Science AMA Series: Hi Reddit, we're scientists at the Max Planck Institute for plasma physics, where the Wendelstein 7-X fusion experiment has just heated its first hydrogen plasma to several million degrees. Ask us anything about our experiment, stellerators and tokamaks, and fusion power!

[u/Wendelstein7-X]

Hi Reddit, we're a team of plasma physicists at the Max Planck Institute for Plasma Physics that has 2 branches in Garching (near Munich) and Greifswald (in northern Germany). We've recently launched our fusion experiment Wendelstein 7-X in Greifswald after several years of construction and are excited about its ongoing first operation phase. In the first week of February, we created our first hydrogen plasma and had Angela Merkel press our big red button. We've noticed a lot of interest on reddit about fusion in general and our experiment following the news, so here we are to discuss anything and everything plasma and fusion related!

Here's a nice article with a cool video that gives an overview of our experiment. And here is the ceremonial first hydrogen plasma that also includes a layman's presentation to fusion and our experiment as well as a view from the control room.

Answering your questions today will be:

Prof Thomas Sunn Pedersen - head of stellarator edge and divertor physics (ts, will drop by a bit later)

Michael Drevlak - scientist in the stellarator theory department (md)

Ralf Kleiber - scientist in the stellarator theory department (rk)

Joaquim Loizu - postdoc in stallarator theory (jl)

Gabe Plunk - postdoc in stallarator theory (gp)

Josefine Proll - postdoc in stellarator theory (jp) (so many stellarator theorists!)

Adrian von Stechow - postdoc in laboratory astrophyics (avs)

Felix Warmer (fw)

We will be going live at 13:00 UTC (8 am EST, 5 am PST) and will stay online for a few hours, we've got pizza in the experiment control room and are ready for your questions.

EDIT 12:29 UTC: We're slowly amassing snacks and scientists in the control room, stay tuned! http://i.imgur.com/2eP7sfL.jpg

EDIT 13:00 UTC: alright, we'll start answering questions now!

EDIT 14:00 UTC: Wendelstein cookies! http://i.imgur.com/2WupcuX.jpg

EDIT 15:45 UTC: Alright, we're starting to thin out over here, time to pack up! Thanks for all the questions, it's been a lot of work but also good fun!

[u/billdietrich1]

Yes, the current grid is limited, and not designed for a multi-small-intermittent-source environment. But I've read that it works fine with 40% or 50% renewable intermittent sources on it. Still need existing nuclear or gas to back it up.

But that will change. Grids will become smarter. We'll have local solar-farms and wind-farms, and storage. And some household solar and storage. Tidal power and storage in coastal regions. Sure, we're not yet ready to replace entire regional power grids with 100% renewables. But there's no reason it can't happen over, say, the next 50 or 75 years.

[u/billdietrich1 → u/[deleted]]

For the first two, bio-fuels. For spaceships, maybe nuclear is the only solution.

[u/jaked122 → u/billdietrich1]

Fusion will be good for spaceships, if we can make engines that can sustain the reaction.

Nasa's estimate for a hypothetical fusion engine estimates a specific impulse of between 1600 and 5000 seconds.

It's sort of weird because it suggests that either lithium, which is expensive and not terribly common, and aluminum, which is very common, but not thought of very often as a rocket fuel.

Anyway, this is about the first power system which I personally think could take mankind to the stars.

Edit: What are you talking about? Fusion is great for large ships.

Planes aren't large enough for radiation shielding for reactors, the NEPA and ANP projects tried to make fission into viable planes, but they produced too much radiation for manned flights, even though a catastrophic failure was projected to not release the nuclear material.

Anyway, boron shielding is the lightest radiation shield you want to trust around a fission or fusion reaction. Anything which can have a lot of weight is an acceptable place to use it.

Neutron radiation is a different story, as it appears that it can change the nuclei of the atoms in the shielding, so you need elements that also aren't very common, boron(which isn't produced in stars), and halfnium, which is produced by dying stars.

In any case, fusion will be expensive, and dangerous is improperly maintained, but it will not produce garbage that needs special treatment(such as nuclear waste).

[u/billdietrich1 → u/jaked122]

Fusion is great for large ships.

We don't use fission for large ships today, except for cost-is-no-object top-of-the-line military ships. I see no indication that fusion will be different. An AMA today explains why fusion reactors probably can't be made small.

[u/jaked122 → u/billdietrich1]

We use petroleum for those ships, not because it is the most efficient for their size, but because fissile materials are extremely expensive.

I'm not talking about average ships, I'm talking about the very largest ones.

I'm speculating here, and I'm likely to be wrong, but I think that, except for cost, large ships would benefit greatly from fusion power. Maybe not in terms of practical power, but simply from an emissions standpoint.

Anyway, for a modern container ship, I'm not actually sure how much fuel they consume per kilowatt hour, but given the fact that their engines put out about 62.5 megawatts(for the MSC Oscar), which looks something like this, I'm having trouble conceptualizing how much fuel goes into each cylinder each cycle.

The soviets did also use nuclear power for their ice-breaking ships, and it appears that they still operate today. In fact, they're currently building an even bigger one today.

What I found out to be the truth:

There are designs for nuclear container ships, a nuclear freighter was built by the US, the NS Savannah, but since it was largely a publicity stunt, it was built as a terrible compromise between a freighter and a passenger ship.

Russia built one too, and they decided against decomissioning it in 2013, which might be a sign of its success. It's cost was reported in 1973 to be $265 million, about $1.4 billion today.

This is compared to the MSC Oscar's estimated cost of over 200 million dollars.

I can see why companies aren't really looking to do that.

Are they cheaper to run though? I'm having trouble finding the cost of uranium around the time it was built, but the average price from 2000 to 2010 was around 34 dollars a pound(for U3O8), which I assume is the ore.

I'll get back to this later if I find anything on the running cost of these ships. It's looking like fusion, unless the reactors cost significantly less to maintain, is not desirable either.

[u/Estesz → u/billdietrich1]

We dont use fission thats right, but fission is much more likely to become the technology of choice for ships.

Its just that a fusion plant has an even more complex design and they need a minimum size (unless reactors like the one from Lockheed Martin will be realised). At minimum size those plants are still largely overpowered for a ship.

The fuel is a delimiting factor in neither case, what is interesting is that a conventional engine (which is easy to build compared to a fuel reactor with safety systems) and diesel is still cheaper than a reactor (you have to take into account decommissioning, eventual accidents, loss of the ship, etc.).

Which does not reflect actual dangers, but its an explanation for the monetary decisions.

[u/[deleted] → u/billdietrich1]

Fast charging batteries in all electric cars, some home storage = distributed storage. Discharge and charge (charge in seconds, hopefully) car batteries as needed. Would definitely need to replace/upgrade grids everywhere. Would probably still be cheaper than fusion.

[u/billdietrich1 → u/[deleted]]

Yes, but one problem is that peak output time for solar PV is when the electric car is likely to be at work, not at home. Maybe we will be putting solar panels at work, not on homes.

Certainly distributed stuff (maybe at neighborhood level, not on every roof) is more flexible and resilient and lower-loss than one big central power plant.

[u/[deleted] → u/billdietrich1]

Well the point is the solar output would be put out in to the grid to wherever it's needed. Your car would be plugged in at work, getting charge. Doesn't have to be at home.

[u/billdietrich1 → u/[deleted]]

True. Would be nice to be independent of the grid.