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Upgrade of the Rudjer Boskovic Tandem Accelerator Facility

Final Report Summary - RBI-AF (Upgrade of the Rudjer Boskovic Tandem Accelerator Facility)

Through the Laboratory for Ion Beam Interactions (LIBI), the Division of Experimental Physics of the Rudjer Boskovic Institute (RBI) operates and maintains the Tandem Accelerators facility that physically consists of the 6 MV Tandem Van de Graaff and 1 MV Tandetron accelerators, associated beam lines and measurement end-stations. The facility is used for research and applications by various clients/collaborators in a range of fields, including nuclear and atomic physics, applications in materials science and development of advanced materials, archaeology and characterisation of cultural heritage objects, etc.

The goal of the RBI-AF project was to stabilise and reinforce the existing research potentials of the RBI Tandem Accelerator Facility in order:
(i) to strengthen its presence at the European Research Area by maintaining and increasing its involvement in cooperative research projects on equal basis with partners from the EU and third countries by offering modern state of the art experimental facilities and know-how;
(ii) to meet demands of its clients/collaborators from various sectors of the national, regional and inter-regional character, in line with the RBI mission, vision and adopted values.

Through the project, the facility strengthened its possibilities to continue giving its services to traditional clients / collaborators, and in a more efficient way. In addition, the project opened up further possibilities for the facility to offer new subjects and activities, and to increase linkage with clients / collaborators from various sectors of the national and regional character, thus increasing the number of clients / collaborators and services. This was achieved by physical upgrading of certain measurement capabilities; upgrade of the 6 MV tandem accelerator to provide required ion beams in more efficient way; by preparing promotion brochures, upgrade the facility web site, and organising a workshop for targeted user-groups.

Upgrades supported by the project included:
(i) upgrade of the in-air analysis end station;
(ii) upgrade of the focusing capabilities of the existing ion microbeam end station;
(iii) upgrade of the material modification end station.

In addition, the project supported upgrade of:
(iv) 6 MV EN tandem accelerator vacuum system;
(v) its negative sputtering ion source.

With the upgrade of the in-air end station (external beam) we strengthened our ability to make ion beam analysis (IBA) with the ion beam extracted in air, which practically means that we are able to make analytical measurements of samples that cannot be exposed to vacuum. The end-station is at the moment equipped with the standard Si(Li) X-ray detector for in air PIXE measurements. There are several sectors of applications, one being materials science (analysis of large objects that physically cannot be inserted in vacuum chamber) and the other one archaeometry or more generally 'analysis of cultural heritage objects' (analysis of fragile and precious objects that cannot be inserted in vacuum or sampled). Within the project we made the sample stand that allows fine manual XYZ sample translation, which is in addition equipped with stepper motors for computer controlled XYZ sample translation.

Within the RBI-AF project the focusing capabilities of the existing ion microbeam end station were improved. This was achieved by the installation of the new magnetic quadrupole pair in between the analysing and switching magnets of the 6 MV EN Tandem accelerator system and by upgrading the ion microbeam triplet configuration to the quintuplet magnetic quadrupole configuration. In this way we slightly improved demagnification (compared to the triplet configuration), and significantly improved focussing capabilities of heavier ions.

The new end-station was designed and installed with unique capability: ion beams from two accelerators may be delivered to a sample simultaneously for materials modification studies, and/or for ion beam analysis.

The 6MV EN tandem accelerator vacuum system was improved by:
(i) the exchange of the old four cryogenic vacuum pump stations with modern air-cooled turbo-molecular vacuum pumps at the 6 MV accelerator;
(ii) the exchange of the old vacuum gauges with new modern devices; and
(iii) by adding turbomolecular vacuum pump station inside the high-voltage terminal of the accelerator.

Before this project the 6MV accelerator was equipped with the home-made sputtering ion source which has been already in use for more than a decade. It is simple and easy to operate, but it has disadvantages (frequent maintenance, low currents). In addition, irrespective of this project we obtained some SNICS ion source components. Under this project we completed the 'new' sputtering ion source. This required design and installation of new high-voltage platform (S) to accomodate this ion source and the existing 'alphatros' ion source. In addition, we purchased and assembled all the missing components to complete the system, including ion beam optical elements (the injection accelerating tube, high voltage extraction and focusing electrodes), high voltage and other power supplies and control devices, and vacuum system components (vacuum tubes, flanges, pumps).

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