Plasma equilibrium reconstruction of jet discharges using the imas modelling infrastructure

International audienceThe reconstruction of Tokamak plasma equilibrium is a fundamental step in the understanding of fusion plasma physics since it sets the starting point for all subsequent plasma modelling applications and experimental data interpretation. The verification and validation of the numerical codes used to reconstruct plasma equilibrium, using as many available input experimental data e.g. magnetic field or flux measurements, density and temperature diagnostics and polarimetry diagnostics, is essential both for physics model interpretation and when qualifying and extrapolating for ITER. In the framework of the EUROfusion Work Package on Code Development for Integrated Modelling, a scientific Kepler workflow for the reconstruction of Tokamak plasma equilibrium was prototyped, using the ITER Integrated Modelling and Analysis Suite (IMAS). The workflow can seamlessly use any sort of data from Tokamak experiments and call equilibrium reconstruction codes such as EQUAL, EQUINOX, NICE, EFIT++ and SDSS, all using the same physics and engineering data ontology and methods for accessing the data. In the paper, plasma equilibrium reconstructions on dedicated JET plasma dischargesare shownusing at first magnetic data only and subsequently considering also other constrains suchas Motional Stark Effect(MSE). Results with magneticsonly give a good qualitative and quantitative agreement between the codes while including MSE, as anticipated, a substantial improvementofthe core plasma profilesis achieved

Improved flux-surface parameterization through constrained nonlinear optimization

Parameterization of magnetic flux-surfaces is often used for magnetohydrodynamic stability analysis and microturbulence modeling in tokamaks. Shape parameters for such local parameterization of a (numerical) equilibrium are traditionally computed analytically using geometrically derived quantities. However, often the shape is approximated by the average of values for different sections of the flux-surface contour or a truncated series, which does not guarantee an optimal fit. Here, instead nonlinear least squares optimization is used to compute these parameters, with a weighted sum of squared error cost function that is robust to outliers. This method results in a lower total absolute error for both the parameterization of the flux-surface contour and the poloidal magnetic field density than current methods for several parameterizations based on the well-known "Miller geometry."Furthermore, rapid convergence of shape parameters is achieved, no approximate geometric measurements of the contour are needed, and the method is applicable to any analytical shape parameterization. Validation with local, linear gyrokinetic simulations using these optimized shape parameters showed reduced root mean square errors in both the growth rate and frequency spectra when compared with simulations based on numerical equilibria. In particular, the popular Turnbull-Miller parameterization benefits from this approach, extending its usability closer toward the last-closed flux-surface for cases with minor up-down asymmetry.</p

Comparing pedestal structure in JET-ILW H-mode plasmas with a model for stiff ETG turbulent heat transport

A predictive model for the electron temperature profile of the H-mode pedestal is described, and its results are compared with the pedestal structure of JET-ILW plasmas. The model is based on a scaling for the gyro-Bohm normalized, turbulent electron heat flux qe/qe,gB resulting from electron temperature gradient (ETG) turbulence, derived from results of nonlinear gyrokinetic (GK) calculations for the steep gradient region. By using the local temperature gradient scale length L-Te in the normalization, the dependence of q(e)/q(e,g)B on the normalized gradients R/L-Te and R/(Lne) can be represented by a unified scaling with the parameter eta(e) = L-ne/L-Te, to which the linear stability of ETG turbulence is sensitive when the density gradient is sufficiently steep. For a prescribed density profile, the value of R/L-Te determined from this scaling, required to maintain a constant electron heat flux qe across the pedestal, is used to calculate the temperature profile. Reasonable agreement with measurements is found for different cases, the model providing an explanation of the relative widths and shifts of the T-e and n(e) profiles, as well as highlighting the importance of the separatrix boundary conditions. Other cases showing disagreement indicate conditions where other branches of turbulence might dominate.This article is part of a discussion meeting issue "H-mode transition and pedestal studies in fusion plasmas'

Full-orbit studies of wave-particle interaction on the Mega Ampere Spherical Tokamak

