Tailoring Beam Shape Using a Coplanar Quadrupole Focusing Structure in Carbon Nanotube Cold Cathode Electron Gun

Carbon nanotubes (CNTs) cold cathode has excellent electron emission characteristics and showed its importance in vacuum electronic device applications. Facing various demand on electron beam with different devices, the cold cathode electron gun as a component for generating electron beam raises a challenge for controlling the beam which possess high-speed electrons due to the high driven field from a cold cathode. Here, a coplanar quadrupole focusing structure is proposed to adding in a CNT cold cathode electron gun to realize a multifunctional electron beam shape tailoring. In principle, the field emission electrons were first decelerated then adjusted by the focusing electrode modules to achieve multiple functions, including beam focusing, sheet beam adjusting, and beam shifting. In the experimental results, the area compression ratio of the electron beam was 34.6; a round beam spot with a diameter of 2.76 mm was compressed to a sheet beam with a width of 0.15 mm; a beam position shifting was as large as 2.22 mm in radial cross section. This work demonstrates the feasibility of tailoring the beam shape of electron beam in a cold cathode gun according to the device application requirements.