Deuterium results at the negative ion source test facility ELISE

The ITER neutral beam system will be equipped with large radio frequency (RF) driven negative ion sources, with a cross section of 0.9 m × 1.9 m, which have to deliver extracted D⁻ ion beams of 57 A at 1 MeV for 1 h. On the extraction from a large ion source experiment test facility, a source of half of this size is being operational since 2013. The goal of this experiment is to demonstrate a high operational reliability and to achieve the extracted current densities and beam properties required for ITER. Technical improvements of the source design and the RF system were necessary to provide reliable operation in steady state with an RF power of up to 300 kW. While in short pulses the required D⁻ current density has almost been reached, the performance in long pulses is determined in particular in Deuterium by inhomogeneous and unstable currents of co-extracted electrons. By application of refined caesium evaporation and distribution procedures, and reduction and symmetrization of the electron currents, considerable progress has been made and up to 190 A/m² D⁻, corresponding to 66% of the value required for ITER, have been extracted for 45 min.