29th Symposium on Fusion Technology (SOFT 2016)

P2.002 Modelling and analysis of the JET EP2 neutral beam FEID curved end plate

6 Sep 2016, 14:20

1h 40m

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

Board: 2

Poster A. Experimental Fusion Devices and Supporting Facilities P2 Poster session

Speaker

Alastair Shepherd (Culham Centre for Fusion Energy)

Description

Neutral beam injection systems have proved themselves as the most effective form of auxiliary heating in tokamak plasmas. In positive ion based systems once the beam is neutralised there are many residual ion components which must be intercepted by suitable ion dumps. A particular challenge for ion dump design occurs when the dump must be placed close to a focus point as is the case for the curved end plate of the JET NBI full energy ion dump. Molecular ion species though of low power are focused at this place. As part of the EP2 upgrade to increase neutral beam power and duration, the ion source configuration was changed from Supercusp 130kV/60A configuration to Chequerboard 125kV/65A. This allowed for significant increase in neutral beam power but also lead to a fourfold increase in molecular residual ions. The curved FEID end plate was re-designed as an actively cooled element using swirl tubes. Following a failure of this plate in 2014 additional analysis was carried out to determine likely causes of the failure and to improve its performance. This paper describes enhanced modelling of the power loading, improvements to the power handling capabilities and additional features to improve fatigue life. Monte-carlo simulations of each of the nine residual ion components which are intercepted by the plate shows a peak power density of 25MW/m² 2 and compares well with recently installed fast thermocouple measurements. Analytical calculations and simulations with the Charged Particle Optics (CPO) code are used to investigate the potential for movement of the residual ion focus due to space charge neutralisation effects. Cooling performance is significantly enhanced by improved water channel flow which is both modelled and confirmed by experiment. Fatigue life, calculated from ANSYS modelling is improved using a slot arrangement to relieve stresses created from focussed heat load distribution.