How might a realistic antimatter reactor work?

[Dave]

This is a terrible idea, and pardon me for my ignorance, but what if you skipped the wall and injected the anti-matter (very small amounts of antimatter) into the water itself? Then you wouldn't have to replace the metal plate you were using, just the water you annihilated.

Granted, Wikipedia tells me you get 90 TJ of energy per gram of annihilation, but if you inject really, really small amounts at the bottom of a tank of water, you could use the resulting heat / steam directly off the top. Plus, if you paint the tank walls matte black, you could recapture the light energy as heat, using water either inside or outside the tank.

[Covenant]

What you'd probably do is fire a beam of antimatter into the center of a block of a dense substance, like Tungsten, which will absorb the radiation and heat up. This heat will boil surrounding water and power a turbine. Simple as that. Safe, effective, and very basic.

[Starglider]

The energy comes out as high-energy (~0.9 GeV) gamma radiation (and neutrinos, which escape harmlessly). You need something like a foot of lead to absorb that kind of radiation reliably. The water idea would require a fairly big tank and some way of injecting the antiparticles into the center, if you want to absorb most of the gamma with the water instead of the shielding.

perhaps a way around this would be to inject a cloud of ions in with the reaction. These ions would absorb the photons from the reaction and heat up.

This won't work. A diffuse cloud of ions will not absorb a significant amount of hard gamma radiation.

[Count Dooku]

What you'd probably do is fire a beam of antimatter into the center of a block of a dense substance, like Tungsten, which will absorb the radiation and heat up. This heat will boil surrounding water and power a turbine. Simple as that. Safe, effective, and very basic.

Tungsten isn't very dense. Not compared to lead, anyway

[Count Dooku]

What you'd probably do is fire a beam of antimatter into the center of a block of a dense substance, like Tungsten, which will absorb the radiation and heat up. This heat will boil surrounding water and power a turbine. Simple as that. Safe, effective, and very basic.

Tungsten isn't very dense. Not compared to lead, anyway [b/]

BTW, don't listen to that guy. He obviously didn't look up the density of the two before he posted. Your lack of foresight is probably what got you killed, Dooku.

[Darth Wong]

Assume that the antimatter is created elsewhere. How might a reactor to harness the energy released from the matter/antimatter reaction work, and what would the maintenance costs and safety concerns include?

That depends on just how fantastic your base technology is supposed to be. Is it hard-science realistic, or Star Trek style nonsense?

My first idea for it was to have a system slowly feeding the fuel into a chamber where it reacts, heating the wall of the chamber. On the other side, some constantly water runs past it, absorbing the heat to run a turbine giving electricity and to keep the walls from melting.

That's similar to the existing concept for a tokomak fusion reactor, and it would carry all of the same difficulties, greatly increased by the danger and difficulty of storing and pumping antimatter.

It was suggested to me that magnetic fields could be used to keep the eat from getting to the walls entirely. I argued that magnets don't affect light (which would be main product of an antimatter reaction), but perhaps a way around this would be to inject a cloud of ions in with the reaction. These ions would absorb the photons from the reaction and heat up. The magnetic field could then control them and the forces upon it might be used to harness the electricity from the reaction.

Are you talking about real magnetic fields here, or the absurd Star Trek type of magnetic fields, which act like invisible steel pressure vessels? If you're talking about real magnetic fields, this idea is completely preposterous; you cannot maintain the kind of density you are obviously thinking of. If you are thinking of Star Trek "magnetic fields", then yeah, go ahead and knock yourself out. The more convoluted, the better. It sounds more "sophisticated" and "futuristic".

This seems like it would be cheaper to maintain than my first idea, but with all those ions in there with the reaction, maintaining and controlling the input of fuel might become harder, thus I would think it is less safe than the simple steam turbine idea.

Am I right so far? What else might work?

The real problem with shooting antimatter at anything is that a sufficiently large reacting mass will create way too much energy, which will cause all kinds of problems. You need to find a way to make the reaction as diffuse as possible, ie- spread it out over a large area.

If you're talking about generating power, there is a certain temperature range you want for any given working fluid. If it's too hot, then it becomes extremely difficult to process and can damage your piping and pumping equipment as well as turbines. If it's too cold, then your thermodynamic efficiency drops into the toilet.

