I am well aware of how nuclear devices function (how small fission triggers initiate fusion reactions, clean bombs, fission-fusion-fission, the differences between U-238 and U-235 and Pu-239...etc.

i was simply questioning if a large conventional device could intiate a fusion reaction, but they question was really moot to begin with.

For initiating fusion, you need about 200,000,000 degrees Celsius, and about 10 million atmospheres. If it was that simple, we wouldnt have been trying to create a self-sustaining reaction for the last 40 years, it'd be done by now.
I'm not 100% sure on the numbers, but basically if you multiply them together they have to be greater than 5x 10 ^ 22 (I think). There is a number at which fusion becomes self-sustaining, we've yet to reach within 10% of it, but they are creating a new fusion plant soon (at the cost of, supposedly, $5 billion) which should be able to be self sustaining for a few seconds... From there it's a simple step into the first commerical plant

Originally posted by browha
For initiating fusion, you need about 200,000,000 degrees Celsius, and about 10 million atmospheres. If it was that simple, we wouldnt have been trying to create a self-sustaining reaction for the last 40 years, it'd be done by now.
I'm not 100% sure on the numbers, but basically if you multiply them together they have to be greater than 5x 10 ^ 22 (I think). There is a number at which fusion becomes self-sustaining, we've yet to reach within 10% of it, but they are creating a new fusion plant soon (at the cost of, supposedly, $5 billion) which should be able to be self sustaining for a few seconds... From there it's a simple step into the first commerical plant

This is not the only one problem with commercial nuclear fusion.
The next one is also how to isolate 200,000,000 degrees hot plasma from it's surroundings. No material is able to handle such temperatures. The energy isolation fields (EM or laser fields) will be necessary.

They've already done it in the Nuclear Fusion Reactor in the United Kingdom, it is no longer an issue

really? they managed to solve that prob here? hmm never heard about it hmm very interesting.

for a couple of milli seconds yes

i noticed a camera plane on that MOAB drop - maybe some better ones are going to surface soon

It never REALLY was a problem, just using very powerful electromagnets
what is the problem, however, is to create a fusion plant large enough to sustain the reaction.. They can initiate it fine, it's just that currently it doesnt generate enough power to be self-sustaining... When the $5 billion dollar one is complete, it will be nearly self-sustaining/completely self-sustaining, I'm kinda sketchy on the details atm not sure.
Still, the next step from there can ONLY be a self-sustaining fusion reactor!

Howdy all.

As a nuclear engineer, perhaps I can shed some light on this topic. browha was actually pretty close to the necessary criteria for self-sustaining fusion. There's three parameters we are concerned with: density, confinement (reaction) time, and temperature. The product of these three tells you whether or not self-sustaining fusion can occur. The actual criterion depends upon the plasma (deuterium, tritium, helium-3, etc), but at a temperature of 20 keV (~200 million Kelvin), density*time needs to be greater than 10e20 to 10e21 s/m^3.

I should point out that there's two ways to produce fusion that are being researched: magnetic confinement and inertial confinement. Magnetic confinement is the more common of the two, and several devices have been built which can nearly produce more power than is input. The newly proposed reactor, ITER (International Thermonuclear Experimental Reactor) is fully expected to produce power. The hopes for inertial confinement lie mainly in the National Ignition Facility (NIF) being constructed at Lawerence Livermore. It will use lasers to compress a fuel pellet to acheive the necessary parameters. However, these are methods to produce confined self-sustaining reaction. Weapons don't have nearly the same limits imposed on them, for obvious reasons.

You may be wondering, but what about weapons? They're kinda reluctant to teach us the principles of nuclear weapons (go figure), but I'll try my best. Does a large conventional explosion have the energy to produce fusion? Yes - but the issue is harnessing that energy. You would have to transfer a large fraction of the explosive energy to the fuel (probably deuterium or tritium), which would be difficult at least. You're best bet would be to create a shell of explosive around the fuel, and compress the fuel to create the density and temperature necessary. However, such a directed explosive is not easy to produce, and would most likely destroy itself before the compression wave reached the necessary magnitude. I have heard of people trying to design a conventional trigger, with little success. The implications of such a device would be huge. For one thing, it would be possible to create "clean" bombs of immense power - most of the fallout from a nuclear weapon is from the fission products, while the products of fusion reactions are nonradioactive or decay very quickly. A friend of mine who was theorizing on this topic with me put it this way - "Imagine soldiers being able to fire a 120-mm mortar that packs the punch of a 500-lb bomb." Perhaps in the future conventional explosives will be developed that can succeed in triggering a fusion reaction.

Hopefully I came close to answering the question somewhere in that dissertation on nuclear fusion.

Anybody heard something about cold-fusion? I read about it in some sci-fi books (don't laugh at me) but I don't know what exactly it is. I think the coldfusion occurs at much much lower temperatures than normal "hot" fusion and the reactors could be smaller etc. I don't know if it is just a science-fiction or no. So can me somebody explain it?

Thanks for the post I have studied fusion to some degree.
cold fusion has claimed to be achieved many times, but has never been replicated.
I dont really understand the theory behind it, but basically it's creating and collapsing bubbles to make several million degrees c in standard water solutions, supposed to be able to initiate fusion. I think this is how it is done in the Morgan Freeman film which eludes my name, that includes KEanu Reeves

Originally posted by browha
...basically it's creating and collapsing bubbles to make several million degrees c in standard water solutions, supposed to be able to initiate fusion.

What you're referring to is "bubble fusion", otherwise known as sonofusion. The theory behind this is that bubbles can be formed in an ammonium deuteride solution, and collapsed through cavitation. Theoretically these bubbles can collapse so fast that huge pressures and temperatures can be reached in the center, thus triggering fusion. This is just a different form of inertial confinement fusion, not to be confused with "cold fusion".

"Cold fusion" was first reported by researches at the University of Utah in 1989. They claim that that were able to fuse deuterium obtained by electrolysis of heavy water (D2O) with a Palladium cathode. Their claim was based upon the detection of gamma rays and neutrons. However, the neutron claim was later retracted, and while many researchers have tried to reproduce their experiment, even improve upon it, there has been little success. The general consensus in the scientific community is that "cold fusion" is junk science. I should point out that there is almost as much skepticism towards sonofusion as there is towards "cold fusion." However, Dr. Rusi Taleyarkhan, who first claimed to achieve sonofusion, currently has an experiment going on here at Purdue, and the rumor going around the department is that results look good. But that's just a rumor.

I think this is how it is done in the Morgan Freeman film which eludes my name, that includes KEanu Reeves

"Chain Reaction" Pretty crappy movie, imho. They claimed they were doing "cold fusion," but as far as I can tell they were just producing hydrogen - i.e. electrolysis. It was cool seeing 1/4 of Chicago getting annihalated, though.

nod it looked like electrolysis but then recombusting the product or something to produce energy.... which isnt possible
If only it were that easy