Orbit-space sensitivity of fast-ion diagnostics

Research output: Book/ReportPh.D. thesis

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The sensitivity of fast-ion diagnostics in magnetic confinement fusion can be quantified in the form of weight functions. They can be used to relate the fast-ion distribution function in phase space to a measurement in a diagnostic measurement bin. Via tomographic inversion, weight functions can be used to reconstruct the fast-ion distribution function from diagnostic measurements. Due to the magnetic field, the fast ions must follow fixed trajectories known as orbits. This work continues to build upon orbit weight functions, which can be utilized to reconstruct the full gyro-averaged fast-ion distribution in tokamaks. Orbit weight functions for neutron emission spectroscopy and gamma-ray spectroscopy for one-step fusion reactions were developed and analyzed in this project. Gained insights include: a high sensitivity to trapped orbits whose tips are inside the line-of-sight of the diagnostic, and an increased understanding of the optimal positioning and orientation of diagnostic sightlines. In addition, this project also birthed new ways of using fast-ion orbits to analyze diagnostics. These include: 1) The decomposition of diagnostic signals, fast-ion distributions and weight functions, in terms of their fast-ion orbit-type origin. 2) Interactive analysis of which fast-ion orbit types pass through certain (R; z) points. 3) The mapping of poloidal and toroidal transit times for all of orbit space, which could provide further insight into the interaction between fast ions and e.g. Alfvén eigenmodes. A code framework was created to enable future use of the new tools developed in this work. This is envisioned to increase the vital understanding of the behaviour of fast ions in tokamak fusion plasmas.
Original languageEnglish
PublisherDepartment of Physics, Technical University of Denmark
Number of pages202
Publication statusPublished - 2022


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