Forward Modeling of Motional Stark Effect Spectra

Abstract

A forward model for Motional Stark effect spectra is developed. The forward model includes beam attenuation and considers the detection of partially polarized light. The forward model is applied to simulate spectra for Wendelstein 7-X. A fit version is used to analyze data from experimental spectra from ASDEX Upgrade. The fit validates the model and enhances the confidence in the simulation. The structure and the content of the model is described to allow modular implementations to guide physics-based diagnostic designs.

Spectrally resolved motional Stark effect measurements on ASDEX Upgrade

“…Here instead, the data are fitted to a forward model 13,14 . Practically, the forward model has much less parameters than the multi-Gaussian model.…”

“…6 and is composed of the following contributions: the Stark spectrum (d MSE ) 13,14 , the active CX line (d CX ), a continuous background, e.g. Bremsstrahlung radiation, (d Bg ), and impurity lines (d Imp ).…”

“…Experimental set-up FIG. 1 shows the experimental set-up of the sMSE diagnostic at ASDEX Upgrade (major radius R = 1.65 m, minor radius r = 0.5 m) 13,14 . The maximum magnetic field is B = 3.1 T. For the sMSE a magnetic field of about 2 to 2.6 T is applied.…”

Investigation of fast ion pressure effects in ASDEX Upgrade by spectral MSE measurements

“…To pronounce the aforementioned main spectral features, a constant background is subtracted from the spectral data. Data analysis of the experimental data D is made by fitting a forward model resulting in synthetic data d. The fit results in the best fitting values for the Lorentz field E L [15,19,20]. The model consists of a constant background signal ( d Bg ), carbon impurity lines ( d Imp ), active charge exchange ( d CX ), a fast ion D α signal ( d FIDA ) [1,21] and the ZMSE pattern ( d ZMSE ).…”

Motional Stark Effect Measurements Of The Local Magnetic Field In High Temperature Fusion Plasmas

“…However, in particular in smaller fusion experiments, using relatively large high power heating beams, inversion techniques might become necessary to infer the plasma parameters from the line integrals through the beam diameter. Using a forward model to describe the measured data the line integration can be implemented in a straightforward way 20 . Finally, in some cases also the influence of the neutral beam on the plasma has to be considered.…”