A linear transformer driver (LTD) generator capable of delivering up to 0.9 MA current pulses with 160 ns rise time has been assembled and commissioned at University of California San Diego. The machine is an upgrade of the LTD-III pulser from Sandia National Laboratories, consisting of 40 capacitors and 20 spark gap switches, arranged in a 20-brick configuration. The driver was modified with the addition of a new trigger system, active premagnetization of the inductive cores, a vacuum chamber with multiple diagnostic ports, and a vacuum power feed to couple the driver to plasma loads. The new machine is called compact experimental system for Z-pinch and ablation research (CESZAR). The driver has a maximum bipolar charge voltage of AE100 kV, but for reliability and testing, and to reduce the risk of damage to components, the machine was operated at AE60 kV, producing 550 kA peak currents with a rise time of 170 ns on a 3.5 nH short circuit. While the peak current is scaled down due to the reduced charge voltage, the pulse shape and circuit parameters are close to the results of the cavity and power feed models but suggest a slightly higher inductance than predicted. The machine was then used to drive wire array Z-pinch and gas puff Z-pinch experiments as initial dynamic plasma loads. The evolution of the wire array Z pinch is consistent with the general knowledge of this kind of experiment, featuring wire ablation and stagnation of the precursor plasma on axis. The gas puff Z pinches were configured as a single, hollow argon gas shell, in preparation for more structured gas puff targets such as multispecies, multishell implosions. The implosion dynamics agree generally with 1D magnetohydrodynamics simulation results, but large zippering and magneto-Rayleigh-Taylor instabilities are observed. The CESZAR load region was designed to accommodate many load types to be driven by the machine, which makes it a versatile platform for studying Z-pinch plasmas. The completion of the CESZAR driver allows plasma experiments on energy coupling from LTD machines to plasma loads, instability mitigation techniques and magnetic field distributions in Z pinches, and interface dynamics in multispecies implosions.
We present the design of a gas-puff injector for liner-on-target experiments. The injector is composed of an annular high atomic number (e.g., Ar and Kr) gas and an on-axis plasma gun that delivers an ionized deuterium target. The annular supersonic nozzle injector has been studied using Computational Fluid Dynamics (CFD) simulations to produce a highly collimated (M > 5), ∼1 cm radius gas profile that satisfies the theoretical requirement for best performance on ∼1-MA current generators. The CFD simulations allowed us to study output density profiles as a function of the nozzle shape, gas pressure, and gas composition. We have performed line-integrated density measurements using a continuous wave (CW) He-Ne laser to characterize the liner gas density. The measurements agree well with the CFD values. We have used a simple snowplow model to study the plasma sheath acceleration in a coaxial plasma gun to help us properly design the target injector.
Abstract. Wind waves play an important role in the climate system, modulating the energy exchange between the ocean and the atmosphere and effecting ocean mixing. However, existing ship-based observational networks of wind waves are still sparse, limiting therefore the possibilities of validating satellite missions and model simulations. In this paper we present data collected on three research cruises in the North Atlantic and Arctic in 2020 and 2021 and the SeaVision system for measuring wind wave characteristics over the open ocean with a standard marine navigation X-band radar. Simultaneously with the SeaVision wind wave characteristic measurements, we also collected data from the Spotter wave buoy at the same locations, and we ran the WaveWatch III model in a very high-resolution configuration over the observational domain. SeaVision measurements were validated against co-located Spotter wave buoy data and intercompared with the output of WaveWatch III simulations. Observations of the wind waves with the navigation X-band radar were found to be in good agreement with buoy data and model simulations with the best match for the wave propagation directions. Supporting datasets consist of significant wave heights, wave directions, wave periods and wave energy frequency spectra derived from both SeaVision and the Spotter buoy. All supporting data are available through the PANGAEA repository – https://doi.org/10.1594/PANGAEA.939620 (Gavrikov et al., 2021). The dataset can be further used for validation of satellite missions and regional wave model experiments. Our study shows the potential of ship navigation X-band radars (when assembled with SeaVision or similar systems) for the development of a new near-global observational network providing a much larger number of wind wave observations compared to e.g. Voluntary Observing Ship (VOS) data and research vessel campaigns.
Рассматриваются ключевые показатели качества (KPI-Key Performance Identifier) сети мобильной связи одного из региональных сотовых операторов РФ, а именно процент неуспешных соединений по протоколу E-RAB (EPS Radio Access Bearer) в сегменте стандарта LTE-A. В рамках исследования приводится динамика изменения параметра во времени, проводится анализ статистических и корреляционных характеристик выбранного KPI, а также приводится список возможных причин неуспешных соединений с долями, показывающими преобладание той или иной причины у рассматриваемого оператора. В целях выявления устойчивых состояний работы сети по выбранному критерию в статье приводится кластеризационный анализ доступной статистики методами K-средних и EM-алгоритма. В качестве критериев выбора количества показательных кластеров использованы критерий сгиба для метода K-средних и информационный критерий Байеса (BIC-Bayesian Information Criterion). В рамках повышения детализации по выявленным причинам отклонений значений неуспешных соединений по протоколу E-RAB от нормальной штатной работы мобильной сети предложена схема программно-аппаратного комплекса (ПАК) сбора и передачи информации для нужд мониторинга. Все составляющие предлагаемого ПАК являются решениями с открытой лицензией и открытыми исходными кодами, что позволит внедрить предлагаемую систему с минимальными экономическими затратами. Результаты, полученные в рамках исследования, могут представлять интерес и для других операторов мобильной связи в рамках работ по анализу, планированию и оптимизации ресурсов сетей стандарта LTE-A в рамках одного региона или часового пояса.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.