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The Tandem MP, constructed by the High Voltage Engineering Corporation, has been working at LNS since 1983 and can accelerate ions from protons to gold, being capable of reaching a tension of 14MV at the terminal.

The beam to be injected into the Tandem is made up of negative ions (charge state -1) produced in a “sputtering” source, installed on a platform that allows us to achieve a maximum injection energy of 450keV.

In order to maintain the elevated electrical potential of terminal acceleration, transporting the electrical charges was based on the use of an isolated belt until 2015, pulled at a maximum velocity of 17 metres a second. In January 2015, the belt system was replaced with the new Pelletron system, based on the use of a chain made up of a series of metallic cylinders (pellets) linked by isolating nylon structures that transport the charges to the terminal highly efficiently and reliably. Through this upgrade, the stability of the tension at the terminal is far more stable than that achieved with the belt, presenting oscillations that remain contained within 0.02%.

The charge transport system and the accelerating column have to work in an environment full of isolating gas SF6 at high pressure in order to prevent possible discharges due to the high electrical potential. For this reason, the Tandem is inside an approximately 300-cubic-metre iron tank capable of sustaining gas pressure higher than 9 atm. A complex system of re-circulating and drying of the gas guarantees that the correct functional parameters of purity and humidity are maintained while it is working.

Essentially, all the elements can be accelerated, once the noble gases have been excluded, with an energy that can reach 200 MeV for the heavier ions and with a transmission close to 80%.

The Tandem is an ideal accelerator for carrying out measurements at different energy values, in as much as the beam preparation and energy variation times are rapid. In over thirty years, the scientific environments in which the Tandem beams have been used successfully are many, of which the study of the functions of excitation and nuclear astrophysics. Moreover, the Tandem was used to accelerate the first radioactive beam at LNS, the 8Li. Besides the activities of scientific research, the measurements carried out with Tandem beams aimed at application activities are diverse; among them the study of radiation damage on electronic components and the characterisation of archaeological finds.

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