Collisional radiative model for more accurate measurements of plasma parameters from a helium beam diagnostic

With a helium beam diagnostic, the local electron density and temperature at the plasma edge can be measured with high spatiotemporal resolution. For this purpose, helium is injected as a thermal beam, and the light emission resulting from the interaction with the plasma is evaluated using a collisional radiative model.
 

Temperature and density profiles created by the new ("dynamic model") and old model ("static model") in comparison. For the density comparison, the lithium beam diagnostic was added. Especially in the temperature one can see a significant difference between the models, whereas the new evaluation also corresponds to the expected physical behavior. 

Building on existing atomic data, scientists at IPP have developed a novel collisional radiative model that describes the real processes in the plasma as accurately as possible. This model takes into account the dynamic state occupation of the injected helium atoms in the plasma and the reabsorption of self-emitted radiation.

The density profiles evaluated with the model are in agreement with those from other diagnostics. In particular, the electron temperature profiles have greatly improved and now no longer show an unphysical increase toward the wall. Thus, more accurate temperature and density profiles can now be obtained, which are valuable for physical studies of the dynamics of the plasma edge.

This work was recently published in the journal Plasma Physics and Controlled Fusion.

D. Wendler et al 2022 Plasma Phys. Control. Fusion 64 045004
https://doi.org/10.1088/1361-6587/ac49f8

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