Theoretical M/AM reactor for SF-story

[Almeisan]

I do not know if this is the correct forum but it seemed to theoretical for the Nuc Engineering forum.

Ok I am 'designing' this space vessel capable of traveling inbetween star systems about 400-500 years in the future. I do not want much time dilation(for obvious reasons) so its going to use some kind of space/time bending/manipulation to travel FTL. This of course requires a lot of energy. So a M/AM reactor is pretty obvious. Fission and fusion do not give enough energy and the other theories are too much theory to create a convincing pseudoscientific solution with.

I am going to assume that some kind of antimatter is going to be available in magnetic bottles. I am not a educated physicist so I might need some help on some of these things. The energy generated by the reaction isn't really an issue(well it kind of is). Its very great. Now I have only been able to find drawings of M/AM propulsion systems. These just throw the energy generated by the annihilation out into space. But that isn't going to be enough for my ship. I need electrical energy for the space/time warping device. How do I use the energy? How do I get a high efficiency? This design is going to be very advanced.

I was thinking about using the reactor both to generate electricity and as a propulsion device(when needed). How do I convert the energy? The most suggested way is to use protons and antiprotons. I have looked it up and this creates on average 3 pions. Two are going to be neutral and will decay into gamma rays very fast. The othe pion will be either positive or negative, traveling at close light speed and will carry 60% of the energy created by the annihilation(I read a 70% somewhere else). Now pions aren't massless so there is not a 100% mass to energy conversion. I could look up the masses and calculate the efficiency up till now buts let's assume its 100% to make it easier.

In most designs for propulsion systems the gamma photons are not used because they have no charge and fly through most matter. But this way we lose 40% of the energy. That really cuts into the efficiency. Plus all those gamma particles flying around all over the ship isn't very nice. We need shielding anyway. So I would like to make something up to explain how we can use the gamma particles.

Now the pions decay after 21 meters. In the designs I saw I get the idea that this creates even more energy. If so we probably want to use that energy too. The ship is going to be pretty big(but not big enough for the decay (into neutrinos/electron?)1,5 km later). So we have these pions (and maybe the gamma particles) and we have only a fraction of a second before they are gone to get some energy out of them. I have no clue how. If I would heat water to make the steam run a turbine I would almost need a whole ocean onboard. I have looked at a few other ways, thermocoupling comes to mind, but I also thought about using the magnetic field of the particles to create a flux change in a coil. This is a crazy idea as far as I can tell. If we ignore the focussing of the particles for a minute then we need a extremely small coil. Now if this actually wrong and when I am not misunderstanding something then this would generate a lot of energy, so the coil would heat up and burn because it will be so extremely small. Does a superconductor solve this problem? Of course most superconductors need to be cooled nowadays and that would probably be impossible with something that small. But wouldn't the flux changes be too small, or too unstable to generate a real current? You could split up the positive and negative pions and shoot them through in groups or something but would that work? Of course practical problems can be solves(read: ignored) but I am very unsure about the theoretical ones too.



And what about storage? Would very efficient H2 fuel cells work? Of course storing a large percentage of power would be impossible but some backup power is needed. Plus all the normal systems need to run on a stable power source.

Does someone have any ideas? If so, thanks.

Hmm, I could have made this post a lot shorter...

 

[Blistering Peanut]

That was a very interesting read however I haven't amassed enough knowledge to be able to contribute yet. I think your problem is that you have a 24th(?) century idea but are still using 21st century technology. When I read the bit about heating water to turn a steam turbine I laughed. Just imagine a 2 million tonne, kilometer long vessel in space... with plumes of steam rising out of it. In the future we will have much better technology for using the left over particles. An idea could be to make some sort of ion drive using the charged pions

 

[Almeisan]

Of course its not going to use water, obviously :) I just pointed out the problem. Its just a hole in my knowlegde. I am not sure if there are some real ideas out there. I wasn't able to find any, most SF ideas assume 100% efficiency and ignore all the real problems.

The only ion drive thing I know of is a propulsion device, ionising gas so the ions are being emitted at high speeds. But the propulsion part is already fixed, we would just use the charged pions as propulsion. I have found 4 different systems of anti-matter propulsion. But I also need electricity to power a space/time manipulating system.

 

[LURCH]

In most designs for propulsion systems the gamma photons are not used because they have no charge and fly through most matter. But this way we lose 40% of the energy. That really cuts into the efficiency. Plus all those gamma particles flying around all over the ship isn't very nice. We need shielding anyway. So I would like to make something up to explain how we can use the gamma particles.

Now the pions decay after 21 meters. In the designs I saw I get the idea that this creates even more energy. If so we probably want to use that energy too. The ship is going to be pretty big(but not big enough for the decay (into neutrinos/electron?)1,5 km later). So we have these pions (and maybe the gamma particles) and we have only a fraction of a second before they are gone to get some energy out of them. I have no clue how.

The key here is probably the term, "most matter". If all you're looking for is some PSB, I would suggest that the shielding around the reaction chamber performs both these functions. An unobtanium lining could become charged by having electrons stripped off when bombarded with gamma (thus preventing the entire crew from becoming "The Incredible Hulk"^TM).

To make the design a little more up-to-date than "dilythium crystals", you could make this lining a liquid metal like those proposed in fusion research. This metal would flow at high speeds, held in place by a strong magnetic field. This highspeed flow would increase the chances of a pion making impact with a nucleus (of the metal), thereby recovering the energy of that particle. And, if the flow were properly directed, I suppose any material debris from these collisions could be directed back into the reaction chamber, where they woulld simply be more matter for te amtimatter to anihilate with.