Nuclear technology aspects of ITER vessel-mounted diagnostics

Abstract

ITER has diagnostics with machine protection, basic and advanced control, and physics roles. Several are distributed on the inner and outer periphery of the vacuum vessel. They have reduced maintainability compared to diagnostics in ports. They also endure some of the highest nuclear and EM loads of any diagnostic for the longest time. They include:Inductive sensors for time-integrated and raw inductive measurements; Steady-state magnetic sensors to correct drifts of the inductive sensors;Bolometer cameras to provide electromagnetic radiation tomography; Microfission chambers and neutron activation stations to provide fusion power and fluence; MM-wave reflectometry to measure the plasma density profile and the plasma-wall distance and;Wiring to service magnetics, bolometry, and in-vessel instrumentation. This paper summarises the key technological issues these diagnostics arising from the nuclear environment, recent progress and outstanding R&D for each system.

ITER diagnostic challenges

“…Second, with the knowledge gained from the fundamental research, to design sensors for minimum effect(s) in the application on ITER and, in parallel, to mitigate with redundancy and alternative methods, particularly for critical measurements. There has been considerable progress with understanding the pertinent effects of radiation on the materials used for magnetic sensors [20,21]. Magnetic sensors are generally composed of a metallic winding, a supporting insulating structure and an electromagnetic screen, the whole mounted on a supporting structure.…”

“…Within the research programme, specific experiments are carried out on tokamaks under the auspices of the IEA-ITPA Joint Experiments. There is now an extensive body of literature on most aspects of the problem: for example, deposition of impurities erosion of the mirror surfaces, and mitigation methods, for example shutters [19,20]. The performance of mirrors in the neutron, gamma and X-ray environment is also an area of potential concern.…”

Assessment of the Structural Vibration Effect on Plasma Current Measurement Using a Fiber Optic Current Sensor in ITER

“…For this measurement, inductive sensors have been utilized as a common method [ 1 ]. However, these sensors are based on the measurement of the time derivate of a magnetic field, which can induce measurement drift due to the long steady state operation of the ITER since integrators are used to retrieve the plasma current [ 2 , 3 ]. A fiber optic current sensor (FOCS) measures the plasma current by means of the Faraday effect [ 4 , 5 ].…”

Realization and Tests of Prototype Fluxgate Magnetic Sensors for the ITER Neutral Beam Injectors

“…However, such a high sensitivity is unnecessary for our application and their use would involve the installation of a glass bulb containing alkali gas and light sources, not suitable to be installed inside the NBI vessel. Pick-up coils (also called Mirnov coils) with a time integration of the output signal are not suitable, because the radiation-induced electromotive force (some microvolts, caused by neutrons hitting the coils conductors) would produce an unacceptable measurement drift during the long experimental pulses [ 12 ], but first and foremost because stationary or slow-varying magnetic fields must be sensed. It is possible to overcome these difficulties using a fluxgate-type magnetometer (see Figure 2 ), since its sensing part is simple, intrinsically robust and does not require delicate semiconductor components.…”