Thermonuclear Bomb-in-a-Bottle

[Shubedobedubopbopbedo]

The thermonuclear bomb is the only man-made machine capable of producing excess energy from nuclear fusion. To describe the mechanism briefly:

Stage 1 - chemical explosive - compresses the fissionable radioactive material to critical density so that it starts producing enough neutrons to sustain a chain of fission reactions.

Stage 2 - fission explosive - minimum amount of fissionable material undergoing a chain reaction to detonate explosively and compresses the fusionable material to sufficient temperature & density to undergo sustained fusion reactions.

Stage 3 - fusion explosive - fuel pellet transmutes into heavier elements, releasing the fusion energy of the atomic nuclei. Energy released from fusion reactions dwarfs that of the fission and chemical explosives. EMP and blast effects result.


I'm no expert, but it seems to me that Stage 2 fission reaction puts a lower limit on the explosive energy of the bomb. Due to this, bombs cannot be scaled down and used to produce electricity. The explosion can't be contained because it's too big, and would obliterate any reasonable containment vessel. If a different mechanism can be devised that replaces the Stage 2 fission explosive, then the whole process could be scaled down.

The National Ignition facility uses lasers to replace Stages 1 & 2, vaporizing the outer surface of a fuel pellet, and producing the imposive shockwaves needed for fusion to occur.

Other mechanisms that mimic the bomb include General Fusion's approach using synchronized and isotropically symmetric pneumatic rams impacting on a the walls of a spherical container to produce implosive shockwaves in an internal liquid-gas-plasma medium. Fusion reactions heat the medium, which is continuously pumped in from one side, and out the other side to remove heat and extract energy.

Does anyone know of other approaches to fusion that mimic the stages of a bomb?

[D Tibbets]

The fuion plasma is not pumped out to enerate energy. The high speed fusion ions, along with X-rays, neutrons,etc fly out radially and hit the first wall, producing heat. The only ones that I might concider as 'pumping' out the fusion products to generate electricity would be perhaps P-B11 fueled Dense Plasma Focus, RFC (?), and Polywell- there the charged fusion ions are directed( ~pumped) directionally to produce electricity through direct conversion. There would be realitively few neutrons hitting/ sputtering and heating the walls. There would still need to be robust cooling needed to extract the heating from x-rays and gamma rays. All others depend on the first wall heating, power is then derived from a coolant fluid pumped through the wall and powering a steam tubine or other heat engine.
The spent fusion products (after losing their kinetic energy to direct conversion grids or by hitting the wall) need to be efficiently pumped out of the machine to prevent poisoning the reaction or exceeding vacuum limits, but this has nothing to do with power generation (there could be some intermediate arangements with aneutronic fuels- like P-B11 or less efficiently with D-He3.

Laser, Z-pinch, DPF, and some versions of FRC are pulsed machines.
Also, consider machines that require ignition (like a bomb). These include Tokamaks, laser, Z- pinch, DPF (?), etc. Polywells and FRC (?) do not have ignition as part of their fuel cycle. They are power amplifiers as opposed to bombs.

Dan Tibbets

[93143]

All others depend on the first wall heating, power is then derived from a coolant fluid pumped through the wall and powering a steam tubine or other heat engine.

He's talking about General Fusion. You're both wrong. Also, you didn't read his post carefully enough...

General Fusion uses a liquid lead/lithium mixture as the "first wall". So your description is wrong.

It isn't a liquid/gas/plasma mixture; the liquid and plasma are distinct, and the only part pumped, as such, through the reactor is the liquid metal (though presumably fusion ash gets embedded/dissolved and pumped out with it, and perhaps the "gas" part comes in with the tritium breeding). So his description is wrong.

But it certainly solves the "first wall problem" handily - unless the lead/lithium mixture turns out to contaminate the fusion plasma too much even in pulse mode...

