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Wendelstein 7-X: Gigajoule energy turnover generated for eight minutes

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Re: Wendelstein 7-X: Gigajoule energy turnover generated for eight minutes

#101

Post by KyleBerezin »

waterheater wrote: post #80
white_dragon88 wrote: post #10

Earlier quoted context omitted.

You know enough to say more. Say more!

I'm not that guy, but I can speak to what you're asking. I've followed Wendelstein 7-X for almost a decade. Nuclear fusion occurs at extremely-high temperatures. As you heat your fusion fuel to sufficiently-high temperatures to allow fusion, the matter transitions into a plasma, which is great: plasmas react to electromagnetic fields. As such, a major challenge with achieving viable nuclear fusion is making a vessel…

One guy asked why the mobius aspect is needed and I couldn't answer. I know a lot of stellarators aren't odd-period like Wendelstein, and the old designs didn't do folding at all. Do you know what improvements the mobius design has over something like TJ-II?

Re: Wendelstein 7-X: Gigajoule energy turnover generated for eight minutes

#102

Post by Bjartr »

Simon_O_Rourke wrote: post #72
KyleBerezin wrote: post #3

Ahh, Wendelstein is that stellerator reactor. The stellerator is really cool, and an alternative to a tokamak reactor. Tokamak is the doughnut shaped reactor, and it has a problem where the plasma near the outer circumference has less magnetic confinement. The stellerator is similar, but confines the plasma to a ribbon and folds it over on itself in a mobius-like arrangement. I used to be really interested in this, b…

Just curious as to why a Mobius strip type arrangement is better than a toroid? Is it anything to do with the turbulence in the plasma flow being easier to control?

I think it's about ensuring the plasma heat/energy distribution is more uniform so you get fewer outlier particles with high enough energy to escape confinement and damage the interior of the reactor. Or something like that.

Re: Wendelstein 7-X: Gigajoule energy turnover generated for eight minutes

#103

Post by eis »

dale_glass wrote: post #75
Retric wrote: post #69

Earlier quoted context omitted.

You messed up at your last step 1 millionth = 1mm, 10 millionth = 0.1mm, 100 millionth = 0.01mm 0.01mm is very difficult when you’re talking large custom objects with complex shapes.

Oh, English fail on my part then. I had assumed that 100 millionths of a metre == 100 * 1/1000000.

The german site of the source speaks of 0.1mm so you were correct

   > bei Toleranzen von teilweise nur 0,1 Millimeter
https://www.ipp.mpg.de/de/aktuelles/presse/pi/2020/01_20

Re: Wendelstein 7-X: Gigajoule energy turnover generated for eight minutes

#104

Post by aidenn0 »

runako wrote: post #57
amelius wrote: post #24

Earlier quoted context omitted.

Isn't this similar to the monetary meaning of the word turnover? Like turnover : profit energy turnover : net energy output?

Possibly the poster is from a country like America where "turnover" is not a preferred term to refer to gross receipts of a business. (Americans typically use "revenue" instead.)

I am indeed from the US and had never heard "turnover" to mean gross receipts.

Re: Wendelstein 7-X: Gigajoule energy turnover generated for eight minutes

#105

Post by nerdponx »

tsimionescu wrote: post #59
karmajunkie wrote: post #30

This is perhaps an obvious question to some, but I'll ask it anyway: How is the power generated here converted into usable electricity? I know for conventional fission reactors the heat of fission is basically used to run a steam turbine. Given the extreme heat of the plasma, and that it must be magnetically suspended so that it doesn't even touch the sides of the containment, how is that heat transferred to some oth…

Most of the answers are missing the actual (proposed) mechanism. The energy of the reaction is mostly carried away as high-energy neutrons. So, the way to get energy back is to "capture" those neutrons. Since neutrons are not electrically charged, you can't use them to directly create electricity, so all you're left with is using them for heat. Unfortunately, since they are electrically neutral, they're also relative…

It's always fascinating to me that, no matter how many interesting new ways to release lots of energy we develop, we are still stuck with the same method for converting it to electricity: release the energy as heat, use heat to make steam, use steam to drive generator.

