Why Can't We Just Force A Sustained Fusion Reaction Via A Lot Of Mass Flow?

[Spacescifi]

People always say the heat is too much, when we have virtually unlimited mass to shed the waste heat.

We know how to create a fusion reaction, but trying to contain it with a magnetic field is like trying to band jello with a rubber band. It will slip out inevitably.

So I propose a solution that, while expensive and it might increase global warming by some degree, WON'T slip out the fusion plasma unless you desire it to.

Idea: Create the fusion reaction some way and sustain it.

If we don't know how to sustain it or have a way of doing so then that's the main problem. I thought we did.

I assumed holding the reaction was the problem because it melted everything.

Yet there should be a way to keep a fusion reaction chamber from melting on earth.

 

How? Regenerative rocket based cooling. Pump liquid helium or liquid hydrogen through the reaction chamber walls to keep them from melting.

Will probably need either a spherical or cylindral shaped reactor since either is better for even flow of pumped liquid to cool it.

Outside the fusion reactor building you would see rocket bluish plumes shooting up into the sky instead of steam plumes you see at nuclear plants, because more energy would be generated and thus more heat.

 

Can this be done or am I oversimplifying it? Because if I thought of this surely somebody would have come up with a reason not to.

 

I hope the answer is not liquid hydrogen and liquid helium are too expensive to burn constantly at a fusion plant. Because I don't think they are. We have more hydrogen than we could want.

As for money, we (the USA) already spend ridiculous amounts on matters arguably less important, so that argument does not hold either.

 

But if physics says it cannot be done, I can accept that.

Edited June 3 by Spacescifi

[Terwin]

While fusion reactions taking place at temperatures and pressures that melt or vaporize normal materials is a serious problem, another problem, just as large is that we need to keep the high temp and pressure inside the reaction.  If we pump out heat by cooling the walls, then the reaction gets too cold to continue.  Even just reaching out and touching the walls of the containment vessel means losing too much heat for fusion to continue.

If you have a better idea for focusing and containing heat at temperatures that melt structural materials, and without letting any of that heat escape, then that would be a big help, but just cooling thee walls does no good if you want to sustain the reaction.

 

Note: even Jupiter cannot sustain the heat and pressure needed for an ongoing fusion reaction, it is that hard.

Edited June 3 by Terwin

[Spacescifi]

15 minutes ago, Terwin said:

While fusion reactions taking place at temperatures and pressures that melt or vaporize normal materials is a serious problem, another problem, just as large is that we need to keep the high temp and pressure inside the reaction.  If we pump out heat by cooling the walls, then the reaction gets too cold to continue.  Even just reaching out and touching the walls of the containment vessel means losing too much heat for fusion to continue.

If you have a better idea for focusing and containing heat at temperatures that melt structural materials, and without letting any of that heat escape, then that would be a big help, but just cooling thee walls does no good if you want to sustain the reaction.

 

Note: even Jupiter cannot sustain the heat and pressure needed for an ongoing fusion reaction, it is that hard.

OK, I think part of my idea will be necessary to deal with the heat, but to focus and contain the heat we would need either reflectors or beams to focus it.

I guess this is difficult because it is essentially trying to make a stable system out of extreme hot and cold, when by nature one will attempt to overtake the other.

Maybe a bunch of masers would help to focus the heat (they penetrate well).

 

A more advanced version would be X-ray lasers causing a fusion reaction.

Come to think of it.... maybe total containment is not the way? Maybe we should not do it that way?

Could we not cause a fusion reaction and sustain it while letting some of it blow out as exhaust like a rocket? While a bunch of masers shoot downward into the rocket plume to keep the heat balanced for whatever is lost?

 

And so the exhaust is not totally wasted we could make it turn a turbine or something so we are not radiating the air with radioactive fusion exhaust.

 

What I am saying is this is hard but impossible it should not be.

Fusion literally seems to require going big or staying home.

Micro fusion reactors will probably always be fiction.

Another big problem is neutrons caused from fusion damage materials.

Ideally a fusion reactor would want low to zero neutrons, and that can be done with pure fusion designs that do not rely on fission as a trigger.

Edited June 3 by Spacescifi

[Terwin]

Using lots of input energy to maintain a fusion reaction seems to be a fairly reasonable activity:

https://www.itnonline.com/content/world-record-strongest-nuclear-fusion-reaction-steady-state-system-achieved-phoenix-and

Sounds like they have been using sustained fusion reactions as a neutron source for manufacturing medical materials since before 2019.

