Abstract: A device and method for producing an ultra pure molecular beam of elemental molecules utilizing a reduced thermal gradient filament construction in an effusion cell is provided. The effusion cell comprises a crucible having an open and a closed end and at least one heating filament distributed immediate the crucible. The at least one heating filament or filaments are provided having a first portion having a first pitch in proximal relationship to the open end of the crucible and having a second portion having a second pitch wherein the first pitch is of a higher spatial frequency than the second pitch. The heating filament is non-inductively wound about the crucible and positioned in conformity to the outside structure of the crucible. The heat shield is positioned proximate and about the crucible and heating filament or filaments. The heating filaments are connected to a controllable electric power supply producing a near constant temperature along the long axis of the crucible.