Probe manipulators for Wendelstein 7-X and their interaction with the magnetic topology

Probe manipulators are a versatile addition to typical plasma edge diagnostics.Equipped with material samples they allow for detailed investigation of plasma–wall interaction processes,such as material erosion,deposition or impurity transport pathways.When combined with electrical probes,a study of scrape-off layer and plasma edge density,temperature and flow profiles as well as magnetic topologies is possible.A mid-plane manipulator is already in operation on Wendelstein 7-X.A system in the divertor region is currently under development.In the present paper we discuss the critical issue of heat and power loads,power redistribution and experimental access to the complex magnetic topology of Wendelstein 7-X.All the aforementioned aspects are of relevance for the design and operation of a probe manipulator in a device like Wendelstein？7-X.A focus is put on the topological region that is accessible for the different coil current configurations at Wendelstein 7-X and the power load on the manipulator with respect to the resulting different magnetic configurations.Qualitative analysis of power loads on plasma-facing components is performed using a numerical tracer particle diffusion tool provided via the Wendelstein 7-X Webservices.

Numerical estimate of multi-species ion sound speed of Langmuir probe interpretations in the edge plasmas of Wendelstein 7-X

The recently modified EMC3-EIRENE code package has been widely applied as an edge-plasma analysis tool and resulted in successful validation against various measured trends seen in stellarator and tokamak plasma boundaries.It has been shown that the code package applied for Wendelstein 7-X(W7-X)discharges in the interpretive mode can assess the impact of impurity effects on the electron density,measured by a set of Langmuir probes.In particular the spatial quantification of impurities and effects from the effective charge state Zeff and effective mass meff,which are non-trivial to record by diagnostics,were examined.The results showed that earlier assumptions of the effective charge-state distribution and effective mass for reported Langmuir probe measurements must be revised.Subsequently,reprocessing these measurements with code-interpreted spatial profiles of the effective charge state and effective mass led to an overall improved physical consistency.

Magnetic configuration effects on the edge heat flux in the limiter plasma on W7-X measured using the infrared camera and the combined probe

Controlling the heat and particle fluxes in the plasma edge and on the plasma facing components is important for the safe and effective operation of every magnetically confined fusion device.This was attempted on Wendelstein 7-X in the first operational campaign,with the modification of the magnetic configuration by use of the trim coils and tuning the field coil currents,commonly named iota scan.Ideally,the heat loads on the five limiters are equal.However,they differ between each limiter and are non-uniform,due to the（relatively small） error fields caused by the misalignment of components.It is therefore necessary to study the influence of the configuration changes on the transport of heat and particles in the plasma edge caused by the application of error fields and the change of the magnetic configuration.In this paper the upstream measurements conducted with the combined probe are compared to the downstream measurements with the DIAS infrared camera on the limiter.

Production of Charged Heavy Quarkonium-Like States at the LHC and Tevatron

We study prompt hadroproduction of the charged bottomonium-like states Z±b(10610) and Z±b(10650), and the charged charmonium-like states Z±c(3900) and Z±c(4020), at the Tevatron and the LHC, provided that these states are S-wave hadronic molecules. Using two Monte Carlo event generators, Herwig and Pythia, to simulate the production of heavy meson pairs, we derive an order-of-magnitude estimate of the production rates for these four particles. Our estimates yield a cross section at the nb level for the Zb(10610) and Zb(10650). The results for the Zc(3900) and Zc(4020) are larger by a factor of 20–30. These cross sections are large enough to be observed, and measurements at hadron colliders in the future will supplement the study using electron-positron collisions, and therefore allow to explore the mysterious nature of these exotic states.

Ab initio molecular dynamics and materials design for embedded phase-change memory

The Ge_(2)Sb_(2)Te_(5)alloy has served as the core material in phase-change memories with high switching speed and persistent storage capability at room temperature.However widely used,this composition is not suitable for embedded memories—for example,for automotive applications,which require very high working temperatures above 300℃.Ge–Sb–Te alloys with higher Ge content,most prominently Ge2Sb1Te2(‘212’),have been studied as suitable alternatives,but their atomic structures and structure–property relationships have remained widely unexplored.Here,we report comprehensive first-principles simulations that give insight into those emerging materials,located on the compositional tie-line between Ge_(2)Sb_(1)Te_(2) and elemental Ge,allowing for a direct comparison with the established Ge_(2)Sb_(2)Te_(5)material.Electronic-structure computations and smooth overlap of atomic positions(SOAP)similarity analyses explain the role of excess Ge content in the amorphous phases.Together with energetic analyses,a compositional threshold is identified for the viability of a homogeneous amorphous phase(‘zero bit’),which is required for memory applications.Based on the acquired knowledge at the atomic scale,we provide a materials design strategy for high-performance embedded phase-change memories with balanced speed and stability,as well as potentially good cycling capability.