A heating assembly (36) for heating a cathode (38) of an electron gun (30) of an exposure apparatus (10) includes a radiation source (42) and a beam shaper (44). The radiation source (42) generates a source beam (46). The beam shaper (44) receives the source beam (46) and selectively shapes the source beam (46) into a shaped beam (48) that is directed to the cathode (38). In certain embodiments, the beam shaper (44) can readily change the shape and intensity profile of the shaped beam (48) to achieve a desired electron beam (32) from the electron gun (30). In one embodiment, the radiation source (42) generates a pulsed source beam (46).