29th Symposium on Fusion Technology (SOFT 2016)

P4.029 Beam transmission dependence on beam parameters for TJ-II Neutral Beam Injectors

8 Sep 2016, 14:20

1h 40m

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

Board: 29

Poster B. Plasma Heating and Current Drive P4 Poster session

Speaker

Macarena Liniers (Laboratorio Nacional de Fusión)

Description

Neutral Beam injection has some well-established effects on plasma behaviour, such as the power threshold observed in L to H confinement mode transitions or the fast ion excitation of Alfvén modes, whose underlying mechanisms are still under investigation. In recent TJ-II experimental campaigns emphasis has been made in the characterisation of those Neutral Beam related effects. A study of Alfvén mode excitation as a function of beam parameters is under way, in which the dependence of the observed eigenmodes on the beam energy and current is examined. In order to carry out these studies, neutral beam parameters (beam energy and current) are made to vary in a wide range. To discriminate the effects of beam energy and beam current on plasma behaviour, beam energy scans are performed at a fixed current value and beam current scans at fixed energy. Such parameter scans involve beam perveance variations which affect the beam transmission, therefore a proper estimate of the power and fast particle current reaching the plasma calls for a previous determination of the beam transmission for each set of parameters. Beam transmission is determined by the beam divergence, which is usually obtained from the Gaussian beam power density profile at or near the beam focus. At TJ-II, beam profiles near the beam focus can be obtained by infrared thermography of the Target Calorimeter, a retractable target made of textured graphite (CFC graphite CX-1001U) that fully intercepts the beam at the duct exit [1]. After applying the appropriate coordinate transformation, beam divergence is obtained for each set of parameters in the energy and current scans. Computer simulation of the beam transport through the different apertures along the beam path finally yields the power and fast particle current transmitted to the plasma.