Antimatter: Plasma Drive
Plasma Core Antimatter Drive
The hybrid designs (ACMF and AIM) discussed in previous sections seem quite complicated. They require the juxtaposition of the three highest energy yielding technologies known to humankind just to create a spacecraft that is barely capable of leaving the solar system. What if we just used the highest energy yield technology and forgot about the other two?
Indeed this is possible, but it requires a lot more antimatter than we are currently capable of producing. However, someday we will have actual antimatter factories, rather than relying on retrofitted particle accelerators in scientific laboratories. Dr. Robert Forward has shown, based on his findings in a study of antimatter production, that if a dedicated antimatter factory were built now, it could be approximately 6000 times more efficient than Fermilab's and CERN's antimatter production facilities (bringing it up to a grand 0.01% efficiency).
The theoretical maximum efficiency for antimatter production is 50% (it is not 100% because every production of an antiparticle is accompanied by the production of its normal-matter twin), so there is even more room for improvement.
Once we have ways of producing large amounts of antimatter, we will be able to make pure antimatter/matter reactor drives. What follows is a discussion of one such "pure" drive called a Plasma Core drive.
A very simple design for an antimatter drive would be to have antimatter/matter annihilation occur inside a tungsten cylinder. The tungsten would absorb the gamma rays and pions from the reaction, causing the tungsten to heat up. Through small holes in the cylinder, normal hydrogen gas would be passed. The hydrogen would take heat from the tungsten, simultaneously cooling the tungsten core and heating the hydrogen gas. The hot gas would then be expelled from the core to produce thrust.
This kind of drive is what is called a "solid core" drive. Obviously, this idea is limited by the melting point of tungsten (or whatever solid was used). The next step, then, would be to replace the solid core with some sort of liquid core. Why stop there, though? Why not replace it with a gas core. In fact, one might as well go all the way to a plasma core. Indeed, there is no point in developing drives using solid, liquid, or gas cores because all have lower thrust ability and higher antimatter needs than the hybrid antimatter/nuclear designs.
Figure 9 shows the basic concept behind a plasma core drive:
As with the AIM drive, magnetic and electric fields would serve to contain the plasma and the propellent (which would also be a plasma by the time it had exited the rocket). Antiprotons would be injected into the plasma core, anhiliating and heating the plasma. Heat would be rapidly transfered to the propellent which would be expelled from the drive at high velocity.
The plasma core drive is a good example of a pure antimatter/matter drive, but there is little that it could do that the AIM and ACMF drives could not. Therefore, it may never be built. More likely, AIM, ACMF, and other hybrids will continue to be used until such a time as we have enough antimatter to create a Beamed core drive, with which we could send manned missions to nearby star systems like Alpha Centauri!