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
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.
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
- 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.