Structural Design of an Electrostatic Shield at $-$ 600 kV for the MITICA Beam Source

MITICA (Megavolt ITER injector and concept advancement), the full-scale prototype of ITER heating neutral beam (HNB), is under construction at the Neutral Beam Test Facility (NBTF), Padua, Italy. It is designed to accelerate deuterium negative ion beam with a 40-A current up to 1 MeV. In order to test the capability of the beam source (BS) to withstand a total voltage of 1 MV, it has been decided to conduct electrical tests with a “BS mockup” reproducing the geometry relevant for high-voltage (HV) holding. In addition, these tests will study the influence of an electrostatic shield, referred to as ES06. The ES06 approximately follows the estimated
$-$
600-kV equipotential surfaces inside the vacuum domain, surrounding the parts of the accelerator and ion source at a potential between
$-$
600 kV and
$-$
1 MV to eliminate the largest gaps between the rear side of the BS and the grounded vessel with a voltage difference up to 1 MV. Moreover, the ES06 must be compatible with the real MITICA BS. The ES06 is a complex object with several conflicting constraints (electrostatic and mechanical, together with implications relative to remote handling and integration). It also adds a nonnegligible weight to the accelerator. This article describes the design of the ES06, the numerical models, and the load cases tested and, in particular, presents a mechanical analysis of both the mockup and the real MITICA BS with the ES06 mounted on, including seismic verifications. The design of the ES06 is verified in all the cases tested.