a field emitter array includes electron - beam source elements , each including a cathode for emitting electrons and a gate provided in the vicinity of the cathode . to emit electrons from the cathode by the field emission effect , a cathode voltage is applied to the cathode and a gate voltage is applied to the gate . an anode is arranged in proximity to the cathode and supplied with a positive anode voltage to capture electrons from the cathode in a first mode of operation . in a second mode of operation of the field emitter array , a negative anode voltage is supplied to the anode to urge electrons emitted by a first cathode , back toward a second cathode supplied with a cathode voltage which attracts electrons , to clean the second cathode .