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Successful second round of fusion experiments with Wendelstein 7-X

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Re: Successful second round of fusion experiments with Wendelstein 7-X

#191

Post by pfdietz »

yholio wrote: post #153
jerf wrote: post #45

Earlier quoted context omitted.

If the Stellerator, or any of its descendants, turn out to be the answer to practical fusion, it would have been contingent on vast quantities of computational power being available cheaply. It does not matter how much money you poured into your Stellerator project in 1970, you could never have built the 7-X, because there would have been no way to produce that design in the first place. Personally, I think one of th…

An exact replica of Falcon 9 was impossible 40 years ago, of course. But a replica with 50% lower thrust, 10% lower ISP and 60% it's payload capacity for a similar inflation-adjusted price was certainly possible. It wasn't the computational revolution that made SpaceX possible, the basic technology is more or less the same as it was in the 60s. The Merlin engine has it's roots in the '90s NASA Fastrac design, evolved…

One technology that F9 manufacture uses extensively wasn't even invented until the 1990s.

I refer to Friction Stir Welding, the wonderful technique that welds aluminum alloys by plastic deformation below their actual melting points.

The landing algorithms for the F9 first stage make use of advances in optimization algorithms that weren't available 40 years ago as well (as well as exploiting faster processors).

Re: Successful second round of fusion experiments with Wendelstein 7-X

#192

Post by pfdietz »

SmellyGeekBoy wrote: post #187
yholio wrote: post #153

Earlier quoted context omitted.

An exact replica of Falcon 9 was impossible 40 years ago, of course. But a replica with 50% lower thrust, 10% lower ISP and 60% it's payload capacity for a similar inflation-adjusted price was certainly possible. It wasn't the computational revolution that made SpaceX possible, the basic technology is more or less the same as it was in the 60s. The Merlin engine has it's roots in the '90s NASA Fastrac design, evolved…

Both you and I (and hopefully most of HN) know that fusion is safe. But I can't imagine the public perception being great if "fail early and iterate quickly" was attached to anything with "nuclear" in the name.

The main problem that fission has isn't safety, it's cost. Fusion promises to make this main problem worse, not better.

Re: Successful second round of fusion experiments with Wendelstein 7-X

#193

Post by pfdietz »

philwelch wrote: post #139
hyperbovine wrote: post #11

Earlier quoted context omitted.

Err no, money is not "the only thing" keeping us from having fusion power. I can think of one other thing which is that it's damn hard to create stellar-core conditions inside of a small containment vessel on Earth. It's not obvious that throwing more money at the problem is going to change this. After all, fusion research has been funded in some form or another since the 1950s. I'll bet if you added up all the resea…

> It's not obvious that throwing more money at the problem is going to change this. After all, fusion research has been funded in some form or another since the 1950s. That's not very long. The first liquid-fueled rocket was in 1914, and the moon landing wasn't until 1969, and even that was only possible with very high levels of funding far beyond what's invested in fusion power today. Babbage built the Difference En…

We do know there are inherent problems with fusion, particularly DT fusion. In fact, we've known for 35 years or more. Even if the plasma physics issues are magically solved, fusion has grave engineering obstacles.

http://www.askmar.com/Robert%20Bussard/The%20Trouble%20With%...

https://pure.mpg.de/rest/items/item_2131865/component/file_2...

It's interesting examining the recent efforts, public and private, in light of these venerable critiques.

Re: Successful second round of fusion experiments with Wendelstein 7-X

#194

Post by londons_explore »

michaelmachine wrote: post #72
saganus wrote: post #5

Does anyone have any idea how do they take pictures of the plasma? That seems quite hard considering the temperatures and the strong magnetic field.

There is a video available here as well: https://www.youtube.com/watch?v=Gtf-1JibORg

Those videos show surprising 'hotspot' lines - I would expect the plasma to be far more evenly distributed.

Re: Successful second round of fusion experiments with Wendelstein 7-X

#195

Post by pfdietz »

whyisthis122 wrote: post #161
nine_k wrote: post #12

With fusion devices having trouble to confine the plasma for long times, I wonder if a massively-parallel fusion plant woud be feasible. Let's assume that plasma destabilisation does not damage the device, and is a mundane event. Build 10 or even 20 fusion devices (economy of scale!) feeding the common heat buffer, e.g. a large reservoir of a molten salt or metal. Feed conventional turbines off the heat of the heat t…

Why is this upvoted? It shows a severe lack of physics knowledge. The whole goal of fusion is to get the energy amplification, Q, to be > 1, which requires the triple product n T t to be above some threshold. n is density, T is temperature, t is confinement duration. This is Lawson's criteria, you should look it up to educate yourself. Your proposal doesn't help n, T, or t, hence doesn't help Q. Also, there are econo…

DT fusion reactors have inherent diseconomies of scale. That's because their power output is limited by what the first wall can withstand. By the square-cube law, the volumetric power density of a DT reactor must go down as its linear dimensions increase.

