Skunk Works Reveals Compact Fusion Reactor Details • Hacker News Board

Re: Skunk Works Reveals Compact Fusion Reactor Details

#221

Post by Zikes » Wed, Oct 15, 2014, 6:59 PM UTC

guelo wrote: post #210

nabla9 wrote: post #164

I'm not seeing any top physicists working in this program (McGuire is not one). I would be willing to bet 1000 EUR that their math and modeling does not add up, or they have skipped some details. Problem with fusion research like this is that the closer you get self sustainment or energy generation, the harder it gets and problems pile up. This project looks like many other similar projects that have gone bust. They…

If you have to periodically throw away your reactor and buy a new one because of neutron damage that would be a positive thing for a company like Lockheed.

Maintenance costs alone would be astronomically lucrative.

Re: Skunk Works Reveals Compact Fusion Reactor Details

#222

Post by jfoutz » Wed, Oct 15, 2014, 7:00 PM UTC

rayiner wrote: post #213

jsmthrowaway wrote: post #194

Earlier quoted context omitted.

It's always a safe bet that the top Hacker News comment will always be "won't work, it's too hard." It's like sitting around for a year trying to sell a project at my current employer, with everybody and their lead telling you "that'll never work," then you implement in a weekend and those same people start nitpicking what you've come up with. (What happened to it'll never work? "Well, your CSS isn't great.") Honestl…

That's hardly ever true. In my experience, Hacker News is full of people from the software field; folks whose professions are often unconstrained by physics,[1] and who have a generally optimistic "this can happen" mentality. That's why everyone here believes we'll have fully self-driving cars in 5-6 years. In the rest of the engineering world, the answer to any question is: it'll be harder than you think it'll be (p…

> Did you know that coal plants, which still make up the majority of U.S. energy production, are only about twice as efficient today than they were a century ago?

Wasn't most of the effort put into making them MUCH MUCH cleaner? I mean, the https://en.wikipedia.org/wiki/Cuyahoga_River doesn't catch on fire anymore, and the amount of https://en.wikipedia.org/wiki/Acid_rain seems pretty tolerable compared to the early 80's

Re: Skunk Works Reveals Compact Fusion Reactor Details

#223

Post by krapp » Wed, Oct 15, 2014, 7:00 PM UTC

javajosh wrote: post #218

macinjosh wrote: post #211

Earlier quoted context omitted.

It is also a safe bet that the response to the original comment's response will be some guy saying how being hopeful about something is complete nonsense. It's turtles all the way down. Guess we should just give up on Internet commenting. /s

Interestingly, the heat for this pattern is always taken by the last comment, for some strange reason. Maybe it's the communities way of saying "Duh, we know this happens, and the way we stop conversations from going down the meta-toilet is to not have them." Although I would say it's more fair to downvote every comment that fits the pattern, to the root, rather than just the latter ones.

>Although I would say it's more fair to downvote every comment that fits the pattern, to the root, rather than just the latter ones.

That's a good way to lose your comment-voting privileges - I just noticed my ability to vote on comments disappeared at some point.

Re: Skunk Works Reveals Compact Fusion Reactor Details

#224

Post by anigbrowl » Wed, Oct 15, 2014, 7:04 PM UTC

On a tangent, is there any fundamental reason that reactors are always built to drive turbines rather thermocouples - do they simply not scale up to the amount of heat a typical reactor puts out, or what?

Re: Skunk Works Reveals Compact Fusion Reactor Details

#225

Post by Anjin » Wed, Oct 15, 2014, 7:05 PM UTC

al2o3cr wrote: post #197

charonn0 wrote: post #175

Earlier quoted context omitted.

> the plasma leaks out of the ends of the magnetic containment According to this link[1] posted by another commenter, they create a "axisymmetric mirror by positioning zones of high magnetic field near each end of the vessel so that they reflect a significant fraction of plasma particles escaping along the axis of the CFR." [1]: http://aviationweek.com/technology/skunk-works-reveals-compa...

When you're dealing with a plasma at 20 million kelvin, the leftovers from that "significant fraction" that don't get reflected can really ruin your day... LLNL scientists almost tested a similar device (see 'MFTF') but the project was cancelled in 1986 before it was turned on.

It is possible though that though earlier attempts failed because the computational resources and the plasma dynamics modeling available at the time were not sufficient to design such a reactor.

I would guess that we have a much better understanding of plasma physics and faaaaar greater ability to model it now - that could lead to designs that can mitigate previously discovered issues with the concept.

Re: Skunk Works Reveals Compact Fusion Reactor Details

#226

Post by waterlesscloud » Wed, Oct 15, 2014, 7:05 PM UTC

rayiner wrote: post #213

jsmthrowaway wrote: post #194

Earlier quoted context omitted.

It's always a safe bet that the top Hacker News comment will always be "won't work, it's too hard." It's like sitting around for a year trying to sell a project at my current employer, with everybody and their lead telling you "that'll never work," then you implement in a weekend and those same people start nitpicking what you've come up with. (What happened to it'll never work? "Well, your CSS isn't great.") Honestl…

That's hardly ever true. In my experience, Hacker News is full of people from the software field; folks whose professions are often unconstrained by physics,[1] and who have a generally optimistic "this can happen" mentality. That's why everyone here believes we'll have fully self-driving cars in 5-6 years. In the rest of the engineering world, the answer to any question is: it'll be harder than you think it'll be (p…

Did you know computer chips are infinitely more efficient than they were a century ago?

They too are a product of applying new discoveries and then engineering around the constraints of physics.

Things change. Progress is made.

