Hydrogen minority ion cyclotron resonance heating in presence of the iter-like wall in jet

The most recent JET campaign has focused on characterizing operation with the "ITER-like" wall. One of the questions that needed to be answered is whether the auxiliary heating methods do not lead to unacceptably high levels of impurity influx, preventing fusion-relevant operation. In view of its high single pass absorption, hydrogen minority fundamental cyclotron heating in a deuterium plasma was chosen as the reference wave heating scheme in the ion cyclotron domain of frequencies. The present paper discusses the plasma behavior as a function of the minority concentration X[H] in L-mode with up to 4MW of RF power. It was found that the tungsten concentration decreases by a factor of 4 when the minority concentration is increased from X[H] ≈ 5% to X[H] % 20% and that it remains at a similar level when X[H] is further increased to 30%; a monotonic decrease in Beryllium emission is simultaneously observed. The radiated power drops by a factor of 2 and reaches a minimum at X[H] ≈ 20%. It is discussed that poor single pass absorption at too high minority concentrations ultimately tailors the avoidance of the RF induced impurity influx. The edge density being different for different minority concentrations, it is argued that the impact ICRH has on the fate of heavy ions is not only a result of core (wave and transport) physics but also of edge dynamics and fueling

Characterization of ion cyclotron resonance heating in presence of the ITER-like wall in JET

Carbon is not compatible with the long term use required for plasma facing components in future fusion reactors of the tokamak type e.g. from the point of view of erosion and tritium retention.Wand Be were chosen as plasma facing materials for ITER. JET was equipped with beryllium (as opposed to C or C-coated) walls in the shutdown of 2010-2011. To sustain the very high heat loads inevitably falling on it and thus excluding the use of metals with a low melting point such as Be and in spite of the fact that its radiation is significant because of its large Z, a Tungsten (W) orW-coated divertor was simultaneously installed. The recent JET campaign has focused on characterizing high density high temperature operation with this "ITER-like" wall (ILW). One of the questions that needed to be answered is whether the auxiliary heating methods do not lead to unacceptable high levels of impurity influx preventing fusion-relevant operation. This paper briefly reports on two aspects of the present understanding of ion cyclotron resonance heating (ICRH) or radio frequency (RF) heating in presence of the ILW: ICRH-specific impurity influx and heating performance. They are complementing related discussions on heat loads, and on plasmaWcontent and possible sources. A much more extensive study will be published elsewhere

Fernando SEBASTIÁN AGUILAR, Nueva Evangelización. Fe, cultura y política en la España de hoy, Ed. Encuentro, Madrid 1991, 302 pp. [RECENSIÓN]

\u3cp\u3eThe most recent JET campaign has focused on characterizing operation with the «ITER-like» wall. One of the questions that needed to be answered is whether the auxiliary heating methods do not lead to unacceptably high levels of impurity influx, preventing fusion-relevant operation. In view of its high single pass absorption, hydrogen minority fundamental cyclotron heating in a deuterium plasma was chosen as the reference wave heating scheme in the ion cyclotron domain of frequencies. The present paper discusses the plasma behavior as a function of the minority concentration X[H] in L-mode with up to 4MW of RF power. It was found that the tungsten concentration decreases by a factor of 4 when the minority concentration is increased from X[H] ≈ 5% to X[H] % 20% and that it remains at a similar level when X[H] is further increased to 30%; a monotonic decrease in Beryllium emission is simultaneously observed. The radiated power drops by a factor of 2 and reaches a minimum at X[H] ≈ 20%. It is discussed that poor single pass absorption at too high minority concentrations ultimately tailors the avoidance of the RF induced impurity influx. The edge density being different for different minority concentrations, it is argued that the impact ICRH has on the fate of heavy ions is not only a result of core (wave and transport) physics but also of edge dynamics and fueling.\u3c/p\u3

A novel path to runaway electron mitigation via deuterium injection and current-driven MHD instability

