A contaminant trap apparatus arranged in a path of a radiation beam to trap contaminants emanating from a radiation source configured to produce the radiation beam is disclosed. The contaminant trap apparatus includes a rotor having a plurality of channel forming elements defining channels which are arranged substantially parallel to the direction of propagation of the radiation beam, the rotor including electrically chargeable material and arranged to be electrically charged as a result of the operation of the radiation source; and a bearing configured to rotatably hold the rotor with respect to a rotor carrying structure, wherein the apparatus is configured to (i) control or redirect an electrical discharge of the rotor, or (ii) suppress an electrical discharge of the rotor, or (iii) both (i) and (ii).