 

Seems like fusion itself is not hard, just self-sustaining fusion.

[darthgently]

59 minutes ago, Terwin said:

Using lots of input energy to maintain a fusion reaction seems to be a fairly reasonable activity:

https://www.itnonline.com/content/world-record-strongest-nuclear-fusion-reaction-steady-state-system-achieved-phoenix-and

Sounds like they have been using sustained fusion reactions as a neutron source for manufacturing medical materials since before 2019.

 

Seems like fusion itself is not hard, just self-sustaining fusion.

Or, technically, ppl have been using a  sustained fusion reaction since the dawn of agriculture at least

One could probably count drying jerky in hunter gatherer ages

[Spacescifi]

1 hour ago, Terwin said:

Using lots of input energy to maintain a fusion reaction seems to be a fairly reasonable activity:

https://www.itnonline.com/content/world-record-strongest-nuclear-fusion-reaction-steady-state-system-achieved-phoenix-and

Sounds like they have been using sustained fusion reactions as a neutron source for manufacturing medical materials since before 2019.

 

Seems like fusion itself is not hard, just self-sustaining fusion.

 

If we had ridiculously strong magnets (1000-5000 tesla) could that make containing and compressing fusion plasma in a vacuuum chamber easier?

Or does magnetic field strength not really matter and plasma would leak out anyway killing the fusion reaction?

I would a imagine a scifi fusion plant to be powered by a plasmoid within a vacuum chamber, suspended in space and compressed into fusion while being sustained by uber 5000 tesla magnets.

Meanwhile the chamber walls are cooled with reaction mass constantly (LH or liquid helium).

 

Or is fusion too much even for the master of magnetism lol?

https://www.deviantart.com/lordkai/art/Magneto-X-men-97-tribute-1043949214

 

Edited June 3 by Spacescifi

[kerbiloid]

The reaction mass is negligible, it can't cool anything but fingers.

1 000 MW = 10⁹ J/s = 10⁹/(4.2*10¹² ) = 2.4*10^-4 kt/s = 2.4*10^-4 / 80 = 3*10^-6 kg of D/DT / s = 3 mg of D/DT / s
As heat power : electric power = 3..4, it means 10 mg of burnt fusion fuel per second.

***

The ridiculously strong magnets need ridiculously high power, but it anyway will not make the fusion zone stable itself.

[K^2]

14 hours ago, Spacescifi said:

People always say the heat is too much, when we have virtually unlimited mass to shed the waste heat.

The problem with heat is keeping it in.

And while magnetic confinement helps a little, an object at "only" a few million Kelvin will be radiating a trillion times more energy than the surface of the Sun inch-for-square inch, and mostly in X-Ray. And you usually want to go a little hotter to get the reactions going. The thermal radiation energies involved start at a dental X-Ray and go up if you want to have a livelier reaction rate. At these frequencies, we only know how to reflect X-Ray at very shallow angles. To prevent energy losses, you need to send that heat back in or run the reaction so fast there is no time for reactants to cool. Since nothing can reflect the radiated heat back in, the only way to avoid losses over time is to have you reactor be really big. Id est, the Sun. Your other options is running the reaction really fast, either in a continuous beam in a toroidal reactor or in spikes using either ablative or magnetic compression. All three of these have to work with fairly rarified plasma to function, so getting high mass flow rates simply isn't an option.

There is a secret third option. Catalyzed fusion. Muons bring the barrier down enough that you can almost get away with room temperatures. Though, of course, a few thousand Kelvin won't hurt for a faster reaction. Trouble is that muons decay, and we haven't figured out how to make them efficiently. You solve that, and we'll have cheap, reliable (almost) cold fusion. You don't, and we're stuck compressing plasma really, really fast in large and expensive reactors.

[Spacescifi]

On 6/3/2024 at 10:19 PM, K^2 said:

The problem with heat is keeping it in.

