Experimental conditions to suppress edge localised modes by magnetic perturbations in the ASDEX Upgrade tokamak

Access conditions for full suppression of Edge Localised Modes (ELMs) by Magnetic Perturbations (MP) in low density high confinement mode (H-mode) plasmas are studied in the ASDEX Upgrade tokamak. The main empirical requirements for full ELM suppression in our experiments are: 1. The poloidal spectrum of the MP must be aligned for best plasma response from weakly stable kink-modes, which amplify the perturbation, 2. The plasma edge density must be below a critical value, $3.3 \times 10^{19}$~m$^{-3}$. The edge collisionality is in the range $\nu^*_i = 0.15-0.42$ (ions) and $\nu^*_e = 0.15-0.25$ (electrons). However, our data does not show that the edge collisionality is the critical parameter that governs access to ELM suppression. 3. The pedestal pressure must be kept sufficiently low to avoid destabilisation of small ELMs. This requirement implies a systematic reduction of pedestal pressure of typically 30\% compared to unmitigated ELMy H-mode in otherwise similar plasmas. 4. The edge safety factor $q_{95}$ lies within a certain window. Within the range probed so far, $q_{95}=3.5-4.2$, one such window, $q_{95}=3.57-3.95$ has been identified. Within the range of plasma rotation encountered so far, no apparent threshold of plasma rotation for ELM suppression is found. This includes cases with large cross field electron flow in the entire pedestal region, for which two-fluid MHD models predict that the resistive plasma response to the applied MP is shielded

Pedestal and Er profile evolution during an edge localized mode cycle at ASDEX Upgrade

The upgrade of the edge charge exchange recombination spectroscopy diagnostic at ASDEX Upgrade has enabled highly spatially resolved me asurements of the impurity ion dynamics during an edge-localized mode cycle ( ELM ) with unprecedented temp oral resolution, i.e. 65 μ s. The increase of transport during an ELM induces a relaxation of the ion, electron edge gradients in impurity density and fl ows. Detailed characterization of the recovery of the edge temperature gradients reveals a difference in the ion and electron channe l: the maximum ion temperature gradient T i is re-established on similar timescales as n e , which is faster than the recovery of T e .Afterthe clamping of the maximum gradient, T i and T e at the pedestal top continue to rise up to the next ELM while n e stays constant which means that the temperatur e pedestal and the resu lting pedestal pressure widen until the next ELM. The edge radial electric fi eld E r at the ELM crash is found to reduce to typical L-mode values and its ma ximum recovers to its pre-ELM conditions on a similar time scale as for n e and T i . Within the uncertainties, the measurements of E r align with their neoclassical predictions E r,neo for most of the ELM cycle, thus indicating that E r is dominated by collisional processes. However, between 2 and 4 ms af ter the ELM crash, other contributions to E B ́ fl ow, e.g. zonal fl ows or ion orbit effects, could not be excluded within the uncertainties.European Commission (EUROfusion 633053

A novel two-stage kinetic model for surface DBD simulations in air

In this work, a novel 0D model for the evaluation of O-3 and NO2 produced by a surface dielectric barrier discharge (SDBD) in a closed environment is presented. The model is composed by two coupled sub-models, a discharge sub-model and an afterglow one. The first one, simulating the discharge regime and consequently including electron impact reactions, aims to calculate the production rates of a set of key species (atomic oxygen, excited states of molecular oxygen and molecular nitrogen). These latter are the input of the afterglow sub-model, that simulates the afterglow regime. We introduce a methodology to relate the production rates of the above mentioned species to the input power of the SDBD reactor. The simulation results are validated by a comparison with experimental data from absorption spectroscopy. The experimental measurements are carried out as follows. First, the discharge is turned on until the NO2 number density reaches steady state. Then, the discharge is turned off for several minutes. Finally, the discharge is turned on again to observe the effects of the NO2 concentration on ozone dynamics. The entire process is done without opening the box. The system operating in all the above-listed conditions is simulated for three different levels of input power

Full suppression of Edge Localised Modes with non-axisymmetric magnetic perturbations at low plasma edge collisionality in ASDEX Upgrade

EUROfusion Consortium 6330

Experimental conditions to suppress edge localised modes by magnetic perturbations in the ASDEX Upgrade tokamak

Access conditions for full suppression of edge localised modes (ELMs) by magnetic perturbations (MP) in low density high confinement mode (H-mode) plasmas are studied in the ASDEX Upgrade tokamak. The main empirical requirements for full ELM suppression in our experiments are: 1. The poloidal spectrum of the MP must be aligned for best plasma response from weakly stable kink-modes, which amplify the perturbation, 2. The plasma edge density must be below a critical value, m−3. The edge collisionality is in the range (ions) and (electrons). However, our data does not show that the edge collisionality is the critical parameter that governs access to ELM suppression. 3. The pedestal pressure must be kept sufficiently low to avoid destabilisation of small ELMs. This requirement implies a systematic reduction of pedestal pressure of typically 30% compared to unmitigated ELMy H-mode in otherwise similar plasmas. 4. The edge safety factor q95 lies within a certain window. Within the range probed so far, , one such window, has been identified. Within the range of plasma rotation encountered so far, no apparent threshold of plasma rotation for ELM suppression is found. This includes cases with large cross field electron flow in the entire pedestal region.EUROfusion Consortium 63305