Assessment of line of sight characteristics of ITER bolometer prototype collimators

Giannone

et al. 2017

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The ITER bolometer diagnostic will have to provide accurate measurements of the plasma radiation in a varying thermal environment of up to 250• C. Current fusion experiments perform regular in-situ calibration of the sensor properties, assuming stable calibration parameters within short discharge times, e.g. 10 s on ASDEX Upgrade. For long-pulse fusion experiments, e.g. W7-X, the diagnostic is operated with water cooling for achieving a stable temperature environment. However, ITER will be equipped with about seventy bolometer cameras and is planned to have discharge times of up to 1 h. Due to space restrictions, active cooling is not available for all locations. Thus, an alternative approach is required to allow for compensation of the changing calibration values due to thermal drifts. This paper demonstrates a method using the Wheatstone bridge current of the sensor to calculate in real-time the changing calibration values, such as the heat capacity and the thermal time constant. It is shown, that the thermal calibration parameter drift can be calculated by either extrapolating from the initial values or using a previously determined look-up table. Measurements in the ITER bolometer vacuum test facility (IBOVAC), used to simulate ITER-relevant thermal and vacuum environment, show that the change of the calibration values can be predicted during repeated thermal cycles over a duration sufficient for ITER discharges and even longer. Confidence intervals for the typical in-situ calibration method are determined and compared with the proposed extrapolation and look-up method for ITER, showing that these methods provide an equivalent quality of the measurement results.

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Section: Discussion and Further Workmentioning

confidence: 99%

Calibration parameter drift compensation of metal resistive bolometers operating in a thermal varying environment

Penzel

Giannone

et al. 2017

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“…The tool was once developed for the measurement and assessment of the ITER bolometer diagnostic [7] and is based on work conducted at JET [12] [13]. Experience to analyse and evaluate the results were gained during the collimator development for ITER [14]. IBOROB was then completely automatized with National Instruments LabVIEW and the Imaging Lab Robotics Library for KUKA [15] and can be controlled completely through a GUI [16] in the automatic mode of the robot.…”

Section: Experimental Set-upmentioning

confidence: 99%

“…Experience to analyse and evaluate the results were gained during the collimator development for ITER [14]. IBOROB was then completely automatized with National Instruments LabVIEW and the Imaging Lab Robotics Library for KUKA [15] and can be controlled completely through a GUI [16] in the automatic mode of the robot. The necessary programs can be remotely loaded and executed along with the definition of the measurement parameters.…”

Section: Experimental Set-upmentioning

confidence: 99%

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Automated in situ line of sight calibration of ASDEX Upgrade bolometers

Penzel

Bernert

et al. 2014

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The ITER Bolometer Robot Test Rig (IBOROB) is a robot-based diagnostic tool, which allows the measurement of the lines of sight (LOS) of the ITER bolometer prototypes. Up to now, it was only used as a LOS characterization device for the ITER collimator development. IBOROB was further developed and can now be operated in ASDEX Upgrade during a regular maintenance shutdown. At present, once a diagnostic like the bolometry is mounted inside the vessel, the actual LOS orientations are not measured, they are derived from CAD. The new procedure allows the fully automatic three-dimensional in situ measurement of bolometer LOS. The spatial distribution, the poloidal and toroidal alignment in the experiment coordinate system (CS), can be determined. The absolute accuracy, in reference to the tokamak CS, is provided by an additional calibration performed with a measurement arm by FARO Technologies Inc. Therefore, the amount of misalignment from the theoretical expectations can be quantified. In addition specific camera type dependencies such as internal camera reflections can be identified. Due to the high position accuracy of the robot, the LOS can be resolved with a spatial resolution of up to 0.1• . The method is explained in detail and results from two exemplary bolometer foil cameras obtained in a first set-up in ASDEX Upgrade are presented. The different steps and components needed to apply the measurements in the vessel are described with a focus on the constraints, e.g. geometrical, for an application of this method in a tokamak. Finally the consequences of the results are extrapolated to ITER and evaluated.

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Optimisation of design parameters for collimators and pin-holes of bolometer cameras

Kálvin

2014