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Old 12-13-2019, 10:38 PM   #1
Agemegos
 
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Default [Ultra-Tech] HEDM explosive triggers for clean fusion

A little while ago I asked about using the high energy-density materials in TL9 chemical rocket fuels to make ultra-tech explosives with high REF: http://forums.sjgames.com/showthread.php?t=162196

An SF story that I read recently suggested using "meta-stable materials" in place of a fission trigger to initiate fusion for the pulse unit of an orion drive. It made a point of "meta-stable materials" being more of a proliferation threat than the plutonium required for conventionally-triggered fusion explosives.

Does all that bear examination?

Are HEDM explosives in the ballpark for initiating fusion without fission? I had a bit of an impression that neutrons from the primary, moderated by the channel filler, were important and not just the heat and pressure.

Is it plausible that clandestine production of HEDM might be significantly harder to detect and monitor than that of fissibles?

If you want to run a technothriller with an HEDM mcguffin, ought the HEDM to be being used to initiate fusion, or is it Dan Brown enough all by itself?
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Old 12-13-2019, 10:44 PM   #2
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Default Re: [Ultra-Tech] HEDM explosive triggers for clean fusion

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Originally Posted by Agemegos View Post
An SF story that I read recently suggested using "meta-stable materials" in place of a fission trigger to initiate fusion for the pulse unit of an orion drive. It made a point of "meta-stable materials" being more of a proliferation threat than the plutonium required for conventionally-triggered fusion explosives.
They're probably talking about excited nuclear isomers. Which has occasional burst of people being interested and then proves to not actually work (like Hf-178m2 excitement in the oughts).
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Old 12-13-2019, 11:18 PM   #3
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Default Re: [Ultra-Tech] HEDM explosive triggers for clean fusion

Well, it depends on the fusion process. DT fusion needs a lot more energy density than the 216 MJ/kg that HEDMs can provide (DD needs a little less, but it produces much less energy). The key factor with HEDMs is that they compress the fuel, which increase density greatly, though you would need a compression of around 10,000x to get fusion at a high enough rate to make it worthwhile.

The hafnium trigger is an interesting possibility, but hydrogen is really awesomely bad at absorbing gamma rays, so it would never create net energy in a pellet small enough to be useful. There are a few other strategies, some thermonuclear weapons use lithium fusion, and they might get hot enough for a clean burn, though the HEDM would fuse with the lithium (not really a major issue). For example, 1 kg of metallic hydrogen surrounding 1 gram of lithium-7 might be sufficient for a 96 metric ton clean fusion explosion. That would be one heck of a firecracker.
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Old 12-13-2019, 11:30 PM   #4
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Default Re: [Ultra-Tech] HEDM explosive triggers for clean fusion

There's also antimatter-catalyzed microfission, though I think that uses conventional fissionables, just in smaller quantities.
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Old 12-14-2019, 02:59 AM   #5
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Default Re: [Ultra-Tech] HEDM explosive triggers for clean fusion

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They're probably talking about excited nuclear isomers. Which has occasional burst of people being interested and then proves to not actually work (like Hf-178m2 excitement in the oughts).
Very likely. The story was published in 2011.

I'm just interested in knowing whether it's something that I ought to be aware of in a setting that posits Spaceships' "HEDM chemical fuel" and the HEDX that I plan to base on it and use to replace DEXAX.
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Old 12-14-2019, 03:20 AM   #6
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Default Re: [Ultra-Tech] HEDM explosive triggers for clean fusion

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Very likely. The story was published in 2011.

I'm just interested in knowing whether it's something that I ought to be aware of in a setting that posits Spaceships' "HEDM chemical fuel" and the HEDX that I plan to base on it and use to replace DEXAX.
I strongly doubt that any chemical explosive is sufficient to trigger fusion.
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Old 12-14-2019, 04:04 AM   #7
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Default Re: [Ultra-Tech] HEDM explosive triggers for clean fusion

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I strongly doubt that any chemical explosive is sufficient to trigger fusion.
That's pretty much what I figured, though as Fred Brackin pointed out most of the HEDM candidates (such as metallic hydrogen) aren't really chemical.
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Old 12-14-2019, 07:23 AM   #8
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Default Re: [Ultra-Tech] HEDM explosive triggers for clean fusion

