The Frankfurt 200 mA proton source

For the International Fusion Materials Irradiation Facility (IFMIF) scenari o, a 140 mA deuterium beam in continuous wave (cw) mode with an atomic yiel d of above 85% is required. The normalized root-mean-square emittance shoul d be less than 0.2 pi mm mrad at the entrance of a RFQ. As part of a concep tual design for IFMIF, a new ion source has been developed and is tested at the Institut fur Angewandte Physik in Frankfurt. The ion source is of the volume type with a tungsten cathode driving the discharge. Both cw and puls ed mode are possible and were studied. First experiments were carried out w ith deuterium. 80 mA deuterons with a D+ fraction of above 90% were extract ed [A. Maser , Rev. Sci. Instrum. 67, 1054 (1996)]. In order to avoid neutr on generation by the d-d reaction, hydrogen was used instead of deuterium l ater on. As far as the ion source and plasma production processes are conce rned, the use of hydrogen instead of deuterium is equivalent because of the ir similar atomic shells. Recently, a 200 mA proton beam at 55 kV was extra cted in cw mode (according to Child-Langmuir, 200 mA H+ corresponds to 140 mA D+) with a H+ fraction of 93%. This article will give a detailed descrip tion of the ion source and the essential experimental results. Especially, the influence of important physical parameters (such as discharge current a nd strength of the filter field) on the H+ fraction was studied. By using d ifferent kinds of auxiliary gases, the influence on the H+ fraction and the noise level were investigated, too. (C) 2000 American Institute of Physics . [S0034-6748(00)58102-7].