Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X

We present recent highlights from the most recent operation phases of Wendelstein 7-X, the most advanced stellarator in the world. Stable detachment with good particle exhaust, low impurity content, and energy confinement times exceeding 100 ms, have been maintained for tens of seconds. Pellet fueling allows for plasma phases with reduced ion-temperature-gradient turbulence, and during such phases, the overall confinement is so good (energy confinement times often exceeding 200 ms) that the attained density and temperature profiles would not have been possible in less optimized devices, since they would have had neoclassical transport losses exceeding the heating applied in W7-X. This provides proof that the reduction of neoclassical transport through magnetic field optimization is successful. W7-X plasmas generally show good impurity screening and high plasma purity, but there is evidence of longer impurity confinement times during turbulence-suppressed phases.EC/H2020/633053/EU/Implementation of activities described in the Roadmap to Fusion during Horizon 2020 through a Joint programme of the members of the EUROfusion consortium/ EUROfusio

A study of catalysts and mechanism in synthesis reactions

It is becoming increasingly evident that surface-generated gas-phase radicals play an important role in the catalytic oxidation of hydrocarbons. The most notable example is the oxidative coupling of methane which is initiated by the formation of CH{sub 3}{center dot}radical at the surfaces of metal oxides. More recently, emphasis has been placed on the secondary reactions that the radicals undergo when they react with a metal oxide surface. These reactions may be important in determining product selectivity, as CH{sub 3}{center dot}radicals will collide with the surface many times before they react with another CH{sub 3}{center dot}radical. If secondary surfaces results in complete oxidation, then the selectivity for the oxidative coupling reaction would be severely diminished. Another current aspect of the work is the emanation of OH{center dot}radicals from platinum and palladium metal surfaces. Hydroxyl radicals are known to be chain carriers during combustion reactions, and the metal surface may serve to introduce these radicals into the gas phase. 10 refs., 3 figs

Destructive adsorption of carbon tetrachloride on lanthanum and cerium oxides

The destructive adsorption of CCl4 on La2O3 and CeO2 in the absence of any oxidant, such as oxygen, has been studied by X-ray photoelectron spectroscopy and insitu Raman spectroscopy as a function of the reaction temperature and the amount of CCl4 injected. La2O3 was much more reactive than CeO2, and CCl4 destruction started at around 300°C with the rapid formation of LaOCl, and the release of CO2 into the gas phase. The complete transformation of LaOCl into LaCl3 was much more difficult to obtain, and required high reaction temperatures and large amounts of CCl4. In the case of CeO2, CCl4 destruction started at around 450°C, and was accompanied by the reduction of Ce(IV) to Ce(III) and the formation of CeOCl as an intermediate product. The complete transformation of CeO2 into CeCl3 was only observed at reaction temperatures near 600°C. These results are compared with those recently reported for alkaline earth metal oxides