The JOREK non-linear extended MHD code and applications to large-scale instabilities and their control in magnetically confined fusion plasmas

JOREK is a massively parallel fully implicit non-linear extended magneto-hydrodynamic (MHD) code for realistic tokamak X-point plasmas. It has become a widely used versatile simulation code for studying large-scale plasma instabilities and their control and is continuously developed in an international community with strong involvements in the European fusion research programme and ITER organization. This article gives a comprehensive overview of the physics models implemented, numerical methods applied for solving the equations and physics studies performed with the code. A dedicated section highlights some of the verification work done for the code. A hierarchy of different physics models is available including a free boundary and resistive wall extension and hybrid kinetic-fluid models. The code allows for flux-surface aligned iso-parametric finite element grids in single and double X-point plasmas which can be extended to the true physical walls and uses a robust fully implicit time stepping. Particular focus is laid on plasma edge and scrape-off layer (SOL) physics as well as disruption related phenomena. Among the key results obtained with JOREK regarding plasma edge and SOL, are deep insights into the dynamics of edge localized modes (ELMs), ELM cycles, and ELM control by resonant magnetic perturbations, pellet injection, as well as by vertical magnetic kicks. Also ELM free regimes, detachment physics, the generation and transport of impurities during an ELM, and electrostatic turbulence in the pedestal region are investigated. Regarding disruptions, the focus is on the dynamics of the thermal quench (TQ) and current quench triggered by massive gas injection and shattered pellet injection, runaway electron (RE) dynamics as well as the RE interaction with MHD modes, and vertical displacement events. Also the seeding and suppression of tearing modes (TMs), the dynamics of naturally occurring TQs triggered by locked modes, and radiative collapses are being studied.Peer ReviewedPostprint (published version

Evaluation of core beta effects on pedestal MHD stability in ITER and consequences for energy confinement

The maximum stable pedestal pressure has been shown to increase with core pressure and in combination with profile stiffness this can lead to a positive feedback mechanism. However, the effect is shown to saturate for high β in ASDEX-Upgrade [1]. This paper investigates whether this effect appears in ITER scenarios, using ideal MHD numerical codes HELENA and MISHKA for different ITER scenarios from inductive 7.5-15 MA plasmas to steady-state scenarios at 10 MA. No pedestal pressure saturation is found for inductive scenarios; on the contrary for the 10MA steady-state scenario the pedestal pressure is the same for a wide range of total β and is limited by low n kink-peeling modes. Finally, a comparison of the achievable pressure for various levels of core profile stiffness is made with the IPB98(y,2) scaling law.</p

Estudio de cohortes en atención primaria sobre la evolución de sujetos con prediabetes (PREDAPS). Fundamentos y metodología

El estudio PREDAPS pretende determinar el riesgo de desarrollo de diabetes y aparición de complicaciones vasculares en sujetos con prediabetes e identificar los factores asociados. Se trata de un estudio observacional de seguimiento de una cohorte de 1.184 sujetos con prediabetes y otra cohorte de 838 sujetos sin alteraciones en el metabolismo de la glucosa. Los datos de la etapa basal se obtuvieron de pacientes que acudieron a centros de Atención Primaria en España a lo largo del año 2012. Los sujetos con prediabetes fueron clasificados en tres grupos: aquellos que sólo tenían alteradas las cifras de glucemia en ayunas -entre 100 y 125 mg/dl-, aquellos que sólo tenían alterado el nivel de HbA1c -entre 5,7 y 6,4%- y aquellos que tenían alterados ambos parámetros. La información sobre sus características sociodemográficas, antecedentes familiares y personales, estilos de vida y tratamiento farmacológico se obtuvo de la historia clínica y de la entrevista realizada en la consulta por el médico. Se realizó un examen físico para determinar peso, talla, perímetro de la cintura y presión arterial y se realizaron análisis de sangre y orina. El estudio PREDAPS puede contribuir a disminuir la incertidumbre en las estrategias individuales de prevención en los sujetos con prediabetes. El seguimiento anual durante cinco años de los participantes posibilitará conocer el riesgo de desarrollo de diabetes mellitus tipo 2 y el de complicaciones macro y microvasculares en los tres grupos de sujetos con prediabetes, así como averiguar los posibles factores asociados a esos riesgos. The PREDAPS study aims to determine the risk of developing diabetes and the risk of vascular complications in patients with prediabetes and identify factors associated with those risks. It is a prospective observational study of a cohort of 1184 subjects with prediabetes and another cohort of 838 subjects with no alterations in glucose metabolism. The data at baseline were obtained from patients attending primary care centers in Spain throughout 2012. Subjects with prediabetes were classified into three groups: those who had only altered the fasting blood glucose levels -between 100 and 125mg/dl-, those who had only altered the HbA1c level -between 5.7 and 6.4% - and those who had altered both parameters. Information on sociodemographic characteristics, personal and family history, lifestyle and drug therapy was obtained from medical records and the interview with the doctor in the consultation. It was also performed a physical examination to determine weight, height, waist circumference and blood pressure were performed and blood and urine analysis. The PREDAPS study may help to reduce uncertainty in individual prevention strategies in subjects with prediabetes. Annual monitoring of patients recruited for five years will enable to know the risk of developing diabetes type 2 and the risk of macro-and microvascular complications in the three groups of subjects with prediabetes and determine the factors associated with those risks