Relativistic electron (RE) beams at high current density (low safety factor, q ( a )) yet very low free-electron density accessed with D-2 secondary injection in the DIII-D and JET tokamak are found to exhibit large-scale MHD instabilities that benignly terminate the RE beam. In JET, this technique has enabled termination of MA-level RE currents without measurable first-wall heating. This scenario thus offers an unexpected alternate pathway to achieve RE mitigation without collisional dissipation. Benign termination is explained by two synergistic effects. First, during the MHD-driven RE loss events both experiment and MHD orbit-loss modeling supports a significant increase in the wetted area of the RE loss. Second, as previously identified at JET and DIII-D, the fast kink loss timescale precludes RE beam regeneration and the resulting dangerous conversion of magnetic to RE kinetic energy. During the termination, the RE kinetic energy is lost to the wall, but the current fully transfers to the cold bulk thus enabling benign Ohmic dissipation of the magnetic energy on longer timescales via a conventional current quench. Hydrogenic (D-2) secondary injection is found to be the only injected species that enables access to the benign termination. D-2 injection: (1) facilitates access to low q ( a ) in existing devices (via reduced collisionality & resistivity), (2) minimizes the RE avalanche by 'purging' the high-Z atoms from the RE beam, (3) drives recombination of the background plasma, reducing the density and Alfven time, thus accelerating the MHD growth. This phenomenon is found to be accessible when crossing the low q ( a ) stability boundary with rising current, falling toroidal field, or contracting minor radius-the latter being the expected scenario for vertically unstable RE beams in ITER. While unexpected, this path scales favorably to fusion-grade tokamaks and offers a novel RE mitigation scenario in principle accessible with the day-one disruption mitigation system of ITER

Feedback control of the sawtooth period through real time control of the ion cyclotron resonance frequency

Modification of the sawtooth period through ion cyclotron resonance frequency (ICRF) heating and current drive has been demonstrated in a number of experiments. The effect has been seen to depend critically on the location of the ICRF absorption region with respect to the q = 1 flux surface. Consequently, for ICRF to be a viable tool for sawtooth control, one must be able to control the ICRF absorption location in real time so as to follow variations in the location of the q = 1 surface. To achieve this, the JET ICRF system has been modified to allow the JET real time central controller to control the frequency of the ICRF generators. An algorithm for real time determination of the sawtooth period has been developed and a closed loop controller, which modifies the frequency of the ICRF generators to bring the measured sawtooth period to the desired reference value, has been implemented. This paper shows the first experimental demonstration of closed loop sawtooth period control by real time variation of the ICRF wave frequency

Über den Zusammenhang von Kommunikation und Lernen im schulischen Kontext. Ein Modell Kommunikationsorientierter Schulsozialarbeit auf der Grundlage der Gewaltfreien Kommunikation von Marshall B. Rosenberg

