Since　the　cathodes　with　concave　surfaces　are　required　for　the　practical　applications　in　most　high-power　vacuum　electron　devices,　characteristics　of　nanosized-Scandia　Doped　Dispenser　(SDD)　cathodes　with　concave　surfaces　have　been　investigated,　especially　in　dc　applications.　A　space　charge-limited　(SCL)　dc　current　density　of　over　50　A/cm(2)　has　been　measured　at　1000　degrees　C-b.　An　on-going　life　test　with　a　dc　load　of　up　to　40　A/cm(2)　at　970　degrees　C-b　has　been　completed　about　3000　hours　of　operation　to　date.　The　emission　performance　of　the　cathode　was　further　evaluated　in　an　electron　gun　test　tube,　which　is　a　part　of　an　mm　wave　CW-TWT,　before　the　practical　application　in　the　real　devices.