Advanced tokamak diagnostics

Experiments on the current generation of large tokamaks have demonstrated that the core confinement properties are sufficiently good that the tokamak program can move forward to studies of long-pulse tokamaks with reactor-like properties in the core. On-going experiments show the benefits of plasma shaping and the capabilities of divertor design. Very good confinement has been obtained in magnetic field configurations which have been created with a region with reversed magnetic shear inside the plasma, and these results encourage further experiments in present devices extending the pulse length and improving the plasma performance, and moving forward to another generation of tokamaks. The significant challenges in plasma measurement are being addressed in the design work in progress for the international tokamak experimental reactor (ITER), and were being studied for the tokamak physics experiment (TPX). There will have to be extensive capabilities for using diagnostic signals in the control of the magnetic fields, heating and current drive sources, and fuelling. Clearly, many of the properties of the plasma in the divertors must be measured to allow the control of the gas flows and of the first-wall temperatures. This paper will describe some aspects of preparing diagnostic systems for next-generation devices.