Zum ersten geht es um die Leitfrage, wie Schulsozialarbeit dazu beitragen kann, dass Schulbildung nicht nur für einen anpassungsbereiten Teil der Schüler/innen Teilhabe befördert, sondern auch diejenigen erreicht, die dazu neigen, sich von ihr abzuwenden. Hierfür wird im ersten Teil der Arbeit zunächst untersucht, wie Lernen aus neurobiologischer, pädagogischer und psychologischer Perspektive verstanden werden kann, welche Faktoren Lernprozesse begünstigen bzw. hemmen und wie die subjektive Tätigkeit des Lernens auf schulisch-gesellschaftlicher Ebene in einen Kanon des Lernens einfließt. In den beiden darauffolgenden Kapiteln werden zunächst wesentliche Aspekte der zwischenmenschlichen Kommunikation mit Bezug auf psychologisch-soziologische Kommunikationstheorien umrissen und anschließend zu dem Sachverhalt übergeleitet, dass jedes Lernen immer auch eine komplexe Kommunikationsleistung ist. Neben der Relevanz, Kommunikation in der Schule zu thematisieren, wird darin ebenso aufgezeigt, an welcher Stelle der Kommunikationsbegriff in der Schul- und Sozialpädagogik an eine Grenze gelangt. Innerhalb der zweiten Kernfrage wird betrachtet, wie eine Kooperation von Schule und Jugendhilfe idealer Weise aussehen könnte, in der die wissenschaftlichen Erkenntnissen zu Lernverläufen offensiv einbezogen werden. Dem liegt eine Analyse des deutschen allgemeinbildenden Schulwesens zu Grunde. Hierin wird die Schulpflicht und auch die Selektivität, welche mit der Einführung verschiedener Schulformen einhergeht, in deren historischen Wurzeln betrachtet, worin einzelne Wellen der Bildungsreformen ersichtlich werden. Vertiefend dazu wird aufgezeigt, welche Faktoren Bildungsreformen begünstigten bzw. hervorriefen und welche Kräfte dem horizontalen Schulwesen in Deutschland und damit der Verringerung des selektiven Gehalts von Schule, entgegen wirkten. Denn Inklusionsleistungen, zu denen Schulsozialarbeit unter anderem berufen ist, finden keinen Bedarf, wenn nicht vorher eine Exklusion stattfand. Welche Möglichkeiten Schulsozialarbeit für allgemeinbildende Schulen dahingehend eröffnen kann, sich inhaltlich und methodisch anzureichern, weiterzuentwickeln, zu öffnen und zu vernetzen, sowie ein Blick auf die Herausforderungen für eine gegenseitig integrierende Kooperation, wird im darauffolgenden Teil, im Hinblick auf eine Charakterisierung von Schulsozialarbeit aufgezeigt. Dem folgt ein Einblick in das Konzept der Gewaltfreien Kommunikation, und daran anschließend ein Rahmenkonzept Kommunikationsorientierter Schulsozialarbeit. Dieses verbindet wissenschaftliche Erkenntnisse zu Lernverläufen und das Konzept der Gewaltfreien Kommunikation mit den ermittelten Schwachstellen von Schule, was schließlich einen ideellen Ausblick über sozialpädagogische Handlungsfelder in der Schule gibt. Und letztendlich schließt die Arbeit mit einer schlussfolgernden Zusammenfassung ab.The first central question is about, what schoolsocialwork could contribute to the actual school-situation, that not only adaptionable pupils getting reached, but also those ones, whose are tended to anticipate themselves from school. Therefore in the first part of the work gets analyzed, how learning out of the perspective of neurobiology, education and psychology can be understood, which factors are suppporting respectively blocking learning-processes and how the subjective learning-activity is connected to the school-societal-level. In the both following chapters initially it gets outlined main aspects of the interpersonal communication related to psychologic-sociological communication-theories, bridging to the point where every learning also is a complex communication-activity. Next to the relevance to broach the issue of communication in school, it also gets illustrated on which point the communication-term is coming to a border within the school- and social pedagogy. Inside the second central question gets considered how an ideal cooperation of school and youth welfare can look like, wherein the scientific knowledge to learning-processes offensive getting included. The analysis of the german, general-education-system is the first base therefor. Herein gets regarded the historical roots of the school-obligation and also the selectivity, which results automatically out of different kindes of schools. This showes single waves of education-reformes. Deepening to that it gets demonstrated which factors were supporting respectively effecting education-reformes and which power was working against the horizontal school-system in Germany, and therein working against the reduction of the selective content of school. Because inclusion-activities, to which schoolsocialwork is appointed, does not have a necessity, if not before happened an exclusion. Which possibilities schoolsocialwork can develop for general-education-schools, to get with regard to contents and methodes enriched, advanced, opened up and linked, as well as building up a mutual integrative cooperation, gets brought out in the following part within a characterisation of schoolsocialwork. Thereafter it is about to gain inside the concept of nonviolent communiation which followes a frame-concept of communication-oriented schoolsocialwork. These connects scientific findings of learning processes and the concept of the nonviolent communication with the determined weak points of school, which gives finally an forecast about social pedagogic spheres of activity in schools. And eventual the work is closing with a deductive abstraction