29th Symposium on Fusion Technology (SOFT 2016)

P1.037 Helium neutral beam injection into ASDEX Upgrade

5 Sep 2016, 14:20

1h 40m

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

Board: 37

Poster B. Plasma Heating and Current Drive P1 Poster session

Speaker

Christian Hopf (Max Planck Institute for Plasma Physics)

Description

ASDEX Upgrade’s (AUG) neutral beam injection (NBI) is primarily designed for deuterium injection and delivers 20 MW heating power from two injectors with four beams each at 60 and 93 keV, respectively. As opposed to the cryosorption pumps of the JET NBI, the Ti getter pumps of the AUG NBI with a pumping speed of ~ 3×10⁶6 L/s for D2 do not pump helium at all, leaving only the conventional pumps with < 6×10³3 L/s for He. This imposes constraints on the possible operation in helium. In order to prepare for AUG He plasma campaigns, serious trials to operate the AUG NBI with He began in 2014. It was found that despite the lack of high speed pumping up to two beams per injector could be operated simultaneously at reduced feed gas flow without particular restrictions on the beam-on time. For injector 1 the power per beam was limited to ~ 560 kW at 40 keV by the required filament current in its arc sources, while for injector 2 the limitation came from the bending magnet’s power supply that restricted the beam energy to 68 keV and the NBI power to ~ 750 kW per beam. Thus the maximum available NBI heating power in He amounts to 2.6 MW for 10 s. Helium neutral beam injection into plasma was first tried out in 2014 for two discharges. In 2015 a dedicated He campaign used He NBI in a total of 44 discharges. As He is almost not pumped in the injectors the neutral gas flow into the torus is comparable with the total He gas puff. The paper will discuss the operational possibilities and constraints of He NBI on AUG and give examples of the NBI heating profiles for some of the He target plasmas of 2015.