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Idomura, Yasuhiro
no journal, ,
Hydrogen isotope mixing phenomena in tokamak plasmas are analyzed using a full-f gyrokinetic model. Numerical experiments based on the hydrogen isotope mixing experiment on JET are conducted using plasma profiles before and after deuterium (D) pellet injection into a hydrogen (H) plasma. Before the injection, the density profiles of bulk H ions are maintained in a quasi-steady state. However, after the injection, the density profiles of bulk H and pellet D ions exhibit transient relaxation on the energy confinement time scale, indicating hydrogen isotope mixing. The balance of toroidal angular momentum shows that hydrogen isotope mixing is driven by toroidal electric field stress.
Idomura, Yasuhiro
no journal, ,
We analyze turbulence transition between linear and saturated Ohmic confinement (LOC-SOC) regimes using the global full-f gyrokinetic simulation code GT5D on the Fugaku supercomputer. The LOC-SOC transition is characterized by the change of intrinsic rotation profiles with a density ramp. This feature is reproduced by numerical experiments, and its mechanism is clarified. The change of collisionality, which depends on the density, induces a transition of dominant micro-instability from trapped electron modes (TEMs) to ion temperature gradient driven modes (ITGs). TEMs and ITGs have different asymmetries in turbulent spectra with respect to the wavenumber in the direction of the magnetic field, leading to the change of momentum transport in the LOC-SOC transition.