Ideas for imaginary sci-fi M/AM reactors:

1) Huge numbers of particle accelerators firing anti-electrons at steam piping. The steam pipe is made out of low-density material to reduce the likelihood of particle interactions, and the particles are literally fired right through the walls of the pipe (at sufficiently high velocities, the probability of a collision are quite low, particularly if the wall is fairly thin). The pipe is sized so that the statistical probabilities favour a collision with the extreme high-pressure steam inside (say, 90% probability of hitting the steam, 10% probability of hitting something else). Of course, this means that the system is limited to 90% efficiency at best, and there will be a tremendous amount of waste heat, not to mention the fact that the piping and surrounding structure will run very hot.

2) On the storage side, I always thought that a fun idea would be to have the antimatter stored as some mundane material, like water. But it's stored in ... wait for this ... an anti-iron tank. In other words, the tank is made out of antimatter iron, so it can very safely store antimatter. And because it's iron, it's ferromagnetic, which means it is relatively easy to manipulate with magnets. It might even have a built-in system for releasing the antimatter, also entirely made out of antimatter and powered by electromagnetic induction from the surrounding containment system, which is made from ordinary matter but which is separated from the anti-iron tank. The anti-iron tank might even have antimatter permanent magnets on it, to make it even easier to safely store it. Of course, because of the extreme difficulty of fabricating this equipment, the antimatter storage equipment is the single most expensive part of the entire ship.

PS. As far as I know, the anti-iron storage tank idea is mine. I don't recall ever seeing it anywhere else, although if it has been used elsewhere, feel free to correct me.

[Kuroneko]

It's an absolutely brilliant idea for sci-fi. Suggestions of storing ferromagnetic antimatter fuel are quite common--there was even a US patent regarding this, I think--but I've never seen a larger antimatter container proposed before.

[Gil Hamilton]

The anti-iron tank seems like a really cool idea, though casting that thing would be a hell of a bear to do, as you basically would have to have a whole slew of anti-matter foundry equipment.

However, if we are chugging out anti-iron, and the anti-whatever you are alloying it with, you can make the stuff pure, without any sort of smelting. With that sort of hypertech, I suppose we could handwave a casting process for anti-matter.

[Shroom Man 777]

It would be cool if this sci-fi scenario would involve buying anti-iron storage tanks from anti-matter aliens from an anti-matter parallel dimension... for outrageous fees!

The situation would be reversed for them, and we'd be selling them iron storage tanks for outrageous fees as well!

[Revy]

What about non-neutral plasma? Suppose your handwaved manufacturing plant can produce two specific types of plasma to serve as fuel; one that is positively charged and another that is negatively charged. You hook the two fuel tanks up to your reactor, feed the two kinds of plasma together, and use the energy from the resultant anhilation.

The big problem seems to be gamma rays, but apparently NASA is experimenting with using positrons as an alternative to antiprotons. According to an article I read (Here), they say that positron anhilation produces gamma rays with 400 times less energy. Which would seem to make for a less powerful but at least safer and more manageable power source. It has advantages over nuclear reactors as well because there is no residual radiation left over once the fuel is expended, so you aren't left with radioactive waste.

As another thought, if you could find some way to create a time dilation effect, might that not make the whole thing much easier? The problem with M/AM is that it gives off pottentially huge amounts of energy in a short space of time, and the only difference between power generation and an all-out explosion is the timing involved in the energy release. By creating a large or dense M/AM reaction that would ordinarily blow you sky high, might a time dilation field not slow that reaction down to safe levels, allowing you to collect the energy released over a longer period of time instead of all at once? If so, you could even control the energy output by adjusting the level of time dilation (for example, increasing the flow of time would release more energy, and vice versa).

[Darth Wong]

What about non-neutral plasma? Suppose your handwaved manufacturing plant can produce two specific types of plasma to serve as fuel; one that is positively charged and another that is negatively charged. You hook the two fuel tanks up to your reactor, feed the two kinds of plasma together, and use the energy from the resultant anhilation.

You can't store plasma in tanks. It will instantly cool down and become ordinary gas. Also, plasma is bulk neutral, because it is composed of positive and negative ions. You can't make positively charged or negatively charged plasma.

