Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

ipp.mpg.de

Post reply on HN
Print view View original

141–150 of 322 posts

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

#141

Post by extrapickles »

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?

It primarily has to do with the physical construction of the magnets, in a toroid the inside of the toroid effectively has more windings per meter of circumference than the outside causing uneven containment.

With mobius strip you regularly flip between inside and outside, so the plasma particles get more even force applied.

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

#142

Post by pfdietz »

moffkalast wrote: post #122
pfdietz wrote: post #99

I greet W7-X with a huge yawn. A reactor based on stellarators will still be very large and have very low volumetric power density. The beta is not good, so these would only work with DT, and suffer from the generic problems of all DT schemes.

What makes tokamaks so much better at power density? After all it's the exact same setup, just shaped differently and without the center coil?

I didn't say that. Both tokamaks and stellarators on DT will have lousy volumetric power density. Indeed, any DT scheme will suffer in that respect.

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

#143

Post by Retric »

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.

No your correct, I just read it wrong. Really needed to pay attention to the s.

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

#144

Post by willis936 »

moffkalast wrote: post #120
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.

The last time it was in the news I think naysayers listed the main caveat with stellerators as something along the lines of very low plasma density compared to tokamaks, which makes them unable to get anywhere close to the energy break even point.

Doesn't really track. Stellarators can operate above the Greenwald density limit. They just have shorter confinement times for a given field strength and major radius.

http://fusionwiki.ciemat.es/wiki/Greenwald_limit

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

#145

Post by nerdponx »

jessriedel wrote: post #128
nerdponx wrote: post #105

Earlier quoted context omitted.

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.

The reason just that this is a simple process for which a steam turbine can achieves 90% of the thermodynamic optimum. To my knowledge, the only reason people consider alternatives is to reduce capital costs. You're still capped by thermodynamics though.

That's what I was wondering: if heat -> steam -> turbine is close enough to the theoretical upper limit and you get diminishing returns by other means.

Still, it seems very indirect. Like generating solar power by using a parabolic mirror to heat water instead of photovoltaic panels... but of course I just found an example of doing that too: https://en.wikipedia.org/wiki/Parabolic_trough

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

#146

Post by fastneutron »

gus_massa wrote: post #134
MichaelZuo wrote: post #123

Earlier quoted context omitted.

Which doesn't make sense for power generation since there will always be some percentage of neutrons produced by any type of fusion reaction that can only be useful for generating steam. To entirely skip the steam cycle portion is to intentionally make a much less efficient design. For space-constrained, high-value, applications where economics don't matter that much, such as a submarine, that would make sense, but o…

They plan to use 2D + 3He -> 4He + 1H, so no neutrons https://en.wikipedia.org/wiki/Aneutronic_fusion#Candidate_re... (I'm still not convinced of their explanations, but a fast proton may be easy to catch by the magnetic field and create the effect they want.)

Nitpick: You’re always going to get some parasitic D+D reactions because it’s reaction cross section is appreciably higher than D + 3He below 50 keV, and non-negligible even after the crossover point.

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

#147

Post by wizzwizz4 »

dekhn wrote: post #91
themagician wrote: post #63

Earlier quoted context omitted.

I find the geometry of things like this fascinating. We typically think in such simple shapes. I feel like my brain can do triangle, rectangle and maybe hexagons and that's about it. I remember when I finally understood radians enough to really understand circles and waveforms—I felt so enlightened. Like I actually remember the moment when it clicked. For years I was just "doing the work" without actually understandi…

I can't really think in (visualize) 3d shapes, so I depend a lot on 3D geometry programs when I design things like for my microscope. A fair number of people I've talked to can visualize complex shapes in their head, rotate them around, do interference checking, etc.

Aphantasia? https://en.wikipedia.org/wiki/Aphantasia

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

#148

Post by klodolph »

colordrops wrote: post #131
KyleBerezin wrote: post #114

Earlier quoted context omitted.

Yea they are kinda confusing, especially when you get into the 3D ones like klien bottles and roman surfaces. I also recently learned that if you make a mobius shaped transmission line (like a ladder line) and you send a pulse down it, that pulse will continue looping until it dissipates (or forever if it is a superconductor). https://www.microwavejournal.com/articles/21001-printed-reso... I have no idea if there are…

Are real life superconductors ideal, i.e. they truly would store a charge forever (at least until the material disintegrated)? Or is there some sort of loss, albeit much less than typical resistance?

1. Something “in a superconducting state” has zero resistance, but the transition to superconducting states is not sudden, and there are various things which disrupt that state like magnetic fields.

2. Alternating currents will dissipate even with zero resistance, because the circuit will emit EM waves.

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

#149

Post by pfdietz »

fizigura wrote: post #46
KyleBerezin wrote: post #18

Earlier quoted context omitted.

Yea, but compare the financial burden of that compared to a solar farm of the same output. Not to mention the technical risk.

Solar farms on farmland? That won't scale to the energy needs of 8bn+ people if we still want to keep feeding them. Especially a non-vegetarian diet.

Where did he say on farmland?

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

#150

Post by pfdietz »

fizigura wrote: post #43
t0mas88 wrote: post #28

Earlier quoted context omitted.

For less than 15 billion euro you could buy enough solar to power a country the size of the Netherlands. With 5 billion to spend on batteries you might even make it through night time usage. Or in other words: Fusion is too expensive at this point to be useful.

The same was said 20 years ago about solar power. Then some countries stepped up the subsidies game and booom, prices fell dramatically since suddenly everybody wanted a piece of the cake. And competition drove this all down. All you need is for somebody to start. Or we just keep telling ourselves that it's too expensive, shrug, and move on. Also note how the goal posts changed. Until recently, everybody made fun of…

And it was pointed out 40 years ago that DT fusion will be inherently expensive (specifically, more expensive than fission, which itself has demonstrated it cannot compete.)

https://orcutt.net/weblog/wp-content/uploads/2015/08/The-Tro...

Post reply on HN