Departmental Seminar

Newly uncovered physics of critical MHD and Alfvénic instabilities with 2-D imaging diagnostics in tokamak plasmas

Professor Hyeon K. Park
Ulsan National Institute of Science and Technology,
Ulsan, Korea

The complex system like fusion plasma needs comprehensive visualization diagnostics to establish firm physics basis through precise validation so that fully validated modellings can be established for design of the future reactor with predictive capabilities. Such need motivated developing the 2-D ECEi system for tokamak plasmas and almost two decades long deployment of this system in many fusion plasma devices has uncovered critical new physics of the MHD and Alfvénic instabilities. Through validation of theoretical models with the newly uncovered physics, modellings have either gained a high confidence or been substantially improved. In sawtooth physics, the discarded full reconnection model is vindicated and the ballooning mode model may not be adequate for this instability. In NTM physics, it is demonstrated that the 2-D ECEi data can determine critical parameters such as ’ and c with high confidence. The observed anisotropic distribution of the turbulence and its flow in presence of the 2/1 island is validated by the modelled potential and gyro-kinetic calculation of the turbulence. Validation process of the measured RSAE Alfvén eigenmode structures has improved deficiencies of models. In study of the ELM and ELM-crash suppression with RMP, validation of the ELM structure and dynamics of entire ELM cycle has provided an opportunity to improve the physics model. The dynamics of broadband turbulence induced by RMP in suppression experiment may shed a light on the physics of multi-interaction between the broadband turbulence, growth/decay of the ELMs and enhanced transport at the pedestal region. Importance of symmetry in reconnection process for the crash time scale and role of magnetic shear in the 1/1 kink mode in sawtooth instability may be relevant to the kink instability of the filament rope in solar flare.

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