The big problem seems to be gamma rays, but apparently NASA is experimenting with using positrons as an alternative to antiprotons. According to an article I read (Here), they say that positron anhilation produces gamma rays with 400 times less energy. Which would seem to make for a less powerful but at least safer and more manageable power source. It has advantages over nuclear reactors as well because there is no residual radiation left over once the fuel is expended, so you aren't left with radioactive waste.

Positron/electron annihilation produces just as much energy per unit mass.

As another thought, if you could find some way to create a time dilation effect, might that not make the whole thing much easier? The problem with M/AM is that it gives off pottentially huge amounts of energy in a short space of time, and the only difference between power generation and an all-out explosion is the timing involved in the energy release. By creating a large or dense M/AM reaction that would ordinarily blow you sky high, might a time dilation field not slow that reaction down to safe levels, allowing you to collect the energy released over a longer period of time instead of all at once? If so, you could even control the energy output by adjusting the level of time dilation (for example, increasing the flow of time would release more energy, and vice versa).

Frankly, "time dilation field" is about as realistic as "magic spell of slowing".

[Revy]

You can't store plasma in tanks. It will instantly cool down and become ordinary gas.

I was generalising. By 'tanks' I meant whatever storage device is actually used to store plasma in real life. I don't know what that actually is, but I assume there is such a thing, despire my lack of appropriate terminology naming.

Also, plasma is bulk neutral, because it is composed of positive and negative ions. You can't make positively charged or negatively charged plasma.

I knew that plasma is usually neutral, however I keep hearing about 'nonneutral plasma' and when I looked it up there were mentions of instances of plasma containing more of one charge than another, and, more rarely, entirely one charge. Besides, if I google non neutral plasma I get the names of entire research institutes and projects for it, so I assume there actually is such a thing.

Positron/electron annihilation produces just as much energy per unit mass.

So was that article talking out of it's ass then? It could be, it's just that it's on NASA's webpage so I figured they were telling the truth, but being ignorant of science I couldn't say myself. If it is wrong then their entire proposal sounds like a dead end then.

Frankly, "time dilation field" is about as realistic as "magic spell of slowing".

Time dilation does exist though. Granted I cannot forsee how to make an artificial field that slows time down however and wherever you want, but it was just a thought.

As perhaps a more realistic alternative, reducing the temperature of something slows it down doesn't it? When you get to near-absaloute zero matter and energy practically stop moving altogether. Could you not then use an extremely low-temperature reaction chamber to counteract the extreme energy release from a M/AM reaction? Very low temperatures would slow a reaction down, possibly helping to safely regulate it.

[Darth Wong]

You can't store plasma in tanks. It will instantly cool down and become ordinary gas.

I was generalising. By 'tanks' I meant whatever storage device is actually used to store plasma in real life. I don't know what that actually is, but I assume there is such a thing, despire my lack of appropriate terminology naming.

You don't understand. You can't store plasma like a normal gas. It will cool down and become ordinary gas. You have to make plasma on-site, by heating it up.

Also, plasma is bulk neutral, because it is composed of positive and negative ions. You can't make positively charged or negatively charged plasma.

I knew that plasma is usually neutral, however I keep hearing about 'nonneutral plasma' and when I looked it up there were mentions of instances of plasma containing more of one charge than another, and, more rarely, entirely one charge. Besides, if I google non neutral plasma I get the names of entire research institutes and projects for it, so I assume there actually is such a thing.

It's possible to make a plasma more or less negatively charged, or to use an electron gun to fire electrons at something, but in the context of your thread, where you're talking about storing it in contact with other materials, it will immediately correct itself. And the more of a charge it has, the more violently it will resist any kind of storage.

Positron/electron annihilation produces just as much energy per unit mass.

So was that article talking out of it's ass then? It could be, it's just that it's on NASA's webpage so I figured they were telling the truth, but being ignorant of science I couldn't say myself. If it is wrong then their entire proposal sounds like a dead end then.

It's possible you don't understand what the page was really saying.

Frankly, "time dilation field" is about as realistic as "magic spell of slowing".

Time dilation does exist though. Granted I cannot forsee how to make an artificial field that slows time down however and wherever you want, but it was just a thought.

