Design, interface development and structural analyses of SPIDER vacuum vessel

Abstract

In the framework of the activities foreseen for PRIMA (Padova Research on Injector Megavolt Accelerated) the SPIDER experiment plays an essential role with respect to the goal of extracting from an ITER size negative ion source an ion beam aiming to reach 70 A H-, 50 A D- and 100 keV of acceleration energy. The SPIDER ion source, the 100 keV accelerator, a Short Pulse Calorimeter and a beam dump will be housed inside a vacuum vessel purposely designed for this scope, given the high number of internal and external interfaces between the vessel and the other auxiliary subsystems as diagnostics, pumping, inspection, power supply and cooling. The SPIDER vacuum vessel is a cylindrical vessel made of AISI 304 L stainless steel and composed of four main components: two cylindrical modules (beam source module and pumping module) and two torispherical lids (rear lid and front lid). The whole vessel is approximately 6 m long and the internal diameter is 4 m. The two cylindrical modules are connected by means of a bolted flange vacuum sealed with Viton ® o-rings. The two lids are connected to the relevant cylindrical module by means of bolted clamps. All the vessel modules and lids feature a large number of ports to interface the vessel and the internally hosted systems with the auxiliary subsystems. In particular three large vertical electrical bushings (internal diameter of about 700 mm) have been positioned on the beam source module. Each bushing consists of a ceramic ring closed by a metallic flange able to assure vacuum tightness and polarized at −112 kV. The bushing positioned on the top of the vessel houses the feedthroughs for power supply and signal cables; the other two positioned on the bottom are dedicated to the inlet/outlet of beam source cooling and gas injection systems. All the vessel modules are mounted on a rail system to facilitate installation and maintenance operations inside the experiment hall. The most important design issues and solutions are presented in this paper together with analyses descriptions and results.