Flux surface shaping effects on tokamak edge turbulence and flows

Shaping of magnetic flux surfaces is found to have a strong impact on turbulence and transport in tokamak edge plasmas. A series of axisymmetric equilibria with varying elongation and triangularity, and a divertor configuration are implemented into a computational gyrofluid turbulence model. The mechanisms of shaping effects on turbulence and flows are identified. Transport is mainly reduced by local magnetic shearing and an enhancement of zonal shear flows induced by elongation and X-point shaping.Comment: 10 pages, 11 figures. Submitted to Physics of Plasma

Soil erosion by landing rockets Final report

Cratering effect of descending rocket exhaust expected from soft earth landin

The effects of multiple trap spacing, baffles and brine volume on sediment trap collection efficiency

The hydrodynamic effects on trapping efficiency of sediment trap cross-frame position, baffles and brine volume were evaluated in three short-term (\u3c1 week) experiments in a temperate shallow marine environment (Evans Bay, Wellington Harbour, New Zealand). The effects of trap position and brine were further investigated during two open ocean, free-floating sediment trap deployments (1-2 days) near the Subtropical Front (STF), east of New Zealand. In the Evans Bay experiments (numbered I-III), cross-frames, each holding 12 cylindrical traps (inside diameter 9 cm, height 95 cm), were moored 3 meters above the seafloor in 15-18 m water depths at three randomly selected inner harbor sites. Triplicate subsamples from each cylinder were analyzed for total dry weight and mass fluxes calculated. The STF deployments utilized JGOFS MULTI-traps (inside diameter 7 cm, height 58 cm) attached to cross-frames moored at three depths (120, 300 and 550 m) on drifting arrays (Experiments IV and V). MULTI-trap samples were analyzed for total particulate mass, carbon and nitrogen. Results from Experiments I and V indicate that a spacing of about 3-trap diameters was sufficient to minimize inter-trap interactions and maintain trapping efficiency among traps suspended on a cross-frame at the same depth. Furthermore, baffles had no effect on trapping efficiency and an undetectable impact on zooplankton swimmer populations also collected in traps (Experiment II). In Experiment III, traps that were filled completely with high-density salt brine (50‰ excess NaCl) collected 2-3 times less material than traps with a basal brine height equivalent to 1- and 2.5-trap diameters. In contrast, high levels of inter-site variability confounded the STF MULTI-trap deployments during Experiment IV. However, variability in flux measurements from both Experiments III and IV increased 2 to 3-fold in brine-filled traps. Thus, the potential for brine-filled traps to undercollect material with higher levels of variability could possibly explain previously reported inaccuracies in the sediment trap method

Second Harmonic Generation from Phononic Epsilon-Near-Zero Berreman Modes in Ultrathin Polar Crystal Films

Immense optical field enhancement was predicted to occur for the Berreman mode in ultrathin films at frequencies in the vicinity of epsilon near zero (ENZ). Here, we report the first experimental proof of this prediction in the mid-infrared by probing the resonantly enhanced second harmonic generation (SHG) at the longitudinal optic phonon frequency from a deeply subwavelength-thin aluminum nitride (AlN) film. Employing a transfer matrix formalism, we show that the field enhancement is completely localized inside the AlN layer, revealing that the observed SHG signal of the Berreman mode is solely generated in the AlN film. Our results demonstrate that ENZ Berreman modes in intrinsically low-loss polar dielectric crystals constitute a promising platform for nonlinear nanophotonic applications

Cover slip external cavity diode laser

The design of a 671 nm diode laser with a mode-hop-free tuning range of 40 GHz is described. This long tuning range is achieved by simultaneously ramping the external cavity length with the laser injection current. The external cavity consists of a microscope cover slip mounted on piezoelectric actuators. In such a configuration the laser output pointing remains fixed, independent of its frequency. Using a diode with an output power of 5-7 mW, the laser linewidth was found to be smaller than 30 MHz. This cover slip cavity and feedforward laser current control system is simple, economical, robust, and easy to use for spectroscopy, as we demonstrate with lithium vapor and lithium atom beam experiments.Comment: 7 pages, 6 figures, submitted to Review of Scientific Instruments 7/29/0

Video Manipulation Techniques for the Protection of Privacy in Remote Presence Systems

Systems that give control of a mobile robot to a remote user raise privacy concerns about what the remote user can see and do through the robot. We aim to preserve some of that privacy by manipulating the video data that the remote user sees. Through two user studies, we explore the effectiveness of different video manipulation techniques at providing different types of privacy. We simultaneously examine task performance in the presence of privacy protection. In the first study, participants were asked to watch a video captured by a robot exploring an office environment and to complete a series of observational tasks under differing video manipulation conditions. Our results show that using manipulations of the video stream can lead to fewer privacy violations for different privacy types. Through a second user study, it was demonstrated that these privacy-protecting techniques were effective without diminishing the task performance of the remote user.Comment: 14 pages, 8 figure