Untersuchung zur Lernkultur in Online-Kursen

Ausgehend von einer veränderten, durch Lern- und Kompetenzorientierung geprägten Lernkultur analysieren die Autorinnen zwölf mehrwöchige Online-Kurse mit insgesamt 130 Teilnehmer/innen. Die Autorinnen nehmen ein Klima der hohen Wertschätzung unter den Lernenden wahr sowie gegenseitiges Feedback in den Reflexions- und Diskussionsprozessen, welches das Lernen verstärkt. Die Hypothese, dass in rein virtuellen, mehrwöchigen Weiterbildungskursen eine veränderte Lernkultur gefördert und gelebt wird, wird mittels halbstrukturierter Interviews sowie qualitativer Inhaltsanalyse der Beiträge in den Diskussionsforen untersucht. (DIPF/ Orig.

The magnetic model of the LHC in the early phase of beam commissioning

The relation between field and current in each family of the Large Hadron Collider magnets is modelled with a set of empirical equations (FiDeL) whose free parameters are fit on magnetic measurements. They take into account residual magnetization, persistent currents, hysteresis, saturation, decay and snapback during initial part of the ramp. Here we give a first summary of the reconstruction of the magnetic field properties based on the beam observables (orbit, tune, coupling, chromaticity) and a comparison with the expectations. The most critical issues for the machine performance in terms of knowledge of the relation magnetic field vs current are pointed out.peer-reviewe

First field test of FiDeL the magnetic field description for the LHC

The start-up of the LHC has provided the first field test for the concept, functionality and accuracy of FiDeL, the Field Description for the LHC. FiDeL provides a parametric model of the transfer function of the main field integrals generated by the series of magnets in the LHC powering circuits, comprising superconducting and normal-conducting main optical elements and high-order harmonic correctors. The same framework is used to predict harmonic errors of both static and dynamic nature, and forecast appropriate corrections. In this paper we make use of beam-based measurements taken on the first LHC beams to assess the first-shot accuracy in the prediction of the current setting for the main arc magnets.peer-reviewe

Thermal-hydraulics of helium cooled First Wall channels and scoping investigations on performance improvement by application of ribs and mixing devices

The first wall (FW) of DEMO is a component with high thermal loads. The cooling of the FW has to comply with the material's upper and lower temperature limits and requirements from stress assessment, like low temperature gradients. Also, the cooling has to be integrated into the balance-of-plant, in a sense to deliver exergy to the power cycle and require a limited pumping power for coolant circulation. This paper deals with the basics of FW cooling and proposes optimization approaches. The effectiveness of several heat transfer enhancement techniques is investigated for the use in helium cooled FW designs for DEMO. Among these are wall-mounted ribs,. large scale mixing devices and modified hydraulic diameter. Their performance is assessed by computational fluid dynamics (CFD), and heat transfer coefficients and pressure drop are compared. Based on the results, an extrapolation to high heat fluxes is tried to estimate the higher limits of cooling capabilities

Thermal-hydraulics of helium cooled First Wall channels and scoping investigations on performance improvement by application of ribs and mixing devices

The first wall (FW) of DEMO is a component with high thermal loads. The cooling of the FW has to comply with the material's upper and lower temperature limits and requirements from stress assessment, like low temperature gradients. Also, the cooling has to be integrated into the balance-of-plant, in a sense to deliver exergy to the power cycle and require a limited pumping power for coolant circulation. This paper deals with the basics of FW cooling and proposes optimization approaches. The effectiveness of several heat transfer enhancement techniques is investigated for the use in helium cooled FW designs for DEMO. Among these are wall-mounted ribs,. large scale mixing devices and modified hydraulic diameter. Their performance is assessed by computational fluid dynamics (CFD), and heat transfer coefficients and pressure drop are compared. Based on the results, an extrapolation to high heat fluxes is tried to estimate the higher limits of cooling capabilities

DEMO diagnostics and burn control

The development of the control system for a tokamak demonstration fusion reactor (DEMO) faces unprecedented challenges. First, the requirements for control reliability and accuracy are more stringent than on existing fusion devices: any loss of plasma control on DEMO may result in a disruption which could damage the inner wall of the machine, while operating the device with larger margins against the operational limits would lead to a reduction of the electrical output power. Second, the performance of DEMO control is limited by space restrictions for the implementation of components (optimization of the tritium breeding rate), by lifetime issues for the front-end parts (neutron and gamma radiation, erosion and deposition acting on all components) and by slow, weak and indirect action of the available actuators (plasma shaping, heating and fuelling). The European DEMO conceptual design studies include the development of a reliable control system, since the details of the achievable plasma scenario and the machine design may depend on the actual performance of the control system. In the first phase of development, an initial understanding of the prime choices of diagnostic methods applicable to DEMO, implementation and performance issues, the interrelation with the plasma scenario definition, and the planning of necessary future R&D have been obtained

Systems engineering perspective to the integration of the heating and current drive system in the EU DEMO: Analysis of requirements and functions

In the framework of the EUROfusion Consortium, the Work Package Heating and Current Drive (WPHCD) is undertaking the development and design of the DEMO Heating and Current Drive (HCD) system, supported by the Work Package Plant Level Systems Engineering, Design Integration and Physics Integration (WPPMI). As the DEMO project is in the Pre-Conceptual phase, its development is dominated by uncertainties on system requirements, and by different DEMO designs and scenarios. In this context, a number of outstanding technology and physics issues, e.g. related to safety, neutronics, performance and reliability, need to be resolved using an integrated approach. For coping with these boundary conditions, we present an initial analysis of HCD requirements and functions through the development of a System Architecture model, i.e. through describing the HCD system in terms of its functions and their interdependencies. Scope of the work is to address uncertainties i) associated with different reference scenarios (e.g. pulsed and steady-state tokamak) and operational concepts; ii) related to system performances. The assessment is part of integration activities, consisting of both systems engineering methodologies and design analysis, all aiming to ensure consistency in the overall EU DEMO plant design