Coupling JOREK and STARWALL for Non-linear Resistive-wall Simulations

The implementation of a resistive-wall extension to the non-linear MHD-code JOREK via a coupling to the vacuum-field code STARWALL is presented along with first applications and benchmark results. Also, non-linear saturation in the presence of a resistive wall is demonstrated. After completion of the ongoing verification process, this code extension will allow to perform non-linear simulations of MHD instabilities in the presence of three-dimensional resistive walls with holes for limited and X-point plasmas.Comment: Contribution for "Theory Of Fusion Plasmas, Joint Varenna - Lausanne International Workshop, Villa Monastero, Varenna, Italy (27.-31.8.2012)", accepted for publication in Journal of Physics Conference Serie

Non regression testing for the JOREK code

Non Regression Testing (NRT) aims to check if software modifications result in undesired behaviour. Suppose the behaviour of the application previously known, this kind of test makes it possible to identify an eventual regression, a bug. Improving and tuning a parallel code can be a time-consuming and difficult task, especially whenever people from different scientific fields interact closely. The JOREK code aims at investing Magnetohydrodynamic (MHD) instabilities in a Tokamak plasma. This paper describes the NRT procedure that has been tuned for this simulation code. Automation of the NRT is one keypoint to keeping the code healthy in a source code repository.Comment: No. RR-8134 (2012

Quantifying Model Complexity via Functional Decomposition for Better Post-Hoc Interpretability

Post-hoc model-agnostic interpretation methods such as partial dependence plots can be employed to interpret complex machine learning models. While these interpretation methods can be applied regardless of model complexity, they can produce misleading and verbose results if the model is too complex, especially w.r.t. feature interactions. To quantify the complexity of arbitrary machine learning models, we propose model-agnostic complexity measures based on functional decomposition: number of features used, interaction strength and main effect complexity. We show that post-hoc interpretation of models that minimize the three measures is more reliable and compact. Furthermore, we demonstrate the application of these measures in a multi-objective optimization approach which simultaneously minimizes loss and complexity

MHD stability of fully non inductive discharges in Tore Supra

12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)During the 2003 experimental campaign, the aim of realizing reliable fully non inductive discharges has been successfully completed in Tore Supra. One the major difficulties in optimizing this scenario comes from MHD stability issues. Indeed, the current profile obtained with LH antennas in these experiments is prone to the triggering of single or double tearing modes. Under certain conditions, the discharges enters in a regime of permanent MHD activity. The present work investigates the MHD properties of these fully non-inductive discharges in the operational space defined by the toroidal magnetic field B, the total plasma current Ip, and the mean parallel index of LH waves . Linear MHD stability properties divide the operational space in regions separated by rational values of the minimum of the safety factor. We discuss in our work the localisation of the transition between benign MHD activity and the MHD regime

Ethics, politics and migration: Public debates on the free movement of Romanians and Bulgarians in the UK, 2006–2013

Public debates on immigration have become the subject of much concern, particularly in the UK. This article applies an ethical lens to assess changes in public debates over intra-EU migration in six UK national newspapers during 2006 and 2013. It finds an almost complete dominance of communitarian justifications, mainly based on welfare chauvinism, but a notable increase in security-related arguments and a decrease in economic nationalist ideas. Alternative cosmopolitan arguments about immigration go from rare to virtually absent. The discussion links these shifts to a failure of the UK centre-left to overcome historic difficulties in presenting a coherent narrative on immigration policy

Solitary magnetic perturbations at the ELM onset

Edge localised modes (ELMs) allow maintaining sufficient purity of tokamak H-mode plasmas and thus enable stationary H-mode. On the other hand in a future device ELMs may cause divertor power flux densities far in excess of tolerable material limits. The size of the energy loss per ELM is determined by saturation effects in the non-linear phase of the ELM, which at present is hardly understood. Solitary magnetic perturbations (SMPs) are identified as dominant features in the radial magnetic fluctuations below 100kHz. They are typically observed close (+-0.1ms) to the onset of pedestal erosion. SMPs are field aligned structures rotating in the electron diamagnetic drift direction with perpendicular velocities of about 10km/s. A comparison of perpendicular velocities suggests that the perturbation evoking SMPs is located at or inside the separatrix. Analysis of very pronounced examples showed that the number of peaks per toroidal turn is 1 or 2, which is clearly lower than corresponding numbers in linear stability calculations. In combination with strong peaking of the magnetic signals this results in a solitary appearance resembling modes like palm tree modes, edge snakes or outer modes. This behavior has been quantified as solitariness and correlated to main plasma parameters. SMPs may be considered as a signature of the non-linear ELM-phase originating at the separatrix or further inside. Thus they provide a handle to investigate the transition from linear to non-linear ELM phase. By comparison with data from gas puff imaging processes in the non-linear phase at or inside the separatrix and in the scrape-off-layer (SOL) can be correlated. A connection between the passing of an SMP and the onset of radial filament propagation has been found. Eventually the findings related to SMPs may contribute to a future quantitative understanding of the non-linear ELM evolution.Comment: submitted to Nuclear Fusio

The Internal-External Security Nexus and EU Police/Rule of Law Missions in the Western Balkans

Common Security and Defence Policy (CSDP) police/rule of law missions in the Western Balkans are increasingly guided by externally imposed normative agendas that respond primarily to EU internal security needs rather than functional imperatives or local realities. In line with these needs, EU police reform efforts tend to prioritise effectiveness and crime fighting over longer- term democratic policing and good governance reforms. In practice this means that police reform initiatives are technocratically oriented, yet value ridden fitting EU security concerns and needs. As a result, the police reform process can be—and often is—disconnected from the political and socio-economic reforms necessary for long-term stability and sustainable peace. Police assistance in Bosnia and Herzegovina has been shaped by a determined albeit questionable focus on organised crime and corruption. The focus of EU police reform in Macedonia on primarily crime-fighting aspects of policing has compromised the functioning of the Macedonian police. Similarly, the politics of (non-)recognition of Kosovo's self-proclaimed independence and the intrusiveness of EULEX Kosovo's executive mandate contravene meeting local challenges