European Space Agency experiments on thermodiffusion of fluid mixtures in space

Abstract.: This paper describes the European Space Agency (ESA) experiments devoted to study thermodiffusion of fluid mixtures in microgravity environment, where sedimentation and convection do not affect the mass flow induced by the Soret effect. First, the experiments performed on binary mixtures in the IVIDIL and GRADFLEX experiments are described. Then, further experiments on ternary mixtures and complex fluids performed in DCMIX and planned to be performed in the context of the NEUF-DIX project are presented. Finally, multi-component mixtures studied in the SCCO project are detailed

Modifiable risk factors associated with prediabetes in men and women: A cross-sectional analysis of the cohort study in primary health care on the evolution of patients with prediabetes

Background: Prediabetes is a high-risk state for diabetes development, but little is known about the factors associated with this state. The aim of the study was to identify modifiable risk factors associated with the presence of prediabetes in men and women. Methods: Cohort Study in Primary Health Care on the Evolution of Patients with Prediabetes (PREDAPS-Study) is a prospective study on a cohort of 1184 subjects with prediabetes and another cohort of 838 subjects without glucose metabolism disorders. It is being conducted by 125 general practitioners in Spain. Data for this analysis were collected during the baseline stage in 2012. The modifiable risk factors included were: smoking habit, alcohol consumption, low physical activity, inadequate diet, hypertension, dyslipidemia, and obesity. To assess independent association between each factor and prediabetes, odds ratios (ORs) were estimated using logistic regression models. Results: Abdominal obesity, low plasma levels of high-density lipoprotein cholesterol (HDL-cholesterol), and hypertension were independently associated with the presence of prediabetes in both men and women. After adjusting for all factors, the respective ORs (95% Confidence Intervals) were 1.98 (1.41-2.79), 1.88 (1.23-2.88) and 1.86 (1.39-2.51) for men, and 1.89 (1.36-2.62), 1.58 (1.12-2.23) and 1.44 (1.07-1.92) for women. Also, general obesity was a risk factor in both sexes but did not reach statistical significance among men, after adjusting for all factors. Risky alcohol consumption was a risk factor for prediabetes in men, OR 1.49 (1.00-2.24). Conclusions: Obesity, low HDL-cholesterol levels, and hypertension were modifiable risk factors independently related to the presence of prediabetes in both sexes. The magnitudes of the associations were stronger for men than women. Abdominal obesity in both men and women displayed the strongest association with prediabetes. The findings suggest that there are some differences between men and women, which should be taken into account when implementing specific recommendations to prevent or delay the onset of diabetes in adult population

3D simulations of vertical displacement events in tokamaks: A benchmark of M3D-C 1, NIMROD, and JOREK

