Simulations of COMPASS vertical displacement events with a self-consistent model for halo currents including neutrals and sheath boundary conditions

The understanding of the halo current properties during disruptions is key to design and operate large scale tokamaks in view of the large thermal and electromagnetic loads that they entail. For the first time, we present a fully self-consistent model for halo current simulations including neutral particles and sheath boundary conditions. The model is used to simulate vertical displacement events (VDEs) occurring in the COMPASS tokamak. Recent COMPASS experiments have shown that the parallel halo current density at the plasma-wall interface is limited by the ion saturation current during VDE-induced disruptions. We show that usual magneto-hydrodynamic boundary conditions can lead to the violation of this physical limit and we implement this current density limitation through a boundary condition for the electrostatic potential. Sheath boundary conditions for the density, the heat flux, the parallel velocity and a realistic parameter choice (e.g. Spitzer's resistivity and Spitzer-Harm parallel thermal conductivity) extend present VDE simulations beyond the state of the art. Experimental measurements of the current density, temperature and heat flux profiles at the COMPASS divertor are compared with the results obtained from axisymmetric simulations. Since the ion saturation current density (Jsat) is shown to be essential to determine the halo current profile, parametric scans are performed to study its dependence on different quantities such as the plasma resistivity and the particle and heat diffusion coefficients. In this respect, the plasma resistivity in the halo region broadens significantly the Jsat profile, increasing the halo width at a similar total halo current

Evaluation of first wall heat fluxes due to magnetic perturbations for a range of ITER scenarios

The proposed use of magnetic perturbations for edge-localized mode (ELM) control in ITER poses a number of integration issues, among them the localized heat fluxes (footprints) on the plasma-facing components (PFCs). They may provide the benefit of spreading the heat flux, thus reducing its peak value, but they may cause a localized erosion of the PFCs. We present calculations of heat fluxes for a range of ITER plasma parameters. The efficiency of our method enables us to perform calculations for a range of assumptions on the SOL width and to optimize the coil configuration to yield the largest power flux spreading. The optimal coil configuration is not sensitive on SOL parameters and is also close to the one which is considered optimal for ELM control. The proximity of footprints may cause significant power loads on the upper wall

Non-linear gyro-kinetic Ion Temperature Gradient (ITG) and Trapped Electron Modes(TEM) turbulence modelling in X-point geometry with Resonant Magnetic Perturbations(RMPs)

International audienceMotivation: study of turbulence during RMPs which are used for Edge Localized Modes (ELMs) suppression in existing tokamaks and foreseen for ELMs control in ITER

