B Can Antimatter-Matter Be Used as Rocket Fuel?

[Nugatory]

I assume you mean net production...

I'm not sure what you mean by "net" production. What other kind is there?

Don't assume when you can calculate. How many particles is 17 grams worth of antiprotons? How does that compare with the sort of production rates described by https://arxiv.org/pdf/1408.0759.pdf?

 

[mfb]

What would it take to scale it up, if that were the sole purpose and anything goes? Of course having a containment system that blends well with propulsion would be a plus...

If anything goes, build a trillion times the CERN accelerator complex (you can skip the SPS, the LHC and a couple of smaller components as they don't contribute). A trillion times 1000 antihydrogen atoms is 1.7 ng, you can use it to release 300 kJ. Well... not there yet. The bottleneck is the last part, the production of the neutral atoms and their storage. If you can build 10¹⁵ of them and keep the accelerators, you can produce 1.7 μg to release 300 MJ, roughly corresponding to 10 kg of rocket fuel. You cannot build 10¹⁵ antimatter traps, however. And even if you could, you would have the antimatter in 10¹⁵ different locations.

The first issue is the raw production rate of antiprotons. While that is not its target, MYRRHA should get a huge antiproton production once it is operational, something like 10²⁰ antiprotons per year, or 0.17 milligrams. That sounds nice, but you have to make a beam out of them, losing some of them, and they have to be fast to be kept in a beam - if you do that naively by just reversing an accelerator you lose basically all of them.
To get more slow antiprotons, you have to cool them. CERN's antiproton decelerator (AD) can do this, but it takes time, and it doesn't work well with a continuous antiproton source (such as MYRRHA). The AD uses a weaker but pulsed beam to produce a batch of 30 million relatively slow antiprotons (5.3 MeV) every 100 seconds, or 10¹³ antiprotons per year. Cooling them down to capture them in a trap loses something like 99.99% of these, so you get a few thousand every 100 seconds or a billion per year. These you have to mix with positrons and wait until some form antihydrogen, which takes some time, and you lose some more antiprotons.

Storing macroscopic amounts at the same place and time would probably need solid antihydrogen, levitated by electrostatic forces. That would lead to yet another lossy conversion process, and it is unclear how to start that process.

 

[Vanadium 50]

I'm with Nugatory - what other kind of production is there?

urely we could get it down to thousands or hundreds of years?

How do you calculate this? It sounds like your objection is that you don't like the answer.

 

[jerromyjon]

I'm not sure what you mean by "net" production. What other kind is there?

I meant that gross production of antiparticles, like how mfb broke it down, leads to a very low amount being containable, therefore net production would be the amount that could be contained. (perhaps as solid antihydrogen) Sorry for asking what you all probably think are silly questions but I can't find much of anything of value online, and the lack of detail of what I have found leaves more questions than understanding.
Thanks for the link, it looks very interesting, I'll read it tonight!

It sounds like your objection is that you don't like the answer.

Of course, that is my objection! It is just a slight step from "impossible"... and I really hate the word impossible. It's not that I doubt your estimate, based on existing methods, it's just that I'm dreaming that *someday* it might be possible, and wondering if there are any hypothetical ways of achieving it quicker.

 

[mfb]

We don't know any quicker way apart from increasing the beam currents, the cooling of things and so on, but these are all incremental steps.

 

[Vanadium 50]

It is just a slight step from "impossible"... and I really hate the word impossible.

Roughly the same factor of a billion or more is what you need to get to the moon by flapping your arms. Sometimes the word "impossible" is the right one.