The Earthing System of the PRIMA Neutral Beam Test Facility based on the Mesh Common Bonding Network Topology

PRIMA is a large experimental facility under realization in Padova, aimed to develop and test the Neutral Beam Injectors for the ITER experiment. Two separate experiments, SPIDER and MITICA, will be hosted in the PRIMA facility. MITICA will be the first full size IT ER injector aiming at operating up to the full acceleration voltage (1 MV) and at full power (16.5 MW). The operation of these devices involves high RF power and very high voltage. Frequent and intense electrical breakdowns inside the beam sources occur re gularly. Several sensitive diagnostics systems are needed for control and characterization of the physical phenomena, which must operate in this hostile environment. The presence of a widespread and carefully optimized earthing system is of paramount impor tance to achieve a satisfying immunity from disturbances for equipment and diagnostics. The paper describes the design and the realisation of the earthing system of the PRIMA facility, which is based on the MESH - Common Bonding Network (MESH - CBN) topology, as recommended by IEC and IEEE standards (IEC 61000 - 5 - 2, IEC 62305, IEEE 1100, IEE 142) for installations where high levels of Electromagnetic Interferences are expected. A similar approach was also chosen for ITER, so that PRIMA will represent a useful te st bed for these techniques in conditions very similar to the ITER ones. The principles of the MESH - CBN approach were adapted to the PRIMA layout, which is composed by several buildings, that are independent for seismic and architectural reasons, but are l inked by many electrical conduits and hydraulic pipelines. The presence of two independent experiments was taken into account, as well as the availability of huge foundations with a large number of piles and pillars. Buildings parts dedicated to host contr ol rooms and sensitive equipment were treated with particular care.