Sunday, May 11, 2008

Science of IRON MAN: Fusion


The coolest superhero movie in years, and one particuarly dear to those who work on spacesuits is IRON MAN! A protective suit that amplifies the wearer's strength dates to Heinlein's STARSHIP TROOPERS, and has inspired anime like BUBBLEGUM CRISIS. It is as natural outgrowth of spacesuit technology, and one such application will be discussed tomorrow. Today we'll focus on Iron Man's energy supply. What is that glowing thing in his chest?

Iron Man's power supply is a small version of the display reactor at Stark Industries. A similiar display appeared at the New York World's Fair of 1964. The Tokomak is a donut-shaped magnetic bottle for containing hot plasma. Controlled fusion has long held the promise of limitless energy, but requires temperatures and pressures similiar to the Sun's interior. Despite decades of work, controlled fusion remains as it was in 1964, just around the corner. Doctor Octopus in SPIDER MAN 2 was still working on fusion. Hopefully ITER or the National Ignition Facility in Livermore will finally make it practical.

Humans presumptuously think they understand the Sun, enough to reproduce it in a lab. Containing plasma at temperatures of millions of degrees is like holding smoke with rubber bands. As readers of this blog know, our Sun works by pulling the plasma inward. The Sun was ignited by a tiny Black Hole that drew gas toward it until temperatures and pressures allowed fusion to commence. The Black Hole is still there, quite at home in the Sun's hot centre.

Tony Stark is shown carefully making a ring of palladium. This material is key to "cold fusion" experiments. Could Stark have perfected cold fusion in a cave? His chest device combines the shape of a Tokomak with palladium rings. Though the initial hype about cold fusion was discredited, determined researchers are still working on it. Since such work is considered un-mainstream, we can sympathise and wish them luck.

Though some of us are fortunate to live off the grid, the search for energy is always on the world's mind. A lecture in 1908 about the future of energy would have been about coal and oil. In 1905 someone had written down E=mc^2, though the world had as yet taken little notice. By 1945 the world had built a nuclear reactor and an atomic bomb. What surprises could someone be cooking up in the dark of a cave? The energy of a Black Hole would make even nuclear fusion look crude.

UPDATE: Stark mentions in passing that his chest device produces 3 GJ/sec, or 3000 megawatts! That's enough watts to light 3 million homes, power not just the suit but the lights of Los Angeles too. An exaggeration?

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12 Comments:

Blogger nige said...

"The Tokomak is a donut-shaped magnetic bottle for containing hot plasma. Controlled fusion has long held the promise of limitless energy, but requires temperatures and pressures similiar to the Sun's interior. Despite decades of work, controlled fusion remains as it was in 1964, just around the corner."

Controlled nuclear fusion by magnetic confinement of hot plasma is a joke. Strong magnetic fields are never perfectly uniform and the pressure of plasma needed to cause deuterium and tritium nuclei to fuse is immense! So you always get instabilities develop.

The situation is similar to trying to use a low-density fluid to compress a higher-density fluid, in other words you get a form of Taylor instability develop.

The magnetic field causes the plasma to not be uniformly compressed, but to break up into jets where the magnetic field is slightly weaker. Because you can't make the magnetic field perfectly uniform, this is inevitable.

It's like squeezing an orange with your hands. You don't end up with a uniformly compressed orange. You end up with juice squirting into somebody's eye.

The radioactive waste from a controlled nuclear fusion reactor, if if could be made to work efficiently, would in practical terms be even worse than that from nuclear fission!

At least the 300 fission products decay, as a mixture, faster than the inverse of time. The fission product dose rate falls as about t^{-1.2} where t is time after fission. In any case, fission products have been proved to be safely confined with only a few feet migration over a time span of 1.7 billion years, as a result of the intense natural nuclear reactors in concentrated uranium ore seams at Oklo, in Gabon:

"Once the natural reactors burned themselves out, the highly radioactive waste they generated was held in place deep under Oklo by the granite, sandstone, and clays surrounding the reactors’ areas. Plutonium has moved less than 10 feet from where it was formed almost two billion years ago."

- http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml

But for fusion, you get the accumulation of relatively long lived iron-59, iron-55, cobalt-60, nickel-63, and many other nuclides which are caused by the capture in reactor materials of high energy neutrons from the fusion process. E.g., the fusion of tritium and deuterium releases 17.6 MeV, of which 14.1 MeV is carried by the neutron. This massive neutron energy is to be compared to the thermalized neutrons of 0.025 eV energy! As a result, whereas in fission you can reprocess the fuel rods to extract the radioactive waste without the whole reactor becoming dangerously radioactive, in fusion the whole reactor becomes almost uniformly contaminated by neutron capture in the structural elements! There is nothing you can do about this.

Controlled nuclear fusion has a lot in common with string theory in terms of over-hype, and failure. The most sensible way to use safe nuclear fusion energy is to further develop solar power and other ways to extract the energy of fusion being carried out in the sun's core.

12:06 AM  
Blogger Lobo7922 said...

Instead of a tokamak, I tought it was some kind of polywell:
http://en.wikipedia.org/wiki/Polywell
I was wondering, since you know a lot more phisycs than me, what is your opinion about the whole polywell thing? Do you think its possible?

2:25 AM  
Blogger mark said...

"great sky river" by greg benford features exoskeleton suits-- ever read that? wonderful sci-fi...

8:22 AM  
Blogger Matti Pitkanen said...

I think that cold fusion people have earned the public image of pseudoscientist for the brutal reason that hot fusion hegemony wants to preserve the funding. Of course, reductionistic theoreticians regard it as humiliating to even consider the possibility that things go badly wrong already at the level of nuclear physics.

There exists surprisingly precise data about selection rules involved. There is also evidence for cold nuclear reactions in living matter based on simple but ingenious experimentation. A further striking finding from year 2004 is that an astrophysical object at distance of 10 billion light years have essentially same abundances of heavy elements as solar system. Fusion in stellar interiors would predict much smaller abundances (factor of 1/10 if I remember correctly).

I have worked rather detailed models for cold fusion and cold nuclear reactions in living matter: large values of Planck constant and scaled up variant of weak interactions would be involved. The model allows a considerable part of heavier elements to be produced outside stellar interiors.

For references and details see this.

5:22 PM  
Blogger L. Riofrio said...

For nige: Given their rate of progress, you may be right again.

For lobo: The shape of the movie machine and its name suggested a Tokomak. Bussard was a smart man. Given the huge sums spent on mainstream fusion, his project deserves the small amount of funding needed to test it.

For mark: I've not read that one but such suits have become a staple of sci fi.

For matti: Your comments are most welcome. The data about heavy element abundances is very interesting! As you know, I am sympathetic to changing "constants."

7:30 PM  
Blogger Stephen said...

E=MC^2? About 10% of my power comes from it. Hardly ignored. Worked at the Fermi II nuke plant south of Detroit for a few months, nearly a decade ago. Fission, of course.

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Blogger Pandoras_Key said...

This seems like the right place to ask.

... What are the theories on flight propulsion. Energy, as well as mechanics?

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