Energetic particles with super-Alfv\'enic speeds could potentially drive Alfv\'enic instabilities in a magnetically confined plasma. The driven waves can influence the fast particle distribution function as energetic particles are redistributed or lost to the vessel wall leading to a reduction in energetic particle confinement and heating efficiency. This thesis investigates the interaction between particles and waves via full orbit numerical simulations. The work presented herein takes steps towards the development of a capability to assess whether future reactor scenarios will be susceptible to these adverse effects or not. A full orbit particle tracking code has been developed to calculate particle trajectories and more importantly to compute particle orbital frequencies as they are followed in the simulation. Based on the wave-particle resonance condition, resonant particles are identified using this code for realistic tokamak geometries. Experimental observations of fast-ion driven waves on the MAST tokamak are presented. Magnetic perturbations in the kilo-Hertz range are detected by a set of high resolution Mirnov coils during the neutral beam injection heating phase where the mode frequency is observed to chirp downwards over the course of a magneto-hydrodynamics (MHD) burst. A decrease in fast-ion deuterium alpha signals is found to be correlated with the electromagnetic bursts indicating fast ion redistribution during the MHD activity. Simulation results suggest that the increase in plasma pressure is disproportional to the increase in NBI heating power in the presence of MHD modes. The effect of instabilities on energetic particle behaviour has been analysed by calculating resonance maps and resonant particle orbits. Full orbit calculations show that the chirping frequency broadens the wave-particle resonance region which can result in enhanced particle transport. Preliminary attempts have been made to evaluate fast particle transport induced by chirping modes using the non-linear full orbit \texttt{HALO} code. The chirping behaviour of the mode frequency is simulated by an ad-hoc function similar to experimental measurement. Calculations are performed for a simple cylindrical tokamak geometry and a mocked-up alpha particle distribution. An $n=6$ toroidal Alfv\'en eigenmode (TAE) is found numerically for this equilibrium. The results of the simulations show that fast particles are transported outwards from the plasma centre when chirping modes are present while no significant particle transport is seen when the mode frequency is constant. The level of transport is affected by either mode amplitude or chirping rate. These results suggest that the inclusion of a chirping effect is necessary to study particle redistribution in the presence of fast-ion modes when considering plasma scenarios in the future

Annual report 2015

Accessions considered in the study. Overview of the material considered in this study. For all materials, the GenBank identifier, the accession and species name as used in this study (Species) as well as their species synonyms used in the donor seed banks or in the NCBI GenBank (Material source/Reference) are provided. The genome symbol, and the country of origin, where the material was originally collected are given. The ploidy level measured in the scope of this study and the information if a herbarium voucher could be deposited in the herbarium of IPK Gatersleben (GAT) is given. Genomic formulas of tetraploids and hexploids are given as “female x male parent”. The genomes of Aegilops taxa follow Kilian et al. [74] and Li et al. [84]. Genome denominations for Hordeum follow Blattner [107] and Bernhardt [12] for the remaining taxa. (XLS 84 kb

Analysis of Plasma Filaments with Fast Visible Imaging in the Mega Ampère Spherical Tokamak

The cross-field transport of particles in the scrape-off layer (SOL) of magnetic fusion devices is dominated by the convection of coherent filamentary plasma structures. In this thesis, we present a new technique for the analysis of filaments in fast visible camera data. The new technique operates by inverting the background subtracted emission in the camera images onto a basis set of uniformly emitting field line images, constructed using information from magnetic equilibrium reconstructions. The output of the inversion is a 2D mapping of emission parametrising the average intensity of field lines in the SOL by the coordinates of their intersection with the mid-plane. Filaments manifest in the inverted emission profile as blobs of raised emission. A filament detection technique has been developed to identify these regions of increased emission and fit them with 2D Gaussians. This yields the positions, widths and amplitudes of the filaments. A tracking algorithm is then applied to calculate the filaments velocities and lifetimes. Data from a synthetic camera diagnostic is used to assess the capabilities and limitations of the new technique and quantify its errors. This exercise shows it can detect ~36% of all filaments in the analysis region, corresponding to ~74% of filaments above the targeted amplitude threshold. This sensitivity is achieved with a true positive detection rate of 98.8%. Standard errors in the radial and toroidal positions of the filaments are estimated to be ~2 mm, while errors in the toroidal and radial widths are around ~3 mm and ~7 mm respectively. The shapes of the probability density functions (PDFs) of the filament parameters are also qualitatively recovered and the effect of filament overlap on filament amplitude measurements is investigated. Valuable insight is gained into effects from the non-orthogonality of the field line basis functions and the resulting spatial dependence of the measurement errors. Finally, the technique is applied to MAST data and compared to Langmuir probe measurements. Good agreement is found between the two diagnostics, including exponential waiting times and symmetrical conditionally averaged waveforms. Measurements of the PDFs of filament properties provide valuable inputs for analytic models of SOL transport and show filament lifetimes to be exponentially distributed. The depth of field of the technique enables measurement of the toroidal filament spacing, with results supporting the assertion that filaments are generated uniformly and independently, and are thus described by Poisson statistics underpinning several analytic models