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.
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.
Thanks a lot for this research. Seing the comments here I think it's really important to make breakthroughs and progress more visible to the public. Otherwise the impression that "we're always 50 years away" stays strong.
In the 2037 timeframe, modeling trends doesn’t matter as much as looking at the actual players. I think odds are good because you have at least 4 very well funded groups shooting to have something before 2035: commercial groups including CFS, Helios, TAE, also the efforts by ITER. Maybe more. Each with generally independent approaches. I think scientific viability will be proven by 2035, but getting economic viability could take much longer.
Companies like Commonwealth Fusion Systems are an example of those utilizing high-temperature superconductors which did not exist commercially when ITER was being designed.
> The design operating current of the feeders is 68Ka. High temperature superconductor (HTS) current leads transmit the high-power currents from the room-temperature power supplies to the low-temperature superconducting coils 4K (-269°C) with minimum heat load.
HTS current feeds are a good idea (we also use them at CFS, my employer: https://www.instagram.com/p/DJXInDUuDAK/). It's HTS in the coils (electromagnets) that enables higher magnetic fields and thus a more compact tokamak.
The thing is, most people don't actually want to solve their phone addiction even if they say they do.
In reality, they want to read news while waiting at a doctor's office, play games while they take the subway, and see Instagram updates from friends throughout the day.
And if you already want a less capable device, it's called an Apple Watch, but it comes with a little screen that is way more useful than laser projection, and will soon surely have a powerful LLM it can access. (And paired with AirPods it does a much better job preserving your audio privacy.)
So it's hard to see how this is going to succeed, when Apple can just copy the good part (LLM) as part of the Watch.
IMO "Solves iPhone addiction" is more or less a rephrasing of "people will quickly get bored of this".
It's just a smartphone, except you can't run third-party software, can't directly interface with it, and can't connect it to other machines. And instead of holding an N-million pixel, M-million-colour, extremely high-constrast display directly in your hand, you have to indirectly project (meaning extremely LOW contrast) a single-colour display onto your hand from a projector that's shaking around being clipped to your clothes.
The only single hypothetical upside I can see to this tech is that it might lower the two-second delay in looking at my phone caused by putting my hand in my pocket before raising my hand, but you could say that that goes against the goal of solving phone addiction.
This is not a thing. "Screens" aren't 'separating us from one another', or 'distracting us'; that's fuzzy verbalistic nonsense, made up by marketers who want to sell you non-phones, and bloviating op-ed columnists who don't have a clue. It's so ridiculous, that everyone has seen the memes debunking it.[0][1]
True invasiveness is expressed as: "how long does it take me to do this thing I want to do?" In other words, you need a human-computer interface that reduces friction as close to zero as possible. The phone won because it's the best at that. The "pin" is orders of magnitude worse, so it won't catch on.
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.
Thanks. We published a number of prepublication versions over the past year on arXiv to gather feedback from the physics community before submitting to Physics of Plasmas last December. The version linked to above (and in the tweet) is the peer reviewed version which was published yesterday.
Author here. The black curve represents the hot-spot ignition condition for a laser inertial confinement fusion (ICF) experiment (like the NIF). This means that during the short period of inertial confinement, the self-heating exceeds all losses in the hot spot leading to an increase in temperature due to self heating. It only applies to the black 'x' points.
The Q_sci^MCF contours correspond to scientific energy gain (ratio of fusion power to heating power crossing the vacuum vessel boundary) for a magnetic confinement experiment.
For ICF we can't draw simillar Q_sci^ICF contours because the total fusion energy released depends on the degree to which the ignited hot-spot propagates a burn in the surrounding cold fuel. And this depends on other variables like the symmetry of the implosion which are not captured in this plot.
If you're curious to read more about this check out Section III.F of the linked paper (pp.10-11).
Surprising to see so much negativity here. Limiting to a small number of headlines is a useful mechanic. I can see this going in a number of interesting directions.
Agree. The places I go on the web have become more and more centralized/limited. I think projects like this that help to surface and aggregate interesting content from the web (which is really what I come to HN to find) are great.
Sure, and once it goes in an interesting direction, I think people would be more positive. This idea, poorly executed, undercuts its own claimed value, wasting time instead of saving time.
Pointing that out is useful feedback, and I'm sure it would have been done in a much harsher way 10 years ago.