So? Aging exists too, but that doesn't mean you can make aging or de-aging fields.

As perhaps a more realistic alternative, reducing the temperature of something slows it down doesn't it? When you get to near-absaloute zero matter and energy practically stop moving altogether. Could you not then use an extremely low-temperature reaction chamber to counteract the extreme energy release from a M/AM reaction? Very low temperatures would slow a reaction down, possibly helping to safely regulate it.

Here's an exercise: I will just say "no" and you will do some research to find out why this idea would never ever work.

[Darth Wong]

It's an absolutely brilliant idea for sci-fi. Suggestions of storing ferromagnetic antimatter fuel are quite common--there was even a US patent regarding this, I think--but I've never seen a larger antimatter container proposed before.

Thanks. It's the sort of thing that only a gearhead like me would think of

Of course, the tank would be more difficult to fabricate than no tank, but if they can create and manipulate ferrous antimatter, then this seems like an obvious next step, at least to me. And the "back end" of technology for most sci-fi series is usually more impressive than the front-end anyway, like the vast spaceborne matter/antimatter production plants that the Star Trek Federation and Klingons must have.

However, if we are chugging out anti-iron, and the anti-whatever you are alloying it with, you can make the stuff pure, without any sort of smelting. With that sort of hypertech, I suppose we could handwave a casting process for anti-matter.

If you have accelerators which can fire the ferrous antimatter atoms in a particular direction, you could, in theory, build up a tank atom by atom, provided the impact velocity is not too great. Another method would be to fabricate a chunk of anti-iron and then use lasers to remove excess material until you get the shape you want. Of course, this would take a very long time and yes, the resulting piece of equipment would be really expensive, but that was part of the premise anyway. The bonus is that it allows you to use many kinds of antimatter fuel which are normally impractical for storage, and to pump them far more easily.

[Revy]

So what you're saying is that you cannot store plasma because if it cools down then it will become ordinary gas. But then wouldn't that mean all you need to store it is enough heat to keep the gas a plasma? I mean if the only thing stopping you from keeping it in a warehouse somewhere is temperature, well what's the problem? I suppose the actual heat required is simply too great to maintain over any length of time, but can't you use materials that have little heat conductivity to reduce the rate of the plasma cooling?

As to the article, I'll quote the relevant bit;

Previous antimatter-powered spaceship designs employed antiprotons, which produce high-energy gamma rays when they annihilate. The new design will use positrons, which make gamma rays with about 400 times less energy.

The context is that scientists were wary of using antiproton reactions because of dangerous levels of gamma radiation being released, and that they are looking at using positrons instead because, as the quoted bit says, a positron anhilation releases less energy intensive gamma rays, which, given the context, pressumably equates to a safer form of fuel than antiprotons.

So? Aging exists too, but that doesn't mean you can make aging or de-aging fields.

Well to be fair, aging is a physical change, whilst time dilation is not. Also, you only have to look to the time dilation effects produced by our own planet to see an actual real-life example of time dilation, but I doubt you'll find it that easy to point to an actual instance of someone reverse-aging.

I admit though that I picked up on the time dilation idea because it's something of a small recurring sci-fi brainbug, and not really a feasible idea. I just didn't realise it was so unfeasible, but I do now.

Here's an exercise: I will just say "no" and you will do some research to find out why this idea would never ever work.

I'll take your word for it. I'm the poster child for 'layperson' unfortunately. It's just fun to talk about these kinds of things, although it certainly would help if I had more (or indeed any) knowledge of physics and reactors.

[RedImperator]

Of course, the tank would be more difficult to fabricate than no tank, but if they can create and manipulate ferrous antimatter, then this seems like an obvious next step, at least to me.

That's a pretty big "if". Every antimatter manufacturing scheme I've heard of produces anti-hydrogen. If that's your starting point, you'd have to fuse it repeatedly to get anti-iron. That sounds like a bigger headache than storing antimatter to begin with.

[Darth Wong]

So what you're saying is that you cannot store plasma because if it cools down then it will become ordinary gas. But then wouldn't that mean all you need to store it is enough heat to keep the gas a plasma? I mean if the only thing stopping you from keeping it in a warehouse somewhere is temperature, well what's the problem? I suppose the actual heat required is simply too great to maintain over any length of time, but can't you use materials that have little heat conductivity to reduce the rate of the plasma cooling?

