International Doctoral College in Fusion Science and Engineering
 Thesis catalogue
Analyses and forward modelling of X-ray imaging crystal spectrometer data for transport studies in WEST and W7X
PhD Code: 2016-DC-20:
Mobility
  • Host institute 1: AM07-Aix- Marseille Université (Home University) - FP8-Institut de Recherche sur la Fusion par confinement magnétique, Saint-Paul-lez-Durance, France (Home Institution)
  • Host institute 2: FP1-Ghent University (Host University)
  • Host institute 3: AM04-ITER Organization - FP9-Max-Planck-Institut für Plasmaphysik Garching und Greifswald
Research fields:
  • F6. Diagnostics, plasma control and data analysis
Promotor(s):
  • Prof. Alexandre Escarguel (promotor) - Dr. Christel Fenzi (mentor)
  • Prof. Kristel Crombé (co-promotor)
  • Dr. Robin Barnsley (mentor)
  • Dr. Marc Beurkens and Dr. Andreas Langenberg (mentors)
Contact Person and email: Christel Fenzi - christel.fenzi@cea.fr

Subject description
Background: Plasma transport understanding is one of the main issues for ITER. To address the physics of transport, accurate measurements are needed for detailed comparisons with theoretical predictions from modern computer codes. In particular, kinetic profiles (ion / electron densities, temperatures and flows), whose gradients are a source of free energy for the plasma turbulence responsible for the confinement losses, are extremely important for understanding and modelling the energy, momentum and impurity transport. In the frame of the WEST project, a high resolution X-ray imaging crystal spectrometer (XICS) is being developed. The diagnostic design is similar to the edge XICS system foreseen in ITER. The system will provide high accuracy and spatially resolved ion and electron temperatures, ion density and toroidal / poloidal rotation velocity profiles from He-like Iron, H-like and He-like Argon impurity measurements. The diagnostic requires sophisticated processing in order to estimate the temperature and velocity radial profiles from the spatially and spectrally resolved measurements. Existing techniques must be investigated in detailed and optimized before providing a machine generic method, which is a crucial step forward for integrated modelling and advanced understanding of the physics mechanisms at play in tokamak experiments. In particular, the physics of plasma rotation enters directly many relevant physics issues for ITER: a strong shear in the rotation profile is known to reduce the turbulent transport by breaking apart the turbulent eddies, centrifugal effects are dominant for heavy impurity transport and offer a mean to prevent their accumulation and the associated high radiation losses in the plasma core, etc. This will be investigated in WEST using the XICS diagnostic, but also in the stellerator W7X (where an XICS system has been developed as well) hence providing a large view of underlying physics with two different magnetic configurations.

Expected outcomes

Objective: XICS diagnostic requires sophisticated processing in order to estimate the radial profile of temperature and velocity from the spatially and spectrally resolved measurements. One first part of the work will consist of adapting an existing XICS data analysis software to make it machine-generic, in view of the exploitation of the WEST XICS diagnostic. Such a spectral analysis software relies on tomographic techniques which must be applied to the line integrated data in order to get profile information. This is a key point for the analysis. The algorithms will have to be evaluated and optimized with advanced signal processing techniques. It is indeed crucial to minimize uncertainties in measurement of Ti and Vf (respectively determined from the spectral line width and Doppler shift) provided the multiple factors already contributing, such as inherent spectrometer resolving power, binning by the detector of the continuous spectral line intensity distribution into strips of finite width, statistical uncertainty from fitting a Gaussian function to the spectral line, background from X-ray continuum. In the second part of the work, a forward modelling software (synthetic diagnostic) will be developed to simulate the signals measured by the diagnostic for given plasma conditions (ion and electron temperatures, electron density and Ar concentration). Synergy on forward modelling approach could be could found with W7X, where Bayeasian methods have been applied for profile inversion: the method will have to be evaluated then applied to the WEST case, or an alternative approach will be proposed. Coupled to predictive transport simulations of Ar, the forward modelling will help quantifying the signal-to-noise ratio as a function of the injected Ar density and to study the compatibility of the Ar density level with operational constraints (e.g. radiative power) in WEST Tungsten environment. Finally, the last part of the work includes plasma transport studies in WEST and W7X, hence allowing gaining experience on both devices, adressing more particularly plasma rotation and momentum transport issues.

 

Time line and mobility scheme (research need to be performed for at least six month in two different countries): Mobility plan proposal (to be adjusted at the beginning of the PhD depending on foreseen WEST and W7X experimental schedules): Months 1 - 2 : IRFM, CEA-Cadarache / Aix-Marseille University Months 3 - 8 : IPP-Greifswald Months 9 - 20 : IRFM, CEA-Cadarache / Aix-Marseille University Months 21 - 26 : IPP-Greifswald Months 27 – 36 : IRFM, CEA-Cadarache / Aix-Marseille University

 

Original document: 2016-DC-20



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