mJAstro- It's based on this concept:
http://en.wikipedia.org/wiki/Magnetic_sail basically it generates a big magnetic field which get's pushed by the solar wind.
Chrismeuve, Ozylot- Thanks. It's one of those spacecraft propulsion ideas that's always mentioned but I've only seen 1 or 2 renderings of it in action, so I wanted to try it.
Actually reviewing the premise I was confused I thought you had to add plasma to your magnetic field but rereading it I don't think you have to, the magnetic field interacts with the plasma ejected from the sun. So the fuel tanks are actually unnecessary. But I'm debating using it anyways, for heat radiation. Since heat radiation seems to be such a problem for these realistic spacecraft designs, I thought maybe I could line the inside of my tube with the radiators, then have some plasma/charged gas particles running over the radiators to pick up the heat & re-radiate it out into space as it circulates along the magnetic sail. It's inefficient, as half the heat would be radiated back inside the magnetic sail toward the spaceship, but the mgnetic sail is a huge torus many times larger than the ship, so I'd hoped the sheer scale of it would make it worthwhile. Hopefully someone more scientific here can let me know if this is unfeasible.