Novel inferences of ionisation & recombination for particle/power balance during detached discharges using deuterium Balmer line spectroscopy

The physics of divertor detachment is determined by divertor power, particle and momentum balance. This work provides a novel analysis technique of the Balmer line series to obtain a full particle/power balance measurement of the divertor. This supplies new information to understand what controls the divertor target ion flux during detachment. Atomic deuterium excitation emission is separated from recombination quantitatively using Balmer series line ratios. This enables analysing those two components individually, providing ionisation/recombination source/sinks and hydrogenic power loss measurements. Probabilistic Monte Carlo techniques were employed to obtain full error propagation - eventually resulting in probability density functions for each output variable. Both local and overall particle and power balance in the divertor are then obtained. These techniques and their assumptions have been verified by comparing the analysed synthetic diagnostic 'measurements' obtained from SOLPS simulation results for the same discharge. Power/particle balance measurements have been obtained during attached and detached conditions on the TCV tokamak.Comment: The analysis results of this paper were formerly in arXiv:1810.0496

Ballistic magnon transport and phonon scattering in the antiferromagnet Nd2_2CuO4_4

The thermal conductivity of the antiferromagnet Nd$_2$CuO$_4$ was measured down to 50 mK. Using the spin-flop transition to switch on and off the acoustic Nd magnons, we can reliably separate the magnon and phonon contributions to heat transport. We find that magnons travel ballistically below 0.5 K, with a thermal conductivity growing as $T^3$, from which we extract their velocity. We show that the rate of scattering of acoustic magnons by phonons grows as $T^3$, and the scattering of phonons by magnons peaks at twice the average Nd magnon frequency.Comment: 4 pages, 3 figures, one figure modifie

Intrinsic Water Transport in Moisture-Capturing Hydrogels

Moisture-capturing hydrogels have emerged as attractive sorbent materials capable of converting ambient humidity into liquid water. Recent works have demonstrated exceptional water capture capabilities of hydrogels while simultaneously exploring different strategies to accelerate water capture and release. However, on the material level, an understanding of the intrinsic transport properties of moisture-capturing hydrogels is currently missing, which hinders their rational design. In this work, we combine absorption and desorption experiments of macroscopic hydrogel samples in pure vapor with models of water diffusion in the hydrogels to demonstrate the first measurements of the intrinsic water diffusion coefficient in hydrogel–salt composites. Based on these insights, we pattern hydrogels with micropores to significantly decrease the required absorption and desorption times by 19% and 72%, respectively, while reducing the total water capacity of the hydrogel by only 4%. Thereby, we provide an effective strategy toward hydrogel material optimization, with a particular significance in pure-vapor environments.Schweizerischer Nationalfonds zur F?rderung der Wissenschaftlichen Forschung 10.13039/501100001711Peer Reviewe

Low-temperature phonon thermal conductivity of cuprate single crystals

The effect of sample size and surface roughness on the phonon thermal conductivity $\kappa_p$ of Nd$_2$CuO$_4$ single crystals was studied down to 50 mK. At 0.5 K, $\kappa_p$ is proportional to $\sqrt{A}$, where $A$ is the cross-sectional area of the sample. This demonstrates that $\kappa_p$ is dominated by boundary scattering below 0.5 K or so. However, the expected $T^3$ dependence of $\kappa_p$ is not observed down to 50 mK. Upon roughing the surfaces, the $T^3$ dependence is restored, showing that departures from $T^3$ are due to specular reflection of phonons off the mirror-like sample surfaces. We propose an empirical power law fit, to $\kappa_p \sim T^{\alpha}$ (where $\alpha < 3$) in cuprate single crystals. Using this method, we show that recent thermal conductivity studies of Zn doping in YBa$_2$Cu$_3$O$_y$ re-affirm the universal heat conductivity of d-wave quasiparticles at $T \to 0$.Comment: 4 pages, 4 figure

Critical currents and giant non-dissipative drag for superfluid electron-hole pairs in quantum Hall multilayers

Superfluid properties of electron-hole pairs in a quantum Hall four-layer system are investigated. The system is considered as a solid state realization of a two-component superfluid Bose gas with dipole-dipole interaction. One superfluid component is formed in the top bilayer and the other component - in the bottom one. We obtain the dispersion equation for the collective mode spectrum and compute the critical parameters (the critical interlayer distance and the critical currents) versus the filling factor. We find that the critical currents of the components depend on each other. The maximum critical current of a given component can be reached if the current of the other component is equal to zero. The non-dissipative drag effect between the components is studied. It is shown that in the system considered the drag factor is very large. Under appropriate conditions it can be about 10 per sent, that is at least in three order larder than one predicted for two-component atomic Bose gases.Comment: 18 pages, 7 figure

