The VIVITRON is a Van de Graaff tandem electrostatic accelerator. Our focus here will be to highlight the points making the VIVITRON a different machine from others of the same kind.

Initially designed to operate at voltages up to 35 MV, 10 years of studies and observations have shown that the upper limit was closer to 25 MV than the initial value. Yet even at that value, the VIVITRON remains the most efficient machine of this type in Europe and is one of only three machines able to reach 20MV in the world.

Apart from its size, a little bigger than the largest existing machines (tank length 50 m, tank diameter in the middle 8.5 m, 60 t of SF6 dielectric gas) the VIVITRON differs mainly on the following points:

• The inner mechanical structure is made of large dimension longitudinal girders and radial insulators posts. The materials used are fibre glass epoxy in the former case and aluminium oxide charged araldite in the latter. Both materials have the required electrical and mechanical characteristics for this type of use.



• Seven porticoes holding 7 discrete electrodes (intershields) equally spaced by insulators, ensure a quasi-uniform field distribution everywhere inside the tank.
  
  
• The charging system is made of a belt running between both ends of the tank. During summer 1997, two "down-charge" power supplies were added to the usual "up-charge" power supplies improving the stability by a factor of 3.
  
  
• Electronic devices inside the terminal high voltage electrode and other places inside the tank are fully protected against spark discharge.



• The control system of the machine is fully computerized. It is made of 13 real time computers spread over the site and 5 workstations located in the control room, connected together with a private Ethernet optical network.