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Comment by spuz | Hacker News Reader

> The experiments produced 59 megajoules of energy over five seconds (11 megawatts of power).

> This is more than double what was achieved in similar tests back in 1997.

> It's not a massive energy output - only enough to boil about 60 kettles' worth of water. But the significance is that it validates design choices that have been made for an even bigger fusion reactor now being constructed in France.

I thought this was interesting as 59 megajoules of energy or 11 megawatts of power seems more than you would need to boil 60 kettles' of water. In fact, it takes 4,184 joules to raise the temperature of 1kg of water by 1 degree. Or 313800 joules to raise 1kg of water by 75 degrees. That means JET could have boiled about 188 kg of water.

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That calculation is correct if you assume that by "boil water" they mean to bring the water to 100°C (which is what you'd use a kettle for usually).

However to go from liquid water to water vapor you need to add even more energy [0]. The enthalpy of vaporization for water is 2257 kJ/kg, it takes much more energy to boil water at 100°C than it takes to get there from room temperature.

Warming by 75 degrees + boiling = 2570 kJ/kg -> enough to boil 23 liters of water

I'm guessing in reality the energy needed to operate the kettles would lie somewhere in between, as a small part of the water will be boiled and most of it kept around 100°C. For 2L kettles the value seems in the right ballpark.

[0] https://en.wikipedia.org/wiki/Enthalpy_of_vaporization

>In fact, it takes 4,184 joules to raise the temperature of 1kg of water by 1 degree. Or 313800 joules to raise 1kg of water by 75 degrees. That means JET could have boiled about 188 kg of water.

This is missing the heat of vaporization[1] needed to actually boil the water though, i.e. to turn 100C liquid water to 100C steam. That's another 2250kJ/kg on top of the 313.8kJ/kg you've mentioned.

It's why steam is such a great carrier of energy for industrial applications.

I guess you could argue that you wouldn't evaporate all water in the kettle, but then you do want a rolling boil. It's probably a bit up for discussion at which point you'd stop heating the kettle.

[1] https://en.wikipedia.org/wiki/Enthalpy_of_vaporization

> I guess you could argue that you wouldn't evaporate all water in the kettle...

One does not have to argue for that interpretation - raising the temperature to boiling point, not boiling it dry, is indisputably the accepted and intended meaning of the phrase wherever English is spoken... though it would fit with a certain stereotype of scientists if a bunch of plasma physicists did not know how to make a pot of tea!

Start by assuming a spherical teapot in a vacuum...

indisputably the accepted and intended meaning of the phrase wherever English is spoken

Not exactly. In American English "bring a pot to a boil" is much more common. When I read "enough energy to boil 60 kettles of water" I thought "vaporize".

Point taken - I can't dispute the fact that you read it this way!

> Not exactly. In American English "bring a pot to a boil" is much more common. When I read "enough energy to boil 60 kettles of water" I thought "vaporize".

Disagree that this is a) a much more common phrasing or b) that your interpretation would be the common one. I've yet to run into a situation where somebody asked me to "boil some water" and intended for me to vaporize all the water in some vessel.

It's entirely disputable as evidenced by this conversation.

It's also an incredible waste of time to argue over definitions. They're always disputable because they always arise in response to two people using a word differently. Maybe they're wrong and you're right, or maybe others also use the word that way—it doesn't matter. Humility and aiming at mutual understanding is far more worthwhile.

This issue is indeed trivial, but I don't know how, in general, we are going to achieve mutual understanding without establishing an agreed-upon semantics.

It's not possible to fix a particular semantics outside a particular time and context, and certainly not possible to do so in general.

Here, as soon as someone recognizes that the amount of energy cited is way higher or lower than would be implied by their own definition, they should 1) identify the difference ("Boil here means 'boil n kettles dry' rather than 'bring n kettles to boil'") and 2) in most cases, avoid the wasted debate by adopting the other person's language if further conversation using the concept is needed.

