Bulletin of the American Physical Society
71st Annual Gaseous Electronics Conference
Volume 63, Number 10
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session NR4: High Pressure Discharges II |
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Chair: Anne Bourdon, LPP, Ecole Polytechnique Room: Oregon Convention Center A107-A109 |
Thursday, November 8, 2018 8:00AM - 8:30AM |
NR4.00001: The Role of Streamers in the Initiation of Electrical Discharges in the Earth's Atmosphere Invited Speaker: Ningyu Liu Streamers are filamentary plasmas that are created by self-propagating ionization waves. They are precursors of spark discharges in laboratory experiments, and are also key components of electrical discharges in the earth's atmosphere, such as lightning, jets and sprites. Despite hundreds of years of research, how lightning originates inside thunderclouds is poorly understood. The problem is that the measured thunderstorm electric field is well below the threshold value to start electrical discharges. A hypothesis for lightning initiation is that thundercloud hydrometeors (water droplets or ice particles) can enhance thunderstorm electric field sufficiently to initiate streamers, which then lead to initiation of lightning leaders. Although streamer discharges can be investigated through laboratory experiments in a controlled manner, their properties in unconfined systems like a thunderstorm are not well studied. About thirty years, high-altitude discharges now called jets and sprites were discovered, and it has been found that streamers are the building blocks of those massive discharges. The research studies on jets and sprites have shed light on the physics of streamer initiation and propagation in a large, electrode-less environment. In this talk, we discuss our recent observational and modeling work on understanding the initiation of lightning, jets and sprites. The discussion is focused on the role played by streamers in the initiation of those phenomena. [Preview Abstract] |
Thursday, November 8, 2018 8:30AM - 8:45AM |
NR4.00002: Effects of electron-heavy particle relaxation time on the initiation of laser-induced breakdown Ippei Yokota, Kohei Shimamura, Shigeru Yokota Laser induced discharge phenomena has been studied in various fields such as space propulsion, drag reduction of supersonic aircraft and combustion ignition. The objective of this study is to investigate the state of the immediately after laser plasma generated, and the detailed breakdown process. In atmospheric discharge of laser, free electrons absorb energy from laser by inverse Bremsstrahlung. Inelastic collisions between heavy particles and free electrons occur, and the energy is transferred from free electrons to heavy particles. The energy transfer from free electrons to heavy particles is important in considering the nonequilibrium state of initial laser breakdown process. We investigated the difference of using different species of gas such as Argon, Helium, Nitrogen, Oxygen, Air and Carbon dioxide, in the atmospheric pressure. In these conditions, 1 J TEA CO$_{\mathrm{2}}$ laser was irradiated in the chamber with an Eschelle spectrometer. The duration time between non local thermodynamic equilibrium (LTE) state to LTE state was quantitatively obtained in the different gaseous form. The ratio between the LTE transition time and the relaxation time is approximately 0.5 to 0.8\texttimes 10$^{\mathrm{3\thinspace }}$in the various gaseous media. This result suggests that the time to local thermal equilibrium is simply explained by the relaxation time between electrons and heavy particles. [Preview Abstract] |
Thursday, November 8, 2018 8:45AM - 9:00AM |
NR4.00003: Combination of open pulse discharge with a capillary discharge for controlling breakdown scenario Irina Schweigert, Andrey Alexandrov, Petr Bokhan, Dmitry Zakrevsky Picosecond breakdown in high-voltage open pulse discharge was registered in experiments and in PIC MCC simulations at gas pressure of 10-20 Torr and 10-20 kV in our previous studies. The open discharge is the type of discharge in small gap (0.2--10 mm) with strong electric field and transparent anode, where the processes outside the gap can affect the discharge development. A disadvantage of plasma devices based on the open pulse discharge is a non-controlled moment of starting of breakdown with increasing a voltage front. To solve this problem, in this work the combined discharge is developed. It is shown in the experiment that a delay of breakdown can be provided with a combination of open high voltage discharge and capillary discharge. For simulation of the breakdown in this combined discharge consisting from open and capillary discharges we have developed a hybrid model, including 2D fluid model for slow electrons and ions, kinetic collisional model for fast electrons and Poisson equation for the electrical potential distribution. The hybrid 2D fluid and PIC MCC simulations show the features of evolution of discharge current in the combined open $+$ capillary discharge. [Preview Abstract] |
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