Re: Wendelstein 7-X: Gigajoule energy turnover generated for eight minutes

#106

Post by andbberger »

aquafox wrote: post #56

Interesting fact: Nuclear fusion, even if we'll make it work, won't stop global warming, because the heat it creates heats up the earth enough to bring us outside the Paris agreement: https://twitter.com/rahmstorf/status/1605967891928596481

this is a basic consequence of thermodynamics and true for all power generation. the only thing to be done to minimize waste heat is to to increase temperature of the hot side of the heat engine, with ie advanced fission reactors.

and fusion never had any advantage over fission anyways, other than that people aren't scared of it yet.

Re: Wendelstein 7-X: Gigajoule energy turnover generated for eight minutes

#107

Post by magicalhippo »

snarkconjecture wrote: post #16
aidenn0 wrote: post #8

What is "energy turnover" in this usage? [edit] Found it: "Energy turnover is defined as the amount of heat multiplied by the duration of the discharge[1]." By "amount of heat" I assume they mean "heating power delivered to the plasma" b/c the the only way to multiply by time and get Joules is to start with power. 1: https://gigazine.net/gsc_news/en/20230227-wendelstein-7-x-en...

Yes, it's a little buried but the article says > The energy turnover results from the coupled heating power multiplied by the duration of the discharge The numbers: > The energy turnover of 1.3 gigajoule was achieved with an average heating power of 2.7 megawatts, whereby the discharge lasted 480 seconds Also: > Within a few years, the plan is to increase the energy turnover at Wendelstein 7-X to 18 gigajoules, with…

How long does it take to restart after losing stability?

Ie, would it be feasible in a power plant scenario to settle for 30-60 minutes of stability, and just restart?

Re: Wendelstein 7-X: Gigajoule energy turnover generated for eight minutes

#108

Post by waterheater »

KyleBerezin wrote: post #101
waterheater wrote: post #80

Earlier quoted context omitted.

I'm not that guy, but I can speak to what you're asking. I've followed Wendelstein 7-X for almost a decade. Nuclear fusion occurs at extremely-high temperatures. As you heat your fusion fuel to sufficiently-high temperatures to allow fusion, the matter transitions into a plasma, which is great: plasmas react to electromagnetic fields. As such, a major challenge with achieving viable nuclear fusion is making a vessel…

One guy asked why the mobius aspect is needed and I couldn't answer. I know a lot of stellarators aren't odd-period like Wendelstein, and the old designs didn't do folding at all. Do you know what improvements the mobius design has over something like TJ-II?

The helical path creates a twist in the plasma which cancels out the drift forces. This is what I meant by "tricking" the plasma. User mjfl gives an even more technical explanation:

> By twisting the plasma into a shape where the curl of B (proportional to J) is parallel to B, i.e. a helix, the cross product is 0, and thus there are no net magnetohydrodynamic forces on the plasma.

Hope all that's a good answer for you.

> Mobius aspect

You might avoid using the word "Mobius" and instead use "helical." A Mobius strip is important because it has two faces which form a single surface. The surface aspect isn't relevant in this context, so a term which refers to the shape would likely dispel confusion in a reader.

As far as I'm aware, each section of a stellarator is periodic in its own right, which means the end and start points of each section are the same. Though I'm not certain, the choice of four versus five is more likely an engineering factor rather than one of physics, whereas the distinction between a tokamak and stellarator is of physics and not just engineering.

Re: Wendelstein 7-X: Gigajoule energy turnover generated for eight minutes

#109

Post by sp332 »

pfdietz wrote: post #94
sp332 wrote: post #86

Earlier quoted context omitted.

It's a been a long time, but in a talk at Google, I think Bussard said that power output scales with the 5th power of the radius of the device. There's really no point making a small one.

Bussard's last reactor concept, polywell, didn't work.

Oh right, I had WB-7 confused with Wendelstein 7.

Re: Wendelstein 7-X: Gigajoule energy turnover generated for eight minutes

#110

Post by juujian »

mjfl wrote: post #67

The Stellarator is theoretically a superior design over the Tokamak, designed to neutralize the JxB force, where J is the current through the plasma and B is the magnetic field guiding the plasma around the device. By twisting the plasma into a shape where the curl of B (proportional to J) is parallel to B, i.e. a helix, the cross product is 0, and thus there are no net magnetohydrodynamic forces on the plasma.

'Theoretically' is the right word for sure. iirc, the predecessor of the Wendelstein led to the bankruptcy of the engineering firms building the parts, because tolerances were so tight and they failed multiple times to land within the constraints.
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