Personnel Responsible: Victor Joco

The main facility of our center is a 5MV terminal voltage tandem accelerator. It was designed and constructed by High Voltage Engineering Europe (HVEE) as the first Coaxial High Current Tandetron Accelerator of 5MV using the Cockroft-Walton power supply system (previously, terminal voltages were never higher than 3 MV with this system and the power supply itself was perpendicular to the acceleration stage).

This novel design guarantees a more reliable operation, low ripple and high stability at a terminal voltage of 5 MV, allowing for a better energy ion determination and, therefore, higher confidence in experimental results. This type of accelerator is the best suited for Ion Beam Analysis techniques applied to Materials Science, Archaeometry, Environmental Science, etc.., but also Positron Emission Tomography (PET), deep-level light-ion implants in semiconductors, or accelerator mass spectrometry (AMS) of various elements.

What follows is a brief description of the working principles of such an accelerator, from the Ion sources to the switching magnet.

Tandem accelerators differ from single-ended in two mayor points. For the same terminal voltage the ions accelerated in the first type can achieve much more energy, since they are accelerated twice, once to the terminal voltage itself and another, after negative to positive charge exchange, till the end of the accelerator. The charge exchange is obtained by stripping of electrons when ions cross a well defined region at the terminal, which is filled with high purity nitrogen gas.

The second important difference is that negative ions, which are more difficult to obtain, need to be injected at the beginning of the acceleration process. On the other hand, ion sources can be placed out of the accelerator tank, allowing for an easier maintenance and selection of the desired ion species.

At CMAM there are two ion sources allowing for virtually any element from H to U:

Schematic drawing of the accelerator: