Antimatter propulsion I was reading about antimatter propulsion systems on the internet, and apparently they would work by letting matter and antimatter react and then the reaction would be (magnetically) channeled out through a nozzle. So what I was wondering about was that if the matter and antimatter react in a combustion chamber, how would the chamber be designed as to not let the reaction destroy it? Most articles were low on specifics and there was nothing on the internet about how the combustion would work. Am I missing something here or is that a flaw in the design?
 A: Those sources are typically low on specifics because the specifics do not exist i.e., matter/antimatter propulsion is a purely theoretical construct which makes mathematical sense but which cannot be implemented in practice for among other things the issue you cite (what do you make the antimatter storage tank and the "combustion chamber" out of?). 
In addition, the only methods currently at hand for manufacturing and then storing antimatter are absurdly inefficient, making a matter/antimatter rocket engine absurdly expensive. 
So, you'll read about this in "gee-whiz" science articles and in sci-fi stories, where the specifics "need not concern us". 
A: Well if the antimatter is the positron, the only matter particle that needs to be kept away is the electron. So a proton swarm would do. A positron can only annihilate an electron not a proton. The electrons can be added to perform the reaction between the positron and electrons and this can form the propulsion. On top of the proton preventing the positron from hitting the electron in the containers, magnetic traps can hold the positrons in the center of the reaction. If the reaction was sent out through the nozzle propulsion would not be that great, that is because the result of the electron positron annihilation which are gamma rays is not a good propulsion. What needs to happen is on top of the energy leaving the nozzle some of the matter and antimatter also needs to leave the nozzle. However only a small amount of matter and antimatter needs to leave. This can create the required thrust to push on the antimatter spaceship.