Re: Skunk Works Reveals Compact Fusion Reactor Details

#227

Post by nabla9 » Wed, Oct 15, 2014, 7:06 PM UTC

tonyplee wrote: post #185

nabla9 wrote: post #164

I'm not seeing any top physicists working in this program (McGuire is not one). I would be willing to bet 1000 EUR that their math and modeling does not add up, or they have skipped some details. Problem with fusion research like this is that the closer you get self sustainment or energy generation, the harder it gets and problems pile up. This project looks like many other similar projects that have gone bust. They…

How much dangerous are the neutrons from such device? Similar to radiation, worst? Time sell any oil company stocks, mutual fund holding?

>How much dangerous are the neutrons from such device?

Fusion neutron (14 MeV) from fusion reactor is exactly as energetic as fusion neutron emitted by a neutron bomb and causes equal damage (just distributed over longer time). They have 10x as much energy as fission neutrons and travel at speed of 52,000 km/s (17.3% of the speed of light). Neutron capture before they hit and damage magnets, electronics or wear out materials is important part of the fusion reactor design.

Re: Skunk Works Reveals Compact Fusion Reactor Details

#228

Post by toomuchtodo » Wed, Oct 15, 2014, 7:13 PM UTC

rayiner wrote: post #213

jsmthrowaway wrote: post #194

Earlier quoted context omitted.

It's always a safe bet that the top Hacker News comment will always be "won't work, it's too hard." It's like sitting around for a year trying to sell a project at my current employer, with everybody and their lead telling you "that'll never work," then you implement in a weekend and those same people start nitpicking what you've come up with. (What happened to it'll never work? "Well, your CSS isn't great.") Honestl…

That's hardly ever true. In my experience, Hacker News is full of people from the software field; folks whose professions are often unconstrained by physics,[1] and who have a generally optimistic "this can happen" mentality. That's why everyone here believes we'll have fully self-driving cars in 5-6 years. In the rest of the engineering world, the answer to any question is: it'll be harder than you think it'll be (p…

> Did you know that coal plants, which still make up the majority of U.S. energy production, are only about twice as efficient today than they were a century ago?

Did you know that wind and solar are already at grid parity in over half the world? And that in many large first-world countries (Germany, Australia) the price of energy goes negative during daylight hours because of the amount of energy produced by renewables?

Re: Skunk Works Reveals Compact Fusion Reactor Details

#229

Post by FiatLuxDave » Wed, Oct 15, 2014, 7:17 PM UTC

adamzerner wrote: post #87

I don't know much about fusion. It seems that the breakthrough they're talking about is that reactors are ~10x smaller. Why is this a big deal? Square footage is plentiful. I thought the problems are safety and how much energy it could produce.

One big difference is the smaller the device, the quicker and cheaper it is to iterate. If it takes 15 years and $X billion to build and test your device, then progress gets measured on a per-lifetime instead of per-year basis. If your device can be built in a year and for $X millions instead, the testing and debugging can be done much faster. For a software dev comparison, think waterfall versus agile.

Re: Skunk Works Reveals Compact Fusion Reactor Details

#230

Post by chisophugis » Wed, Oct 15, 2014, 7:17 PM UTC

danbruc wrote: post #184

ufmace wrote: post #161

Earlier quoted context omitted.

That's peak power, though. Basically no street car is designed to be able to produce peak power for more than a minute or two at a time, and probably very few can do it for more than a few seconds. I'm pretty sure that car doesn't have the cooling capacity to cool itself at full power like this plant would have to.

You can drive your average care at peak power for an hour without problems. The problem with the Veyron is that at top speed the tires will wear off in 15 minutes and you will run out of fuel after online 12 minutes but I think it is not really limited by its cooling capacity - at 400 km/h a LOT of air passes through its 10 radiators.

Ballpark calculation:

400km/h ~ 100m/s

air intake cross section ~ 1m^2

==> ~ 100m^3/s of air going through radiator

density of air ~ 1kg/m^3

==> ~ 100kg/s of air going through radiator

specific heat of air ~ 1kJ/(kg * degC)

==> 100kJ/(s * degC) == 100kW/degC

temperature difference between air entering and leaving the radiator ~ 10degC

==> 1MW

So handling 2.5MW waste heat doesn't seem out of the question from this analysis.

As another ballpark "upper bound" analysis, consider that copper is one of the most thermally conductive materials, with thermal conductivity ~ 400 Wm/(m^2 degC), let's round that up to 1kWm/(m^2degC).

Let's assume that there is a thermal conducting surface of 1m^2 (i.e. the surfaces of the pipes that interface with the radiators). Let's assume that the copper is 1mm thick (= 1m/1000). Let's see what temperature difference would be needed to transfer 1MW of heat across:

1MW == 1kWm/(m^2degC) * 1m^2 * (1000/1m) * deltaT degC

==> deltaT ~ 1 degC

which again doesn't seem out of the question.

As another ballpark "upper bound", the convective heat transfer coefficient for forced air is ~ 100W/(m^2degC), which means that assuming that the radiator fins are 100 degC above the air temperature, in order for the fins to transfer 1MW of power to the air, you would need an area of

1MW == 100W/(m^2degC) * 100 degC * area m^2

==> area ~ 100m^2 of surface area in the radiator, which doesn't seem unreasonable (a radiator 1m^2 area * 10cm deep, made up of thin plates spaced 1mm apart has this total surface area).

So they Veyron dissipating ~ 1MW in waste heat at 400km/h doesn't fail any of these basic sanity tests.

More complicated though is the interaction between the stages considered here. For example, how do we interface our 1m^2 of copper with our 100m^2 of radiator? Making the radiator fins thin lets us pack more surface area into the same volume, but also makes it difficult to keep the "edges" of the fins at a sufficiently high temperature so that they pull their weight transferring heat to the air: since the "copper tubing" has significantly less surface area, it only contacts (and thus transfers heat to) the radiator fins "sparsely".