The Importance of the Neutral Beam Test facility to ITER

energy. To achieve ITERs objectives to operate with high fusion power, Pfus ~ 500 MW with fusion gain, Q=10 for 400 s in a baseline scenario, and Pfus > 250 MW, Q=5 operation for 3600 s in advanced scenarios ITER relies on the realisation of the auxiliary heating systems, of which one of the most important is the Neutral Beam injection system. A total power of 33 MW from the two heating neutral beam (HNB) injectors is envisaged in the present scenario. To achieve the required heating and current drive necessary from the neutral beams, the injectors are required to provide 1 MeV D0 neutral beams created by accelerating deuterium negative ions to -1 MV across 5 electrostatic grids. These stringent requirement have never been demonstrated on any existing machine to date, making them first of a kind with significant physical and technological challenges. In addition, a beam line at lower energies, 100kV is also envisaged as a diagnostic neutral beam (DNB), to realise charge exchange measurements. One of the advantages of neutral beams as a technique for heating, current drive, and momentum input is that their coupling to the plasma is not strongly dependent upon the edge conditions of the tokamak plasma, and the interaction with the plasma takes place primarily through a relatively wellunderstood mechanism, two-body collisions. As a consequence, a neutral beam test facility (NBTF) can be utilized effectively to develop, test, and improve the neutral beam capabilities at a location remote from the ITER machine, with a high degree of confidence that it will function in a similar fashion when installed on the tokamak, and that it will drive effects within the confined plasma which are largely predictable. The ITER NBTF, is intended to capture these benefits for ITER, and for both the primary heating and current drive beams (HNB) and the DNB. The NBTF will consist of two complementary test facilities at Consorzio RFX in Padua, a 1 MV test bed (MITICA), which differs from an actual injector only in the diagnostic capability, and an ion source test bed (SPIDER) which is capable of testing a full size ITER ion source at full parameters, but with an higher degree of flexibility and at reduced voltage of 100 kV. The NBTF is the centrepiece of a coordinated development effort, including subsidiary test facilities in Japan, Europe and India, that will result in the experience and information necessary to proceed with the finalization of the ITER neutral beams. Having such a facility for the development of neutral beams allows the inherent technological and physics risks of Neutral beam injectors to be mitigated. These risks can be summarised in a few main categories, HV Holding, Optics and Ion source efficiencies. This paper will outline the importance of the NB system to ITER and highlight the importance of the NBTF in ensuring that these systems are successfully realised on the ITER machine.