This is not just quibbling, since bad power density is a huge problem with fusion.

Look at ITER. The volumetric power density (gross fusion power/volume of reactor proper, not including the building or auxiliary equipment) is 0.05 MW/m^3. Compare that to a PWR primary reactor vessel, which have a power density around 20 MW/m^3. The smaller designs like ARC or Lockheed's concept have power density around 0.5 MW/m^3.

Re: Successful second round of fusion experiments with Wendelstein 7-X

#196

Post by pfdietz »

alexgmcm wrote: post #10
chiefalchemist wrote: post #2

"Although Wendelstein 7-X is not designed to generate energy, the device is intended to prove that stellarators are suitable for use in power stations. With Wendelstein 7-X the intention is to achieve for the first time in a stellarator the quality of confinement afforded by competing devices of the tokamak type." This was at the very end. While competition is certainly a positive, this doesn't sound like they're int…

From my classes some years ago IIRC the main benefit of the Stellarator was the lack of a plasma current which is no longer needed for plasma heating due to advances in neutral beam injection technologies. The plasma current seems to create some instabilities so we may be able to achieve better confinement with a device that doesn't have one. I would also agree with the other comments that we can't afford to put all…

The big advantage of stellarators vs. tokamaks is their lack of disruptions. Tokamak disruptions are a very serious problem that, if not well-solved, promise to put tokamaks into the technology garbage can. A disruption can, in the worst case, generate runaway relativistic electron beams that can melt holes through the first wall.

The first and primary goal of ITER is to show that the disruption problem can be and has been solved. If they don't do this, ITER will never be allowed to operate with a DT plasma. And they are still scrambling to solve the problem.

Re: Successful second round of fusion experiments with Wendelstein 7-X

#197

Post by EastLondonCoder »

philwelch wrote: post #127
jerf wrote: post #45

Earlier quoted context omitted.

If the Stellerator, or any of its descendants, turn out to be the answer to practical fusion, it would have been contingent on vast quantities of computational power being available cheaply. It does not matter how much money you poured into your Stellerator project in 1970, you could never have built the 7-X, because there would have been no way to produce that design in the first place. Personally, I think one of th…

> Personally, I think one of the answers to "tech seems to have stalled" is that it's easy to underestimate how important cheap computational power is, even without "AI", to moving forward. For another example, as fantastic as the 1960s space projects may have been, I think they just weren't economically sustainable, so it isn't that amazing that they didn't become a self-sustaining industry right away. I think it's…

I think you should expand this absolutely excellent post into an article.

Re: Successful second round of fusion experiments with Wendelstein 7-X

#198

Post by xenophonf »

xxgreg wrote: post #146
sballin wrote: post #142

Earlier quoted context omitted.

Here's a source, unfortunately paywalled, from 1989: https://www.tandfonline.com/doi/abs/10.13182/FST90-A29178 I do research at W7-X, so I can confirm that to the best of my knowledge, the design was computed a long time ago. Building the actual device took a while.

Do you have any links to a high level description of how this would be hooked up to a powerplant? Would this be used to heat water as per a typical fission plant?

The W7-X isn't a fusion power plant, so such a description doesn't exist. It's the chemistry equivalent of a test tube, not an internal combustion engine.

Re: Successful second round of fusion experiments with Wendelstein 7-X

#199

Post by sobrevivendo »

petra wrote: post #121
wefarrell wrote: post #115

Earlier quoted context omitted.

Pouring in money advances computation. Microprocessors were a direct result of the space race and space weapons systems. No other industry would have justified the trillions of dollars in investment that was required to fit advanced computers into a small space when mainframe systems did the job just fine. Missiles and spaceships required systems that could calculate trajectories and be small enough to launch into sp…

>> when mainframe systems did the job just fine. Didn't people see the value that cheaper/more compute power will give them back than ?

People from the future will look back at us and ask:

"Didn't people see the value that cheaper/more electric power will give them back than ?"

Re: Successful second round of fusion experiments with Wendelstein 7-X

#200

Post by drjesusphd »

ghaff wrote: post #119
wuliwong wrote: post #100

Earlier quoted context omitted.

I agree. I hear the comments about a lack of funding but to me it isn't necessarily a lack of vision from politicians and businessmen. I have a Ph.D. in physics and even worked for 6 months full-time in the Princeton Plasma Physics Lab as an undergraduate and I still hav mixed feelings about fusion power, particular vs other non-fossil fuel options.

Among other things, there's a perception of fusion as this clean, infinite energy source. I haven't followed fusion carefully for a good many years but back when I was studying material science, radiation embrittlement of fusion reactor shielding was an area of active research. It wasn't clear that you didn't end up with just as much radioactive waste from fusion as you did with fission. Don't know what the current t…

Yes, neutron activation is an issue that needs to be handled safely. But the isotopes produced this way tend to be short-lived, with half lives around a decade. Not the same challenge of storing radioactive waste on geological timescales.
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