High-current-density　sheet　beams　directly　generated　from　scandia-doped　dispenser　cathodes　have　been　studied　for　application　to　vacuum　electron　devices　like　terahertz　sources.　Rectangular　beams　with　current　densities　of　over　50　A/cm(2)　have　been　developed　and　demonstrated　to　maintain　for　several　hundred　hours　with　the　cathode　operating　stably　at　950　degrees　C-b.　Beam　forming　structures　have　been　investigated　and　optimized　by　means　of　beam　profile　simulation　and　confirmed　by　test　results.