Bolometer developments in diagnostics for magnetic confinement fusion

The plasma radiation is an essential part of the power balance in current and future magnetic confinement fusion experiments and gives crucial insight for the challenges of power exhaust and divertor detachment as well as valuable information to understand plasma instabilities and transport effects. It is typically measured using various types of bolometers. Present day experimental devices, both the tokamak and stellarator, make use of metal resistor bolometers and infrared imaging video bolometers (IRVB), depending on the main focus of the respective measurement. The well-established sensor for absolutely calibrated measurements is the metal resistor bolometer. AXUV diodes, often used in conjunction with bolometers, are ideal for observing fast transient events in a plasma due to their very short response times, but their sensitivity varies significantly over the full radiation spectrum and degrades over their lifetime. In cases where many lines-of-sight are needed to observe radiation profiles in complex geometries IRVB offers the ability to integrate high channel counts in rather narrow installation volumes. Fibre-optic bolometers are a new development promising measurements immune to electro-magnetic interference. These diagnostic concepts are presented as well as their pros and cons. For future devices like ITER and DEMO, R and D efforts are required to adapt sensors and diagnostic schemes to the harsh nuclear environment. An overview will be given over the activities for sensor development and integration challenges, which may also be relevant for long pulse operation in present experiments.