IEEE TRANSACTIONS ON NUCLEAR SCIENCE, JUNE 1967 A STUDY OF A DUOPLASMATRON ION SOURCE WITH AN EXPANSION CUP Mohamed E. Abdelaziz and Ahmed M. Ghander UAR Atomic Energy Establishment Cairo, Egypt, UAR Summary This work describes a stu@ly of the Duoplasmatron ion source for the purpose of investigating the condit- ions necessary to imljrove its per- formance. First a general review is made of theoretical considerations involved in the sources plasma mechan- ism and the geometry of the extraction system. Then the experimental work deals with the arc discharge charact- eristics as well as the sourceds per- formance when the beam is extracted with a simple Pierce extracting elec- trode. Through an invar anode insert a 70 mA was obtained at 35 kV. The main improvement was then due to beam extraction from an expansion cup which rendered a 300 mA beam at a low- er voltage of 18 kV. The use of different anode materials has indicated the influence of mag- netic field penetration on plasma foc- using within the expansion cup. A beam current reaching 1 ampere was noticed when a non-magnetic anode was used. 1. Introduction Recent developments on high current accelerators for nuclear disintegrat- ion, ion injectors for thermonuclear resea.rch and ionic propellers for space vehicles have stimulated deep interest in the study of high current ion sources. Among the different types of intense ion sources in use to- day, the Duoplasmatron is featured with its high ionization efficiency, high current density and the possibility of yielding a beam with a reasonably good quality due to the focusing proper- ties of its extraction system. Since the first type of Duoplasma- tron was introduced by von Ardennel many subsequent developments have been mainly concentrated on its extraction system which is certainly the most critical in ion source design. However, for the extracted bean to contain a high current density it is also essential that the sources plasma has to be sufficiently rich with ioniza- tion densities so that it could supply the ion emitting surface with the required current density. The mecha- nism by which int6nse ionizatian is produced within the arc chamber of the Duoplasmatron makes it unique in satisfying such requirements. Consequently a review is first made of the theoretical considerations connected with the two main problems of the source, i.e. the plasma theory and the theory of ion beam extraction. This is followed by an experimental investigation of the sourceb perfor- mance, also on the two main problems. Thus, the arc discharge and ion-beam extraction characteristics are obtain- ed experimentally under different con- ditions. Interpretation and analysis of these results is based on the the- oretical studies presented here. 2. Theory of the Duoplasmatron Ion Source. In the basic Duoplasmatron config- urationl a low pressure arc is pro- duced between a cathode and an anode. A conical intermediate electrode causes mechanical constriction, while a strong magnetic mirror between the intermediate electrode and the anode causes magnetic constriction. Thus a very dense plasma is created in the vicinity of the extraction aperture. Plasma penetration through the anode aperture permits a large area plasma boundary to emit an ion beam on the application of a highly negative potential to the extractor. In the following both problems are treated, namely the plasma theory and that of ion beam extraction. 2.1 Plasma, Theor of the Duoplasmatron. The normal arc discharge (one with- out constrictions) consists of three regions2: the cathode drop with a voltage drop approximately equal to 46