Development of ITER diagnostic window assemblies

Most of ITER's diagnostics will be provided with viewing lines (optical, microwave, spectroscopic) for the monitoring of key characteristics of the plasma or for the achievement of physical measurements inside the vacuum vessel. For many of them the nature of the physical signal transmitted through the viewing lines requires the implementation of window assemblies incorporating either Glass/Ceramic or Beryllium window. The main requirements of the Diagnostic Window Assemblies are the transmission of the signals without attenuation or disturbances, the containment of vacuum, the confinement of in-vessel radioactive materials. Although they are generally not in direct viewing of the plasma, they are exposed to severe environmental conditions in normal and accidental conditions. The concept chosen for ITER Diagnostic Window Assemblies is based on a system of two windows with a monitored interspace, largely inspired from previous large machine solutions. Such a system is able to satisfy the transmission and vacuum requirements. Although this capability has previously proven a high reliability level, ITER conditions, which are more stringent, impose the requirement for improvement of existing designs and even the development of novel solutions, in particular to assure the radioactive material confinement function, which must be met in all circumstances including all off-normal conditions. Moreover the qualification of these concepts shall meet the nuclear safety requirements, although non metallic and beryllium components are not covered by existing codes and standards. This paper presents designs of window assemblies for different diagnostics. It gives an update of the current R&D programme implemented to solve several technical issues specific to ITER. Finally it presents the approach to the demonstration that safety requirements will be met by these components, involving the development of ITER Practice for replaceable non-metallic windows. (C) 2013 Elsevier B.V. All rights reserved.