Schwartz, J. A.; Emdee, E. D.; Jaworski, M. A; Goldston, R. J.
Abstract:
The lithium vapor box divertor is a concept for handling the extreme divertor heat fluxes in magnetic fusion devices. In a baffled slot divertor, plasma interacts with a dense cloud of Li vapor which radiates and cools the plasma, leading to recombination and detachment. Before testing on a tokamak the concept should be validated: we plan to study detachment and heat redistribution by a Li vapor cloud in laboratory experiments.
Mass changes and temperatures are measured to validate a Direct Simulation Monte Carlo model of neutral Li.
The initial experiment involves a 5 cm diameter steel box containing 10g of Li held at 650 degrees C as vapor flows out a wide nozzle into a similarly-sized box at a lower temperature. Diagnosis is made challenging by the required material compatibility with lithium vapor. Vapor pressure is a steep function of temperature, so to validate mass flow models to within 10%, absolute temperature to within 4.5K is required. The apparatus is designed to be used with an analytical balance to determine mass transport. Details of the apparatus and methods of temperature and mass flow measurements are presented.
Schwartz, Jacob; Emdee, Eric; Goldston, Robert; Jaworski, Michael
Abstract:
The lithium vapor box divertor is a potential solution for power exhaust in toroidal confinement devices. The divertor plasma interacts with a localized, dense cloud of lithium vapor, leading to volumetric radiation, cooling, recombination, and detachment. To minimize contamination of the core plasma, lithium vapor is condensed on cool (300°C to 400°C) baffles upstream of the detachment point. Before implementing this in a toroidal plasma device with a slot divertor geometry, we consider an experiment with a scaled baffled-pipe geometry in the high-power linear plasma device Magnum-PSI. Three 15 cm-scale open cylinders joined by 6 cm diameter ‘nozzles’ are positioned on the plasma beam axis upstream of a target. The central box may be loaded with several tens of grams of lithium, which can be evaporated at 650°C to produce a vapor predicted, using a simple plasma-neutral interaction model, to be dense enough to cause volumetric detachment in the plasma. The power delivered to the target and box walls as measured by increases in their temperatures after a 10 s plasma pulse can be compared to determine the effectiveness of the vapor in detaching the plasma. Direct Simulation Monte Carlo simulations are performed to estimate the flow rates of lithium vapor between the boxes and to estimate the trapping of H2 delivered by the plasma in the boxes, which could inadvertently lead to detachment. Details of the geometry, simulations, and possible diagnostic techniques are presented.
These data include 39 structured interview transcripts. Each case is someone who worked at the time for Uber, UberEats, Lyft, and/or Amazon Flex (Amazon’s contractor delivery service). These data were collected between July and September 2019. All but one of the interviews occurred over the phone. My questions are focused on the structure of their gig work jobs and the technology they used at work or expected to use at work in the future. I included a description of the data, the recruitment methods, and the discussion guide in this ReadMe file.
F. M. Laggner, A. Diallo, B. P. LeBlanc, R. Rozenblat, G. Tchilinguirian, E.Kolemen, the NSTX-U team
Abstract:
A detailed description of a prototype setup for real-time (rt) Thomson scattering (TS) analysis is presented and implemented in the multi-point Thomson scattering (MPTS) diagnostic system at the National Spherical Torus Experiment Upgrade(NSTX-U). The data acquisition hardware was upgraded with rt capable electronics (rt-analog digital converters (ADCs) and a rt server) that allow for fast digitization of the laser pulse signal of eight radial MPTS channels. In addition, a new TS spectrum analysis software for a rapid calculation of electron temperature (Te) and electron density (ne) was developed. Testing of the rt hardware and data analysis soft-ware was successfully completed and benchmarked against the standard, post-shot evaluation. Timing tests were performed showing that the end-to-end processing time was reproducibly below 17 ms for the duration of at least 5 s, meeting a 60 Hz deadline by the laser pulse repetition rate over the length of a NSTX-U discharge. The presented rt framework is designed to be scalable in system size, i.e. incorporation of additional radial channels by solely adding additional rt capable hardware. Furthermore, it is scalable in its operation duration and was continuously run for up to 30 min, making it an attractive solution for machines with long discharge duration such as advanced, non-inductive tokamaks or stellarators.
Amazonian deforestation causes systematic changes in regional dry season precipitation. Some of these changes at contemporary large scales (a few hundreds of kilometers) of deforestation have been associated with a ‘dynamical mesoscale circulation’, induced by the replacement of rough forest with smooth pasture. In terms of decadal averages, this dynamical mechanism yields increased precipitation in downwind regions and decreased precipitation in upwind regions of deforested areas. Daily, seasonal, and interannual variations in this phenomenon may exist, but have not yet been identified or explained. This study uses observations and numerical simulations to develop relationships between the dynamical mechanism and the local- and continental-scale atmospheric conditions across a range of time scales. It is found that the strength of the dynamical mechanism is primarily controlled by the regional-scale thermal and dynamical conditions of the boundary layer, and not by the continental- and global-scale atmospheric state. Lifting condensation level and wind speed within the boundary layer have large and positive correlations with the strength of the dynamical mechanism. The strength of these relationships depends on time scale and is strongest over the seasonal cycle. Overall, the dynamical mechanism is found to be strongest during times when the atmosphere is relatively stable. Hence, for contemporary large scales of deforestation this phenomenon is found to be the prevalent convective triggering mechanism during the dry and parts of transition seasons (especially during the dry-to-wet transition), significantly affecting the hydroclimate during this period.