You don't understand. The instant plasma touches any solid material, it will lose its state. Plasma is both ultra-hot (thousands of K) and very low-density (comparing plasma and air is like comparing air and lead). You simply do not store plasma in tanks. Period.

And yes, I know, they do it in Star Trek. That is because Star Trek is written by arrogant asshole laypeople who call it "serious science fiction" but shit on science every chance they get.

As to the article, I'll quote the relevant bit;

Previous antimatter-powered spaceship designs employed antiprotons, which produce high-energy gamma rays when they annihilate. The new design will use positrons, which make gamma rays with about 400 times less energy.

The context is that scientists were wary of using antiproton reactions because of dangerous levels of gamma radiation being released, and that they are looking at using positrons instead because, as the quoted bit says, a positron anhilation releases less energy intensive gamma rays, which, given the context, pressumably equates to a safer form of fuel than antiprotons.

Per unit mass, it's still the same energy. What they're talking about is the fact that electrons are miniscule, so the actual photon emitted by the reaction is going to be lower-frequency than the ones emitted by a proton/antiproton reaction.

So? Aging exists too, but that doesn't mean you can make aging or de-aging fields.

Well to be fair, aging is a physical change, whilst time dilation is not. Also, you only have to look to the time dilation effects produced by our own planet to see an actual real-life example of time dilation, but I doubt you'll find it that easy to point to an actual instance of someone reverse-aging.

"Time dilation effects produced by our own planet?" Our planet does not significantly dilate time.

I admit though that I picked up on the time dilation idea because it's something of a small recurring sci-fi brainbug, and not really a feasible idea. I just didn't realise it was so unfeasible, but I do now.

The idea of taking a phenomenon that occurs at .99c and assuming you can make a "field" out of it is part of what's wrong with sci-fi writing today. People do that; they take all kinds of scientific phenomena and assume they can weaponize them.

Here's an exercise: I will just say "no" and you will do some research to find out why this idea would never ever work.

I'll take your word for it. I'm the poster child for 'layperson' unfortunately. It's just fun to talk about these kinds of things, although it certainly would help if I had more (or indeed any) knowledge of physics and reactors.

Well, there's always school for that.

[Darth Wong]

Of course, the tank would be more difficult to fabricate than no tank, but if they can create and manipulate ferrous antimatter, then this seems like an obvious next step, at least to me.

That's a pretty big "if". Every antimatter manufacturing scheme I've heard of produces anti-hydrogen. If that's your starting point, you'd have to fuse it repeatedly to get anti-iron. That sounds like a bigger headache than storing antimatter to begin with.

Is it? If you're talking about storing antimatter without ferromagnetism, then you have to use magnetic interactions which are orders of magnitude weaker. And you have to somehow use this piss-weak non-ferromagnetic interaction to keep this material from moving around inside the storage chamber so that none of it touches the sides of the chamber, even as you accelerate and maneuver the ship. It's impractical on many levels.

The fact is that you want to front-load all of the engineering difficulty. If it is ten times more difficult to make it up-front and only twice as good at the point of use, then it's still worth it, because the point of manufacture is a static facility with relatively unlimited resources, whereas the point of use is a spacecraft with limited resources, limited space, and far more challenges.

This is even more true when you're talking about making storage tanks instead of fuel. You can re-use the storage tank over and over, whereas the fuel can only be used once. It absolutely makes engineering and economic sense to use a tank which is extremely difficult to make but which allows the use of much cheaper fuel, and a much safer (and cheaper to operate) spacecraft.

[Wyrm]

Positron/electron annihilation produces just as much energy per unit mass.

So was that article talking out of it's ass then? It could be, it's just that it's on NASA's webpage so I figured they were telling the truth, but being ignorant of science I couldn't say myself. If it is wrong then their entire proposal sounds like a dead end then.

Positron/electron annihilation produces less energetic gamma rays, which may be easier to deal with.

