Status report of the 28GHz superconducting electron cyclotron resonance ion source VENUS (invited)

Abstract

The superconducting versatile electron cyclotron resonance ͑ECR͒ ion source for nuclear science ͑VENUS͒ is a next generation superconducting ECR ion source designed to produce high-current, high-charge-state ions for the 88-Inch Cyclotron at the Lawrence Berkeley National Laboratory. VENUS also serves as the prototype ion source for the rare isotope accelerator ͑RIA͒ front end, where the goal is to produce intense beams of medium-charge-state ions. Example beams for the RIA accelerator are 15 p A of Kr 17+ ͑260 e A͒, 12 p A of Xe 20+ ͑240 e A of Xe 20+ ͒, and 8 p A of U 28+ ͑230 e A͒. To achieve these high currents, VENUS has been optimized for operation at 28 GHz, reaching maximal confinement fields of 4 and 3 T axially and over 2.2 T on the plasma chamber wall radially. After a commissioning phase at 18 GHz, the source started the 28 GHz operation in the summer of 2004. During that ongoing 28 GHz commissioning process, record ion-beam intensities have been extracted. For instance, measured extracted currents for the low to medium charge states were 270 e A of Xe 27+ and 245 e A of Bi 29+ , while for the higher charge states 15 e A of Xe 34+ , 15 e A of Bi 41+ , and 0.5 e A of Bi 50+ could be produced. Results from the ongoing 28 GHz commissioning as well as results using double-frequency heating with 18 and 28 GHz for oxygen and xenon are presented. The effect of the minimum B field on the ion source performance has been systematically measured for 18 and 28 GHz. In both cases the performance peaked at a minimum B field of about 80% of the resonance field. In addition, a strong dependence of the x-ray flux and energy on the minimum B field value was found.

Limitation of the ECRIS performance by kinetic plasma instabilities (invited)

“…Figure 1 shows the performances of VENUS, RAM-SES (RIKEN liquid-He-free SC-ECR), SuSI (NSCL), and JYFL 14 GHz A-ECR, operating at frequencies of 14-18 GHz, as a function of B min /B ECR . The given data have been chosen for display because the original references [3][4][5] explicitly show the effect of varying B min /B ECR -ratio on the extracted beam currents. The extracted currents of highly charged ions have been normalized with respect to the maximum current reported for each data set in order to allow the comparison between different ion sources and ion species.…”

Optimization of ECR ion sources for high charge state beam generation

“…Experience in this field started with the test of SERSE source at 28 GHz [12] and has been recently confirmed from measurements on the VENUS source [13]. In both cases the maximum RF power was limited by the liquid helium (LHe) boiloff.…”

High density ECR plasmas for the production of intense highly charged ion beams

“…the VENUS source at LBNL in USA [6]. According to these two experiences, the MS-ECRIS source has been designed in the frame of the EURONS initiative, funded by the European Union, with the aim to produced an ECR plasma confined by a B-minimum magnetic trap with the highest design values up to date.…”