ITER Torus Diamond Window Unit: FEM Analyses and Impact on the Design

Abstract

The ITER torus diamond window unit is part of the electron cyclotron (EC) upper launcher (UL) used to direct high power microwave beams generated by the gyrotrons into the plasma for heating and current drive (H&CD) applications. The UL consists of an assembly of ex-vessel waveguides (WGs) and an in-vessel port plug (PP). The diamond window units form vacuum and confinement boundaries between the torus volume and the transmission lines (TLs) which guide beams between 1 and 1.5 MW at 170 GHz from the gyrotrons to the launcher. There are eight window units attached to the assembly of the WGs, one unit for each WG. The design strategy of the unit is to have a very rigid outer frame able to withstand the potential external loads acting on the unit while thin copper cuffs brazed to the diamond disk allow indirect cooling of the disk to remove the EC power absorption during the beam transmission. The load combination given by the stringent ITER seismic level 2 (SL-2) event occurring during baking of the torus vessel is the design driver for the outer frame of the unit. In fact, the assembly of the WGs is connected from one side to the ceiling of the ITER port cell area by a support frame and to the UL PP from the other side. Movements of the torus vessel due to baking, seismic and plasma disruption events, result in forces and moments acting on the units. Furthermore, during a seismic event, the unit is subject to additional loads induced by the oscillation of the support frame attached to the ceiling. An outer frame surrounding the window unit is thus required to ensure the structural integrity and the confinement function of the unit. This paper shows how the design of the window unit was assessed and optimized by finite element method (FEM) analyses. A specific methodology was developed to carry out the analyses with respect to the seismic and baking loads. At Karlsruhe Institute of Technology (KIT), FABRY-PEROT resonators measure the loss tangent of the diamond disk and it is then used as input to the computational fluid dynamics and FEM analyses aiming to assess the design. The impact of the FEM analyses on the design of the window unit is discussed also together with the manufacturing aspects of the unit.