Physics R and D in support of ITER/BPX diagnostic development

The development of diagnostics for a next step burning plasma experiment (BPX) is a major challenge. Within the International Tokamak Physics Activity (ITPA), one Topical Group (TG) specialises in diagnostics and aims to support the development and design of the needed systems. Several diagnostics issues have been identified as 'high priority' and form the focus of current work of the TG. The core of this paper is a presentation and discussion of recent progress in the field of these high priority research topics. Moreover, the status of the recently initiated International Diagnostic Database will be briefly described. (author)