The role of plasma-molecule interactions on power and particle balance during detachment on the TCV tokamak
Kevin Verhaegh, Bruce Lipschultz, James Harrison, Basil Duval, Alex Fil, Mirko Wensing, Chris Bowman, Daljeet Gahle, Andrei Kukushkin, David Moulton, Artur Pere… 展开作者
Kevin Verhaegh, Bruce Lipschultz, James Harrison, Basil Duval, Alex Fil, Mirko Wensing, Chris Bowman, Daljeet Gahle, Andrei Kukushkin, David Moulton, Artur Perek, Andrey Pshenov, Fabio Federici, Olivier Février, Omkar Myatra, Andreas Smolders, Christian Theiler
This paper shows experimental results from the TCV tokamak that indicate plasma-molecule interactions involving $D_2^+$ and possibly $D^-$ play an important role as sinks of energy (through hydrogenic radiation as well as dissociation) and particles during divertor detachment if low target temperatures ($< 3$ eV) are achieved. Both molecular activated recombination (MAR) and ion source reduction due to a power limitation effect are shown to be important in reducing the ion target flux during a density ramp. In contrast, the electron-ion recombination (EIR) ion sink is too small to play an important role in reducing the ion target flux. MAR or EIR do not occur during $N_2$ seeding induced detachment as the target temperatures are not sufficiently low.
The impact of $D_2^+$ is shown to be underestimated in present (vibrationally unresolved) SOLPS-ITER simulations, which could result from an underestimated $D_2 + D^+ \rightarrow D_2^+ + D$ rate. The converged SOLPS-ITER simulations are post-processed with alternative reaction rates, resulting in considerable contributions of $D_2^+$ to particle and power losses as well as dissociation below the $D_2$ dissociation area. Those findings are in quantitative agreement with the experimental results.
Nitrogen seeded detachment has been achieved in the Tokamak a Configuration Variable (TCV) in advanced divertor configurations (ADCs), namely X-divertor and X-point target, with and without baffles in H-mode plasmas with high core confinement. Both ADCs show a remarkable reduction in the inter-ELM particle and heat fluxes to the target compared to the standard divertor configuration. 95-98% of the peak heat flux to the target is mitigated as a synergetic effect of ADCs, baffling, and nitrogen seeded detachment. The effect of divertor geometry and baffles on core-divertor compatibility is inves…
Non-dimensional confinement scaling in similar negative triangularity plasmas on the DIII-D and TCV tokamaks
University of California San Diego（加州大学圣地亚哥分校）；General Atomics（通用原子能公司）；Ecole Polytechnique Federale de Lausanne（洛桑联邦理工学院）；Consorzio RFX（RFX联合体）；University of Texas at Austin（德克萨斯大学奥斯汀分校）；Princeton Plasma Physics Laboratory（普林斯顿等离子体物理实验室）；Columbia University（哥伦比亚大学）；College of William and Mary（威廉玛丽学院）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）
The aim of this work is to provide an understanding of detachment at TCV with emphasis on analysis of the Balmer line emission. A new Divertor Spectroscopy System has been developed for this purpose. Further development of Balmer line analysis techniques has allowed detailed information to be extracted from the three-body recombination contribution to the n=7 Balmer line intensity. During density ramps, the plasma at the target detaches as inferred from a drop in ion current to the target. At the same time the Balmer $6\rightarrow2$ and $7\rightarrow2$ line emission near the target is dominate…
Synchrotron radiation observed from runaway electrons (REs) in tokamaks depends upon the position and size of the RE beam, the RE energy and pitch distributions, as well as the location of the observer. We show that experimental synchrotron images of a vertically moving runaway electron beam sweeping past the detector in the TCV tokamak agree well with predictions from the synthetic synchrotron diagnostic Soft. This experimental validation lends confidence to the theory underlying the synthetic diagnostics which are used for benchmarking theoretical models of and probing runaway dynamics. We p…
Results from a database analysis of H-mode electron density profiles on the Tokamak à Configuration Variable (TCV) in stationary conditions show that the logarithmic electron density gradient increases with collisionality. By contrast, usual observations of H-modes showed that the electron density profiles tend to flatten with increasing collisionality. In this work it is reinforced that the role of collisionality alone, depending on the parameter regime, can be rather weak and in these, dominantly electron heated TCV cases, the electron density gradient is tailored by the underlying turbulenc…
The process of divertor detachment, whereby heat and particle fluxes to divertor surfaces are strongly diminished, is required to reduce heat loading and erosion in a magnetic fusion reactor to acceptable levels. In this paper the physics leading to the decrease of the total divertor ion current (It), or 'roll-over', is experimentally explored on the TCV tokamak through characterization of the location, magnitude and role of the various divertor ion sinks and sources including a complete analysis of particle and power balance. These first measurements of the profiles of divertor ionisation and…
High-power TCV scenario for conventional and alternative divertor studies
