A Mass Analyzer System for the High Voltage Terminal of a Van De Graaff Heavy Ion Accelerator

A computer analysis of an electromagnetic mass analyzer system which will be mounted in the high voltage terminal of a planned 3MeV van de Graaff heavy ion accelerator at M.I.T. has been performed. Since one of the main fields of application of this new facility will be ion implantation, a stigmatic focusing analyzer with high transmission is required. It is shown that a magnetic sector field which is formed by plane inclined pole faces meets both these requirements. Second order ion optical calculations for this type of field are given and compared with two more conventional alternatives of stigmatic focusing analyzers namely the homogeneous field fringe field focusing magnet and the rotationally symmetric field with logarithmic field gradient n = 1/2. The complete ion injector system which will consist of a high temperature metal ion source, an extraction and focusing system and a stigmatic double focusing mass analyzer will have a total weight of about 400 pounds and be capable of unit mass resolution at least up to mass number 150.