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How Can Science and Physics Contain Fusion Ignition?


Spacescifi

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Fusion ignition is a self sustaining fusion reaction because the heat is so high that any cooling that does happen due to radiation or loss of mass will not stop the fusion reaction. This is really the key to the dream of endless energy, since fusion will give you electrical power forever.... until the fusion stops, which will happen if the heat lowers somehow or  if magnetic holding fields loosen.

Right now we are not even close to that, the closest we get is by detonating nukes (if the explosion could be contained rather than expanding into the air without destroying everything).

 

So the actual question is... how do you scientifically contain a nuclear blast in atmosphere?

We cannot do it, but if we could what scientific means could we use?

Magnetic fields with some super high strength, more than anything we have done to date. You would need a magnetic field at least as strong as the energy released in a nuclear blast if not greater. I do not know how many Tesla that is, but I know it's a lot!

 

So I wager to bet that if we ever figure out a way to actually contain a self sustaining fusion reaction, we will also have a way to shield against nuclear blast waves in atmosphere.

In vacuum it would be even easier to do, since any blast waves would be much smaller.

Hello scifi shields! Won't shield against the radiation though, so a lot of mass will be required to soak up thermal energy without melting the entire spaceship.

In other words... only truly massive spaceships shoud have a selfsustaining fusion reaction onboard. Small spacecraft would overheat too fast.

What do you think? How can mankind use science and physics to contain a self sustaining  nuclear fusion reaction (AKA nuclear blast, closest we have reached)?

 

EDIT: Fun fact, if containment of self sustaining fusion fails the result will be bad. Why?

It's a contained nuclear blast wave... what do you think will happen when it is released from captivity?

 

Edited by Spacescifi
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Magnetic fields. Very, very strong fields.

And as for nuclear blast shielding... no. A resounding NO.

Sustained fusion for any practical applications is far below power levels of even smallest nuclear warhead.

Even 'dinky' Hiroshima-class bomb was able to set a city on fire with thermal shock (vaporizing unlucky objects not made of steel and concrete near the ground zero). We don't have anything that could contain heat and light generated by nuclear explosion - short of burying it deep enough under the ground (or water).

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23 minutes ago, Scotius said:

Magnetic fields. Very, very strong fields.

And as for nuclear blast shielding... no. A resounding NO.

Sustained fusion for any practical applications is far below power levels of even smallest nuclear warhead.

Even 'dinky' Hiroshima-class bomb was able to set a city on fire with thermal shock (vaporizing unlucky objects not made of steel and concrete near the ground zero). We don't have anything that could contain heat and light generated by nuclear explosion - short of burying it deep enough under the ground (or water).

 

I know. But such fusion schemes so far are energy hogs that produce less energy than the energy spent on them.

Really... fusion seems not like it's worth it if the energy produced is low. I would rather engineer more efficient fission reactors.

Fusion and nuclear lightbulbs are similar, onky fusion is a lot harder due to higher temperatures and leaky magnetic fields.

Trying to hold plasma with a magnetic field is like trying to hold water in a bucket with holes. So far anyway.

Edited by Spacescifi
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I'm not sure calling a fusion reaction for purposes of electrical power generation a "nuclear blast" is accurate. While it is caused by nuclear forces, we are deliberately trying to not create the "blast" part. You're kinda insinuating our current technology in fusion is detonating nukes and scratching our heads. As a layperson, I can easily look at the sun and say that a fusion reaction can be contained with 93 million miles of vacuum, a magnetic field and some ozone. Now someone smarter than me will say "let's make the vacuum smaller and the magnetic field stronger to make it more practical" and we are getting to the ballpark of where we are. Which isn't detonating thermonuclear devices.

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6 hours ago, Meecrob said:

I'm not sure calling a fusion reaction for purposes of electrical power generation a "nuclear blast" is accurate. While it is caused by nuclear forces, we are deliberately trying to not create the "blast" part. You're kinda insinuating our current technology in fusion is detonating nukes and scratching our heads. As a layperson, I can easily look at the sun and say that a fusion reaction can be contained with 93 million miles of vacuum, a magnetic field and some ozone. Now someone smarter than me will say "let's make the vacuum smaller and the magnetic field stronger to make it more practical" and we are getting to the ballpark of where we are. Which isn't detonating thermonuclear devices.

 

Meh. 

The fusion stuff we have done is not self sustaining nor does it pump out enough energy to make it worth mass production. And it will be that way so long we have leaky magnetic fields and power gained<power spent is fusion.

 

From wikpedia:

Fusion ignition is the point at which a nuclear fusion reaction becomes self-sustaining. This occurs when the energy being given off by the fusion reactions heats the fuel mass more rapidly than various loss mechanisms cool it. At this point, the external energy needed to heat the fuel to fusion temperatures is no longer needed.[1] As the rate of fusion varies with temperature, the point of ignition for any given machine is typically expressed as a temperature.

