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.
Tandem accelerators differ from single-ended ones in two mayor points. For the same terminal voltage the ions accelerated in the first type can achieve higher energy, since they are accelerated twice: once to the terminal voltage itself and then, after negative to positive charge exchange, till the end of the accelerator with the multiplicative factor of the charge state obtained. 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.