Bremen 2017 – scientific programme

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P: Fachverband Plasmaphysik

P 5: Plasma Diagnostics

P 5.7: Poster

Monday, March 13, 2017, 16:30–18:30, HS Foyer

Development and implementation of an average Z_eff measurement for ASDEX Upgrade plasmas — •T. Welzel^1,2, A. Kappatou², R. McDermott², U. Stroth^2,1, R. Dux², R. Fischer², T. Pütterich², and The ASDEX Upgrade Team² — ¹Physik-Department E28, Technische Universität München, D-85748 Garching, Germany — ²Max-Planck-Institut für Plasmaphysik, Boltzmannstraße 2, 85748 Garching, Germany

The effective charge Z_eff is an indicator of the plasma purity. Knowledge of Z_eff is important to many physics investigations, however, it is not routinely measured on ASDEX Upgrade. This work aims to develop and implement a fast, automatic and reliable routine measurement of average Z_eff. There are two different ways to determine this value. At ASDEX Upgrade, Z_eff can be inferred from the individual measurements of the dominant impurities in the plasma. Another approach is to determine the average effective charge via background bremsstrahlung emission measurements, which depend upon the wavelength, electron temperature and density as well as on Z_eff. Using other diagnostics to measure the electron density and temperature, Z_eff can be calculated. However, the bremsstrahlung emission measurements can be disturbed for example by light reflected on the tokamak wall. The main focus of this work lies in determining suitable measurements of the bremsstrahlung, which will then be used to provide a routine measurement of the average Z_eff in ASDEX Upgrade. The Z_eff values derived with this method are benchmarked against those obtained by directly measuring the impurity densities in the plasma.