From a physicists perspective, one can wave their hands and omit the power requirements for external coils because they could be made superconducting. That is 'just a problem for the engineers'. Doing so is not a lie, per say, but it is important to know the context if you are not familiar with their reasoning.Wikipedia wrote:Handwaving is a pejorative label applied to the action of displaying the appearance of doing something, when actually doing little, or nothing.
Another 'trick' you'll run into is extrapolating experimental D-D results to equivalent D-T results. This is because tritium is nasty stuff to deal with in real life and drags in extremely expensive handling systems and extra regulations. The behavior of the two reactions is well known and waving your hands at is is a legitimate approach in initial experimental stages.
No one is saying these issues are minor or will magically go away, just that in principle they shouldn't fundamentally matter and proving so is beyond the limitations of the existing experimental device. When you have exhausted what your experiment can teach you, you design and build a more sophisticated experiment which can address the shortcomings of the previous iterations.
Neither of these points are correct. A quick search turns up "Quasisteady High-Conﬁnement Reversed Shear Plasma with Large Bootstrap Current Fraction under Full Noninductive Current Drive Condition in JT-60U" or "Experimental study of neoclassical plasma flow and bootstrap current in the tokamak textor" among other papers. Also, bootstrap currents are a nice bonus that could boost efficiency under certain conditions, but not a fundamental requirement for a tokamak scheme.Chris Bradley wrote:tokamaks have not yet been driven by a bootstrap current, which they would require
Not true. See HT-7, EAST, KSTAR, Tore Supra, or upgrades to JT-60. In other words, most of the newest generation of large reactors.Chris Bradley wrote:have not yet been driven by a superconducting magnet
Again, those with superconducting coils must do this any time they power down their large magnets. Some may dump it into a resistive dummy load or some may pass it back onto the grid but it has to go somewhere. Super conducting magnetic energy storage is a well developed and implemented idea in its own right.Chris Bradley wrote:why don't the experiments recover that energy now?
Most older reactors use resistive copper coils which you can't recover energy from like you could feasibly do with superconducting coils. In the ideal end game scenario, you would never have to shut your SC magnets off. Simple copper is much cheaper and more practical on smaller scales. From a physics standpoint, an amp through a copper turn gives identical results as an amp through one of expensive superconductor. Scientists tend to look at the more interesting and unknown aspects first. Any experiment has limits on scope, current technology level and a finite budget. It dosen't always make sense to add the extra cost and time to integrate every possible feature.
Today, we are in the transition between emphasis on pure experimental physics of the components and the practical engineering of combining them into a full working system.
A physicist doesn't really care how you make a 5 Tesla field happen, an engineer does.
The newer existing reactors listed above are essentially partnered under the ITER umbrella and have been testing superconducting coils and non-inductive heating schemes for many years. The idea is ITER will take things demonstrated in JET, EAST, JT-60 etc and improve on them. Only the newest devices will have cutting-edge technology. Why dosen't my rotary phone have bluetooth?
That's why its called research. Tokamak Fusion Test Reactor, Experimental Advanced Superconducting Tokamak, International Thermonuclear Experimental Reactor and so on.Chris Bradley wrote:absolutely no guarantee that they are tractable problems
Damn those Wright brothers for not landing on the moon.
If someone proves a fundamental physics limitation either theoretically or experimentally, or new generations of devices stop progressing and improving beyond their predecessors, or some other fusion scheme (MTF,ICF, RFP, DPF to name a few) is proven to work on a faster or cheaper scale, I suppose commercial tokamaks will have 'failed'.Chris Bradley wrote:Under what circumstances would 'tokamak' ever be deemed a failed experiment?
So far, none of these things has happened yet.