Phenomena In Tokamaks Research Articles

H-mode. Physics and prospects.

The H-mode has been recognized to be a universal phenom ena in tokamaks with various heating methods. In this article, we present a model picture for the H-mode from the experimental/theoretical view point putting an emphasis on the causality among many H-mode-related observations. Based on the model, the improvements and obstacles caused by the H-mode are explained. The future prospects of the H-mode in the research to realize the ignition plasma are also discussed.

Review of MARFE phenomena in tokamaks

This paper presents a review of MARFEs and detached plasmas. A MARFE is a toroidally symmetric tokamak phenomenon occuring at minor radii near the plasma boundary, defined by a limiter or magnetic separatrix. The MARFE poloidal width is approximately 30° in extent at the smaller major radius edge of the plasma. It is characterized by greatly increased radiation, high ion densities and density fluctuations, and relatively low electron temperature. These changes in the edge plasma are consistent with the MARFE being the manifestation of a thermal instability. MARFEs tend to occur in most tokamaks at similar values of ρ = n e κJ , a fraction of the density disruption limit. A related phenomenon, the detached plasma, is different in that the boundary layer radiation emission is poloidally symmetric. The radiated power, in this case, is approximately equal to the input power, thereby reducing power flows to the limiter to negligible values. A review of experimental data and theoretical treatments of MARFEs and detached plasmas are provided herein. The relationship between boundary layer parameter scalings, the MARFE threshold and the density limit is explored.

Present status of the theory on anomalous transport phenomena in tokamak.

Recent progress of the theory on anomalous transport of tokamak plasmas is reviewed. Topics cover the methods for the transport theory, the applications to the analyses and the comparison with experiments. Contents are the following; §1 Introduction§2 Methods for the transport theory(2.1) Transport by the electric and magnetic fluctuations(2.2) Local transport coefficient(2.3) Boundary condition(2.4) Constraints on the profile§3 Drift waves and microscopic instabilities(3.1) Drift waves(3.2) Microscopic electromagnetic instabilities§4 Convective cell§5 Global MHD instabilities§6 Anomalous resistivity§7 Plasma near the surface§8 Comparison with experiments(8.1) Transport code and analytic model(8.2) Scaling law(8.3) Plasma profile(8.4) Fluctuations(8.5) “Profile consistensy” ansatz and thinking experiment§9 Transport of the heated plasma(9.1) Diffusion in the phase space(9.2) Effect on fluctuations and anomalous transport§10 Summary and discussion

Present status of the theory on anomalous transport phenomena in tokamak.

Present status of the theory on anomalous transport phenomena in tokamak.

Hydrogen ion impact desorption of adsorbed deuterium from stainless steel

The removal of adsorbed deuterium from stainless steel by energetic molecular hydrogen ions (H 2 + and H 3 +) has been studied with secondary ion mass spectrometry. Desorption cross sections for this process range from 1.2 × 10 −16 cm 2 to 5 × 10 −17 cm 2 for incident ion energies 0.3 to 1.5 keV/atom. The cross sections increase as the incident ion energy is lowered. At low energies, direct interactions between incident particles and adsorbate atoms appear to be important in causing desorption. Dissociation of molecular hydrogen ions occurs prior to desorption. The implications of these findings with respect to the mechanisms for ion impact desorption and to fuel recycling phenomena in tokamaks are discussed.

Plasma modeling and first wall interaction phenomena in Tokamaks

Fluxes of neutral hydrogenic particles, alpha particles and electromagnetic radiation to the liner or first wall of both two component tokamaks and large ignited tokamak fusion reactors are estimated using space and time dependent models of tokamak plasmas. Data requirements and the effects of uncertainties in the areas of first wall interaction phenomenon and plasma transport coefficients are described. Des flux de particules neutres hydrogénées, de particules alpha et de radiation électromagnétique à la surface de la première paroi à la fois des tokamaks à deux composants et des réacteurs de fusion tokamak à haute température sont estimés en utilisant des modèles de plasmas de tokamak dépendant de l'espace et du temps. Les exigences des données et les effets des incertitudes dans le domaine des phénomènes d'interaction avec la première paroi et des coefficients de transport du plasma sont décrits. Der Fluss der neutralen Wasserstoffisotope, der α-Teilchen sowie der elektromagnetischen Strahlung auf die Auskleidung oder die innerste Wand von Zweikomponenten- und grossen gezündeten Tokamak-Fusionsreaktoren wird mit Hilfe raumund zeitabhängiger Modelle für Tokamak-Plasmen abgeschätzt. Die Anforderungen an die Daten und der Einfluss der Unsicherheiten auf den Gebieten der Wechselwirkungserseheinungen an der innersten Wand und der Plasmatransportkoeffizienten werden beschrieben.

Plasma modeling and first wall interaction phenomena in Tokamaks

Fluxes of neutral hydrogenic particles, alpha particles and electromagnetic radiation to the liner or first wall of both two component tokamaks and large ignited tokamak fusion reactors are estimated using space and time dependent models of tokamak plasmas. Data requirements and the effects of uncertainties in the areas of first wall interaction phenomenon and plasma transport coefficients are described.

Computation of Tokamak transport

The complexity of the equations describing the transport phenomena in Tokamaks requires the use of numerical codes for simulation. These codes assume that the plasma is a multifluid medium. They involve equations for the evolution of electrons, light ions and current density, equations for heavy ions (impurities) and elaborate models for the evolution of the neutrals of light atoms. These codes allow testing of the existing theories and deduction of empirical rules and coefficients. After we have presented in more detail the Fontenay-aux-Roses code, we give examples of a few applications of this code.