Edge localized mode rotation and the nonlinear dynamics of filaments

Yun

et al. 2017

Sci Rep

Solitary perturbations (SPs) localized both poloidally and radially are detected within ~100 μs before the partial collapse of the high pressure gradient boundary region (called pedestal) of magnetized toroidal plasma in the KSTAR tokamak device. The SP develops with a low toroidal mode number (typically unity) in the pedestal ingrained with quasi-stable edge-localized mode (QSM) which commonly appears during the inter-collapse period. The SPs have smaller mode pitch and different (often opposite) rotation velocity compared to the QSMs. Similar solitary perturbations are also frequently observed before the onset of complete pedestal collapse, suggesting a strong connection between the SP generation and the pedestal collapse.

“…where the phase velocities are assumed close to that of the ballooning mode, i.e., half the ion diamagnetic velocity 20. The radial electric field is given by ref.…”

Section: Resultsmentioning

confidence: 99%

Solitary perturbations in the steep boundary of magnetized toroidal plasma

Yun

et al. 2017

Sci Rep

Contributions to Plasma Physics

“…The ratio of energy lost to the inner and outer divertor targets is close to experimental observations only when flows are included (see Section 3.6). Finally, these flows are necessary to reproduce experimental mode rotation …”

Section: Type‐i Elmsmentioning

confidence: 99%

Insights into type‐I edge localized modes and edge localized mode control from JOREK non‐linear magneto‐hydrodynamic simulations

Hoelzl

Huijsmans

Orain

et al. 2018

Self Cite

Edge localized modes (ELMs) are repetitive instabilities driven by the large pressure gradients and current densities in the edge of H‐mode plasmas. Type‐I ELMs lead to a fast collapse of the H‐mode pedestal within several hundred microseconds to a few milliseconds. Localized transient heat fluxes to divertor targets are expected to exceed tolerable limits for ITER, requiring advanced insights into ELM physics and applicable mitigation methods. This paper describes how non‐linear magneto‐hydrodynamic (MHD) simulations can contribute to this effort. The JOREK code is introduced, which allows the study of large‐scale plasma instabilities in tokamak X‐point plasmas covering the main plasma, the scrape‐off layer, and the divertor region with its finite element grid. We review key physics relevant for type‐I ELMs and show to what extent JOREK simulations agree with experiments and help reveal the underlying mechanisms. Simulations and experimental findings are compared in many respects for type‐I ELMs in ASDEX Upgrade. The role of plasma flows and non‐linear mode coupling for the spatial and temporal structure of ELMs is emphasized, and the loss mechanisms are discussed. An overview of recent ELM‐related research using JOREK is given, including ELM crashes, ELM‐free regimes, ELM pacing by pellets and magnetic kicks, and mitigation or suppression by resonant magnetic perturbation coils (RMPs). Simulations of ELMs and ELM control methods agree in many respects with experimental observations from various tokamak experiments. On this basis, predictive simulations become more and more feasible. A brief outlook is given, showing the main priorities for further research in the field of ELM physics and further developments necessary.

“…It appears with f /n 1 kHz (note the different scaling of the frequency axis). This reduction of velocity compared to the precursor is a result of the E r reduction at the ELM onset from typically 40 to 10 kV m −1 and thereby a relative increase of the toroidal velocity component which is in the ion drift direction [38,39]. Another ingredient for the velocity reduction might be an additional outwards propagation into the region of reduced absolute E r and a possible coupling due to increased mode amplitude to external error fields leading to a braking of the rotation.…”

Section: Experimental Investigationsmentioning

confidence: 99%

Nonlinear coupling induced toroidal structure of edge localized modes

et al. 2017

Self Cite

View the article online for updates and enhancements. Related content Toroidal mode number determination of ELM associated phenomena on ASDEX Upgrade Felician Mink, Elisabeth Wolfrum, Marc Maraschek et al.-High frequency magnetic fluctuations correlated with the inter-ELM pedestal evolution in ASDEX Upgrade F M Laggner, E Wolfrum, M Cavedon et al.-Recent progress in understanding the processes underlying the triggering of and energy loss associated with type I ELMs