Simulation study of divertor geometry for COMPASS Upgrade tokamak

Simulation study of divertor geometry for COMPASS Upgrade tokamakI. Borodkina1,2, A. Kukushkin2,3, S. Wiesen4, D. Boeyaert4, M. Imrisek1,L. Kripner1, M. Peterka1, R. Dejarnac1, M. Komm11Institute of Plasma Physics of the CAS, Za Slovankou 3, 182 00 Prague 8, Czech Republic2National Research Nuclear University “MEPhI”, Moscow, Russia3National Research Center “Kurchatov Institute”, Moscow, Russia4Forschungszentrum Jülich GmbH, Institut für Energie-und Klimaforschung –Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, [email protected] development of divertor design with a reliable solution for the power and impurity particle exhaust is one of the important challenge towards the realization of COMPASS Upgrade (COMPASS-U) project. COMPASS-U with its high plasma and neutral density is of particular interest for ITER in terms of similar divertor plasma and neutral parameters, as well as predicted power decay length and peak power loads to the divertor targets [1].It is essential to efficiently dissipate power in the divertor, probably necessitating operation in a detached regime,to ensure the maximum steady-state power load at the divertor target below 10 ∼15 MW/m2and to maintain a low electron temperature at the target plates~ 5-10eVto suppress erosion.In this contributionwe report on the first systematic modelling examination ofthe effect of different outer and inner divertor target angles, adivertor closure and pumplocations on the main parameters of the COMPASS-U divertor plasma. The simulations are carried outby using the 2D edge plasma code packages SOLPS4.3[2] and SOLPS-ITER [3] for pure D plasma with the fixed anomalous cross-fieldcoefficients corresponded to the predicted power decay lengths. The single-null and the asymmetric double-null magnetic configurations are used with the magnetic equilibriums provided by the FIESTA [4] code for some COMPASS-U scenarios elaborated by the scaling-law based METIS code[5].Several divertorconfigurationswithvarioustargetinclinationanglesaremodelledtostudytheeffectofdivertor closure on detachment, the divertor radiated power and thereforethe peak heat flux density at the divertor target.Impurity seeded cases withneon as the radiating impurity are also considered. The effect ofNe seeding,resulting in anincrease of the total radiative fractionby about two times,on the plasma parameters and the fluxes in the divertor for different divertor configurations is presented and discussed.The neutral gas pressure in the divertor is often considered to be a key control parameter for divertor conditions as neutral gas in divertor helps reaching low plasma temperatures and reduce peak heat fluxes trough power spreading at the divertor targets. SOLPS simulations for COMPASS-U baseline scenario with Ip=2MA and Bt=5T are carried out with the simulation grid includedthe sub-divertor module for more realistic account for neutral gas pressure. The effect of cryo-pump position and widths of gaps between the divertor tiles on neutral gas pressure in divertor is investigated.[1] R. Panek, et al., Fusion Eng. Des.123 (2017)11–16; [2] A.S. Kukushkin, H.D. Pacher, V. Kotov et al., Fusion Eng. Des. 86, 2865 (2011); [3] X. Bonnin et al., Plasma Fusion Res. 11, 1403102 (2016); [4] G. Cunningham, Fusion Eng. Des. 88 (2013) 3238–3247;[5] J.F. Artaud, V. Basiuk, F. Imbeaux, M. Schneider, J. Garcia, et al., Nucl. Fusion 50 (2010)04300

Non-linear gyro-kinetic Ion Temperature Gradient and Trapped Electron Modes turbulence modelling in X-point geometry with Resonant Magnetic Perturbations

The application of 3D magnetic fields such as Resonant Magnetic Perturbations (RMPs) demonstrated suppression/mitigation of Edge Localized Modes (ELMs) in many tokamaks, hence ELMs mitigation by RMPs will be used in ITER to prevent large transient heat and particle fluxes on the ITER divertor

Non-linear gyro-kinetic Ion Temperature Gradient (ITG) and Trapped Electron Modes (TEM) turbulence modelling in X-point geometry with 3D fields, Edge Localized Modes and at negative and positive triangularity shapes

International audienceMotivation. Experimental observation : turbulence increases with RMPs. Why? What kind of turbulence? Reason for density pumpout

Barley starch

This thesis examined barley amylopectin structure and looked for correlations between the structure and physical properties of starch. The structure of amylopectin and gelatinisation and retrogradation of starch were studied in 10 different barley cultivars/breeding lines with differing genetic background. Amylopectin is built up of thousands of chains of glucose monomers, organised into clusters. The detailed fine structure of amylopectin was studied by isolating clusters of amylopectin and their building blocks, which are the tightly branched units building up the clusters. Barley cultivars/breeding lines possessing the amo1 mutation had fewer long chains of DP≥38 in amylopectin and more large building blocks. The structure of building blocks was rather conserved between the different barley cultivars/breeding lines studied and was categorized into different size groups. These different building blocks were shown to be randomly distributed in the amylopectin molecule. The C-chains in amylopectin can be of any length and are a category of chains different from the B-chains. The backbone in amylopectin consists of a special type of B-chains which, when cleaved by α-amylase, become chains of a similar type to C-chains. Gelatinisation and retrogradation (recrystallisation of gelatinised starch) of barley starch was studied by differential scanning calorimetry. The amo1 mutation resulted in a broader gelatinisation temperature range and a higher enthalpy of retrogradation. Other structural features were also found to influence the physical properties of starch. Small clusters and denser structure of the building blocks resulted in higher gelatinisation temperature. Fast retrogradation was observed in barley which had amylopectin with shorter chains and many large building blocks consisting of many chains. Amylopectin structure was also studied in developing barley kernels. Three barley cultivars/breeding lines were grown in a phytotron and kernels were harvested at 9, 12 and 24 days after flowering. The results showed that amylopectin synthesized at later stages of development had a more tightly branched structure. Expression of the enzymes involved in starch biosynthesis is also known to change during endosperm development