SXR Tomography – EPFL

SXR

Not a pressure cooker

SXR Tomography – EPFL
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Magneto-Hydro-Dynamic instabilities (MHD) are detrimental for nuclear fusion, as they reduce the confinement of hot plasma, which is against the sought goal. These instabilities are generally analyzed with magnetic probes and Soft X-Ray detectors (soft ~ energy in the range of 1keV). SXR is a line-integrated measurement of the photons the photodiode through a pinhole. Due to the non-local nature of the measurement, to obtain 2D pictures of SXR emission in plasma requires a tomographic inversion.

Hardware

  • CAD and mechanical workshop: 10 pinhole cameras have been mechanically re-designed, in order to cover the interior of the vessel to provide more lines of sight inside the typical plasma shape. 1 (CAD) + 4 (mechanics) workers
  • Electronic department: new, state-of-the-art micro amplifiers have been designed (the signal is in the range of few nanoAmperes, requiring immediate amplification). A pulsing LED has been installed in each camera to provide in-situ calibration throughout operations. Issues of noise and pick-up have been solved, thanks to the implementation of special noise reduction cables, and Faraday cages). 5 Electronic workers
  • Design and Purchase: the photodiodes have been redesigned and purchased according to specifications, to replace the existing ones that have been worn out by neutrons and common usage. Request and evaluation of quotes.
  • Calibration: absolute energy calibration with a medical X-ray source has been performed. 1 Radiation Expert
  • Data acquisition and management: a new acquisition system has been purchased, tested and installed, which provides a better digitization and an improved bandwidth. IT manager

Software

  • Tomography inversion routines have been improved and developed
  • Data acquisition based on the new system have been written
  • Visualization tools have been implemented
  • The system was completed within financial budget (100k€) and deadline (18 months).

The project involved also the co-ordination of 2 vacuum technicians and 1 worker for the cabling and earthing of the system. A strict collaboration with other scientist was continuously undertaken to improve the project during its actuation. The system is currently being used and has already provided valuable in the understanding of various MHD phenomenon, and led to many publications in scientific journals.