Abstract
To meet the requirements for advanced vacuum electron devices and modern electron beam instruments, dc emission properties of nanosized-scandia-doped impregnated (SDI) cathodes have been investigated in a closely spaced diode configuration system with water-cooled copper anode. The SDI cathodes were made from nanosized-scandia-doped tungsten powder, which was produced by a spray-drying process. A space-charge-limited dc current density of over 60 ${\rm A}/{\rm cm}^{2}$ has been measured at 950 $^{\circ}{\rm C}_{\rm b}$ . An on-going life test with a dc load of 30 ${\rm A}/{\rm cm}^{2}$ at 950 $^{\circ}{\rm C}_{\rm b}$ has completed more than 2000 h of operation to date. The electron cooling for dc beam emission is discussed.
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