Profile Diagnostics

The group develops and operates in particular such diagnostics which are capable to measure the radial distibution – the profiles – of plasma values like electron and ion temperatures or the plasma density. Knowing these values the success of the optimization can be quantified.

Quantities of interest are the profiles of the electron density and of the electron and ion temperature, as well as the profiles of important plasma impurities and of the radial electric field resulting from electron and ion particle transport.

For the first experimental phase (OP1.1) the following diagnostis are being prepared:

  • Laser Interferometry uses the innovative technique of Dispersion Interferometry for a continuous tracking of the average electron density – also in view of a later density control
  • Thomson-Scattering lauches high-power laser pulses and derives the local electron density and -temperature from intensity and spectrum of the laser light scattered at the plasma electrons.
  • the Electron Cyclotron Emission Diagnostic (ECE) derives continuously the local radiation temperature of the electrons by measuring the intensity of the microwave emission resulting from the gyro-motion of the electrons around the magnetic field lines.
  • two Imaging x-ray Spectrometers use the x-ray emission caused by plasma impurities to derive quantities like the local impurity density in the plasma but also the temperature of the exciting plasma electrons.
  • calibrated Neutron Counters observe the eventual emission of neutrons resulting from Deuterium-Deuterium Fusion processes in the plasma

Moreover, modern imaging spectroscopy techniques are studied in cooperation with the University of Canberra.

For the physics experiments in OP1.2 diagnostic extensions and futher diagnostics are being prepared: 

The shape of the density profile will be continuously monitored with a multi-channel Interferometer and the edge region will be tracked by the radar techniques of microwave Reflectometry.

The already tested Diagnostic Injector launches a beam of fast hydrogen atoms like the heating beams of NBI, however, well collimated to improve the spatial resolution but with a lower overall power. The interaction of these hydrogen atoms with the plasma can be used to measure quantities along the beam path: Charge Exchange Spectroscopy measures ion temperature and electric field from light emission by plasma ions that briefly captured one of the beam atoms electrons. These intermittently neutralized plasma ions are no longer confined in the magnetic field such that they leave the plasma where their energy distribution can be measured in Neutral Partical Analysers.

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