Development of a Bi+ source for a heavy-ion-driven ignition facility

As part of a conceptual design for an inertial fusion ignition facility, a prototype driver is being developed for Bit production. The source is driven by an are discharge ionizing bismuth atoms which are evaporated from an oven inside the source chamber. The fraction of the singly ionized bismuth is above 92%. Emittance growth from the ion source to the target is crucial but inevitable. Therefore, although the required beam current is high, the initial ion source emittance still should be low. For that purpose, a multi aperture extraction system was chosen. Seven holes with a radius of 3 mm each make up for an overall emission area of 1.98 cm(2). For that system, the perveance limit was achieved at a beam current of 70 mA and an extraction voltage of 27.5 kV. The corresponding emission current density amounts to 35 mA/cm(2). Furthermore, the effective emittance of a 21 mA - 18.2 keV beam has been measured. It amounts to 0.27 pi mm mrad (80%, normalized, 4 rms). This paper will give a description of the source regarding its prospective use in a heavy-ion-driven ignition facility. In addition, various dependencies between the plasma parameters and the beam composition are presented. The use of other heavy-ions is considered as well as the influence of the extraction geometry on the effective emittance. (C) 1998 Elsevier Science B.V. All rights reserved.