Why can't we simply use an atomic bomb to get the fusion working?

why can not simply explode an atomic bomb inside a recint with plasma and hydrogen so the temperature and power generated will make the

fusion working

Welcome to PF.

What's a "recint"?

an enclosure like a dome or a torus

How is it going to contain the fission bomb explosion? Are you wanting to use a setup sumilar to a fusion bomb that is triggered by a fission explosion? That's a lot of energy to try to contain...

i mean a fision bomb to generate a fusion like in the hydrogen bomb :) the fision bomb would be the 'trigger' to start the fusion process

C'mon, think a bit. There is NO way to contain such a reaction. There is NO way to keep fusion going. There is NO way to do something controlled with the energy.

Rfael said:

why can not simply explode an atomic bomb inside a recint with plasma and hydrogen so the temperature and power generated will make the

fusion working

Because an atomic bomb would blow the reactor apart. And the city it's in.

Rfael said:

i mean a fision bomb to generate a fusion like in the hydrogen bomb :) the fision bomb would be the 'trigger' to start the fusion process

Starting the process isn't very difficult (relatively speaking), it is keeping it going that is the problem
There are several experimental reactors (e.g.. JET) that are able to get a fusion process started; it just doesn't last very long.

How about using tiny amounts of anti-matter? Would that be more realistic?

EDIT: [I'm ofcourse a layman if that wasn't obvious from the question.]

sbrothy said:

How about using tiny amounts of anti-matter? Would that be more realistic?

EDIT: [I'm ofcourse a layman if that wasn't obvious from the question.]

It is not that anti-matter can be found somewhere and can be used. Its production requires energy. And as in every process that converts one form of energy into another form of energy, there will be a loss of energy.

The problem is not to achieve a single fusion event, the problem is to keep it going while being contained. Containment is necessary to be able to use the produced energy in some subsequent process. Otherwise, we would only have reinvented the H-bomb.

fresh_42 said:

It is not that anti-matter can be found somewhere and can be used. Its production requires energy. And as in every process that converts one form of energy into another form of energy, there will be a loss of energy.

The problem is not to achieve a single fusion event, the problem is to keep it going while being contained. Containment is necessary to be able to use the produced energy in some subsequent process. Otherwise, we would only have reinvented the H-bomb.

I'm aware there are no AM-mines anyhere (Avatar nothwithstanding), but, just perhaps, the AM amount needed would be small enough to make the process worthwhile? And I meant just to get the process running.

But yes, smarter people than me ofcourse already considered this. nvm.

Rfael said:

i mean a fision bomb to generate a fusion like in the hydrogen bomb

A reactor is not a bomb. You don't want to release a year or so's worth of energy all at once; you want to release it over a year. A bomb won't do that.

It seems like people think that all we need is a good 'starter fluid' to get the whole pile of wood started, and then we'll be able to get the energy we need out of it.

This is not the case. Fusion is easy to start. High-school students have made fusion reactors. You can do it with some basic high-voltage and high-vacuum equipment for a few hundred to a few thousand dollars. But these reactors take far more energy to run than you could ever get out of them. Probably 1000x more or so.

What we really need is a way to generate and sustain a reaction that produces more energy than it takes to run it. That means getting the plasma density and temperature correct, minimizing ion and electron losses, preventing various plasma instabilities, and creating a cost efficient way to gather and convert the generated energy into electrical power. Every single one of these issues is hard. Really, really hard. People have devoted their entire careers to solving these issues and we still haven't been able to do it after 65+ years.

Contrast this with fission. The very first fission reactor already produced more power than it took to run it, because it doesn't take any power to do so. You just get enough fissile material and shove it together and it naturally starts a chain reaction that can be relatively easily controlled. It is so easy to start and sustain fission that the vast majority of a nuclear power plant's safety and control features are there to STOP the reaction!

The reason fission is so easy is because the nuclei in the elements we use for fission are already unstable and will easily split apart when hit with a neutron, releasing more neutrons when they do so. Not so for fusion. The nuclei we use in fusion do not want to fuse together. They will avoid it unless we slam them together at extremely high speeds and even then they still don't fuse most of the time. What is needed is an environment where the nuclei can repeatedly collide with each other at high speeds. This requires both high temperatures and high densities, which requires using magnetic fields to contain them, which then creates a multitude of problems that must be solved in the form of leakages and instabilities.

All in all, a very, very challenging problem to tackle, but one that we've made steady progress on.

It is perhaps worth pointing out that plasma temperatures and pressures similar to the sun's core won't cut it. Sure you get fusion, but the sun uses less than a billionth of its fuel every year. A giant power plant that produces 1 watt is unhelpful.

To be commercially viable you need to do a billion times better.

In fact, one can - today - make a commercial fusion power plant. You get a bunch of tiny hydrogen bombs. You find an underground salt deposit. Set off the bomb, melt the salt, use geothermal to extract the energy, et Voila!

Why hasn't this happened?

1. It's stupid.
2. It's expensive.
3. It's inefficient.
4. It makes a big radioactive mess.
5. Making and shipping a bunch of small nuclear bombs - what could possibly go wrong with that?
6. Did I mention it's stupid?

Just because you can doesn't mean you should.

We’ve all missed the obvious solution: build a star! What could be easier…..

Vanadium 50 said:

It is perhaps worth pointing out that plasma temperatures and pressures similar to the sun's core won't cut it. Sure you get fusion, but the sun uses less than a billionth of its fuel every year. A giant power plant that produces 1 watt is unhelpful.

To be commercially viable you need to do a billion times better.

The Sun's fusion has many interesting characteristics. Such as, the core only produces 276 W/m^3, which is about the same as a compost heap! The fusion in the Sun is very slow, which is nice because it afforded life the opportunity to evolve. The key limiting step there is the creation of deuterium from hydrogen (creating neutrons, basically). All fusion reactors on Earth start from deuterium or tritium, neatly avoiding this difficult step.
The fundamental feasibility of fusion power is doubtful. In addition to all the problems mentioned above, there is the problem of thermal radiation. To make fusion happen, we need to heat a blob of plasma to over 15M degrees. That plasma is going to emit a huge amount of blackbody radiation - remember, that goes as T^4. So it's a challenge to keep the heat in. In the Sun, this is accomplished by having the core surrounded by the rest of the star. We can't do that on earth.
But why are we trying to build a fusion reactor? We have one nearby - our Sun - and it's free! Solar power is fusion power, with the distinction that it actually works.

FinBurger said:

So it's a challenge to keep the heat in.

Actually, the goal of a nuclear reactor (fission or fusion) is to produce heat in order to produce mechanical energy to drive an electrical generator to produce electricity for whatever purpose deemed necessary to one's economic condition, or making stuff, transporting stuff, buying stuff, or entertainment.

The challenge in fusion is to achieve a stable plamsa and steady-state (well-controlled) plasma density and thermal flux out of the reactor. Another challenge is the mitigation of degradation of the magnetic confinement system and structural components, or at least improve the economics.

I certainly use sunlight during winter to heat the house to the extent possible (i.e., sunny days). It obviously doesn't work when there is no sun, or when the sun is mostly obscured by clouds.

We have a 9.75 kW solar system on the roof, but we still have to pay to be connected to the local grid.