Design procedures and beam transport feasibility experiments are discussed for a novel, millimeter-wave free electron laser (FEL) concept employing short period magnetic undulators and a sheet electron beam. The advantages of this concept include: (1) lower beam voltage ("500 kV) compatible with thermionic Pierce gun technology and conventional power supplies (rather than electron accelerators), (2) a sheet electron beam geometry which enables high power operation without excessively high gun perveance, and (3) a streaming electron beam which is compatible with depressed collector beam energy recovery for enhancing overall system efficiency. Conceptual designs for pulsed and cw high power devices, and a cw low power device are presented.