New fusion reactor about to be switched on.

[SlipStream77]

E71 said:

So far Tokamaks have tried to manage these by local heating, or adjusting other magnetic coils during operation, but it's a horrendous balancing act, and generally results in the plasma cooling down and switching off.

What's actually the limiting factor here? Is it the rate at which the coils are reacting, or maybe a computing power issue?

Edited by SlipStream77 on Monday 14th December 14:32

[annodomini2]

E71 said:

Fusion is a massive technical challenge, and scientists are still struggling to understand what is really happening in the plasma. Modeling plasma is difficult because things are happening on different length scales, and it's impossible to write one code to model all of these together, and predict what will happen in certain conditions.

The fusion environment is by far the most extreme thing on earth, or in the universe. As well as heat from a 100 million degree plasma, there are neutrons being fired out which damage anything which gets in their way, so we need new advanced materials which won't transmute to anything radioactive in the neutron radiation, and will keep their structural and thermal properties. (This is what I am doing my PhD on)

From an engineering perspective, I see Stellarators (like this one in Germany) as a more promising solution than Tokamaks. Tokamaks need a current driven through the plasma to produce the correct magnetic field to contain it in the vessel, but this current can lead to more plasma instabilities. So far Tokamaks have tried to manage these by local heating, or adjusting other magnetic coils during operation, but it's a horrendous balancing act, and generally results in the plasma cooling down and switching off. "Both are terrible beasts," smiles the Scientific Director of W 7-X. "Ours is a beast to build; yours is a beast to operate." (https://www.iter.org/newsline/172/680)

To try and answer the thermodynamics question, most of the heat produced is used in heating the plasma. Since it is a vacuum vessel, the temperature at the walls is (only!) around 1400C, (upto 2000ish in some components), and the coolant will be around 300-800 depending on what design concept you look at. Not that much heat will reach the outside world.

I'm no plasma physicist, maybe one will come along and answer things better.

This is why the aneutronic solutions appear more promising.

[hidetheelephants]

I wonder what's happening with the polywell; it seems to have gone a bit quiet of late. It seemed to be relatively(!) simple as fusion machines go.

[E71]

SlipStream77 said:

What's actually the limiting factor here? Is it the rate at which the coils are reacting, or maybe a computing power issue?

Edited by SlipStream77 on Monday 14th December 14:32

As well as the different length scales, there are many different timescales femtoseconds to seconds for different motions in the plasma. So this complicates the models even more, and I don't think they can find solutions fast enough in real time.

Also, knowing what's happening in the plasma is really difficult. Measurement probes cool the plasma, creating more instabilities. Experimental reactors have loads of diagnostics of all sorts generating GBs of data in an experiment, and analysing this quickly and selecting the useful feedback is a big challenge which is being worked on. A power plant can't have all these diagnostic systems, so the plasma will need to be more stable, and predictive models need to be better.

I don't know much about the coil systems, but I think they have separate coils for controlling these instabilities, so the main confinement coils don't need to be adjusted. I'm not sure how fast these can react, either.

[E71]

anonymous said:

[redacted]

Because neutrons don't have a charge, they aren't affected by a magnetic field, so they can fly out.

This is a challenge for materials testing, because we can't use accelerators to create beams of neutrons and fire them at a material.
You need a charged particle to be accelerated in a magnetic field, so we use heavy ions to simulate radiation damage, but the damage mechanisms are very different on a microscopic scale, so it's not quite the same. It's simply that particle accelerators are very simple, cheap, and easy, and don't make your sample radioactive so we can look at far more materials.

[MrCarPark]

Freeman Dyson recently gave his views on fusion in an interview with The Register:

http://www.theregister.co.uk/2015/10/11/freeman_dy...

Finally, what are your views on fusion? Do you see any real progress being made?

"I think they made a terrible mistake 50 years ago when they stopped doing science and went to big engineering projects. These big engineering projects are not going to solve the problem, and they've become just a welfare programme for the engineers. You have these big projects, both national and international, that are really a dead end as far as I can see. Even if they're successful, they won't provide energy that's useful and cheap.

