Pore geometry of dispenser cathode surface vs. emission characteristics, and Ba recovery characteristics after ion bombardment

A study was conducted to investigate the emission characteristics and barium recovery characteristics after ion bombardment of two types of Ir-coated dispenser cathodes having a pore density on the surface layer of the cathodes of 4=104 and 1.3=104 poresrmm2. Cathode current was measured under pulse operation in a range of 0.1–9% duty cycle. When the duty cycle dependence of emissions was examined, the current densities of both cathodes were the same in the case of 0.1% duty cycle, delivering about 12 Arcm2. The work functions also showed the same value. However, evaluations of 4% duty cycle and 9% duty cycle found that the cathode with a higher pore density showed emission characteristics higher by 50% and 70%. Regarding the recovery time of barium and oxygen after argon ion bombardment with Auger electron spectroscopy AES., the low-pore-density cathode required as long as 3 min for recovery, whereas the high-poredensity cathode recovered in 1.1 min. From the above experiments, it was clarified that emission characteristics under high duty and barium recovery characteristics after ion bombardment can be improved by increasing the pore density of the surface layer. The basic mechanisms leading to these results were also theoretically considered by solving surface diffusion equations. q1999 Elsevier Science B.V. All rights reserved