High current metal ion beam injection experiments

Abstract

High current beams of metal ions have been efficiently transported through the injector beam line of the UNILAC heavy ion linear accelerator. Using a MEVVA high current metal ion source, a beam current of 20 emA of titanium (all charge states, Q = 1,2, and 3) was accelerated to an energy of 2804 keV through a single gap accelerating structure, and a current of over 5 emA of Tiz+ was measured at the Wideroe entrance some 13 meters downstream. The beam pulses were flat and reproducible. In this paper we describe the source configuration used and the results of the injection experiments.The GSI accelerator complex is presently being upgraded by the construction of a large heavy ion synchrotron, SIS (Schwerionen Synchrotron) [1,2], and storage ring, ESR (Experimenteller Speicher Ring) [3,4]. It is a goal of the GSI program to provide energetic, high current beams of metal ions as well as gaseous ion species from these low duty cycle accelerators, and this is the reason for our interest in the experiments reported on here.A high current metal ion source has been developed at LBL [5-81, with which beam currents of several hundreds of milliamperes can be produced from a wide range of metals spanning the Periodic Table. We would like to use this unique ion source for the injection of high current metal ion beams into the GSI UNILAC heavy ion accelerator [9-lo]. Thus the present work addresses the concem of adapting the M E W A source to the GSI UNILAC heavy ion accelerator. Previous work on the application of the MEVVA ion source to the GSI accelerator facilities has been reported by Brown et al. [ll], Keller et al. [12], and Mueller et al. [13]. In this paper we describe the use of the MEVVA ion source and the results of the most w e n t series of experiments to adapt the MEVVA to the UNILAC.llmAQuu The ability of the MEVVA ion source to produce high current beams of metal ions has been well established, but some of the typical beam characteristics have needed improvement for accelerator injector application. Thus, for example, it has often been the case that the beam pulse shape has lacked reproducibility from shot to shot, often with missing pulses. The pulse shape within a single beam pulse has also needed improvement. Finally, t & beam noise (fractional beam current fluctuation level) has been seen to vary quite significantly depending on the precise operating conditions; this has given cause for concem both about possible beam loss due to inadequate space charge neutralization, as well as about accelerator RF regulation problems due to the fast changes in beam loading during the pulse.As well as the original MEVVA II ion source [5,6], we also tried a new source configuration in which the MEWA cathode stem was attached to an anode chamber of the CHORDIS ion source [14], with a permanent magnet (samarium cobalt) multipole structure incorporated within the plasma region between anode and extractor, the possibility of this hybrid providing an interesting configuration was suggested by Keller and Emig [15]. More details...