The Amsterdam quintuplet nuclear microprobe

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Abstract

A new nuclear microprobe comprising of a quintuplet lens system is being constructed at the Ion Beam Facility of the “Vrije Universiteit” Amsterdam in collaboration with the Microanalytical Research Centre of the University of Melbourne. An overview of the Amsterdam set-up will be presented.

Detailed characterisation of the individual lenses was performed with the grid shadow method using a 2000 mesh Cu grid mounted at a relative angle of 0.5° to the vertical lens line focus. The lenses were found to have very low parasitic aberrations equal or below the minimum detectable limit for the method, which was approximately 0.1% for the sextupole component and 0.2% for the octupole component. We present experimental and theoretical grid shadow patterns, showing results for all five lenses.

Section snippets

The Amsterdam ion beam facility

The Ion Beam Facility set-up at the “Vrije Universiteit” Amsterdam is illustrated in Fig. 1. It has been built around a 1.7 MV NEC 5SDH-2 dual tandem Pelletron accelerator. At its centre Nitrogen gas is used for electron stripping. The ion source used is a NEC Alphatross charge-exchange RF source. The electron exchange channel makes use of Rubidium vapour. With this set-up experience has been gained in accelerating H, He, D and N ion beams. We plan to install a Duoplasmatron in the near future

The nuclear microprobe

The quintuplet microprobe build in collaboration with the Microanalytical Research Centre, Melbourne, optically resembles the CSIRO-GEMOC system [2], [3] and is illustrated in Fig. 2. It features a quadrupole quintuplet lens system, which when operated in a high excitation orthomorphic mode will have a demagnification factor of 67 and a working distance of 85 mm. The lenses are mounted on a girder that is vibration isolated from the floor. Contrary to the CSIRO-GEMOC system only the lens

The grid shadow measurements

The grid shadow pattern method [4] was used to test the lenses of the system. The parasitic components were found to be very low: close to the minimum detectable limit.

Each lens was tested using the MP2 system [5] at the University of Melbourne. The lens under test was the only ion optical component on the beam line at the time of the test, with all inactive lenses having been physically removed. Also, precautions [6] were taken to minimise parasitic magnetic fields external to the lens. These

Acknowledgments

This work was supported by an ICES/KIS grant from the Dutch ministry of education and sciences (OC&W) and the ministry of economic affairs (EZ). It is also supported by the Foundation for Fundamental Research of Matter (FOM), which is financially supported by the Netherlands Organization for Scientific Research (NWO).

Many thanks to all people involved at the Microanalytical Research Centre in Melbourne for the kind reception and pleasant stay during the weeks the grid shadow measurements were

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