Optimization of 10Be beam transport at DREAMS
Johannes Lachner1, Georg Rugel1, Konstanze Stübner1, Carlos Vivo-Vilches1, Stephan Winkler1, Anton Wallner1
1Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany
¹⁰Be measurements at DREAMS take up a large fraction of the AMS beam times at the 6MV accelerator at the ion beam center of HZDR. Currently, they are undertaken at a terminal voltage of 4.5 MV [Rugel et al., NIMB 2016]. Here, we investigated potential benefits from a change in accelerator terminal voltage in order to increase the efficiency of ¹⁰Be counting.
Presently, after the stripping in Ar gas in the accelerator, Be2+ ions are directed towards a 1 μm thin SiN foil placed after the analysing magnet on the high-energy side that helps to suppress the ¹⁰B interference by differential energy loss and separation in an electrostatic analyser. After passage through the absorber foil the mean charge state of Be ions is increased and the 4+ charge state is selected and transported to the detector. In this mode of operation, losses of ¹⁰Be ion beam intensity on the way from the low-energy side of the system to the detector are dominated by these two charge exchange processes [Arnold et al., NIMB 2010].
However, there is only limited data for the recharge behaviour of Be in a stripper gas at energies relevant for the measurements at DREAMS [Hofmann et al., NIMB 1987; Niklaus et al., NIMB 1994]. For an argon gas stripper, Niklaus et al. [NIMB 1994], suggest lower terminal voltages for optimal transmission of ¹⁰Be2+. On the other hand, an increase of the overall energy of the Be2+ beam after the accelerator will certainly allow for a higher Be4+ yield after the passage through the absorber foil.
In contrast to the original data by Niklaus et al. [NIMB 1994], we found that increasing the terminal voltage to ≥ 5MV does not reduce the yield of the Be2+ charge state after the accelerator.
As a further recharge to the 4+ charge state is conducted in a foil after the analysing magnet it is desirable to hit the foil with the highest available energy/velocity to have optimal stripping of Be2+ to the naked ion. Thus, the efficiency of ¹⁰Be measurements can indeed be improved by increasing the terminal voltage, both at DREAMS and at other AMS facilities of a similar size that are using the absorber method with a charge exchange from 2+ to 4+ for isobar suppression.
We present data on the performance of the system at higher beam energies documenting an increase in overall detection efficiency by 25%. Under these conditions the interfering isobar ¹⁰B is still well separated, and no additional interferences (e.g. from nuclear reactions) appear in our spectra.
studied Physics at TU München
PhD at ETH Zürich
PostDoc at University of Vienna
at HZDR since 2019