Current status of the design of the ITER bolometer diagnostic

Abstract

The ITER bolometer diagnostic shall provide the measurement of the total radiation emitted from the plasma, a part of the overall energy balance. 550 lines-of-sight (LOS) will be installed in ITER observing the whole plasma from many different angles to enable reliable measurements and tomographic reconstructions of the spatially resolved radiation profile. The LOS are bundled in 71 individual cameras, which will be located behind blanket modules on the vacuum vessel wall, in five divertor cassettes, in two upper port plugs and in one equatorial port plug. For all major design issues solutions have been elaborated and will be presented. The design of collimators has been developed and tested on prototypes to provide an exact definition of the required viewing cones of about 1 • while reliably reducing reflections, stray light and microwave stray radiation. A 3D-shaped ceramic printed circuit board is proposed to hold the sensor, orient it as desired, and provide good thermal contact as well as the bridge for electrically connecting external signal cables to the meanders on the sensor. The design of the camera housing for vacuum vessel and divertor cameras has been optimised for improved management of the thermal heat flow, supported by tests defining material properties and verifying analysis. Additionally, methods have been developed to derive the main design parameters of cameras and decide if pinhole or collimator type is more advantageous. Recently, the system-level design phase started and uses the achieved results to define interfaces and designs for the specific locations in ITER, with a focus on the vacuum-vessel cameras to finalise the interface with blanket modules.

Signal to noise ratio of upgraded imaging bolometer for KSTAR

“…2 Conventional bolometer detectors to be installed in ITER are based on the temperature dependence of the electrical resistance of a metal meander which is thermally coupled to a photon absorbing foil by an intermediate insulating substrate. 3 Using a Wheatstone bridge and associated electronic circuitry to sense the change in the resistance resulting from the heat imparted on the foil by the absorbed photon, the resistive bolometer is susceptible to electromagnetic noise from various sources which are abundant in a fusion device, in particular from ion cyclotron resonant frequency induced noise. 4 In addition, the insulating layer which is needed to electrically isolate the absorbing foil from the sensing meander presents challenges in constructing a resistive bolometer that can survive the extreme temperature swings and nuclear radiation of a fusion reactor.…”

Consideration of signal to noise ratio for an imaging bolometer for ITER

“…The InfraRed imaging Video Bolometer (IRVB) 1,2 represents an alternative to resistive bolometers 3,4 for diagnosing the radiated power distribution in a fusion reactor such as ITER. 5 The IRVB consists of an aperture collimated foil that absorbs broadband radiation from the plasma.…”

Flexible vacuum vessel bolometer camera design in ITER to adapt to the final position of the gaps between Blanket Modules

“…The ITER Bolometer Diagnostic comprises a system of bolometer cameras located in two Upper Port Plugs, one Equatorial Port Plug, five divertor cassettes and 22 in-vessel positions in six different Vacuum Vessel (VV) sectors with a total of about 550 lines of sight (LOS) Ref [1].…”