48 research outputs found
A QSS approach for particle source identification in Tore Supra tokamak
International audienceIn this work, we consider the problem of particle source identification from distributed electron density measurements in fusion plasmas, such as the ones obtained in Tore Supra tokamak. A transport model, suitable for identification purposes, is first proposed based on a simplification of classical particle transport models. We then derive a quasi-steady state (QSS) description, which is shown to converge exponentially towards the true solution. Finally, an identification method is proposed based on the QSS model and a shape approximation of the source term. ToreSupra data is used to illustrate the different results with experimental measurements
SOL RF physics modelling in Europe, in support of ICRF experiments
A European project was undertaken to improve the available SOL ICRF physics simulation tools and confront them with measurements. This paper first reviews code upgrades within the project. Using the multi-physics finite element solver COMSOL, the SSWICH code couples RF full-wave propagation with DC plasma biasing over “antenna-scale” 2D (toroidal/radial) domains, via non-linear RF and DC sheath boundary conditions (SBCs) applied at shaped plasma-facing boundaries. For the different modules and associated SBCs, more elaborate basic research in RF-sheath physics, SOL turbulent transport and applied mathematics, generally over smaller spatial scales, guides code improvement. The available simulation tools were applied to interpret experimental observations on various tokamaks. We focus on robust qualitative results common to several devices: the spatial distribution of RF-induced DC bias; left-right asymmetries over strap power unbalance; parametric dependence and antenna electrical tuning; DC SOL biasing far from the antennas, and RF-induced density modifications. From these results we try to identify the relevant physical ingredients necessary to reproduce the measurements, e.g. accurate radiated field maps from 3D antenna codes, spatial proximity effects from wave evanescence in the near RF field, or DC current transport. Pending issues towards quantitative predictions are also outlined
Modelling of combined ICRF and NBI heating in JET hybrid plasmas
During the 2015-2016 JET campaigns many efforts have been devoted to the exploration of high performance plasma scenarios envisaged for ITER operation. In this paper we model the combined ICRF+NBI heating in selected key hybrid discharges using PION. The antenna frequency was tuned to match the cyclotron frequency of minority hydrogen (H) at the center of the tokamak coinciding with the second harmonic cyclotron resonance of deuterium. The modelling takes into account the synergy between ICRF and NBI heating through the second harmonic cyclotron resonance of deuterium beam ions which allows us to assess its impact on the neutron rate RNT. We evaluate the influence of H concentration which was varied in different discharges in order to test their role in the heating performance. According to our modelling, the ICRF enhancement of RNT increases by decreasing the H concentration which increases the ICRF power absorbed by deuterons. We find that in the recent hybrid discharges this ICRF enhancement was in the range of 10-25%. Finally, we extrapolate the results to D-T and find that the best performing hybrid discharges correspond to an equivalent fusion power of ∼7.0 MW in D-T.This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Dani Gallart would like to thank “La Caixa” for support of his PhD studies.Peer ReviewedPostprint (published version
Optimal estimation of the particle sources in Tore Supra tokamak
International audienc
The Role of the Plasma Current in Turbulence Decrease with Lower Hybrid Waves
We study the effect of lower hybrid waves on edge turbulence using a set of two Langmuir probes inserted in the scrape-off layer of the Tore Supra tokamak. We use the cross-correlation coefficient to assess the interplay between turbulence and the LH waves. We found that turbulence is affected at high plasma current even at relatively low LH powers. When the plasma current is below 1 MA, this effect disappears. Finally, we show that the level of fluctuations and the cross-correlation amplitude are correlated whereas the increase of the first leads to the increase of the second. The role of the plasma current could reflect that the exchange of the RF waves with edge turbulence is occurring in the closed field lines rather in the open field lines range
Toward particle source identification in Tore Supra tokamak
International audienc
Romania (2011)" An Optimal Feedback Approach to Particle Source Identification in Tokamaks
Abstract—A new identification technique is proposed to study the plasma phenomena taking place in the so-called scrapeoff layer and their correlation with the lower hybrid radio frequency antenna in the experimental nuclear fusion tokamak reactor Tore Supra. A deeper knowledge of the plasma behavior in this region would contribute to the achievement of steadystate controlled thermonuclear fusion for power generation. The proposed approach relies on the design of a feedback/feedforward optimized architecture to solve a blind identification problem. While our paper is mostly focused on experimental results for the studied application, it can provide valuable insights on input estimation and model validation for transport phenomena described by partial differential equations