences), but it’s worth noting that the problem isn’t necesarily fusion or MCF conceptually, it’s where the people went into the programme decided to take it. It is possible if things had gone differently that people would now be questioning the need for thorium reactors or other methods for closing the fuel cycle because we have perfectly adequate fission/fusion hybrids that do this job.

But the fundamental point of your post, that ITER doesn’t scale to a good power station (based solely on requiring scalings of the materials rather than a better design) isn’t a fair representation of the field. I think most people working on ITER accept that once they have demonstrated ignition, you need several different DEMOs exploring different concepts.

* (lets leave stellarators aside for the moment, from my perspective they solve a problem that no longer exists while introducing others, thought Stellerator/Tokamak hybrids like the now cancelled NCSX are interesting)

• a huge vacuum chamber
• a huge volume of magnetic field with an energy density toward the upper end of the range of laboratory NMR systems
• huge superconducting magnets to provide this field
• high thermal fluxes
• radioactive components
• first-wall neutron damage at a level expected to displace every atom in the material repeatedly before replacement

As a way to produce heat to boil water to drive steam turbines, this seems far from practical. I find it hard to imagine closing the gap between this class of system and, for example, the new generation of nuclear reactors, or solar photovoltaics, or solar thermal power systems, all of which are already being deployed. The general problems above apply to a wide range of MCF systems, not just to the tokamak configuration.

By the way, the main problem with pursuing this work, in my view, isn’t the monetary cost: It’s the opportunity cost of consuming the creative potential of excellent physicists and engineers. It is precisely the greatness of the technical achievements in this area that is the problem.

In the fullness of time and with the advent of radically less expensive manufacturing technologies, fusion power sources may well become important. The chief demand, though, may be in regions where the power flux from the big fusion machine at the center of the Solar System is attenuated by distance.

Unlike ITER or the exotic alternatives like Polywell, LFTR reactors seem to be mostly “plumbing”. Rather than being tested in 2030 LFTR seems to have been pretty well tested in the 1960′s and 70′s and to have been rejected for power generation more from military considerations than any economic/engineering analysis.

Is a revival of Thorium reactors a practical take on what fusion promised and failed to achieve?