Effect of kinetic resonances on the stability of Resistive Wall Mode in Reversed Field Pinch

The kinetic effects, due to the mode resonance with thermal particle drift motions in the reversed field pinch (RFP) plasmas, are numerically investigated for the stability of the resistive wall mode, using a non-perturbative MHD-kinetic hybrid formulation. The kinetic effects are generally found too weak to substantially change the mode growth rate, or the stability margin, re-enforcing the fact that the ideal MHD model is rather adequate for describing the RWM physics in RFP experiments.Comment: Submitted to: Plasma Phys. Control. Fusio

Non-linear charge reduction effect in strongly-coupled plasmas

The charge reduction effect, produced by the nonlinear Debye screening of high-Z charges occuring in strongly-coupled plasmas, is investigated. An analytic asymptotic expression is obtained for the charge reduction factor which determines the Debye-Hueckel potential generated by a charged test particle. Its relevant parametric dependencies are analyzed and shown to predict a strong charge reduction effect in strongly-coupled plasmas.Comment: 4 figure

Translational toxicology in setting occupational exposure limits for dusts and hazard classification – a critical evaluation of a recent approach to translate dust overload findings from rats to humans

Background We analyze the scientific basis and methodology used by the German MAK Commission in their recommendations for exposure limits and carcinogen classification of “granular biopersistent particles without known specific toxicity” (GBS). These recommendations are under review at the European Union level. We examine the scientific assumptions in an attempt to reproduce the results. MAK’s human equivalent concentrations (HECs) are based on a particle mass and on a volumetric model in which results from rat inhalation studies are translated to derive occupational exposure limits (OELs) and a carcinogen classification. Methods We followed the methods as proposed by the MAK Commission and Pauluhn 2011. We also examined key assumptions in the metrics, such as surface area of the human lung, deposition fractions of inhaled dusts, human clearance rates; and risk of lung cancer among workers, presumed to have some potential for lung overload, the physiological condition in rats associated with an increase in lung cancer risk. Results The MAK recommendations on exposure limits for GBS have numerous incorrect assumptions that adversely affect the final results. The procedures to derive the respirable occupational exposure limit (OEL) could not be reproduced, a finding raising considerable scientific uncertainty about the reliability of the recommendations. Moreover, the scientific basis of using the rat model is confounded by the fact that rats and humans show different cellular responses to inhaled particles as demonstrated by bronchoalveolar lavage (BAL) studies in both species. Conclusion Classifying all GBS as carcinogenic to humans based on rat inhalation studies in which lung overload leads to chronic inflammation and cancer is inappropriate. Studies of workers, who have been exposed to relevant levels of dust, have not indicated an increase in lung cancer risk. Using the methods proposed by the MAK, we were unable to reproduce the OEL for GBS recommended by the Commission, but identified substantial errors in the models. Considerable shortcomings in the use of lung surface area, clearance rates, deposition fractions; as well as using the mass and volumetric metrics as opposed to the particle surface area metric limit the scientific reliability of the proposed GBS OEL and carcinogen classification.International Carbon Black Associatio

Optimisation of Resistive Wall Mode Control in Reversed Field Pinches

Feedback stabilization of magnetohydrodynamic modes in reversed field pinches is analysed for a set of discrete coils driven by voltage control. It is found that the resistive wall mode can be stabilized with a very simple controller structure and with acceptable voltages in the coils. These results are obtained by using a sufficient number of active coils and either sensors for the radial field or sensors for the poloidal or toroidal field placed inside the resistive wall. The result is robust with respect to variations in the plasma equilibrium. Poloidal and toroidal sensors placed outside the wall require a more complicated controller and very high voltages, and do not allow as good control performance as internal sensors

Optimisation of Resistive Wall Mode Control in Reversed Field Pinches

Feedback stabilization of magnetohydrodynamic modes in reversed field pinches is analysed for a set of discrete coils driven by voltage control. It is found that the resistive wall mode can be stabilized with a very simple controller structure and with acceptable voltages in the coils. These results are obtained by using a sufficient number of active coils and either sensors for the radial field or sensors for the poloidal or toroidal field placed inside the resistive wall. The result is robust with respect to variations in the plasma equilibrium. Poloidal and toroidal sensors placed outside the wall require a more complicated controller and very high voltages, and do not allow as good control performance as internal sensors

Optimisation of Resistive Wall Mode Control in Reversed Field Pinches

Feedback stabilization of magnetohydrodynamic modes in reversed field pinches is analysed for a set of discrete coils driven by voltage control. It is found that the resistive wall mode can be stabilized with a very simple controller structure and with acceptable voltages in the coils. These results are obtained by using a sufficient number of active coils and either sensors for the radial field or sensors for the poloidal or toroidal field placed inside the resistive wall. The result is robust with respect to variations in the plasma equilibrium. Poloidal and toroidal sensors placed outside the wall require a more complicated controller and very high voltages, and do not allow as good control performance as internal sensors