Modeling of COMPASS tokamak divertor liquid metal experiments

Two small liquid metal targets based on the capillary porous structure were exposed to the divertor plasma of the tokamak COMPASS. The first target was wetted by pure lithium and the second one by a lithium-tin alloy, both releasing mainly lithium atoms (sputtering and evaporation) when exposed to plasma. Due to poorly conductive target material and steep surface inclination (implying the surface-perpendicular plasma heat flux 12-17 MW/m(2)) for 0.1-0.2 s, the LiSn target has reached 900 degrees C under ELMy H-mode. A model of heat conduction is developed and serves to evaluate the lithium sputtering and evaporation and, thus, the surface cooling by the released lithium and consequent radiative shielding. In these conditions, cooling of the surface by the latent heat of vapor did not exceed 1 MW/m(2). About 10(19) lithium atoms were evaporated (comparable to the COMPASS 1 m(3) plasma deuterium content), local Li pressure exceeded the deuterium plasma pressure. Since the radiating Li vapor cloud spreads over a sphere much larger than the hot spot, its cooling effect is negligible (0.2 MW/m(2)). We also predict zero lithium prompt redeposition, consistent with our observation.

Conceptual design studies for the European DEMO divertor: Rationale and first results

In the European fusion roadmap, reliable power handling has been defined as one of the most criticalchallenges for realizing a commercially viable fusion power. In this context, the divertor is the key in-vessel component, as it is responsible for power exhaust and impurity removal for which divertor targetis subjected to very high heat flux loads. To this end, an integrated R&D project was launched in theEUROfusion Consortium in order to deliver a holistic conceptual design solution together with the coretechnologies for the entire divertor system of a DEMO reactor. The work package \u2018Divertor\u2019 consistsof two project areas: \u2018Cassette design and integration\u2019 and \u2018Target development\u2019. The essential missionof the project is to develop and verify advanced design concepts and the required technologies for adivertor system being capable of meeting the physical and system requirements defined for the next-generation European DEMO reactor. In this contribution, a brief overview is presented of the works fromthe first project year (2014). Focus is put on the loads specification, design boundary conditions, materialsrequirements, design approaches, and R&D strategy. Initial ideas and first estimates are presented

New approaches for magnetic diagnostic of future fusion devices

New approaches for magnetic diagnostic of future fusion devicesI. Ďuran1, S. Entler1, K. Kovařík1, A. Torres1,11, P. Turjanica2, J. Reboun2, L. Viererbl3, D. Najman1,4, M. Kočan5, G. Vayakis5, K. Výborný6, Z. Šobáň6, M. Kohout6, V. Mortet6, A. Taylor6, P. Moreau7, F.P. Pellissier7, A. Le-Luyer7, P. Spuig7, W. Biel8, T. Franke9,101Institute of Plasma Physics of the CAS, Praha, Czech Republic2Faculty of Electrical Engineering, University of West Bohemia, Plzeň, Czech Republic3Research Centre Rez, 250 68 Husinec-Řež, Czech Republic4Czech Technical University in Prague, Praha, Czech Republic5ITER Organization, St Paul Lez Durance Cedex, France6Institute of Physics of the CAS, Praha, Czech Republic7IRFM, CEA, F-13108 Saint Paul lez Durance, France8Institut für Energie und Klimaforschung, Forschungszentrum Jülich GmbH, Germany9EUROfusion Power Plant Physics and Technology (PPPT) department, Garching, Germany10Max-Planck-Institut für Plasmaphysik, Garching, Germany11Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, PortugalThis contribution will review main challenges associated with the deployment of magnetic diagnostic for the EU DEMO fusion reactor, starting from return of experience from ITER, particularly in terms of operational temperature, neutron loads, required accuracy, and limited maintainability. New approaches to local magnetic field sensors design and construction will be introduced, namely metal-ceramic Hall sensors and inductive sensors manufactured using Thick Printed Copper (TPC) technology. Key lessons learned from the process of development, manufacturing, and calibration of ITER outer vessel steady state magnetic diagnostic based on bismuth Hall sensors will be outlined. The development of steady state magnetic sensors for a DEMO reactor is an even more challenging task compared to the ITER sensor system primarily due to approximately two orders of magnitude higher life time neutron fluence at envisaged sensor locations and also due to the higher operational temperature of the sensors. An outlook on some of the perspective design solutions for steady state magnetic sensors tackling the more demanding DEMO requirements will be given. Special attention will be paid to the design of the Hall sensors control electronics, and advanced methods of signal detection which are essential to ensure accurate detection of inherently low output voltages of Hall sensors in the noisy environment of a fusion reactor. Regarding inductive sensors, TPC technology will be introduced as an alternative to Low Temperature Co-fired Ceramics (LTCC) technology for the manufacturing of inductive local magnetic field sensors for DEMO and for their proof-of-principle application in COMPASS-U tokamak. Finally, potential synergy between steady state and traditional inductive approaches of local magnetic field measurements will be highlighted