Comment by apsec112 | Hacker News Reader

Comment by apsec112 | Hacker News Reader

Sorry, but this, by itself, is a totally meaningless article. There might be an actual scientific advance here, but if so, I have absolutely no idea what it is. "100 million degrees" may sound impressive, but it's completely trivial to create a plasma at that temperature; plasma temperatures are typically quoted in electron-volts (eV) or kilo-electron-volts (keV), and a temperature like this probably corresponds to somewhere in the tens of keV. You can make a plasma like this in your garage, and run it as long as you like (there are guides on YouTube). But it won't produce net energy, ie., you won't get more energy out than you put in. To know how impressive this is, we need to know:

- Was net energy produced during this time?

- How much plasma was there, ie, how large of a scale was the experiment at?

- How dense was the plasma?

- How repeatable is the experiment? Could it be run again sustainably, or did it fry all the equipment with fast neutron radiation?

The article doesn't seem to mention any of these, and without them, "100 million degrees" is meaningless.

It's not meaningless if you know the context. Achieving 100M degrees is actually a significant milestone for this type of device. The reactor in the UK has this planned for somewhere in the next year. I don't know SPARC's schedule, maybe it's a bit more secretive but when they achieve 100M it will be in the news as well.

And even if you don't know the context, the article says it's the first in the world to achieve 100M for 20 seconds, good luck doing that in your microwave.

And the specific temperature of 100M degrees might seem arbitrary because it's such a funny sounding amount, but it is actually the precise temperature at which the plasma theoretically starts becoming net positive.

Whether it actually was net positive will obviously be the focus of the researchers for the next weeks, and even if they find the plasma generated energy consistently (which we'd surprised about if it didn't) it still doesn't mean the reactor was net positive as a whole because of inefficiencies.

They will not have fried their expensive reactor intentionally, so if they did that will be sad news. The scale of the experiment is clearly visible from the video. It's a room sized spherical tokamak style device. I'm pretty sure the density of the plasma inside those is a given but I'm not 100% on the physics there.

If I recall correctly, plasma density is a function of temperature and the strength of the containment field. So you’d need to know something about their (presumably YBCO) magnets to work that out.

I just google-translated one of Korean news article. It may help to understand their intention. I guess maintaining plasma for 300 seconds seems one of their milestones to commercial development.

---

KSTAR is setting the world record for ultra-high temperature plasma driving every year since raising the plasma temperature to 100 million degrees for the first time in 2018 and maintaining it for 1.5 seconds. [...] The fusion reactor aims to reach the stage of maintaining 100 million degrees of plasma at KSTAR for more than 300 seconds by 2025. "Most of the physical variables that act as obstacles to commercialization appear within 300 seconds after the plasma temperature rises to 100 million degrees." It means that it is no different from that.” It means that commercial development is possible only after reaching this stage. Director Yoon added, "We plan to maintain it until 30 seconds next year, and then achieve 50 seconds in 2023, 100 seconds in 2024, and 300 seconds in 2025 through facility upgrades."

https://www.hankookilbo.com/News/Read/A2020112318570005798?d...

Wait what? You can create something that runs at 100 million degrees in your garage?

Can you explain a bit more for the unlearned?

I'm not sure about the garage, but you can sure do it in your microwave - NileRed did a video about it: https://www.youtube.com/watch?v=l0u8Vtf2GoQ

Aaand he had to break all of his beakers afterwards: https://www.youtube.com/watch?v=tGqVMbAQhBs

The plasma you can generate in your microwave is nowhere near 100M degrees. The low range of plasma temperature is at around ~6K Celsius.

Such amount of plasma at 100M°K will destroy the whole building. Temperature of nuclear explosion is less than 1M°K.

Build a fusor running roughly at 10kV (Microwave transformers can do that if you modify them a bit, otherwise starter transformers from light fixtures or your car may be able to handle it).

That'll get you in the temperature range. You can also up the voltage to get more exciting effects, fusion is fairly easy to achieve here. Just not net positive fusion.

That's a really silly statement.

I cant create 100 tonnes of nuclear waste in my garage either. However, it's not means for celebration when a giant institution does it.

As OP pointed out, with fusion -- net positive power output is important. Not the temperature achieved.

Sure, here's a guide from Make Magazine:

https://makezine.com/projects/make-36-boards/nuclear-fusor/

The misleading part about almost any mention of "millions of degrees" is that people implicitly expect this happens under earthly conditions, when in fact these values are typically just a reference to the speed of atoms in a rarified environment. Like the sun's corona, it may be very hot, but not very dense. In other words, there is not a lot of energy per volume, just a lot of energy per particle.

For example, a common way to reach "millions of degrees" is to pump the air out of a container to an extreme degree, then introduce trace amounts of a gas, and then accelerate or otherwise heat those few particles.

If this happened under normal pressures, there would be no container material that could withstand these temperatures. But in a near-vacuum, the collisions between the accelerated particles and the walls can be kept low. In an experimental fusion setting like this, they also employ a magnetic field to keep the plasma away from the container.

At the high end what you even mean with temperature gets a bit weird, everything is mostly a very rarefied gas.

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