Study of ergodic divertor edge density regimes on the tokamaks Tore Supra and TEXTOR, and sensitivity of tunnel probe electron temperature measurements to a suprathermal electron component

Controlled thermonuclear fusion offers one possible option to meet our future energy needs in a sustainable way. Magnetic confinement in a so-called 'tokamak'-machine is a possible approach towards the achievement of a burning plasma. An important issue in this tokamak research is the transition of the plasma edge to the inner wall. A first topic that is addressed in this thesis, is the ergodic divertor (ED) configuration. An ED achieves the transition between the confined plasma and the wall in a layer where the flux lines have been ergodized by a proper resonant magnetic perturbation. The connection between up- and downstream plasma parameters during ED operation in the tokamaks Tore Supra en TEXTOR has been investigated experimentally by means of Langmuir probes. As an important first step in the theoretical interpretation of those experiments, a Hamiltonian field line mapping code, which had been previously developed for the TEXTOR dynamic ergodic divertor, has been adapted to the geometry of the Tore Supra ED. Subsequently, this adapted code has been used to study some of the properties of the Tore Supra ED magnetic field line structure, as well as to make a qualitative comparison of the sensitivity of the TEXTOR and Tore Supra ergodic divertor magnetic topology to changes in the central density. A second topic of this thesis concerns certain interpretation issues regarding the current-voltage characteristics obtained by a newly developed type of Langmuir probe for the investigation of edge plasmas. More in particular, the sensitivity of the TP to a small population of nonthermal electrons has been investigated in addition to the influence of suprathermal electrons on the scaling and structure of the Debye and the magnetic sheath at the inside of the tunnel probe

TSO Perspectives to Review a Reactor Concept based on In-Vessel melt Retention (IVR) Strategy for Severe Accident Management

International audienceIn-Vessel melt Retention (IVR) is a Severe Accident (SA) mitigation measure applied in some Pressurized Water Reactors (PWRs) in order to cool down molten fuel (corium) inside the Reactor Pressure Vessel (RPV) by flooding the reactor cavity and cooling the RPV external surface with water. The safety demonstration provided to a national safety authority to support a reactor concept crediting the IVR strategy to enhance safety of an existing plant or to license a new generation design can be based on both deterministic and Probabilistic Risk Assessment (PRA). Experimental data can be used to support analyses or to validate models implemented in computer codes. This paper provides Technical Safety Organisations (TSOs) perspectives to review IVR as SA mitigation measure applied in NPP. The paper is structured as it is advised in the European Technical Safety Organisations Network (ETSON) Technical Safety Assessment Guide ETSON/2013-003