Characterization of geometrical detection-system properties for two-dimensional tomography

Giannone

et al. 2011

In order to derive the local emission profile of the plasma radiation in a fusion device using the line-integrated measurements of the bolometer diagnostic, tomographic reconstruction methods have to be applied to the measurements from many lines-of-sight. A successful reconstruction needs to take the finite sizes of detectors and apertures and the resulting non-ideal measurements into account. In ITER a method for in situ measurement of the geometrical properties of the various components of the bolometer diagnostic after installation is required as the viewing cones have to pass through narrow gaps between components. The method proposed to be used for ITER uses the beam of a laser with high intensity to illuminate the bolometer assembly from many different angles ξ and θ. A light-weight robot from Kuka Robotics is used to efficiently position the laser on many points covering the complete viewing cone of each line-of-sight and to direct the beam precisely into the entrance aperture of the bolometer. Measuring the response of the bolometer allows for the calculation of the transmission function t(ξ, θ), the angular etendue and finally the geometric function in reconstruction space, which is required for the tomography algorithms. Measuring the transmission function for a laboratory assembly demonstrates the viability of the proposed method. Results for a collimator-type camera from a prototype envisaged for ITER are presented. The implemented procedure is discussed in detail, in particular with respect to the automatisation applied which takes the achievable positioning and alignment accuracies of the robot into account. This discussion is extended towards the definition of requirements for a remote-handling tool for ITER.

“…Neglecting reflections one gets in poloidal direction, similar to the results given in [5] for pin-hole cameras:…”

Section: Transmission Function Of the Prototype Collimatorsupporting

confidence: 63%

Section: Transmission Function Of the Prototype Collimatormentioning

confidence: 99%

See 1 more Smart Citation

Development of an automated method for in situ measurement of the geometrical properties of the ITER bolometer diagnostic

Giannone

et al. 2011

“…The method used for the assessment of the LOS characteristic of the ITER bolometer diagnostic components is based on previous work performed at JET [2]. It is currently under development for the utilization as a LOS calibration device in ASDEX Upgrade, the viability of the proposed method was shown previously [1].…”

Section: Experimental Set-upmentioning

confidence: 99%

Assessment of line of sight characteristics of ITER bolometer prototype collimators

Giannone

et al. 2013

This work outlines the present design status of developments on the optimization of line of sight (LOS) characteristics for the ITER bolometry collimators. The verification and measurement of the LOS of the bolometry is an important issue for a reliable operation of the tomographic reconstruction algorithms. Therefore the ITER Bolometer Robot Test Facility (IBOROB) is used as a diagnostic tool in order to analyse signal geometry and assess the performance of different prototypes. The LOS characteristics as a function of number of apertures is presented and the influence of a microwave filtering aperture was determined. The results of the improvement of stray light attenuation by application of the graphite based coating AQUADAG R are evaluated as well and an overview about the current collimator design is given. This paper focuses on the most remarkable results and a way to further possible upgrades is outlined. However, some results are not in accordance with the ones predicted in theoretical calculations. Thus not all key parameters which influence the LOS could be clearly identified yet.

“…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].…”

Section: Experimental Set-upmentioning

confidence: 99%

Automated in situ line of sight calibration of ASDEX Upgrade bolometers

Bernert

et al. 2014

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.