Max Planck Institute for Plasma Physics（马克斯·普朗克等离子体物理研究所）；Eindhoven University of Technology（埃因霍温理工大学）；DIFFER - Dutch Institute for Fundamental Energy Research（荷兰基础能源研究院）
An Inverse Grad-Shafranov Neural Network Approach to Tokamak Magnetic Control
MIT Plasma Science and Fusion Center（麻省理工学院等离子体科学与聚变中心）；École Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院）；Google DeepMind（谷歌DeepMind）；Fusionality SA；Commonwealth Fusion Systems（联邦聚变系统）
In inboard-limited plasmas, foreseen to be used in future fusion reactors start-up and ramp down phases, the Scrape-Off Layer (SOL) exhibits two regions: the "near" and "far" SOL. The steep radial gradient of the parallel heat flux associated with the near SOL can result in excessive thermal loads onto the solid surfaces, damaging them and/or limiting the operational space of a fusion reactor. In this article, leveraging the results presented in [F. Nespoli et al., Nuclear Fusion 2017], we propose a technique for the mitigation and suppression of the near SOL heat flux feature by impurity seed…
In this work we provide experimental insights into the impact of plasma-molecule interactions on the target ion flux decrease during divertor detachment achieved through a core density ramp in the TCV tokamak. Our improved analysis of the hydrogen Balmer series shows that plasma-molecule processes are strongly contributing to the Balmer series intensities and substantially alter the divertor detachment particle balance. We find that Molecular Activated Recombination (MAR) ion sinks from $H_2^+$ and/or $H^-$ are a factor $\sim$ 5 larger than Electron-Ion Recombination (EIR) and are a significan…
We analyze an axisymmetric equilibrium of a plasma endowed with toroidal and poloidal velocity fields, with the aim to characterize the influence of the global motion on the morphology of the magnetic confinement. We construct our configuration assuming that the poloidal velocity field is aligned with the poloidal magnetic field lines and, furthermore, we require that the plasma mass density depend on the magnetic flux function (or equivalently, that the plasma fluid be incompressible). We then derive a sort of Grad-Shafranov equation for such an equilibrium and implement it to tokamak relevan…
Nonlinear generation of global zonal structures in gyrokinetic simulations of TCV and ASDEX Upgrade magnetic configurations
Max-Planck-Institut für Plasmaphysik（马克斯·普朗克等离子体物理研究所）；De Vinci Higher Education, De Vinci Research Center（德芬奇高等教育，德芬奇研究中心）；Institute of Physics, University of Greifswald（格赖夫斯瓦尔德大学物理研究所）；École Polytechnique Fédérale de Lausanne, Swiss Plasma Center（洛桑联邦理工学院，瑞士等离子体中心）
Radio frequency waves are routinely used in tokamak fusion plasmas for plasma heating, current control, and as well as in diagnostics. These waves are excited by antenna structures placed near the tokamak's wall and they have to propagate through a turbulent layer known as scrape-off layer, before reaching the core plasma (which is their target). This layer exhibits coherent density fluctuations in the form of blobs and filaments. The scattering processes of RF plane waves by single blob is studied, with the assumption that the blob has cylindrical shape and infinite length. The axis of the bl…
Detachment, an important mechanism for reducing target heat deposition, is achieved through reductions in power, particle and momentum; which are induced through plasma-atom and plasma-molecule interactions. Experimental research in how those reactions precisely contribute to detachment is limited. In this work, we investigate a new spectroscopic technique to utilise Hydrogen Balmer line measurements to 1) disentangle the Balmer line emission from the various plasma-atom and plasma-molecule interactions; and 2) quantify their contributions to ionisation, recombination and radiative power losse…
During a tokamak discharge, the plasma can vary between different confinement regimes: Low (L), High (H) and, in some cases, a temporary (intermediate state), called Dithering (D). In addition, while the plasma is in H mode, Edge Localized Modes (ELMs) can occur. The automatic detection of changes between these states, and of ELMs, is important for tokamak operation. Motivated by this, and by recent developments in Deep Learning (DL), we developed and compared two methods for automatic detection of the occurrence of L-D-H transitions and ELMs, applied on data from the TCV tokamak. These method…
A machine learning approach has been implemented to measure the electron temperature directly from the emission spectra of a tokamak plasma. This approach utilized a neural network (NN) trained on a dataset of 1865 time slices from operation of the DIII-D tokamak using extreme ultraviolet / vacuum ultraviolet (EUV/VUV) emission spectroscopy matched with high-accuracy divertor Thomson scattering measurements of the electron temperature, $T_e$. This NN is shown to be particularly good at predicting $T_e$ at low temperatures ($T_e < 10$ eV) where the NN demonstrated a mean average error of less t…
A High-order piecewise field-aligned triangular finite element method for electromagnetic gyrokinetic particle simulations of tokamak plasmas with open field lines
Max Planck Institute for Plasma Physics（马克斯·普朗克等离子体物理研究所）；Max Planck Computing and Data Facility（马克斯·普朗克计算与数据设施）
