Radiation-hardened Light Detection and Ranging System for 3D Time-of-Flight Measurement
The MYRRHA reactor, conceived as an accelerator driven system ( ADS), is currently being developed at the Belgian nuclear research centre, SCK·CEN, in Mol, Belgium. It is able to produce sustainable fission energy by bombarding the harmful nuclei with a high neutron flux to transmute long-lived radioactive waste.
An ADS consists of three major parts: a proton accelerator, a spallation source and a sub-critical core. In the MYRRHA reactor, a liquid metal, for which lead-bismuth eutectic (LBE) has been chosen, is selected as the spallation source. In the spallation target, the position of the free liquid metal surface needs to be stabilized in order to guarantee proper heat exchanging and maintaining the spallation process. This can be done by first using a range finding device to continuously monitor the liquid metal surface level. The readout of this level serves as a feedback signal to control a pump, which can adjust the position of the LBE surface through a loop.
A light detection and ranging (LIDAR) system can serve as the rangefinder. The LIDAR detector works on the Time-of-Flight (TOF) principle. It determines the distance from the detector to an object by measuring the traveling time of the light during the trip. A pulsed TOF laser range finding device with mm-accuracy requires major innovations in following critical subsystems:
- A highly-efficient pulsed laser transmitter
- A low-noise optical receiver channel
- A picosecond resolution time-to-digital converter
In this application, since the LIDAR system is placed in the inner-vessel of the MYRRHA reactor, where enriched with gamma-rays, it has to be hardened-by-design against radiation damage. Moreover, the mm-accuracy requirement imposes further challenges on the performances of all electronic subsystems.
A pulsed TOF laser range finder consists of several fully customized rad-hard ASICs has been developed. Specifically, a 5 MGy rad-hard 155 Mb/s VCSEL laser driver, a 4 MGy rad-hard 255 MHz bandwidth 90 dBΩ transimpedance amplifier, and a 5 MGy rad-hard 5.6 ps resolution time-to-digital converter have been designed and assessed. A demonstration of the LiDAR system is shown in the figure below.
Key building blocks of a pulsed LiDAR system were developed and assessed. The proposed LiDAR device brings new opportunities to system integrators in various industrial applications such as 3D scanning and inspection, machine vision, virtual reality, robotic manipulation and autonomous navigation.
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