[kunkmiester]

Modern bombs work a bit differently. The plutonium surrounds the fusionable core, and everything pretty much happens at once--as the plutonium fissions, it pushes inward as well as outward, providing the compression. I'd imagine a second stage is possible, but really big bombs are inefficient anyway. They get to "burning" rather clean as I understand.

There was a proposal to use salt caverns--setting off a bomb melts a sizable amount of the salt, which you then run water through to boil and get steam from. As the salt cools, you drop another bomb down, and do it again. With the right size bomb and setup, you don't have trouble with a lot of stuff getting to the surface, but you'd still need plutonium for the bombs, and that limits how efficient it can be.

[TallDave]

I also read the same article kunk describes.

It seemed plausible, sort of an underground Orion, but would presumably have been similarly toxic politically.

[Skipjack]

I really like what the General Fusion guys are trying. To the layman- me, the concept is really simple. The physics seem to be sound too. Their biggest challenges are engineering challenges: Synchronize the pistons and make the whole thing work for more than a few times before falling apart (because of the stresses). It is really cool for that reason. I also like the Steam Punk feel to it
I can envision the engineers operating it all wearing suits with wests and little gold pocket watches

[djolds1]

Stage 1 - chemical explosive

Stage 2 - fission explosive

Stage 3 - fusion explosive

Stage 4 - second fission layer

And you can keep on stacking stages. IIRC there is no theoretical limit to how many fission-fusion stages you can daisy-chain in a Teller-Ulam device.

I'm no expert, but it seems to me that Stage 2 fission reaction puts a lower limit on the explosive energy of the bomb.

Per Ted Taylor quoted in "Project Orion," the lower end for the minimum possible critical mass is "significantly less than a kilogram."

bombs cannot be scaled down and used to produce electricity. The explosion can't be contained because it's too big, and would obliterate any reasonable containment vessel.

Note that while Orion focused on External Pulsed Propulsion, there was a parallel train of thought that focused on Internal Pulsed Propulsion. AKA Helios. Performance was far less promising than for Orion, but containing kilotonne scale nuclear blasts (Helios was independent of Taylor's critical mass calculations) in relatively small chambers is doable.

http://up-ship.com/blog/?p=5353

Does anyone know of other approaches to fusion that mimic the stages of a bomb?

Google and search the ARXIV archive for "Pure Fusion Explosives," "Fourth Generation Nuclear Weapons," and variations thereof. Bombs without the fissile primary.

[Shubedobedubopbopbedo]

I'm amazed and dismayed by the crude designs that keep popping up wrt nuclear pulse propulsion. It would be child's play for an engineer to do better. I can do better. Right off the top of my head I can see a better design. Probably would outperform Orion and Helios by a 1000-fold. This is what happens when international treaties and politics get in the way and stifle innovation for 40 years. Just like anything else that 40-years old, it's 40-years obsolete. Child's play. That's all I have to say.

[93143]

Is that "all you have to say" because you're afraid to run your idea past a real rocket scientist?

[kunkmiester]

It ain't obsolete until there's either something on paper, or in testing.

[djolds1]

I'm amazed and dismayed by the crude designs that keep popping up wrt nuclear pulse propulsion. It would be child's play for an engineer to do better. I can do better. Right off the top of my head I can see a better design. Probably would outperform Orion and Helios by a 1000-fold.

So give. What is it?

This is what happens when international treaties and politics get in the way and stifle innovation for 40 years. Just like anything else that 40-years old, it's 40-years obsolete. Child's play. That's all I have to say.

Orion and Helios were conceived by first rate minds. IIRC the basic Helios design (Internal Pulsed Propulsion) was conceived of by Teller c. 1946 or so. Execution has been handicapped by politics, not concept. Tho I agree about giving the Precautionary Principle any footing.

[Shubedobedubopbopbedo]

Well, for one thing, the use of a massive pusher plate is just plain dumb. The impact of the blast would require shock absorbers, which in turn would require a cooling system and huge radiators. Not only would a large fraction of the energy of the blast be wasted by not impinging on the pusher plate, a large fraction of the energy impinging on the plate would be wasted as well, damped and converted into heat.