In recent years, the nonlinear 3D magnetohydrodynamic codes JOREK, M3D-C1, and NIMROD developed the capability of modeling realistic 3D vertical displacement events (VDEs) including resistive walls. In this paper, a comprehensive 3D VDE benchmark is presented between these state-of-the-art codes. The simulated case is based on an experimental NSTX plasma but with a simplified rectangular wall. There are differences between the physics models and numerical methods, and the VDE evolution leads to sensitivities on the initial conditions that cannot be avoided as can be done in edge localized modes (ELM) and sawtooth simulations (due to the non-cyclical nature of VDEs). Nonetheless, the comparison serves to quantify the level of agreement in the relevant quantities used to characterize disruptions, such as the 3D wall forces and energy decay. The results bring confidence regarding the use of the mentioned codes for disruption studies, and they distinguish aspects that are specific to the models used (e.g., reduced vs full MHD models). The simulations show important 3D features for a NSTX plasma, such as the self-consistent evolution of the halo current and the origin of the wall forces. In contrast to other reduced MHD models based on an ordering in the aspect ratio, the ansatz-based JOREK reduced MHD model allows capturing many aspects of the 3D dynamics even in the spherical tokamak limit considered here

Axisymmetric simulations of vertical displacement events in tokamaks: A benchmark of M3D-C1, NIMROD and JOREK

A benchmark exercise for the modeling of vertical displacement events(VDEs) is presented and applied to the 3D nonlinear magneto-hydrodynamic codesM3D-C1, JOREK and NIMROD. The simulations are based on a vertically unstableNSTX equilibrium enclosed by an axisymmetric resistive wall with rectangular crosssection. A linear dependence of the linear VDE growth rates on the resistivity ofthe wall is recovered for sufficiently large wall conductivity and small temperatures inthe open field line region. The benchmark results show good agreement between theVDE growth rates obtained from linear NIMROD and M3D-C1simulations as wellas from the linear phase of axisymmetric nonlinear JOREK, NIMROD and M3D-C1simulations. Axisymmetric nonlinear simulations of a full VDE performed with thethree codes are compared and excellent agreement is found regarding plasma locationand plasma currents as well as eddy and halo currents in the wall

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.</p

Reassessing energy deposition for the ITER 5 MA vertical displacement event with an improved DINA model

The beryllium (Be) main chamber wall interaction during a 5 MA/1.8 T upward, unmitigated VDE scenario, first analysed in [J. Coburn et al., Phys. Scr. T171 (2020) 014076] for ITER, has been re-evaluated using the latest energy deposition analysis software. Updates to the DINA disruption model are summarized, including an improved numerical convergence for the 0D power balance, limitations on the safety factor within the plasma core, and the choice to maintain a constant plasma + halo poloidal cross-section. Such updates result in a broad halo region and higher radiated power fractions compared to previous models. The new scenario lasts for ~75 ms and deposits ~29 MJ of energy, with the radial distribution of parallel heat flux q‖r resembling an exponential falloff with an effective λq=75-198 mm. A maximum halo width wh of 0.52 m at the outboard midplane is observed. SMITER field line tracing and energy deposition simulations calculate a q⊥,max of ~83 MW/m2 on the upper first wall panels (FWP). Heat transfer calculations with the MEMOS-U code show that the FWP surface temperature reaches ~1000 K, well below the Be melt threshold. Variations of this 5 MA scenario with Be impurity densities from 0 to 3∙1019 m−3 also remain below the melt threshold despite differences in energy deposition and duration. These results are in contrast to the early study which predicted melt damage to the first wall [J. Coburn et al., Phys. Scr. T171 (2020) 014076], and emphasize the importance of accurate models for the halo width wh and the heat flux distribution q‖r within that halo width. The 2020 halo model in DINA has been compared with halo current experiments on COMPASS, JET, and Alcator C-Mod, and the preliminary results build confidence in the broad halo width predictions. Results for the 5 MA VDE are compared with those for a 15 MA equivalent, generated using the new DINA model. At the higher current, significant melting of the upper FWP is to be expected