Wenyu Xu

Disorder-induced localization in a strongly correlated atomic Hubbard gas.

We observe the emergence of a disorder-induced insulating state in a strongly interacting atomic Fermi gas trapped in an optical lattice. This closed quantum system, free of a thermal reservoir, realizes the disordered Fermi-Hubbard model, which is a minimal model for strongly correlated electronic solids. We observe disorder-induced localization of a metallic state through measurements of mass transport. By varying the lattice potential depth, we detect interaction-driven delocalization of the disordered insulating state. We also measure localization that persists as the temperature of the gas is raised. These behaviors are consistent with many-body localization, which is a novel paradigm for understanding localization in interacting quantum systems at nonzero temperature.

Lithium–metal infused trenches (LiMIT) for heat removal in fusion devices

Observation of liquid lithium flow in metal trenches has been made using a lithium–metal infused trench (LiMIT) tile and is reported here. The flow is self-pumping and uses thermoelectric magnetohydrodynamics to remove heated lithium and replenish it at a lower temperature. Flow velocities have been measured and compared with theoretical predictions.

Performance of the lithium metal infused trenches in the magnum PSI linear plasma simulator

The application of liquid metal, especially liquid lithium, as a plasma facing component (PFC) has the capacity to offer a strong alternative to solid PFCs by reducing damage concerns and enhancing plasma performance. The liquid-metal infused trenches (LiMIT) concept is a liquid metal divertor alternative which employs thermoelectric current from either plasma or external heating in tandem with the toroidal field to self-propel liquid lithium through a series of trenches. LiMIT was tested in the linear plasma simulator, Magnum PSI, at heat fluxes of up to 3 MW m−2. Results of these experiments, including velocity and temperature measurements, as well as power handling considerations are discussed, focusing on the 80 shots performed at Magnum scanning magnetic fields and heat fluxes up to ~0.3 T and 3 MW m−2. Comparisons to predictions, both analytical and modelled, are made and show good agreement. Concerns over MHD droplet ejection are additionally addressed.

Three-dimensional Anderson localization in variable scale disorder.

We report on the impact of variable-scale disorder on 3D Anderson localization of a noninteracting ultracold atomic gas. A spin-polarized gas of fermionic atoms is localized by allowing it to expand in an optical speckle potential. Using a sudden quench of the localized density distribution, we verify that the density profile is representative of the underlying single-particle localized states. The geometric mean of the disordering potential correlation lengths is varied by a factor of 4 via adjusting the aperture of the speckle focusing lens. We observe that the root-mean-square size of the localized gas increases approximately linearly with the speckle correlation length, in qualitative agreement with the scaling predicted by weak scattering theory.

Finite-element simulation models and experimental verification for through-silicon-via etching: Bosch process and single-step etching

In this study, time-dependent simulation models are established for both the Bosch process and single-step through-silicon-via (TSV) etching using SF6 and C4F8 chemistry by employing a finite-element-method method. The simulation models take into account the thermal etching of F radicals, ion-enhanced etching, neutral deposition and ion-enhanced deposition mechanisms, as well as the angular dependence of the ion sputtering with aspect to a surface element. Comparison between the simulation results and experiments suggests that consideration of two ion fluxes (high-energy and low-energy) is critical for matching the simulation etch profile with the experiments. It is found that the underlying reason for the transition formed on the TSVs using the single-step etching originates from the difference of the ion angular distributions of etching species and depositing species. The Bosch process model successfully predicted profile details, such as the top scallops of the TSV profile, and the model established for single-step etching can be used to predict the transition position shown on the sidewalls. The simulation models can be used to study the individual effects of low-energy ions and the high-energy ions in the etching and passivation mechanisms for TSV etching in both Bosch process and single-step etching techniques.