[dale_glass]

It should be noted that "breakeven" is often misleading.

There's "breakeven" as in "the reaction produces more energy than put into it", and there's breakeven as in "the entire reactor system produces more energy than put into it", which isn't quite the same thing.

[sam]

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.

[kristianp]

The article uses the term "scientific breakeven" which I assume is the first one you've stated.

[russdill]

It's always confused me a bit. It's not like if you put 10kWh into the reactor, that 10kWh goes away. You still lose a significant fraction of it in inefficiency of the cycle but it still goes towards heat which can be used to heat steam and turn a turbine. iirc, you can get about 4kWh back.

On the other side of the coin, if you put 10kWh in and get 10kWh of fusion out, that's 20kWh to run a steam turbine, which nets you about 8kWh. So really you need to be producing 15kWh of heat from fusion for every 10kWh you put in to break even.

[willis936]

Cars are a good analogy. You wouldn't talk about miles per gallon until you have an engine that idles. Humans are in the engine building phase.

[trollbridge]

That’s a good analogy - and the situation right now is trying to make a car that doesn’t use its entire tank of fuel before it arrives at the service station.

[Tade0]

You can't always get this much energy back. Sometimes your waste heat is an enormous pool of warm water.

[analog31]

In the laser business, the latter is called "wall plug efficiency," which is laser power out per electrical power in.

[westurner]

"Uptime Percentage", "Operational Availability" (OA), "Duty Cycle"

Availability (reliability engineering) https://en.wikipedia.org/wiki/Availability

Terms from other types of work: kilowatt/hour (kWh), Weight per rep, number of reps, Total Time Under Tension

[gosub100]

Especially since steam turbines are in the 30-40% efficiency range

[internet_points]

and then there's "breakeven" as in "it pays for the investment within X years"