Achievement of the ITER NBI ion source parameters for hydrogen at the test facility ELISE and present Status for deuterium

The ELISE test facility, being in operation since 2013, with its half-size ITER ion source accompanies the ITER NBI development program. Besides consolidation of the ion source design, solving technical problems that arise during operation, gaining early experience in ion source operation and maintenance, ELISE has the task to demonstrate the required ion source parameters required by ITER. ELISE made remarkable progress since then, starting from short pulses (10 s) to the ITER target of 1000 s for Hˉ and 3600 s for Dˉ (with the constraint to extract the beam repetitively for 10 s every ≈150 s). For hydrogen, above 90 % of the required level for the extracted current density has been achieved being limited by the available high voltage power supply and the RF power. For deuterium the performance is limited by the much larger amount of co-extracted electrons; here 65% of the extracted current density is demonstrated for the duration of almost one hour. One of the challenges is the strong temporal dynamics of the co-extracted electrons and several measures were taken as the introduction of potential rods, modifications of the magnetic filter field configuration and improved caesium conditioning. Testing the magnetic field configuration planned for the test facility MITICA (prototype of the ITER beamline) showed very good performance but indicated also that the field strength should be kept variable to control ions and electrons for the two isotopes individually. Regarding the beam homogeneity the global uniformity of better than 90 % is usually achieved. Measurements of the beam divergence by beam emission spectroscopy revealed higher divergences for the horizontal lines-of-sight than for the vertical ones due to the non-compensated zig-zag deflection of the beamlets by the magnets in the extraction grid.