"But it's not clear when you do science, whether you'll discover anything or not. But that's the only answer."

So with fusion, we should go back to the drawing board?

"Yes, and it's not going to solve any problems for the near future.

"But I don't think there is a problem in the near future anyway [laughs]."

[Beati Dogu]

Well it hasn't gone bang with helium plasma, so they're going to start it with hydrogen plasma for the first time. They've asked none other than Chancellor Angela Merkel to throw the big guillotine switch and they'll be live streaming the event.

Coverage starts on 3 February at 2.45 p.m.

http://www.ipp.mpg.de/livestream_e_16

[ikarl]

With Merkel throwing the switch, there's got to be a joke in there if it all goes wrong!

[Beati Dogu]

Here's hoping.

[Sf_Manta]

Results from today, no we didn't blow the world up.. but apparently made one step closer to Fusion technology as an alternative power supply.

http://www.iflscience.com/physics/germanys-fusion-...

[Beati Dogu]

I saw some of the livestream replay earlier. It ran plasma for all of 2 milliseconds.

They want about 30 minutes by 2020. They sure know how to milk it these guys.

[hidetheelephants]

Their PR dept is certainly exceeding all expectations.

[Beati Dogu]

It's a good job there's no pressing need for 'green' electricity while they shut down the power plants that actually work.

[Catatafish]

It would be great to have fusion added to our portfolio of heat machines, but basically the problem is stabilising something that is exploding at 10million degrees, so I'm not holding my breath.

Much better idea is to put all of that cash into solar cell development as you've already got the bestest fusion reactor working very nicely thank you. We just need to exploit it more effectively.

[ikarl]

I disagree, if we really wanted fusion we would have it. If there was a despearate need, and the world pulled it's resources, and diverted more money to the project(s), I'm pretty sure there would be an energy-positive reactor with 5 years.

btw, 10 million degrees is nothing, pretty sure at another site they've exceeded 12 million degrees

[rhinochopig]

ikarl said:

With Merkel throwing the switch, there's got to be a joke in there if it all goes wrong!

Amazing. The leader who killed the German Nuc industry being asked to pull the switch on a Nuc reactor.

[hidetheelephants]

Catatafish said:

It would be great to have fusion added to our portfolio of heat machines, but basically the problem is stabilising something that is exploding at 10million degrees, so I'm not holding my breath.

Much better idea is to put all of that cash into solar cell development as you've already got the bestest fusion reactor working very nicely thank you. We just need to exploit it more effectively.

There's already plenty of money going into improving solar power; much better to direct some money toward improving fission, which can actually provide useful power for an industrial society.

[ikarl]

hidetheelephants said:

There's already plenty of money going into improving solar power; much better to direct some money toward improving fission, which can actually provide useful power for an industrial society.

fission or fusion?

I'd prefer money to be directed towards fusion personally but can accept you POV if you think fission

[Beati Dogu]

rhinochopig said:

Amazing. The leader who killed the German Nuc industry being asked to pull the switch on a Nuc reactor.

She used to be a research physicist too, as well as being a complete fukwit.

[hidetheelephants]

ikarl said:

hidetheelephants said:

There's already plenty of money going into improving solar power; much better to direct some money toward improving fission, which can actually provide useful power for an industrial society.

fission or fusion?

I'd prefer money to be directed towards fusion personally but can accept you POV if you think fission

Nothing wrong with funding fusion, but the lack of research money(in the UK; China are spending loads) for fission frustrates me as it works, it's safe, no noxious emissions, current tech is comparable for cost, but there are low risk improvements which are not being made because of bureaucratic inertia and lack of money, never mind the longer term potential for fission power matching or becoming cheaper than coal power. Even the most ardent cheerleaders acknowledge that fusion is at least 30 years from practicality, fission has been with us for 60 years, quietly generating electricity.