Experiments and interpretive modeling to identify the physics controlling material migration in the boundary of DIII-D, JET and EAST fusion energy tokamaks

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The aim of fusion energy research is to create a 'star in a bottle'. Magnetic fusion research has advanced to the point where the 'bottle' is now the problem. The wall armour is strongly eroded by the hot plasma. Some eroded material deposits back out of the plasma at the original location, causing no problem. However, much of the material migrates some distance within the plasma before depositing out again. The latter creates serious problems: (i) loss of armour lifetime, (ii) pile-up of deposits which can stop reactor operation, (iii) loss of tritium fuel due to co-deposition trapping, (iv) dust creation with safety (chemical explosion) implications, etc. The physics controlling the boundary of magnetic confinement devices such as tokamaks has only been partly identified. In particular material migration is poorly understood. Very fast plasma flows along the magnetic field lines in the boundary have been widely recorded but their cause has only a weak theoretical basis. One of the key tools for material migration research is the injection of isotope tracers such as carbon-13 methane, which experiments our Toronto Group has played the lead role on in the DIII-D tokamak since 2003. The scientific approach that will be taken in the proposed work: I. Create OEDGE-Upgrade, a major upgrade of our University of Toronto interpretive OEDGE code. II. Apply OEDGE-U to interpret dedicated material migration experiments in the DIII-D (US), JET (EU) and EAST (China) tokamaks in order to extract the controlling physics of material migration, specifically for application to the ITER tokamak (joint international). III. Install multiple pop-up probes in the DIII-D wall to provide the more spatially complete diagnostic input on boundary plasma flow fields and electric fields required in order to sufficiently constrain OEDGE-U to be able to identify the physics controlling the tokamak boundary. IV Then sets of repeat, identical, simple-as-possible-plasma, discharges, including 13CH4 injection, will be performed where all the boundary diagnostics are fully exploited to provide as complete a mapping of the boundary plasma as possible for input to OEDGE-U.