Elastic anomalies in HoNi2B2C single crystals

We have measured temperature and magnetic field dependencies of the sound velocities and the sound attenuation in HoNi2B2C single crystals. The main result is a huge softening the velocity of C66 mode due to a cooperative Jahn-Teller effect, resulting in a tetragonal-orthorhombic structural phase transition. Anomalies in the behavior of the C66 mode through various magnetic phase transitions permit us to revise the low temperature H-T phase diagrams of this compound.Comment: v2: a discussion of the C44 mode with the comparison to Y borocarbide was adde

eXtended Reality (XR) virtual practical and educational eGaming to provide effective immersive environments for learning and teaching in forensic science

Online virtual learning resources have been available for learning and teaching in forensic science for some years now, but the recent global COVID-19 related periods of irregular lockdown have necessitated the rapid development of these for teaching, learning and CPD activities. However, these resources do need to be carefully constructed and grounded in pedagogic theory to be effective. This article details eXtended Reality (XR) learning and teaching environments to facilitate effective online teaching and learning for forensic geoscientists. The first two case studies discussed in this article make use of Thinglink software to produce virtual learning and teaching XR resources through an internet system, which was delivered to undergraduate students in 2021. Case one details an XR virtual laboratory-based XRF equipment resource, providing a consistent, reliable and asynchronous learning and teaching experience, whilst the second case study presents an XR virtual learning applied geophysics resource developed for a 12-week CPD training programme. This programme involves recorded equipment video resources, accompanying datasets and worksheets for users to work through. Both case studies were positively received by learners, but there were issues encountered by learners with poor internet connections or computer skills, or who do not engage well with online learning. A third case study showcases an XR educational forensic geoscience eGame that was developed to take the user through a cold case search investigation, from desktop study through to field reconnaissance and multi-staged site investigations. Pedagogic research was undertaken with user questionnaires and interviews, providing evidence that the eGame was an effective learning and teaching tool. eGame users highly rated the eGame and reported that they raised awareness and understanding of the use of geophysics equipment and best practice of forensic geoscience search phased investigations. These types of XR virtual learning digital resources, whilst costly to produce in terms of development time and staff resource, provide a complementary virtual learning experience to in-situ practical sessions, and allow learners to asynchronously familiarise themselves with equipment, environments and techniques resulting in more efficient use of in situ time. The XR resources also allow learners to reinforce learning post in-situ sessions. Finally, XR resources can provide a more inclusive and authentic experience for learners who cannot attend or complete work synchronously

Overview of ASDEX upgrade results in view of ITER and DEMO

Experiments on ASDEX Upgrade (AUG) in 2021 and 2022 have addressed a number of critical issues for ITER and EU DEMO. A major objective of the AUG programme is to shed light on the underlying physics of confinement, stability, and plasma exhaust in order to allow reliable extrapolation of results obtained on present day machines to these reactor-grade devices. Concerning pedestal physics, the mitigation of edge localised modes (ELMs) using resonant magnetic perturbations (RMPs) was found to be consistent with a reduction of the linear peeling-ballooning stability threshold due to the helical deformation of the plasma. Conversely, ELM suppression by RMPs is ascribed to an increased pedestal transport that keeps the plasma away from this boundary. Candidates for this increased transport are locally enhanced turbulence and a locked magnetic island in the pedestal. The enhanced D-alpha (EDA) and quasi-continuous exhaust (QCE) regimes have been established as promising ELM-free scenarios. Here, the pressure gradient at the foot of the H-mode pedestal is reduced by a quasi-coherent mode, consistent with violation of the high-n ballooning mode stability limit there. This is suggestive that the EDA and QCE regimes have a common underlying physics origin. In the area of transport physics, full radius models for both L- and H-modes have been developed. These models predict energy confinement in AUG better than the commonly used global scaling laws, representing a large step towards the goal of predictive capability. A new momentum transport analysis framework has been developed that provides access to the intrinsic torque in the plasma core. In the field of exhaust, the X-Point Radiator (XPR), a cold and dense plasma region on closed flux surfaces close to the X-point, was described by an analytical model that provides an understanding of its formation as well as its stability, i.e., the conditions under which it transitions into a deleterious MARFE with the potential to result in a disruptive termination. With the XPR close to the divertor target, a new detached divertor concept, the compact radiative divertor, was developed. Here, the exhaust power is radiated before reaching the target, allowing close proximity of the X-point to the target. No limitations by the shallow field line angle due to the large flux expansion were observed, and sufficient compression of neutral density was demonstrated. With respect to the pumping of non-recycling impurities, the divertor enrichment was found to mainly depend on the ionisation energy of the impurity under consideration. In the area of MHD physics, analysis of the hot plasma core motion in sawtooth crashes showed good agreement with nonlinear 2-fluid simulations. This indicates that the fast reconnection observed in these events is adequately described including the pressure gradient and the electron inertia in the parallel Ohm’s law. Concerning disruption physics, a shattered pellet injection system was installed in collaboration with the ITER International Organisation. Thanks to the ability to vary the shard size distribution independently of the injection velocity, as well as its impurity admixture, it was possible to tailor the current quench rate, which is an important requirement for future large devices such as ITER. Progress was also made modelling the force reduction of VDEs induced by massive gas injection on AUG. The H-mode density limit was characterised in terms of safe operational space with a newly developed active feedback control method that allowed the stability boundary to be probed several times within a single discharge without inducing a disruptive termination. Regarding integrated operation scenarios, the role of density peaking in the confinement of the ITER baseline scenario (high plasma current) was clarified. The usual energy confinement scaling ITER98(p,y) does not capture this effect, but the more recent H20 scaling does, highlighting again the importance of developing adequate physics based models. Advanced tokamak scenarios, aiming at large non-inductive current fraction due to non-standard profiles of the safety factor in combination with high normalised plasma pressure were studied with a focus on their access conditions. A method to guide the approach of the targeted safety factor profiles was developed, and the conditions for achieving good confinement were clarified. Based on this, two types of advanced scenarios (‘hybrid’ and ‘elevated’ q-profile) were established on AUG and characterised concerning their plasma performance

Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development

An overview of recent results obtained at the tokamak ASDEX Upgrade (AUG) is given. A work flow for predictive profile modelling of AUG discharges was established which is able to reproduce experimental H-mode plasma profiles based on engineering parameters only. In the plasma center, theoretical predictions on plasma current redistribution by a dynamo effect were confirmed experimentally. For core transport, the stabilizing effect of fast ion distributions on turbulent transport is shown to be important to explain the core isotope effect and improves the description of hollow low-Z impurity profiles. The L-H power threshold of hydrogen plasmas is not affected by small helium admixtures and it increases continuously from the deuterium to the hydrogen level when the hydrogen concentration is raised from 0 to 100%. One focus of recent campaigns was the search for a fusion relevant integrated plasma scenario without large edge localised modes (ELMs). Results from six different ELM-free confinement regimes are compared with respect to reactor relevance: ELM suppression by magnetic perturbation coils could be attributed to toroidally asymmetric turbulent fluctuations in the vicinity of the separatrix. Stable improved confinement mode plasma phases with a detached inner divertor were obtained using a feedback control of the plasma β. The enhanced D α H-mode regime was extended to higher heating power by feedback controlled radiative cooling with argon. The quasi-coherent exhaust regime was developed into an integrated scenario at high heating power and energy confinement, with a detached divertor and without large ELMs. Small ELMs close to the separatrix lead to peeling-ballooning stability and quasi continuous power exhaust. Helium beam density fluctuation measurements confirm that transport close to the separatrix is important to achieve the different ELM-free regimes. Based on separatrix plasma parameters and interchange-drift-Alfvén turbulence, an analytic model was derived that reproduces the experimentally found important operational boundaries of the density limit and between L- and H-mode confinement. Feedback control for the X-point radiator (XPR) position was established as an important element for divertor detachment control. Stable and detached ELM-free phases with H-mode confinement quality were obtained when the XPR was moved 10 cm above the X-point. Investigations of the plasma in the future flexible snow-flake divertor of AUG by means of first SOLPS-ITER simulations with drifts activated predict beneficial detachment properties and the activation of an additional strike point by the drifts

The effect of ZSM-5 zeolite crystal size on p-xylene selectivity in toluene disproportionation

The effect of crystal size was explored in this work aiming at enhancing p-xylene selectivity through toluene disproportionation over ZSM-5 zeolite. The different physicochemical properties of ZSM-5 were investigated using various characterization techniques including X-ray diffraction (XRD), pyridine adsorption, Fourier transform infra-red (FTIR), BET surface area by N2 adsorption, inductively coupled plasma (ICP) and scanning electron microscopy (SEM). Each catalyst was tested in a fixed bed reactor at a temperature 475 °C, weight hourly space velocity (WHSV) 3-83 h−1 and two different pressures (1 and 10 bar). ZSM-5 zeolites with crystal sizes 5, 50 and 100 μm were synthesized in house and compared with the commercially obtained ZSM-5 having a crystal size of 0.5 μm. As a result of increasing the crystal size the p-xylene selectivity was improved. This was attributed to the longer diffusion path lengths of the large crystals which imposed more diffusion constraints on the other xylene isomers. ZSM-5 zeolite with the largest crystal size 100 μm achieved the highest p-xylene selectivity (58%) at the highest WHSV 83 h−1. However, this was accompanied by a low conversion (2 wt %). The best combination of p-xylene selectivity (40%) alongside 15 wt % toluene conversion were achieved over ZSM-5 having 5 μm crystal size

Effects of the Physicochemical Properties of Zeolite Catalysts on Their Deactivation in Methanol-to-Hydrocarbons Conversion (A Review)

This review presents the current understanding of the effects of the physicochemical properties of molecular sieve catalysts on their deactivation in methanol-to-hydrocarbons conversion. The catalysts are classified on the basis of the composition of the so-called hydrocarbon pool and the catalyst deactivation rate during methanol conversion. For each group of catalysts, the correlations of their physicochemical properties with their catalytic performance, coke formation, and deactivation behaviors are discussed

Transalkylation of Toluene with 1, 2, 4‐Trimethylbenzene over Large Pore Zeolites with Differing Si/Al Ratios

The catalytic activity, selectivity to xylenes and time-on-stream stability were investigated in the transalkylation of toluene with 1, 2, 4-trimethylbenzene. The catalytic tests were carried out in a fixed bed reactor over zeolite Beta (Si/Al = 12.5, 75 and 150) and Y (Si/Al = 2.6, 6, 15 and 30). The operating parameters used were 400 °C, 1.0 Mpa, H2/HC = 4 and WHSV of 5 h-1. The length of each catalytic testing experiment was 50 hours, and for zeolite beta samples, the highest stability and selectivity to xylenes were achieved using the lowest Si/Al ratio with conversion of 41 wt. % and selectivity of 61 wt. %. In contrast, zeolites Y with Si/Al ratio of 2.6 showed the highest deactivation rate, whereas Y zeolites with Si/Al = 6 – 30 exhibited similar conversion (~ 27 wt. %) and selectivity to xylenes (~ 43 wt. %). The effects of Brønsted and Lewis acid sites on catalytic results are discussed