Basically a fusion reactor in space. Not just for safety, but so that the machinery under the effect of the heat from the reactor is not damaged and so a fusion reaction can be maintained. Of course the reactor would have to be 40 or 50 kilometres in diameter and would still be very hot, but for a limitless supply of energy it might be worth it. The inside of the 'sphere' would be coverred in several layers of solar panels which react to arange of frequencies which could power space industries using the energy to turn water into hydrogen and oxygen and producing synthetic hydrocarbons to be sent back to earth and for industries which require electrolysis. The reaction would be fed by blasting protons into the globe of plasma which would then be compressed by a magnetic field from several modules inside the sphere. The globe of plasma itself will be on the brink of running out of enough energy so that the minimum amount of space and power to the dyson sphere and magnetic field is needed. I bet somone has come up with a similiar idea as the idea of building a reactor big enough to contain a fusion reaction is a pretty obvious solution to achieving fusion power. Perhaps something similiar could be used for the standard nuclear reactors, instead of using isotopes to boil water, using a controlled reaction to power solar panels and generate hydrocarbons safely in space.