And while magnetic confinement helps a little, an object at "only" a few million Kelvin will be radiating a trillion times more energy than the surface of the Sun inch-for-square inch, and mostly in X-Ray. And you usually want to go a little hotter to get the reactions going. The thermal radiation energies involved start at a dental X-Ray and go up if you want to have a livelier reaction rate. At these frequencies, we only know how to reflect X-Ray at very shallow angles. To prevent energy losses, you need to send that heat back in or run the reaction so fast there is no time for reactants to cool. Since nothing can reflect the radiated heat back in, the only way to avoid losses over time is to have you reactor be really big. Id est, the Sun. Your other options is running the reaction really fast, either in a continuous beam in a toroidal reactor or in spikes using either ablative or magnetic compression. All three of these have to work with fairly rarified plasma to function, so getting high mass flow rates simply isn't an option.

There is a secret third option. Catalyzed fusion. Muons bring the barrier down enough that you can almost get away with room temperatures. Though, of course, a few thousand Kelvin won't hurt for a faster reaction. Trouble is that muons decay, and we haven't figured out how to make them efficiently. You solve that, and we'll have cheap, reliable (almost) cold fusion. You don't, and we're stuck compressing plasma really, really fast in large and expensive reactors.

Wait... you are saying that if we make a way or material to reflect X-rays at ANY angle and at a high rate... THEN we could have sustained fusion reactions?

[Terwin]

20 minutes ago, Spacescifi said:

Wait... you are saying that if we make a way or material to reflect X-rays at ANY angle and at a high rate... THEN we could have sustained fusion reactions?

I am under the impression that x-rays tend to interact weakly unless you have a lot of mass/density, and that is not something deuterium is known for(having an atomic mass of 2).

This is why x-rays pass through flesh easily and can be more easily blocked by denser bone.

That being the case, you would need exceptionally high reflectivity.  If, for example, there is a 1% chance of an x-ray being caught by a deuterium atom each time it encounters the atom, and a 1% chance of encountering such an atom with each pass through the reaction chamber, then you would need the average reflection to be better than 99.99% or else the majority of your x-rays will escape before imparting any energy into your fuel mass.

Also, conduction is a very potent means of transferring heat, and even with all your perfect x-ray mirrors, you lose most of your accumulated heat should any of the fuel you are heating come in contact with your containment vessel. 

Then there is the need to extract work from your closed fusion system, so you need a controlled way to extract accumulated heat from your reaction chamber without stalling the reaction.

So perfect x-ray mirrors are not enough, you also need perfect insulation to keep the heat contained in the fuel, which is made harder because you would then need to extract the generated heat from any helium you made so as to pass it on to the incoming deuterium which needs to be hot enough to continue the reaction.

[K^2]

38 minutes ago, Spacescifi said:

Wait... you are saying that if we make a way or material to reflect X-rays at ANY angle and at a high rate... THEN we could have sustained fusion reactions?

Hypothetically speaking, if you were able to make a mirror that reflects any wavelength with near enough to 100% efficiency, you could build a tiny star that sits comfortably in an enclosure that fits in your pocket and can power your car, yes.

The reason you can't has to do with how electrons in matter interact with electromagnetic radiation at such short wavelengths. I can see some kind of hypothetical superconducting degenerate matter being able to do that without flatly breaking known physics, but the kinds of pressures that involves already require being in a core of a star, so that seems entirely moot for any practical purpose.

[domenprevc]

 While using regenerative rocket-based cooling with liquid helium or hydrogen sounds promising, there are several challenges. First, maintaining a stable fusion reaction is incredibly difficult, requiring precise control over temperature and magnetic fields. Cooling the reaction chamber effectively is another hurdle, as the immense heat generated could overwhelm even advanced cooling systems. Additionally, the cost and logistics of constantly supplying liquid hydrogen or helium are significant concerns. While your idea is innovative, the physics and practical limitations make it challenging to implement.

[NFUN]

1 hour ago, domenprevc said:

 While using regenerative rocket-based cooling with liquid helium or hydrogen sounds promising, there are several challenges. First, maintaining a stable fusion reaction is incredibly difficult, requiring precise control over temperature and magnetic fields. Cooling the reaction chamber effectively is another hurdle, as the immense heat generated could overwhelm even advanced cooling systems. Additionally, the cost and logistics of constantly supplying liquid hydrogen or helium are significant concerns. While your idea is innovative, the physics and practical limitations make it challenging to implement.

https://youtube.com/clip/UgkxBCY7U53ZMPz_5GG79Dzg2RcMYZkWVoVh?si=U7SVCH09dTmG7uAS