Abstract
The effect of double frequency heating on the performance of the CERN GTS-LHC 14.5 GHz ElectronCyclotron Resonance (ECR) ion source in afterglow mode is reported. The source of the secondary microwave frequency was operated both in pulsed and continuous wave (CW) modes within the range of 12–18 GHz. The results demonstrate that the addition of the secondary frequency can significantly impact the extracted beam currents and the temporal stability of the beam during the afterglow discharge. For example, up to a factor of 2.6 increase was achieved for 208Pb35+ and a factor of 3.1 for 208Pb37+ compared to single frequency afterglow currents. It is shown that these effects are dependent on the choice of the secondary frequency with respect to the primary one and on the temporal synchronization between the two microwave sources. Overall, the results provide new insight into the afterglow discharge supporting the prevailing understanding of the physical processes behind the phenomenon.
Highlights
Thanks to their reliability in long term operation and capability to produce intense beams of multiply charged heavy ions from a wide selection of gaseous and solid elements, Electron Cyclotron Resonance (ECR) ion sources [1] are employed in a broad range of research and industrial applications
The combination of double frequency heating and afterglow has not been widely studied. It was shown in a recent study, performed with single frequency heating, that the choice of the microwave frequency does impact the afterglow performance [8]. These results suggest that applying double frequency heating could yield additional performance improvements, providing a clear motivation for further studies
GTS-Large Hadron Collider (LHC) is a second generation room-temperature ECR ion source based on the design of the Grenoble Test Source (GTS) by CEA Grenoble (Commissariat à l’Énergie Atomique) [10]
Summary
Thanks to their reliability in long term operation and capability to produce intense beams of multiply charged heavy ions from a wide selection of gaseous and solid elements, Electron Cyclotron Resonance (ECR) ion sources [1] are employed in a broad range of research and industrial applications. At the European Organization for Nuclear Research (CERN) the GTS-LHC 14.5 GHz ECR ion source is used to produce pulsed heavy ion beams for the CERN experimental program, including collider experiments with the Large Hadron Collider (LHC) and fixed target physics studies with the Super Proton Synchrotron (SPS) [2,3]. A selection of methods have been developed to enhance the performance of ECR ion sources, especially in terms of the beam currents of highly charged ions [4].
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