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ENEA - Fusion division

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Radiofrequency Data Acquisition and Processing for Inspection and Metrology Systems

Amplitude Modulate LASER SYSTEM (IVVS) for the ITER in vessel inspection

Model of ITERModel of ITER
In vessel inspection (viewing & ranging) systems, able to withstand the ITER very severe operating conditions, are fundamental to check plasma facing components in order to properly program ordinary and extraordinary maintenance activities. ENEA, in collaboration with the portuguese institute IST, proposed the innovative Laser In Vessel Viewing&Ranging System (IVVS) based on an Amplitude Modulated (AM) laser beam. Presently IVVS seems the only system under testing able to perform, at the same time, viewing&ranging under the ITER operating conditions.

  • The system is able to measure ranges
    and the ranging accuracy is better than
    10-4 (i.e. 0.5 mm @ 5 m).
  • The system obtains amplitude images with
    a high dynamic range, it can resolve many
    thousands of grey levels.
  • The system has a quasi-spherical Field of
    View. The tilt-hidden angle is about +/- 15
    degrees over a full angle of 360 degrees.
    The pan covers 360 degrees.
  • Far and near objects are well focused due
    to the high depth of field. This can be
    further improved by an auto-focus system
    now under development.
  • The laser spot is the source of illumination
    itself, so that no external illumination
    source is necessary.
  • By choosing the appropriate speed of
    acquisition and acquisition time it is
    possible to obtain low resolution or
    medium resolution overall images or high
    resolution zoom images.

 

 

IVVS main features
Characteristics Value Dimension
Laser beam wavelength 840 nm
modulation frequency 80 MHz
Field of Viewing and Ranging 2 – 7 m
Scanning accuracy 0,005 Degrees
Viewing resolution < 1 mm
Ranging accuracy 0.5 mm
Viewing Time 10 µsec/pixel
Ranging Time 300 µsec/pixel
Operating temperature 250 ° C
Operating vacuum 10-9 mbar
Operative radiation level 30
2x104
MSv
total Sv / h
IVVS system Outline

IVVS building blocksIVVS building blocksTwo main blocks compose the IVVS electro optics scheme: the active module and the passive module.
The active module hosts the laser, the photo-detectors and all the related active components.
The passive module is part of the scanning head and hosts the passive optical components of the optical transceiver.
The two modules are connected by means of radiation resistant optical fibers. An 80 mW, 840 nm diode laser is modulated at 80 MHz frequency and the beam is linearly polarized. The sounding beam is transmitted to the prism and then to the target. A rotating prism scans the overall scene over a 165 x 360° field of view. The received optical signals are gathered in both the fiber optics based links and fed to an avalanche detector in the control room. The photocurrent generated in each optical circuit is fed to a low noise preamplifier and followed by the demodulating electronics to detect the amplitude and the phase shift of the received signal.

 

IVVS SCANNING HEADThe SCANNING HEAD is a mechanical and
optical equipment able to scan the scene
Optical Encoders and Encoder ElectronicsThe two angular coordinates of prism are read
using two Optical Encoders and the dedicated
Encoder Electronics equipment
dedicated VME Control&Acquisition SystemA dedicated VME Control&Acquisition System
controls all the function of the system and also
acquires all the information during scanning
process
Radar Electronics equipmentThe back-scattered light is then converted in
two R.F. electrical signals and then processed
in the Radar Electronics equipment to obtain
the amplitude and phase shifting of the received
signal with respect to the launched one