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 FEM analyses. A specific methodology was developed to carry out the analyses with respect to the seismic and baking loads. At KIT, FABRY-PEROT resonators measure the loss tangent of the diamond disk and it is then used as input to the CFD 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.

Diamond Window Technology for Electron Cyclotron Heating and Current Drive: State of the Art

“…Fig. 5 shows that the analyses 9 for the design driver related to the external loads acting on the unit led to an advanced optimum design with resulting stresses well below the allowable limits and to the important conclusion that no stress propagation occurs towards the inner sensitive parts of the window, i.e. the disk and the cuffs.…”

Optimal design of electrical power distribution grid spacers using finite element method

“…FEM has been applied to structure optimization for various applications [41]. These applications are directly related to improvement in equipment design [42][43][44], considering that through the finite element method it is possible to carry out evaluations of force distribution, temperature, and stress in complex structures [45]. Applications of this approach extend to high voltage power systems [46], using FEM makes it possible to assess process deterioration in electrical systems [47].…”

FEM analyses of the ITER EC H&CD torus diamond window unit towards the prototyping activity

“…Many efforts have been made in the design development of the UL window to achieve a sufficient maturity level to enable the start of the prototyping and testing activity in view of the ITER FDR, scheduled in 2020 [2,3]. The FDR related to the diamond disk only was already carried out at the end of 2017 (successfully passed in 2018) due to the long procurement time for the 56 disks, each of which requires weeks to manufacture as the growth process is extremely slow.…”