Field emission device and field emission method

An electric field radiation device comprising:

• a vacuum enclosure formed by sealing a tubular insulator at a first end and a second end to form a vacuum chamber at an inner wall side of the insulator;
• an emitter positioned at the first end of the vacuum chamber and having an electron generating portion disposed to face the second end of the vacuum chamber;
• a guard electrode arranged at an outer circumferential side of the electron generating portion of the emitter;
• a target positioned at the second end of the vacuum chamber and disposed to face to the electron generating portion of the emitter;
• a movable emitter supporting unit configured to move the emitter in both end directions of the vacuum chamber;
• and
• an operating unit connected to the emitter supporting unit and configured to operate the emitter supporting unit,
• wherein the operating unit is configured to change a distance between the electron generating portion of the emitter and the target and fix a position of the emitter at an arbitrary distance by operation of the emitter supporting unit,
• wherein the guard electrode comprises, at a target side thereof, a small diameter portion which the electron generating portion of the emitter contacts and separates from, and
• the electron generating portion of the emitter performs field emission with the position of the emitter fixed.