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I strongly doubt that any chemical explosive is sufficient to trigger fusion.
Depends somewhat on how much fusion, and how big your reactor is. After all something as weak as gravity manages in stars, at admittedly pathetic rates. But no, you are not going to build a portable fusion bomb with a chemical explosive trigger. Metallic hydrogen or metastable helium, well maybe, but they're still well short of the energy range I'd expect. You really need to concentrate a lot of energy into a small *volume*, and chemical explosives start out big for the contained energy and get bigger as they explode. A chemically pumped laser trigger system that reacts so fast it explodes is maybe more plausible, because you can more easily optically focus light into something smaller than just "inside the explosive". Similarly you might use an explosive to generate an electrical surge that that you compress in a system of conductors into a smaller volume magnetically or electrostatically. But you are not going to manage it without something more complicated than the pile of explosives with a fusion fuel in the middle model we use for fission triggered bombs.
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Old 12-14-2019, 10:10 AM   #9
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Default Re: [Ultra-Tech] HEDM explosive triggers for clean fusion

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. But you are not going to manage it without something more complicated than the pile of explosives with a fusion fuel in the middle model we use for fission triggered bombs.
Yeah, the important thing to remember IMHO is that neutrons trigger fission and heat triggers fusion.

This becomes one of the (possibly few) legitimate uses of the word "synergy" when you begin with a fission reaction (started with a natural neutron source) that releases 94% of its' energy in the form of heavy ions that easily make heat.

Then you use that heat to trigger a fusion reaction that puts out 80% of its' energy to make more neutrons which can be used to ingite another fission stage and so on and so on.

To get rid of that unwanted fission you need to generate nuclear heat without a fission reaction and chemical explosions are not on the right order of magnitude to do that.

I have grown more skeptical of "pure" fusion explosions over time. You're talking about shrinking the National Ignition Facility into a portable form while increasing its' output. Even if you do it the result is likely to be less efficient than a fission solution. In our most efficinent multi-stage bombs a greater percentage of the energy is produced by the fission stages. In the old tests the built a multi-stage bomb that got more enrgy from fsuin than fission but it was less efficient than the reverse.

The relative densities of uranium and hydrogen might give you a clue why that was. The ratio is extreme in uranium's favor and for almost all weapon's uses the amount of "kaboom" per unit of volume is what you're most interested in. That'll determine how powerful a device you can fit in a missile silo.

I'm sure you could trigger your pure fusion explosion with enough antimatter and it would even be more powerful than the antimatter alone. However, you can trigger fission with antimatter too and it takes a lot less.
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Old 12-17-2019, 10:25 AM   #10
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Default Re: [Ultra-Tech] HEDM explosive triggers for clean fusion

AFAIK one or two people has put out papers touching on the idea of HEDM 'super explosives' for use with fusion. One of which was the 4th-generation-nuclear weapons guy Andre Gsponer:

https://arxiv.org/pdf/physics/0510071.pdf

https://cryptome.org/2014/06/wmd-4th-gen-quest.pdf

the 2nd one is the one with metallic hydrogen, and nuclear isomers, and others like antimatter I think.

Here's a powerpoint presentation that might be useful too: http://web.archive.org/web/201306101...generation.pdf

The other person I know of on these issues is Friedwardt Winterberg who is the MIMS guy but also turns up if you google 'super-explosives' with his name:

https://www.nextbigfuture.com/2009/0...xplosives.html

https://arxiv.org/ftp/arxiv/papers/0802/0802.3408.pdf

Again this all touches what others already said. And it all seems very optimistic and theoretical. But its sci-fi and if you don't mind fudging details it gives a veneer of plausibility because its possible.

Two other points of interest: One, I know of a paper from 1998 that discusses HE (in some manner) for pure explosions: http://scienceandglobalsecurity.org/...sgs07jones.pdf

Given that one of the ideas has the 'pure fusion' device being a glorified neutron bomb with a YtW hardly better than conventional explosive it doesn't seem as optimistic.

The other 'interesting' detail is that the Army for awhile has been pursuing something they call 'disruptive energetics' which is meant to bridge that gap between conventional and nuclear and their believed implications for military capabilities: https://ndiastorage.blob.core.usgovc...zakJenkins.pdf

Which sounds promising but remember Hafnium bombs also came from that sort of thing and the US military is known (esp through DARPA) to play with all manner of crazy ideas. It dovetails with the Gsponer/Winterberg stuff in 'it may be possible so its useful' optimism though, so I thought it worth mentioning.
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