29th Symposium on Fusion Technology (SOFT 2016)

P2.024 Progress and further plans towards high power negative ion beams at ELISE

6 Sep 2016, 14:20

1h 40m

Foyer 2A (2nd floor), 3A (3rd floor) (Prague Congress Centre)

Board: 24

Poster B. Plasma Heating and Current Drive P2 Poster session

Speaker

Bernd Heinemann (ITER Technology & Diagnostics)

Description

The negative ion source test facility ELISE represents the first step in the European R&D roadmap for the neutral beam injection (NBI) systems of ITER in order to consolidate the design and to gain early experience with a large and modular Radio Frequency (RF) negative ion source. The aim of ELISE is to demonstrate the ITER requirements with respect to extracted negative hydrogen densities (329 A/m²2 H‾, 286 A/m²2 D‾) at an electron-to-ion ratio below one, a source pressure of 0.3 Pa and a beam homogeneity within 10%. The plasma of ELISE is generated by four RF drivers which illuminate half the ITER area, (1x0.9 m²2) with an extraction area of 0.1 m²2 (640 apertures, 14 mm diameter). Restrictions of the power supply allow beam extraction and acceleration up to 60 kV for 10s every 3 min during a continuous plasma operation up to 1h. After three years of operation ELISE has shown remarkable progress: 1 hour plasma discharges with repetitive 10s beam blips every 3 min could be demonstrated with current densities of 94 A/m²2 (H‾) and 57 A/m²2 (D‾) and an electron‑to‑ion‑ratio below 1 at a moderate RF power of 20 kW/driver. Further improvement of the source performance by increasing the RF power is limited by the amount and the temporal stability of co-extracted electrons especially in deuterium operation. Alternative magnetic filter field configurations with different field topology are under evaluation to improve this behaviour and show first promising results. Increasing the RF power is further limited by the thermal heating of RF components and RF break downs which occur randomly around the drivers even at low pressures (10^-6 -6 mbar). Additional cooling and alternative matching configurations are investigated presently to explore the source performance in the high RF power regime.