|Measured quantities::||Energy distribution of fast atoms escaping plasma|
|Spatial resolution:||Chord averaged|
|Temporal resolution:||1 ms|
|Responsible person:||J. Stöckel|
|Collaboration:||Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg|
Fast hydrogen and deuterium atoms are generated in the tokamak plasma due to charge exchange collisions between hot ions and cold neutrals. Their energy distribution function, which reflects the energy distribution of the ion component, is measured by the neutral particle analyzer (NPA) located outside the tokamak vessel. The principle of the NPA is evident from the following figure.
The fast atoms escaping the tokamak vessel enter at first the gas target G, where is partially ionized by stripping collisions. Resulting ions, with the same energy and momentum as the primary neutrals, are analyzed according their momentum in the bending magnet M and, after that, distributed according their masses in the electrostatic analyzer C. The resulting "fan" of ions is registered by two arrays of detectors, spaced vertically (the first one for protons and the second for deuterons). Each detector measures ions in a narrow range of energies. Consequently, twelve values of the energy distribution function are determined simultaneously, from which the central ion temperature is determined.
We will exploit the existing neutral particle ACCORD 12, manufactured at the IOFFE FTI, St Petersburg. The analyzer will be refurbished to increase the number of individual energy channels from 12 to 24. The NPA is absolutely calibrated in the range of energies 0.2 – 70 keV.