Emission characteristics of high-voltage plasma diode cathode for metal surface modification

Electron beam cathodes have been used in various fields such as microscopy, X-ray tubes, welding, and surface modification. Generally, cathodes use metals with lower work function, higher thermal resistance, lower poisoning effects of gases, etc. LaB6, tungsten, and tantalum have normally been used as cathode materials with special materials coated if required. This study investigated the high-voltage plasma diode cathode for surface modifications of metal products such as polishing, hardening and heat treatment. The most fascinating features of this cathode are the high voltage and current that can be obtained at a low vacuum of a few mTorr. However, it is difficult to control the emission current to attain a steady state and to obtain higher brightness than that achieved using a thermal cathode. We studied the emission characteristics in terms of cathode and anode design parameters such as anode distance and cathode shape. Additionally, changes of emission characteristics are discussed in terms of the type of gas, pressure parameter, etc. using the emission resistance, effective breakdown voltage, and brightness. Finally, by measuring the change in surface roughness using the emitted electron beams, we found that the surface roughness values before the process were Ra=0.8 µm and Rz=5.4 µm, whereas those after the process were Ra=0.25 µm and Rz=2.3 µm. The electron beam polishing technology is eco-friendly and can minimize the emission of many harmful materials that arise when existing mechanical or electrochemical polishing technologies are used.