Investigation of the beam trajectory and beam profile development in the 135° gas-filled magnet at the AMS device for medium mass isotopes at the Cologne University

Ms Susan Herb1, Mr. Gereon Hackenberg1, Dr. Markus Schiffer1, Dr. Stefan Heinze1, Prof. Dr.  Alfred Dewald1

1University Of Cologne, Cologne, Germany

First 53Mn and 60Fe test measurements revealed that improvements of our AMS set-up at the FN tandem accelerator should be made to enable the measurement of lower levels isotopic ratios of 10^(-13) and 10^(-16.) Therefore, we aim to improve the isobar separation of the high energy mass spectrometer as well as its transmission.

For a better understanding of the ion beam behavior inside a gas-filled region of a magnet, the development along the flight path inside the magnet was investigated. The beam profile and position along the ion paths was measured in the dispersive direction (x-axis) with dedicated silicon pin diode detector arrays at 4 different locations. In addition, the two-dimensional profile (x/y) was measured at the exit of the magnet. For the measurement inside the magnet, a 60Ni background taken from a 60Fe blank at an initial energy of 100 MeV was injected and particles were verified with the detector arrays. Thereby, we also investigated the effect of using nitrogen to helium as fill-gas.

The measured data was used to test and improve our in-house developed Monte-Carlo simulation code. The code simulates the ion transport in a gas filled magnet taking into account continuous energy loss and successive charge changing collisions as well as angular and energy straggling. The first version of the code was designed for nitrogen gas and was now adapted for helium. The comparison of the calculated and the measured beam trajectories revealed that the gas density effect influencing the ion charge has to be considered [1].

The contribution will report on details of the conducted measurements and compare it with the calculations. Ongoing developments of the simulation code will be discussed.

[1] Betz, 1972, Reviews of Modern Physics, 44.


Susan Herb graduated with a master degree in physics at the University of Cologne in 2018. Her bachelor and master theses included topics like programming data analysis software or creating the framework for automatic measurements at the Cologne 10 MV FN accelerator. Since the start of her Ph.D. project, her main topic is the development of AMS measurements of medium-mass isotopes with gas-filled-magnet, like 60Fe , in Cologne.

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