[Revy]

Per unit mass, it's still the same energy. What they're talking about is the fact that electrons are miniscule, so the actual photon emitted by the reaction is going to be lower-frequency than the ones emitted by a proton/antiproton reaction.

Umm, sorry to ask, but does that mean it'll be safer? That's what I understood from the article - that positron fuel would be safer and easier to use than antiproton. Is it?

"Time dilation effects produced by our own planet?" Our planet does not significantly dilate time.

My point though was to simply hilight an instance of time dilation occuring in real life, as opposed to anti-aging, which as far as I'm aware doesn't occur in real life, and thus show that it wasnt a very fair comparison. I wasnt trying to say that our planets time dilation effect was significant or useful in any way. Just that it *is*. Of course that doesn't mean we can use the existance of such a phenomenon for our own ends, or duplicate it in any way. I know that. I just thought at the time that it might be possible, but I was wrong.

The idea of taking a phenomenon that occurs at .99c and assuming you can make a "field" out of it is part of what's wrong with sci-fi writing today. People do that; they take all kinds of scientific phenomena and assume they can weaponize them.

Agreed, and again I admit that it's exposure to common sci-fi tropes and conventions that made me think that way. Thankfully this site and its people are here and can help people such as myself to learn better.

Well, there's always school for that.

Well yes that's true. I would like to study and learn at least some physics and intend to as well, but living on an island in the middle of nowhere doesn't help matters much.

I have a question though - Destructionator said;

Actually, my primary point behind the thread is to backup an assertion I made earlier today on an IM that a realistic antimatter power plant wouldn't be able to economically outcompete a nuclear reactor, even if the antimatter fuel was free. Therefore, magic free antimatter production will have very little impact upon the world as a whole; only physicists (for research) and terrorists (for bombs with no regard to safety) would have any use for it.

I'm quite curious about this myself. I would have thought that if the technology for creating an AM reactor existed, it would outcompete nuclear power because it produces more energy and results in less waste product (assuming it worked). Why would nuclear power continue to outshine AM power, if the AM fuel was free or easy to come by? And as an aside, how do you think the world would take to it? Nuclear power has a lot of bad press and people in general seem to be reluctant about it, how would people react if some group came out with a AM reactor and proposed it as a new energy source?

[Revy]

Positron/electron annihilation produces less energetic gamma rays, which may be easier to deal with.

Ah, thanks, that's what I was wondering. I brought it up because the point of this thread was about the design of a possible AM reactor, and having a M/AM fuel that's pottentially safer to use than the norm might be significant.

[Wyrm]

Ghetto Edit: Okay, I fail. I missed that Mike already explained what I did the first time reading.

[Darth Wong]

AM power is actually completely worthless as an actual power source for society, because unless you can find a source of naturally existing antimatter, its full-cycle net energy production is negative.

It's really a no-brainer to say that it is easily out-competed by nuclear power, which uses a fuel that you simply dig up out of the ground, rather than one which you have to create yourself (at enormous energy cost, exceeding whatever you would get out of it later).

[Singular Intellect]

AM power is actually completely worthless as an actual power source for society, because unless you can find a source of naturally existing antimatter, its full-cycle net energy production is negative.

It's really a no-brainer to say that it is easily out-competed by nuclear power, which uses a fuel that you simply dig up out of the ground, rather than one which you have to create yourself (at enormous energy cost, exceeding whatever you would get out of it later).

One could argue that practical and efficient use of AM as a energy carrier is an arguement though, correct?

[NoXion]

AM power is actually completely worthless as an actual power source for society, because unless you can find a source of naturally existing antimatter, its full-cycle net energy production is negative.

It's really a no-brainer to say that it is easily out-competed by nuclear power, which uses a fuel that you simply dig up out of the ground, rather than one which you have to create yourself (at enormous energy cost, exceeding whatever you would get out of it later).

One could argue that practical and efficient use of AM as a energy carrier is an arguement though, correct?

Wouldn't that depend on how efficient the antimatter creation process is?

For instance, suppose I had a type I dyson sphere (IE the non-solid kind made of independantly orbiting components) which was harvesting energy from it's parent star (for the sake of argument let's say it's the same type as our own Sun).

Now, how much of that energy could I reasonably expect (in thermodynamic terms at least) to turn to antimatter or use to create antimatter?