Effect of scandia doping method on the emission uniformity of scandate cathode with Sc2O3–W matrix

• The emission uniformity of scandate cathodes has been quantitively obtained.
• The nanoparticles on the cathode surface lead to the electric field enhancement.
• The cathode prepared by spray drying method exhibits good emission uniformity.

Scandia doped tungsten matrix dispenser cathodes were manufactured using scandia doped tungsten powder prepared by mechanical mixing, liquid–solid doping and a spray drying method. It is found the macrostructure of the cathode depended on the powder preparation method. The cathode prepared using the powder prepared by spray drying method had a homogenous and porous matrix characterized with grains with a diameter of less than 1 μm and with many nanoparticles distributing uniformly around these grains. The cathode with submicron structure and uniform distribution of scandia exhibited good emission uniformity. The emission uniformity ΔJ/J of the cathode prepared by spray drying method was 0.17, about 6 times lower than that of the cathode prepared by mechanical mixing method. The calculation results showed that the nanoparticles led to electric field enhancement. A Ba–Sc–O multilayer on the cathode surface and nanoparticles distributing mainly on W grains contributed to the emission property of the cathode.

Emission uniformity of the cathodes prepared by mechanical mixing (a) and spray drying method (b).Figure optionsDownload as PowerPoint slide