A radiation collector (141) comprising a plurality of reflective surfaces (400-405), wherein each of the plurality of reflective surfaces is coincident with part of one of a plurality of ellipsoids (40-45), wherein the plurality of ellipsoids have in common a first focus (12) and a second focus (16), each of the plurality of reflective surfaces coincident with a different one of the plurality of ellipsoids, wherein the plurality of reflective surfaces are configured to receive radiation originating from the first focus (12) and reflect the radiation to the second focus (16). An apparatus (820) shown in FIG. 11 comprising a cooling system (832) and a reflector (831), wherein the cooling system is configured to cool the reflector, the cooling system comprising: a porous structure (823) situated in thermal contact with the reflector, wherein the porous structure is configured to receive a coolant in a liquid phase state; a condenser (825) configured to receive coolant from (826) the porous structure in a vapour phase state, condense the coolant thereby causing the coolant to undergo a phase change to a liquid phase state and output the condensed coolant in the liquid phase state for entry (827) into the porous structure.