Indeed - so it is clear what one should do here, which is to begin by assuming the author is adopting a well-established meaning within the relevant context. For this, we have a couple of clues: one is British English usage, given that this is a press release from a British laboratory, and the other is that there is a meaning in which the calculation works out correctly.

In the light of this, what is your objection to my comment? As far as I can tell, it is in conformance with your numbered principles.

Saying "X is indisputably the accepted and intended meaning of the phrase wherever English is spoken" is not in conformance with those principles at all.

There appears to be a certain irony in how, in your rather sanctimonious posts here, you seem to have generally failed to act in accordance with the very principles that you accuse me of violating.

Of course this is great news, however, it is worth taking into account it took them 25 years just to double the energy output. They are also nowhere near long sustained operation of such reactors. It really requires an order of magnitude increase before nuclear fusion becomes a realistic prospect in two decades.

I understand this just to validate design choices and it is a good step forward. However, it doesn't make nuclear fusion a reality in two decades unless further records are set using this design

From the article I gathered that this run was mostly about validating some design choices for ITER, not about pushing output limits.

Yes in that sense it is a great achievement, however, it only put us a tiny baby step closer to fusion power.

JET ran its moonshot campaign 25 years ago. Moonshot as in "we don't care if the machine runs again", for whatever reason. It hasn't been funded for nuclear operations since then. It's not that it took 25 years to make progress. It took 25 years to find funding.

> That means JET could have boiled about 188 kg of water.

> only enough to boil about 60 kettles' worth of water

Exactly, no one has 3l kettles, but it's the right ballpark. You could also run about 9k kettles for that 5 seconds but not boil them, and if you tried to run 60 kettles consuming all that power for 5 seconds you would have quite the fire...

> no one has 3l kettles

I have! Duckduckgo it.

Yep, just checked mine and its 3l, oops.

But the significance is that it validates design choices that have been made for an even bigger fusion reactor now being constructed in France.

They already started construction on a larger one? What if it had invalidated design choices?

> What if it had invalidated design choices?

The government money was already allocated and even the government can't unring that bell!

Presumably they feel like the major design choices at ITER have already been validated and this experiment validates some more minor design choices.

Is it possible they subtracted the energy required to facilitate the reaction in the first place? So net energy was enough to boil 60 kettles worth of water?

That would be a fusion breakthrough worth mentioning on its own.

"At Jet, two 500 megawatt flywheels are used to run the experiments."

So net power is -989MW, assuming both flywheels are at full pelt the whole time and no power is required before fusion is acheived.

Those are used for the confinement coils. Incredibly, JET uses copper coils. You can't run those all day, so the flywheels are used. The last machine I worked at worked the same way. 16 train motors with 1 ton flywheels spinning at 1600 RPM to be an 11 MW power supply for 1 second every few minutes.

Plasma heating in JET is done via NBI+ICRH and is about 59 MW.

I've seen those copper busbars -- they drill holes for water throughout them. The whole design of high-B field environments is fascinating; you end up with things like Bitte designs with split rings and a whole lot of engineering to stop the copper vapourising. Highly recommended if you're ever in the area – they do two sorts of tours (or did, prior to covid), the "general public" tour and the "scientist" tour. I went on the latter. The sight of two giant robotic arms playing Jenga to train their operators is not one to forget.

I should visit JET sometime. Of all the systems on the machine I worked on (https://hsx.wisc.edu/), the coil current feeds were the most difficult. Trying to cram that much current through a small piece of copper with a discontinuity takes years of effort.

Well my kettle is 3kw and takes about 2 minutes to boil so about 200 of my kettles... BUT they don't say how big the kettle is or how much water it contains so it could be 60 BBC kettles. I bet they drink a lot of tea...

When discussing nuclear power plants we can all debate aspects of the bikeshed.

When discussing fusion power, we can all debate how many kettles we can boil.

Kind of funny :)

3L kettles I guess

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