Ignition should not be confused with breakeven, a similar concept that compares the total energy being given off. The key difference is that breakeven ignores losses to the surroundings, which do not contribute to heating the fuel, and thus are not able to make the reaction self-sustaining. Breakeven is an important goal in the fusion energy field, but ignition is required for a practical energy producing design. In nature, stars reach ignition at temperatures similar to that of the Sun, around 15 million Kelvin (27 million degrees F). Stars are so large that the fusion products will almost always interact with the plasma before it can be lost to the environment at the outside of the star. In comparison, man-made reactors are far less dense and much smaller, allowing the fusion products to easily escape the fuel. To offset this, much higher rates of fusion are required, and thus much higher temperatures; most man-made fusion reactors are designed to work at temperatures around 100 million degrees, or higher. To date, no man-made reactor has reached breakeven, let alone ignition. Ignition has however been achieved in the cores of detonating thermonuclear weapons.

Edited by Spacescifi
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12 hours ago, Spacescifi said:

It's a contained nuclear blast wave... what do you think will happen when it is released from captivity?

It'll create a 40 foot humanoid figure of pure burning plasma rage which bellows 'They thought they could contain me? FOOLS - I SHALL DESTROY THEM ALL... and their little dogs too'

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4 minutes ago, KSK said:

It'll create a 40 foot humanoid figure of pure burning plasma rage which bellows 'They thought they could contain me? FOOLS - I SHALL DESTROY THEM ALL... and their little dogs too'

 

Amusing. 

I would have added, "Especially the cute ones. They make me sick!"

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9 hours ago, Scotius said:

We don't have anything that could contain heat and light generated by nuclear explosion - short of burying it deep enough under the ground (or water).

And now about the atmospheric Orion, when it stays still and starts blasting...

12 hours ago, Spacescifi said:

It's a contained nuclear blast wave...

It's a contained pressure. Unless it's a standing wave.

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Why not ask the professionals?

http://www.psfc.mit.edu/sparc/faq

"

Why are the magnets so important?

To make fusion work, the fuel must be heated to temperatures above 100 million degrees. Matter in that state is called a plasma – where the particles have net electric charge. To be kept hot, this plasma must be very well insulated from ordinary matter. Fusion devices use magnetic fields to provide the thermal insulation that is required. The stronger the magnetic field, the stronger the confining force on the charged particles in the plasma, the better the insulation, which enables a much smaller, better performing fusion device"

Edited by Rakaydos
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On 12/15/2019 at 8:33 AM, Spacescifi said:

if we ever figure out a way to actually contain a self sustaining fusion reaction, we will also have a way to shield against nuclear blast waves in atmosphere

...

The fusion stuff we have done is not self sustaining nor does it pump out enough energy to make it worth mass production. And it will be that way so long we have leaky magnetic fields and power gained<power spent is fusion. 

No. First, ignition is not the same as self sustaining. Wikipedia is normally pretty good, but it sometimes has flaws. Ignition is when the self heating of the reaction is enough to propagate the reaction. Somewhere between breakeven and ignition can be self-sustaining if other systems capture some of the energy given off and re-inject it into the reaction.

"Fusion stuff" that we've done includes H bombs, which absolutely do achieve ignition and go far above breakeven.

ICF fusion would have nothing to do with magnetic fields. It would replace a fission trigger with a laser pulse. As a result, the fusion target can be a much smaller pellet... so its not like containing an H-bomb. Its a matter of scale though, fusing tiny pellets doesn't liberate a lot of energy. Also, for ICF to produce excess power, the pellet really needs to achieve ignition to have a high energy release/total energy ratio (needed because of inefficiency capturing/recapturing the input).

Fission happens spontaneously, and requires no energy input. High rates of fission tend to destroy the reactor and cause a "fizzle" (making A bombs hard to design to get a lot of fission before the device disassembles itself), properly designed, they have negative reaction coefficients, and stabilize at a given power output.

Fusion chain reactions are a much different matter. Magnetic confinement wouldn't behave like a bomb. If the plasma expands, density decreases, reaction rate decreases. Weakening the magnetic fields slows the reaction.

ICF achieving target ignition would behave like mini-bombs, but the "bomb" would be a fixed power. Increasing the target size would cause it to fail to ignite, unless laser power and focal point was also increased (non linear though), so someone couldn't put in a bigger pellet and make the reactor blow itself up. The only way I can see that happening is changing the pellet composition. Replace a P-B pellet (assuming a reactor could ignite that target), with a D-T pellet, and something interesting might happen. 

Sci fi shows that show fusion reactors blowing up like H bombs are just unrealistic.Its power output wouldn't go above what its designed to do.

Quote

Fusion and nuclear lightbulbs are similar, only fusion is a lot harder due to higher temperatures and leaky magnetic fields.

Huh, they are nothing alike... what are you talking about?

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