The group develops and operates plasma diagnostics which allow to quantify the success of the confinement optimization.
Quantities of particular interest are the profiles - the radial distribution from the plasma center to the edge - 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. The latter results from differences in electron and ion particle transport such that the plasma charges up. A further task is the development of diagnostics that allow to study the confinement of fast particles representing the confinement of later fusion products.
For the first experimental phases (OP1) the following diagnostis have been developed and operated:
- Laser Interferometry uses the innovative technique of Dispersion Interferometry for a continuous tracking of the average electron density and thus provides the signal for density control
- Thomson Scattering launches high-power laser pulses and derives the local electron density and electron 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 line emission caused by high-Z plasma impurities to derive quantities like the local impurity density in the plasma, the radial electric field and also the temperature of the exciting plasma electrons
- the Beam Emission - and Charge Exchange Resonance Spectroscopy (CXRS) observes visible light emitted along the trajectories of the neutral particle heating beams resulting from interaction of the neutral hydrogen atoms with plasma particles. From that the local temperature of the plasma ions, the local electric field and other quantities can be derived.
- first tests of fast particle detectors have been performed as well indicating wall loads of fast particles created by the neutral heating beams (NBI) or later from direct ion heating (ICRH).
- calibrated Neutron Counters observe the eventual emission of neutrons as they will result from later deuterium-deuterium fusion processes in the plasma
For the long pulse experiments in OP2 diagnostic extensions and further diagnostics are being prepared:
The shape of the density profile will be continuously monitored with a multi-channel Interferometer and its 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 and with a lower overall power such that continuous measurements become possible in contrast to the limited time of NBI pulses (<10 s). A Beam Emission and Charge Exchange Recombination Spectroscopy system will be installed around this Diagnostic Beam together with Neutral Partical Analysers probing the energy distribution of the particles expelled from the plasma.