I can think of a design, rather commonly found in many mechanical systems in aircraft and elsewhere, that can bypass this inefficiency, reduce the weight manyfold, and increase the spacecraft-averaged specific impulse of each detonation. It gets rid of most of the mass of the pusher plate, all of the mass of the shock absorbers and radiators. I'm not going into details though. I've completed the mathmatical derivations and the mechanism is sound. But I want to develop the details on my own.

[Betruger]

Cue vaporware comment.

[Shubedobedubopbopbedo]

Well, it's all vaporware until its hardware.

The fact is, the 1965 designs were poorly done. They ignored the requirement for radiators, they tried to pass their designs off as safe for human spaceflight, even safe for use in the atmosphere. The drawings are artists impressions of artists impressions - complete garbage.

Like I said, anything done 45 years ago is obsolete. Their designs were based on bad mission concepts and wishful thinking. On the flip-side, they did the best with what they had. But now its 2010+ and its time to move on.

I'm seeing very similar problems with NASA. They can't seem to justify human spaceflight. They want to re-capture the Apollo era, plant another flag on the moon, maybe on Mars. What then? Where do we send humans next? How far do they think humans can go in space? Have they done the math? I doubt it. How will this benefit ordinary people? Will it expand our understanding of the universe we live in? No, it won't. But it'll spend huge gigabucks of taxpayers money to benefit two or three lucky astronauts, no doubt picked from the same group all astronauts are picked from (military fighter pilots). They would spend gigabucks of taxpayers money, on the backs of hardworking citizens, to give extraordinary opportunity to a few who are already successful, and command salaries many times larger than the people they are taking from. They do this so they can stick a flag in the ground on the moon and get their picture taken, smiling no doubt, and make public speeches boasting of their accomplishments upon return. Then they will spend the next 45 years trying to maintain gigabucks of funding for the thing that gives them status: human spaceflight.

They aren't heroes to me. The extraordinary resources squandered just to keep a few astronauts alive in space (doing virtually nothing but floating around, sleeping, and using their zero-g exercise bike) could be spent on so many other things, even if it were just unmanned missions, rovers to more difficult moon landings (Europa, Titan, etc), giant space interferometer telescopes searching for life in other star systems, a working planetary defence system to detect comets and asteroids headed our way - and a way to respond. These are things that would contribute knowledge of the sort that ordinary people can understand, it would expand the cognitive grasp that ordinary people have on the universe they live in. These are things that are of lasting utility to society as a whole. Astronauts don't do any of those things.

Sure, the space shuttle is impressive. I'd like to see a launch in person, not just on TV. Big machines are always impressive. But to carry on doing the same darn thing as if there aren't better ideas out there is just .... what's the word? .... ignorance? complacency? Any number of adjectives apply. I don't think NASA is doing very well though, so I'm not going to push it. I think they are circling the drain, for all the reasons I've given above and more. In the future, I may look to the ESA, and maybe some of the smaller international space agencies, to choose a better direction, better missions, and better return on investment. NASA and all the space advocacy organizations have lost my support.

[kunkmiester]

First, there were a few ideas for a shaped nuclear charge. The simplest was to wrap most of the bomb in materials that would reflect the blast and radiation in one direction. A light material, like foam, would provide an "endcap" which would absorb this energy and provide mass to hit the pusher plate--especially important in space, where there's no atmosphere to provide such.

Second, as I understand it the pulsed nature also helps with cooling, limiting the energy delivered to the pusher plate in that form, and providing time between pulses to dissipate heat.

A fusion-only bomb would open up orion, as well as a dozen other ideas. SOMEONE isn't going to care enough about politics and eco-freaks and all that enough to stop them from doing it. It'll probably be someone like China or India taking my idea of launching ready-built space colonies or something.