Huh? What plasma? Solar wind? Far too sparce.
Only blackbody radiation will work, and that is proportional to the area and to the absolute temperature to the fourth power. This means that, to increase thermal radiation, one must raise the heat sink temperature of whatever heat engine is being used, which then lowers the efficiency.
And this radiator may carry coolant, and so would subject to leakage (from micrometeorite punctures) which could be fatal to the thermal cycle.
David F Mayer