Periodic Reporting for period 1 - FIREFELM (Mastering the energetic particle distribution in a magnetohydrodynamic active plasma)
Berichtszeitraum: 2017-08-01 bis 2019-07-31
Magnetohydrodynamic (MHD) instabilities are a universal phenomenon in laboratory as well as astrophysical plasmas. An example for such an instability is the edge localized mode (ELM) which occurs at the plasma edge of a fusion plasma and ejects a jet of hot plasma similar to solar flares on the edge of the Sun. ELMs appear during a mode of tokamak operation in which energy is retained more effectively and pressure builds up at the edge of the plasma. This mode of operation is also called high confinement mode (H-mode) and is the operational regime foreseen for the next-step fusion device ITER. ELMs eject particles and energy from the plasma thus leading to a transient degradation of the plasma edge and a deterioration of plasma confinement. The successful realization of fusion relies, therefore, in a thorough understanding of edge stability and ELM control. For future fusion devices, the control or even full suppression of ELMs is mandatory.
The overall objective of this project is to advance in the understanding of ELMs and the impact they have on plasma transport.
The impact of edge localized modes (ELMs) on heat and particle transport was studied. Transport simulations show that the ion heat transport is close to the neoclassical level, while the depletion of energy caused by the ELM delays the recovery of the electron temperature. For the first time, beam ion acceleration during ELMs was observed and an analytic model was developed. A resonant mechanism between the beam ion orbits and the parallel electric fields associated with ELMs, that could be responsible for the ion acceleration has been studied. Numerical simulations of fast-ions in a realistic magnetic equilibrium and including a static parallel electric field, implemented through an analytical model which resembles the 3D structure of the perturbation, qualitatively reproduce the experimental observations.