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?

Yeah, it’s slightly buried - the publication with all the details, including the math is linked to in footnote 3 of the explainer article,

https://pubs.aip.org/aip/pop/article/29/6/062103/2847827/Pro...

It’s open access and you can download the PDF directly from there.

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.

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.

If you're interested in wheels, check out The Bicycle Wheel by Jobst Brandt. If you're building wheels it's a must have.

I’m guessing you’re referring to HL-2M which indeed in testing. But that tokamak is not designed to generate electricity but rather to study long pulse durations (~5s) at reactor relevant temperatures.

Author of that article and plot here. SPARC is projected to have energy gain Q >=2 and potentially up to 11[1]. ITER is projected to achieve Q of >=10[2] so I would guess that SPARC's expected triple product would be in the same ballpark as the projected ITER datapoint, perhaps slightly lower, though potentially the same. We'll see!

[1] http://doi.org/10.1017/S0022377820001075

[2] https://www.iter.org/newsline/-/2845

Most of the ports are used for diagnostic equipment, things like laser interferometers to measure plasma density or other devices to measure plasma temperatures. Also some ports are used to inject neutral beams for heating.

I’m working on this exact issue. You can view all fusion energy companies here and filter by location. https://www.fusionenergybase.com/organizations/ You can view each of their funding histories on the company detail page, just click on the company name.

Yes, check out https://www.fusionenergybase.com/ which I've put together. List of organizations are here, https://www.fusionenergybase.com/organizations and individual projects are here, https://www.fusionenergybase.com/projects

ITER and Commonwealth can (and in my opinion should) be seen as complimentary endeavors.

ITER has been designed with relatively conservative magnet technology and will very likely provide the physics results that need to be understood in order for fusion power to become a reality. This includes experimental tests of the physics of plasmas where the heating is dominated by high energy alpha particles rather than external heating. This is a regime that's not yet been studied in a laboratory and there is important research to be done there.

Commonwealth is pushing the envelope of high temperature superconductor magnet technology and is relatively high risk compared to ITER's magnets (and this is a good thing). Lots of ITER technology will be useful to Commonwealth even before ITER turns on. For example decisions about which low activation steels and the huge amount of physics work that's already gone into planning for ITER.

I think the most likely outcome is that both accomplish their goals and contribute to making commercially viable fusion energy a reality in the future.

That’s right, there are other fusion fuels that have only charged fusion products which could be directly converted to electricity. This is in contrast to deuterium - tritium which releases 80% of its energy in a neutron which has zero charge.

Examples of fusion fuels whose main reaction produces only charged products are deuterium helium-3 and proton boron-11. These reactions however require higher temperatures and better confinement characteristics.

The reason why deuterium tritium is the major focus of most (though certainly not all) research is that it has the highest reactivity at the lowest temperature compared to other fuels. Unfortunately it produces a high energy neutron which makes the conversion to electricity more complex.

The typical design for a fusion power plant that runs on deuterium tritium fuel is to place a lithium "blanket" around the plasma. 80% of the energy released in the deutrium - tritium fusion reaction comes out in the energy of a neutron which would be absorbed in the blanket, heating it up and also generating tritium fuel which could then be fed back in as half of the fuel (the other half being deuterium which is abundant in seawater).

You would then run a heat exchanger from the hot lithium to create steam to then turn a turbine and make electricity.

There are a few reasons why the investment is flowing.

1) New enabling technologies, including high temperature superconducting tape, algorithms for plasma control and diagnostics which take advantage of new hardware (GPUs), and advanced manufacturing techniques are now available.

2) Optimism that private companies can synthesize the past 70 years of plasma physics research with these enabling technologies to develop transformative approaches to fusion.

If you're interested I wrote a short article about this topic a few months ago,

https://www.fusionenergybase.com/article/the-number-of-fusio...

Mach's principle. Why is there a "preferred" rotational frame of reference in the universe? Or as stated in this Wikipedia article,

"You are standing in a field looking at the stars. Your arms are resting freely at your side, and you see that the distant stars are not moving. Now start spinning. The stars are whirling around you and your arms are pulled away from your body. Why should your arms be pulled away when the stars are whirling? Why should they be dangling freely when the stars don't move?"

https://en.wikipedia.org/wiki/Mach%27s_principle

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The problem with firing a stream of hydrogen ions at a chunk of Boron 11 is that most of the collisions between the hydrogen and the Boron are glancing blows that will dissipate the energy very quickly. Only a small fraction of the collisions result in a fusion reaction.

This is the reason why most fusion approaches rely on thermal systems. In a thermal system, the ions have a bell-shaped distribution of energies and undergo many collisions before they leave the region in which they are confined and their energy leaves the system.

To achieve net gain, the temperature, density and energy confinement time must be above a certain threshold. If the system is non thermal, like a stream of hydrogen ions where the distribution of energies is a spike, the energy in the hydrogen ions that are deflected by glancing blows must be recaptured somehow.

If new fusion startups like this one are interesting to folks on this thread, here's a list of companies working on fusion energy that I've compiled:

https://www.fusionenergybase.com/organizations/

Tracking the use of different technologies used by companies is a good idea and it’s on the todo list.

As for the materials, yeah I’d like to go deeper there, maybe another article down the road.