Speaker
Description
To reach fusion conditions and control the plasma configuration in ITER, the next step in tokamak fusion research, two neutral beam injectors (NBIs) will supply 17MW each, by neutralizing accelerated negative hydrogen or deuterium ions. The requirements of ITER NBIs (40A/1MeV D- ions for ≤1h, 46A/870keV H- ions for ≤1000s) have never been simultaneously attained. So in the Neutral Beam Test Facility (NBTF, Consorzio RFX, Italy) the operation of the full-scale ITER NBI prototype (MITICA) will be tested and optimised up to full performances, focussing on accelerator (including voltage holding), beam optics, neutralisation, residual ion removal. The NBTF includes also the full-scale prototype of the ITER NBI source with 100keV particle energy (SPIDER), for early investigation of negative ion production and extraction, source uniformity, negative ion current density and beam optics.
This contribution will describe the main results of the first two years of SPIDER operation, devoted to characterizing plasma and beam parameters. Investigation of the efficiency of RF coupling to the plasma in different configurations of the RF circuits and the temporary introduction of a mask reducing the number of beamlets (for a total number of ~100 out of 1280) allowed to extend the operation parameter range, by maintaining the pressure profile within a controlled range to reduce disruptive occurrences. Magnetic filter field effectiveness in reducing the co-extracted electron current was verified, however this field was found to affect the plasma necessitating a modification to the magnetic configuration. A major shutdown, planned for 2021, to solve the issues identified during the operation and to carry out scheduled modifications, will be outlined.
The installation of each MITICA power supply and auxiliary system was completed; mechanical components are under procurement by F4E. Integration. Commissioning and test of the power supplies (PS), procured by different Domestic Agencies, will be presented. In particular, 1.0MV insulating tests were carried out step-by-step and successfully completed. During 2020 PS integrated tests on accelerator dummy load will be carried out, including the resilience to accelerator grid breakdowns using a short-circuit device in vacuum.
The overall programme of the NBTF, aimed at validating the NBI design and at meeting the ITER schedule (requiring NBIs in operation in 2032), will be outlined.