Spectrometer Scan Mechanism for Encountering Jovian Orbit Trojan Asteroids

This paper describes the design, testing, and lessons learned during the development of the Lucy Ralph (L'Ralph) Scan Mirror System (SMS), composed of the Scan Mirror Mechanism (SMM), Differential Position Sensor System (DPSS) and Mechanism Control Electronics (MCE). The L'Ralph SMS evolved from the Advanced Topographic Laser Altimeter System (ATLAS) Beam Steering Mechanism (BSM), so design comparisons will be made. Lucy is scheduled to launch in October 2021, embarking upon a 12-year mission to make close range encounters in 2025 and 2033 with seven Trojan asteroids and one main belt asteroid that are within the Jovian orbit. The L'Ralph instrument is based upon the New Horizons Ralph instrument, which is a panchromatic and color visible imager and infrared spectroscopic mapper that slewed the spacecraft for imaging. The L'Ralph SMM is to provide scanning for imaging to eliminate the need to slew the spacecraft. One purpose of this paper is to gain understanding of the reasoning behind some of the design features as compared with the ATLAS BSM. We will identify similarities and differences between the ATLAS BSM and the L'Ralph SMM that resulted from the latter's unique requirements. Another purpose of this paper is to focus upon "Lessons Learned" that came about during the development of the L'Ralph SMM and its MCE, both mechanism engineering issues and solutions as well as Ground Support Equipment (GSE) issues and solutions that came about during the validation of requirements process. At the time of this writing, the L'Ralph SMM has been flight qualified and delivered to the project

Non-linear Simulations of MHD Instabilities in Tokamaks Including Eddy Current Effects and Perspectives for the Extension to Halo Currents

The dynamics of large scale plasma instabilities can strongly be influenced by the mutual interaction with currents flowing in conducting vessel structures. Especially eddy currents caused by time-varying magnetic perturbations and halo currents flowing directly from the plasma into the walls are important. The relevance of a resistive wall model is directly evident for Resistive Wall Modes (RWMs) or Vertical Displacement Events (VDEs). However, also the linear and non-linear properties of most other large-scale instabilities may be influenced significantly by the interaction with currents in conducting structures near the plasma. The understanding of halo currents arising during disruptions and VDEs, which are a serious concern for ITER as they may lead to strong asymmetric forces on vessel structures, could also benefit strongly from these non-linear modeling capabilities. Modeling the plasma dynamics and its interaction with wall currents requires solving the magneto-hydrodynamic (MHD) equations in realistic toroidal X-point geometry consistently coupled with a model for the vacuum region and the resistive conducting structures. With this in mind, the non-linear finite element MHD code JOREK has been coupled with the resistive wall code STARWALL, which allows to include the effects of eddy currents in 3D conducting structures in non-linear MHD simulations. This article summarizes the capabilities of the coupled JOREK-STARWALL system and presents benchmark results as well as first applications to non-linear simulations of RWMs, VDEs, disruptions triggered by massive gas injection, and Quiescent H-Mode. As an outlook, the perspectives for extending the model to halo currents are described.Comment: Proceeding paper for Theory of Fusion Plasmas (Joint Varenna-Lausanne International Workshop), Varenna, Italy (September 1-5, 2014); accepted for publication in: to Journal of Physics: Conference Serie

Investigating the impact of the molecular charge-exchange rate on detached SOLPS-ITER simulations

Plasma-molecular interactions generate molecular ions which react with the plasma and contribute to detachment through molecular activated recombination (MAR), reducing the ion target flux, and molecular activated dissociation (MAD), both of which create excited atoms. Hydrogenic emission from these atoms have been detected experimentally in detached TCV, JET and MAST-U deuterium plasmas. The TCV findings, however, were in disagreement with SOLPS-ITER simulations for deuterium indicating a molecular ion density ($D_2^+$) that was insufficient to lead to significant hydrogenic emission, which was attributed to underestimates of the molecular charge exchange rate ($D_2 + D^+ \rightarrow D_2^+ + D$) for deuterium (obtained by rescaling the hydrogen rates by their isotope mass). In this work, we have performed new SOLPS-ITER simulations with the default rate setup and a modified rate setup where ion isotope mass rescaling was disabled. This increased the $D_2^+$ content by $> \times 100$. By disabling ion isotope mass rescaling: 1) the total ion sinks are more than doubled due to the inclusion of MAR; 2) the additional MAR causes the ion target flux to roll-over during detachment; 3) the total $D\alpha$ emission in the divertor increases during deep detachment by roughly a factor four; 4) the neutral atom density in the divertor is doubled due to MAD, leading to a 50\% increase in neutral pressure; 5) total hydrogenic power loss is increased by up to 60\% due to MAD. These differences result in an improved agreement between the experiment and the simulations in terms of spectroscopic measurements, ion source/sink inferences and the occurrence of an ion target flux roll-over