Towards fully predictive gyrokinetic full-f simulations: validation and triangularity studies in TCV
Princeton Plasma Physics Laboratory（普林斯顿等离子体物理实验室）；General Atomics（通用原子能公司）；University of California San Diego（加州大学圣地亚哥分校）；Sandia National Laboratories（桑迪亚国家实验室）
In-situ, two-dimensional (2D) Langmuir probe measurements across a large part of the TCV divertor are reported in L-mode discharges with and without divertor baffles. This provides detailed insights into time averaged profiles, particle fluxes, and fluctuations behavior in different divertor regimes. The presence of the baffles is shown to substantially increase the divertor neutral pressure for a given upstream density and to facilitate the access to detachment, an effect that increases with plasma current. The detailed, 2D probe measurements allow for a divertor particle balance, including i…
A new version of GBS (Ricci et al. Plasma Phys. Control. Fusion 54, 124047, 2012; Halpern et al. J. Comput. Phys. 315, 388-408, 2016; Paruta et al. Phys. Plasmas 25, 112301, 2018) is described. GBS is a three-dimensional, flux-driven, global, two-fluid turbulence code developed for the self-consistent simulation of plasma turbulence and kinetic neutral dynamics in the tokamak boundary. In the new version presented here, the simulation domain is extended to encompass the whole plasma volume, avoiding an artificial boundary with the core, hence retaining the core-edge-SOL interplay. A new toroid…
Multi-Machine Scaling Laws for Fuel and Impurity Puffing Rates Sufficient for Detachment Access: a Systematic Review of Magnetic Confinement Fusion Devices
Validation of geometric proxies using negative and positive triangularity plasmas with varying elongation on TCV and multi-machine gyrokinetic simulations
École Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院）；Max-Planck-Institut für Plasmaphysik（马克斯·普朗克等离子体物理研究所）；Istituto per la Scienza e la Tecnologia dei Plasmi, CNR（意大利国家研究委员会等离子体科学与技术研究所）；Plasma Science and Fusion Center, Massachusetts Institute of Technology（麻省理工学院等离子体科学与聚变中心）
École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院）
The analysis of turbulence in plasmas is fundamental in fusion research. Despite extensive progress in theoretical modeling in the past 15 years, we still lack a complete and consistent understanding of turbulence in magnetic confinement devices, such as tokamaks. Experimental studies are challenging due to the diverse processes that drive the high-speed dynamics of turbulent phenomena. This work presents a novel application of motion tracking to identify and track turbulent filaments in fusion plasmas, called blobs, in a high-frequency video obtained from Gas Puff Imaging diagnostics. We comp…
In a typical fusion experiment, the plasma can have several possible confinement modes. At the TCV tokamak, aside from the Low (L) and High (H) confinement modes, an additional mode, dithering (D), is frequently observed. Developing methods that automatically detect these modes is considered to be important for future tokamak operation. Previous work with deep learning methods, particularly convolutional recurrent neural networks (Conv-RNNs), indicates that they are a suitable approach. Nevertheless, those models are sensitive to noise in the temporal alignment of labels, and that model in par…
To improve the low frequency spectrum of magnetic field measurements of future tokamak reactors such as ITER, several steady state magnetic sensor technologies have been considered. For all the studied technologies it is always advantageous to place the sensors outside the vacuum vessel and as far away from the reactor core to minimize radiation damage and temperature effects, but not so far as to compromise the accuracy of the equilibrium reconstruction. We have studied to what extent increasing the distance between out-vessel sensors and plasma can be compensated for sensor accuracy and/or d…
TRIMEG-GKX: an electromagnetic gyrokinetic particle code with a Piecewise Field-Aligned Finite Element Method for Micro- and Macro-Instability Studies in Tokamak Core Plasmas
The understanding of the mechanisms responsible for particle transport is of the utmost importance for magnetized fusion plasmas. A peaked density profile is attractive to improve the fusion rate, which is proportional to the square of the density, and to self-generate a large fraction of non-inductive current required for continuous operation. Experiments in various tokamak devices (AUG, DIII-D, JET, TCV, TEXT, TFTR) have indicated the existence of an anomalous inward particle pinch. Recently, such an anomalous pinch has been unambiguously identified in Tore Supra very long discharges, in abs…
A control oriented, lumped parameter model for the tokamak transformer including the slow flux penetration in the plasma (skin effect transformer model) is presented. The model does not require detailed or explicit information about plasma profiles or geometry. Instead, this information is lumped in system variables, parameters and inputs. The model has an exact mathematical structure built from energy and flux conservation theorems, predicting the evolution and non linear interaction of the plasma current and internal inductance as functions of the primary coil currents, plasma resistance, no…
