sam

Well said about the “lossy crankshaft”. As for what determines Q, that’s up next, stay tuned :)

Power to magnets (at least those not contributing to heating) are assumed to be included in the house load.

Thanks - what browser?

This is mistaken. In space a radiator can radiate to cold (2.7K) deep space. A thermos on earth cannot. The temperature difference between the inner and outer walls of the thermos is much lower and it’s the temperature difference which determines the rate of cooling.

In the context implied above it is the ratio of fusion energy released to laser energy on target or the laser energy crossing the vacuum vessel boundary (they are the same in this case). So it would have been more precise to say "target gain" or "scientific gain".

We are careful to always specify what kind of “breakeven” or “gain” is being referred to on all graphs and statements about the performance of specific experiments in this paper.

Energy gain (in the general sense) is the ratio of fusion energy released to the incoming heating energy crossing some closed boundary.

The right question to ask is then: “what is the closed boundary across which the heating energy is being measured?” For scientific gain, this boundary is the vacuum vessel wall. For facility gain, it is the facility boundary.

It’s the ratio of fusion energy released to heating energy crossing the vacuum vessel boundary.

Companies like Commonwealth Fusion Systems are an example of those utilizing high-temperature superconductors which did not exist commercially when ITER was being designed.

Author here - some other posters have touched on the reasons. Much of the focus on high performing tokamaks shifted to ITER in recent decades, though this is now changing as fusion companies are utilizing new enabling technologies like high-temperature superconductors.

Additionally the final plot of scientific gain (Qsci) vs time effectively requires the use of deuterium-tritium fuel to generate the amounts of fusion energy needed for an appreciable level of Qsci. The number of tokamak experiments utilizing deuterium tritium is small.

This comment thread will go down in history along with the famous HN Dropbox thread.

This thing is incredible and will eventually crush the iPhone. Solves iPhone addiction while retaining the utility of an iPhone? Solid gold.

We only included projected values of SPARC and ITER because they're the only ones whose physics basis has been published in the peer-reviewed literature. We would certainly like to include other devices - hopefully this will encourage more teams to publish results in the literature from which we can extract the required parameters.