Bulletin of the American Physical Society
69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016; Bochum, Germany
Session SR4: Electro-Magnetic Interactions with Plasmas II |
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Chair: Julian Schulze, Ruhr University Room: 3 |
Thursday, October 13, 2016 2:00PM - 2:15PM |
SR4.00001: Extinction of 10.6 $\mu $m laser radiation by free electrons in an argon filamentary discharge at atmospheric pressure S.H. Park, H.J. Yang, A.E. Mironov, S.-J. Park, J.G. Eden Experiments will be described in which the extinction of 10.6 $\mu $m photons by free electrons in a single filamentary discharge is being studied. The extinction ranges from 3 to 10 percent over a path length of 1 cm, depending on the argon flow rate. The temporally- and spatially-averaged electron density in the filament is approximately 10$^{\mathrm{15}}$ cm$^{\mathrm{-3}}$, as determined by Stark broadening of the hydrogen alpha (656.28 nm) and argon I (696.54 nm) lines. Calculations indicate that the observed extinction of 10.6 $\mu $m is attributable to a combination of inverse bremsstrahlung and a negative lens effect, and experimental results will be compared to theoretical calculations based on Boltzmann's equation. The potential application of such high electron density plasmas to studies of fundamental plasma phenomena, as well as optical applications will be discussed. [Preview Abstract] |
Thursday, October 13, 2016 2:15PM - 2:30PM |
SR4.00002: Generation conditions of CW Diode Laser Sustained Plasma Koji Nishimoto, Makoto Matsui, Takahiro Ono Laser sustained plasma was generated using 1 kW class continuous wave diode laser. The laser beam was focused on the seed plasma generated by arc discharge in 1 MPa xenon lamp. The diode laser has advantages of high energy conversion efficiency of 80 {\%}, ease of maintenance, compact size and availability of conventional quartz based optics. Therefore, it has a prospect of further development compared with conventional CO2 laser. In this study, variation of the plasma shape caused by laser power is observed and also temperature distribution in the direction of plasma radius is measured by optical emission spectroscopy. [Preview Abstract] |
Thursday, October 13, 2016 2:30PM - 2:45PM |
SR4.00003: Nanosecond-timescale high-pressure gas discharge in a microwave pulse compressor Anatoli Shlapakovski, Leonid Beilin, Yakov Krasik The results of experimental and numerical studies of the microwave plasma discharge initiated by a nanosecond laser pulse are presented. The discharge is ignited in the pressurized gas filling the switch, which opens the charged resonant cavity, so that the accumulated microwave energy is rapidly released into a load. Fast-framing optical imaging showed that the plasma in the switch appears as filaments expanding along the RF electric field. The temporal evolution of the plasma density was derived from time-resolved spectroscopic measurements. With increasing microwave energy in the cavity, the plasma appears earlier in time after the laser beam enters the switch and its density rises more steeply reaching values which exceed 10$^{\mathrm{16}}$ cm$^{\mathrm{-3}}$ at a gas pressure of 2$\cdot $10$^{\mathrm{5}}$ Pa. Numerical simulations were conducted using the gas conductivity model of plasma and representation of discharge origin by setting initial population of seed electrons treated by PIC algorithm. The results showed good agreement with the experiments and explained how the self-consistent dynamics of the plasma and RF fields determines the quality of microwave output pulses. In addition, the dynamics of the microwave energy absorption in the discharge plasma was studied. It was shown that at a high pressure, even with an unlimited rate of ionization, a significant portion of the stored energy, $\approx $20{\%}, is lost. [Preview Abstract] |
Thursday, October 13, 2016 2:45PM - 3:00PM |
SR4.00004: Ionization processes in combined high-voltage nanosecond -- laser discharges in inert gas. Andrey Starikovskiy, Mikhail Shneider Remote control of plasmas induced by laser radiation in the atmosphere is one of the challenging issues of free space communication, long-distance energy transmission, remote sensing of the atmosphere, and standoff detection of trace gases and bio-threat species. Sequences of laser pulses, as demonstrated by an extensive earlier work, offer an advantageous tool providing access to the control of air-plasma dynamics and optical interactions. The avalanche ionization induced in a pre-ionized region by infrared laser pulses where investigated. Pre-ionization was created by an ionization wave, initiated by high-voltage nanosecond pulse. Then, behind the front of ionization wave extra avalanche ionization was initiated by the focused infrared laser pulse. The experiment was carried out in argon. It is shown that the gas pre-ionization inhibits the laser spark generation under low pressure conditions. [Preview Abstract] |
Thursday, October 13, 2016 3:00PM - 3:15PM |
SR4.00005: Short (ns) and Medium (μs) Time Scale Plasma Induced Changes in Refractive Index of Atmospheric Air Chris Campbell, Kenneth Evans, David Staack Evidence of changes in the refractive index of air caused by pulsed atmospheric glow discharges induced by an applied electric field is presented and discussed. These are due to both thermodynamic and electron density effects. This variable refractive index can theoretically be used to create a method of atmospheric disturbance correction, by affecting the wave fronts of incident laser light. This investigation focused on determining the magnitude and rise time of this effect, which are of interest to the above application. A raytracing model through a plasma disturbance was used to predict the refractive index change, in parallel with experimental measurement. In experiment, an atmospheric glow discharge with a gap width of 2 mm gave rise to a maximum optical path length difference (OPD) of 0.15 $\mu$m. This change occurred within 1 ms, which is in agreement with prediction for thermal modes. In addition at shorter time scales due to a combination of shock wave, thermal and electron density effects of a transient discharge initiation larger OPD changes with a rise time of approximately 100 ns is observed. [Preview Abstract] |
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