Wendelstein 7-X Fusion Reactor Produces Its First Flash of Hydrogen Plasma (gizmag.com)

Zothecula writes: Experimentation with Germany's newest fusion reactor is beginning to heat up, to temperatures of around 80 million degrees Celsius, to be precise. Having fired up the Wendelstein 7-X to produce helium plasma late last year, researchers have built on their early success to generate its first hydrogen plasma, an event they say begins the true scientific operation of the world's largest fusion stellarator.

Comments

This is completely awesome

[Kobun]

And I wish them godspeed. Energy and information are the fundamental limits of the human condition. Fundamental leaps in either arena will be transformative.

Re:This is completely awesome

[Rei]

Interestingly enough, for d-t fusion, the neutrons are not an unwanted waste product, but actually essential. Tritium doesn't grow on trees, you have to make it. And more importantly, d-t fusion only gives off one neutron, and it takes one neutron captured by 6Li to breed 1 tritium (you can also make tritium from 7Li bombardment and not consume the neutron, but due to the cross sections and energies involved its usually not as interesting). So if you use one neutron to make the fuel that produces one neutron, and you can't capture 100% of the neutrons, you're in trouble! You get around this by using a lithium-beryllium blanket, as beryllium is a good neutron "multiplier" (capturing one high energy neutron and yielding two lower energy neutrons). It's also rare, expensive as heck and its dusts are highly toxic, but it's consumed at a tiny rate, so it's mainly just an initial cost (heavy elements like lead can also be used as multipliers but they're not very effective in this context, their cross sections don't extend down as far as beryllium and their (n, Xn) reactions where X>2 don't make up for it). So basically, while you lose some neutrons to unwanted reactions, you overall end up producing enough to produce enough tritium for your reactor to consume. The key point is, you want the neutrons to be hitting your reactor, they're doing you a service ;)

There will of course be unwanted neutron captures, but when you engineer it you're choosing specifically what materials are going to be bombarded, so you can pick materials with low neutron capture cross sections and which capture to isotopes that are either stable or have short half lives. Concrete is great for how cheap it is (light elements in general are, and concrete is mostly made of light stuff). As far as metals go, aluminum is great where heat loads or mechanical stresses aren't excessive. Beryllium is even better, as well as stronger and lighter... but see the aforementioned issues with it. Steel is "okay", usually fine if you're careful about what you alloy it with. You generally want to avoid titanium. Graphite is superb if you run it hot enough (otherwise you risk Wigner energy problems). Composites likewise, although they're more temperature limited. Most common ceramics are made of light elements, which makes them very good to use, although those with heavy elements (like tungsten carbide) should be avoided. Tungsten in general should be avoided unless necessary. Some ceramics like boron carbide/nitride are highly heat and corrosion tolerant, high compressive strength, huge neutron absorbers and don't yield dangerous byproducts, which lets them fit multiple roles at once - so long as there's little tensile or shear stresses. In some cases you may want more of a neutron "window", wherein things like zirconium or lead would be good - particularly specific isotopes of them if you're willing to pay for enrichment. It all depends on the operating environment and geometry.

Re:sunfire / in my stellerator / makes me... happy

[Rei]

The "50 years away" stuff is a really unfair criticism. The amount of progress that's occurred in the past several decades is many orders of magnitude - JT-60 has even gotten to Q=1.25, which means they were getting 25% more power out than they were putting in to maintain the reactor in steady-state operation.

Part of the reason that this concept got started was because of a big mistake early on with the ZETA program. Unbeknownst to them, A) heavy electron bombardment of their detectors was leading to false spectral shift readings, making them think that the temperature was much hotter than it was, and B) there was a possible method to create neutrons that they were unaware could be significant - heavy localized acceleration of ions causing spallation impacts. The unfortunate part was, by coincidence, (B) happened to produce roughly the amount of neutrons that would be expected by (A). So they thought that they were just a short step away from a viable fusion reactor, when in reality they weren't even close. Due to the more primitive technology at the time, not only did they not have detailed computer models that could have warned them to expect the neutrons, but they also didn't have a convenient way to measure neutron energies (it was this that later proved their early conclusions wrong). Their lack of computer models also meant that they were unaware of how much of a problem drift would be.

It's a very different situation today. There's really no question that we can viably produce fusion power today. The real question hanging over our heads is, what is it going to cost? How can we engineer a system to produce power affordably? And that's the real question that's going to take a lot of work to figure out. One thing is for sure, though: the higher the magnetic fields you can get for a given cost, the vastly easier it becomes. And these new high temperature superconductor tapes could push us leaps and bounds even beyond ITER, whether you go with a stellerator, a more traditional tokamak, or really anything else that employs magnetic fields. It's very encouraging for the field to see a route that already looked to be on a positive path get such a "bonus".

Re:sunfire / in my stellerator / makes me... happy

[Anonymous Coward]

As an engineer working in the fusion field, I would not agree it's quite so rosy a picture. *Lots* of issues need to be solved technologically, although I agree with you the physics side of Tokamaks is relatively understood. I.e. it would be a huge shocker if ITER didn't produce the power expected. Tokamaks are however very unreliable with stability, and whether or not these can be controlled and mitigated enough for reliable power production remains to be seen. Further, going from ITER to DEMO is like launching a rocket to space vs. going to the moon; the high energy neutron flux from a fusion reactor will centimeters of the first wall to powder. Getting enough lithium around the wall for tritium breeding and heat removal for a steam cycle is very difficult.

In the end, it's all economics as you say. I can't imagine with the present state of technology a viable commercial fusion reactor online until past 2100. ITER will be ~2030, DEMO ~2070 if ITER cost/is any clue. Say you're making a decision for a company - would you rather spend $20 billion dollars on a very finicky tokamak fusion reactor with tremendous maintenance costs (tritium recycling, lithium management, disruption and instability mitigation systems, etc.), or a gen III or IV nuclear reactor - perhaps a thorium molten salt reactor - that produces the same power reliably for a small fraction of the cost?

Commercial fusion will happen eventually, but in my opinion not without tremendous advances in materials science and superconducting magnets. One can imagine with clever first wall materials and >20 T fields using advanced BSCCO superconducting materials (or other) a reactor might become as affordable as a fission reactor of the same power output. Contrary to what fusion researchers will have you believe, fusion will always be in economic competition with fission.

This PDF sums it up pretty nicely: http://www.askmar.com/Robert%20Bussard/The%20Trouble%20With%20Fusion.pdf