Beam duct for the 1 MW neutral beam heating injector on TCV

Abstract

The Tokamak à Configuration Variable (TCV) has been recently equipped with a 1MW neutral beam heating (NBH) injector A. Fasoli for the TCV team, 2015 [1]. Two new stainless steel ports with rectangular aperture of 170×220mm have been manufactured and installed for this purpose. The NBH injector is connected to one of them via a stainless steel port extension. The port and its extension together form the beam duct between the TCV vacuum vessel (VV) and the NBH injector.A preliminary thermal analysis of the beam duct showed no expectation of thermal events such as overheating. Indeed, although the beam power density near the internal faces of the beam duct reaches ∼10MW/m2, the very grazing incidence angle between the beam axis and the wall was expected to lead to a maximal effective heat flux of ∼350kW/m2 for a maximal duration of 2s, resulting in acceptable temperature rise.As a result, the beam duct did not include any provision for cooling. However, early in 2016 the commissioning of the NBH injector showed high overheating of the port extension, resulting in local melting and ultimately vacuum leak. This paper describes the design and analysis of an actively cooled beam duct and the status of the beam duct.