Is antimatter power theoretically possible? There is a quote and citation on the "Antimatter" page of the obvious encyclopedic site (https://en.wikipedia.org/wiki/Antimatter), saying that positrons could be produced (in the future) at a rate of $250 million per 10 milligrams. Unfortunately, the author of that quote made it in 2006. Yet there is also a growing possibility of harvesting antimatter in the radiation belts, solar wind, or even lightning bolts.
This leads me to consider: If the production (or harvesting) of antimatter becomes practical, is it theoretically possible to have an antimatter electric power supply?
My idea of antimatter power goes like this. Positrons are contained in a vacuum chamber, probably with a magnetic field. Electrons are somehow shot into the chamber, colliding with the blob of positrons. This produces 2 gamma rays. The vacuum chamber is surrounded by solar panels, tuned to receive gamma ray frequencies instead of visible light, and thus converts the gamma rays into DC electric power.
For the sake of concreteness, let me ask 4 questions revolving around the engineering problems:
(1) Is it possible to build efficient solar panels tuned to gamma ray frequencies? They would also need a decent lifetime.
(2) How exactly would electrons be accelerated into the region containing the positrons? My intuition says that if a magnetic field is containing them, then an electron would have a hard time penetrating that field.
(3) Can we get enough power from this to self-sustain the magnetic containment field, as well as the electron accelerator, while still having a decent amount of leftover power to spare?
(4) Are electrons and positrons the best choice of matter-antimatter? From what i've read, it seems the simplest choice of annihilation---they produce just 2 gamma rays at low velocities---but perhaps other kinds of antimatter are easier to contain?
In case your wondering, i'm not trying to make a form of free/cheap power. I just think it would be great if we could replace nuclear reactors, both the plants and the naval drives, with something that has few moving parts with even better energy density. To me, that would be worth a somewhat bigger price than nuclear is today. It would also be nice if space stations and space ships were not so limited in their power generation.
 A: You can't build solar panels tuned to gamma ray frequencies.  Gamma rays are too energetic-creating a hole/conductor pair only yields a few eV, while the Gamma ray is hundreds of keV. It would be better to absorb it as heat and turn the heat into electricity (though there are losses there)  
Unfortunately, the number of positrons in the sources stated are very small.  The radiation belts are electrons and the solar wind is electrons and protons.  Even the lightning is talking about amounts that make radiation doses, not total energy.  If you want positrons, you have to make them from electricity, not the other way around.
A: *

*Positrons have a positive charge and electrons have a negative charge. They would attract each other. Getting them to together is not a problem. You would not have to fire them into a cloud of positrons, as they would just be attracted in. 

*They circulate in opposite directions in a magnetic field. So, containing them is also not a problem.

*The only thing stopping a functioning antimatter power generator, is our ability to produce positrons efficiently. All the other problems are easy fixed.

*One way to produce positrons efficiently is to use a positron breeder process. This process takes some of the gamma rays produced, and turns them back into positrons,and feeds them back into the reactor chamber. In just how to do this efficiently, would be the subject of some recent research. 

A: Anti-matter could potentially have a practical use as high energy-density fuel (or catalyst) for starships. The reason is being the fuel with the highest energy density possible. But the biggest limitation, even beyond the limited production, is the inability to store significant quantities of the substance safely. You could create magnetic containers, but with existing superconductors the mass of the container would exceed the mass of fuel by several orders of magnitude, making its prospect performance much worse that fusion rockets. If you add to the risk of complete destruction at the minimal failure of the containment, then it becomes an unfeasible approach
