Neutron diagnostics at ASDEX and their application for fast ion physics studies

  • Date: –17:15
  • Location: Ångströmlaboratoriet, Lägerhyddsvägen 1 2005
  • Lecturer: Dr. Giovanni Tardini
  • Organiser: Applied Nuclear Physics Division
  • Contact person: Andrea Sperduti
  • Phone: 0728505301
  • Seminarium

The neutron yield is a fundamental measurement since the early days of fusion, as a direct indicator of fusion performance. Moreover, middle-large tokamaks need to monitor the neutron production for safety reason. Tokamaks with D-T operation, obviously, invested more in neutron diagnostics, including different types of neutron spectrometers. ASDEX Upgrade has been equipped with an array of neutron counters since the early 1980's, the most sensitive are calibrated with a Pu238/B source, the others (including 2 fission chambers) are cross-calibrated during plasma operation. However, systematic deviations associated with different calibration campaigns [Tardini NF2013] and the huge changes in the bulky components in the torus hall motivated a re-thinking of the absolute calibration, using a new measurement setup and the Serpent code for modelling neutron transport in the torus hall. In the last 20 years, fast ions physics has attracted increasing interest. Accurate measurements of neutrons has become a requirement, and information on their energy distribution a significant ingredient for any Neutral Beam heated plasma. A BC501A-based Compact Neutron Spectrometer with DAQ has been installed at ASDEX Upgrade and fully characterized at the accelerator facility of the Physikalisch Technische Bundesanstalt in Braunschweig, Germany. Evidence of 2nd harmonic NBI-D acceleration by H-minority ICRF is found, comparing measured Pulse Height Spectra with theoretical predictions based on a RF-kick operator in the NUBEAM/TRANSP code, while the neutron count is also in good agreement with the simulation. Additional neutron diagnostics are considered presently as addition/replacement for the current system, providing better reliability, less pick-up in the electronics and faster time-resolution. A Sci-Fi detector is being tested right now at ASDEX Upgrade.