Voltage holding prediction in multi-electrode multi-voltage systems insulated in vacuum

Abstract

The voltage holding in the 1 MV ITER Neutral Beam Accelerator is recognized to be one of the most critical issues for long lasting beam operation, due to the complex electrostatic structure formed by differently shaped electrodes polarized at different potentials. At present, no model is available to predict the breakdown probability of electrostatic system with a comparable complexity degree. This paper is aimed at proposing an innovative modelling for the voltage breakdown prediction of such complex systems, based on the implementation of the micro particle (clump) induced breakdown Cranberg-Slivkov theory into a statistical approach.I.

HVPTF—The high voltage laboratory for the ITER Neutral Beam test facility

“…8 reports very preliminary results of the conditioning of the 180 mm diameter electrodes with two gap lengths. The max voltage holding (195@10 mm and 230@15 mm) is reached very soon (less than one hour), and corresponds to the values found in literature [3]; actually, the voltage was limited by glow discharge appearance in the electrodes region that made the current increasing above the pre-set current limit of 200 A; the electric field between electrodes is respectively 19.4 MV/m and 15.3 MV/m.…”

“…Three couples of electrodes with three different diameters (108 mm, 180 mm and 300 mm) have been prepared to perform the test campaign aimed at experimentally validating the probabilistic breakdown model described in [2]. In particular, the different diameters would show the so-called area effect in voltage holding described by many authors [4].…”

“…current, pressure and vacuum quality. The HVPTF has two experimental setups: the first is rated to carry out experiment up to 300 kV, devoted to the characterization of the breakdown statistics for the validation of a breakdown model recently developed at the Consorzio RFX [2]; the second setup -derived from [3]-is rated to carry out experiment up to 800 kV, devoted mainly to investigate the effect on the breakdown voltage of electrode material, surface finishing, gas pressure and voltage conditioning procedures. The two setups share the same Vacuum and Gas Injection systems and the same Control and Safety & Interlock Systems.…”

1-MV Vacuum Insulation for the ITER Neutral Beam Injectors

“…Pilan et al [13] are also working to analyze insulation of the accelerator aiming at proposal of an innovative modeling for the voltage breakdown prediction of such complex systems, based on the implementation of the microparticle (clump)-induced breakdown Cranberg-Slivkov theory [14] into a statistical approach.…”