On phenomena in ionized gases
Conclusions and perspectives
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- Current Bearing Anti-Force Waves (Lightning Return Stroke)
- 1. Model, Solution and Results
- Radiation study for DC and microware (mw) HID lamps
- 3. References
- Flow Circulation and Ozone Concentration Generated by Plasma Actuator in a Closed Circuit Pipe
- Figure
- Optical measurement of meter-scale microwave line plasma under atmospheric pressure
- 3. Results and discussion
- Acknowledgement
- Electronic response of a plasma-facing dielectric solid
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4. Conclusions and perspectives New high resolution VUV absorption spectra for a 1
g and b
1 g molecules and atomic oxygen are reported. In the future we will perform kinetic measurements using modulated current. This research was conducted within the LABEX Plas@par project, and received financial state aid managed by the Agence Nationale de la Recherche, as part of the programme "Investissements d'avenir" under the reference ANR-11-IDEX-0004-02.
[1] N de Oliveira, M Roudjane, D Joyeux, D Phalippou, J-C Rodier & L Nahon, Nature
[2]
S. Ogawa and M. Ogawa, Canadian Journal of Physics, 53, (1975) 1845 [3]D.H. Katayama, S. Ogawa, M. Ogawa, and Y. Tanaka, Journal of Chemical Physics, 67, (1977) 2132
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XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Current Bearing Anti-Force Waves (Lightning Return Stroke)
M. Hemmati P 1 P , J. Griffiths P 1 P , M. Bowman P 1
P 1 P
In our investigation of breakdown waves, we apply a one-dimensional, steady-state, three- component fluid model. The electrons are assumed to be the main element in propagation of the wave and the wave is considered to be shock fronted. Our set of electron fluid dynamical equations is composed of the equation of mass flux, equation of conservation of momentum, equation of conservation of energy, plus Poison’s equation. For lightning return strokes, experimentally, few much larger than usual currents have been reported [1]; we intend to examine existence of such large currents; also, for return strokes, some researchers have suggested existence of a relationship between the peak current and wave speed values [2], we intend to find out its validity as well.
Anti-force waves are breakdown waves for which the electric field force on electrons is in the opposite direction of the wave propagation; however, the electron gas temperature is assumed to be large enough to sustain the wave motion. Following the shock front, there is a thin dynamical transition region referred to as the sheath region of the wave; where, the electric field starting with its maximum value at the shock front reduces to zero at the end of the sheath region, and the electrons, starting with an initial speed at the wave front, slow down to speeds comparable to those of heavy particles. For theoretical investigation of anti-force waves with a large current behind the shock front, we will use Hemmati et al.’s [3] modified set of electron fluid dynamical equations and the boundary condition on electron temperature at the shock front. In dimensionless variables, the equations are , ]
v v d d
(1) ), 1
] ) 1 ( [ v v v v d d (2)
d d v v v v d d 2 2 5 ) 2 5 ( ) 1 ( [
], ) 1 ( 3 [ 2 ] 2 2
(3) ) 1 ( d d
(4) . ) 1 ( 1 1 1 1
(5) Where , , represent non-dimensional electron number density, velocity and temperature;
, , , , represent net electric field, ionization rate, position within the sheath region and current at the shock front; and
are wave parameters. For lightning return strokes, experimental current values measured are generally in the 5-30 kA range; however, some, for example Rakov [1], has reported the highest recorded peak currents in Japan to be 280, 320 and 340 kA. Our dimensionless current, 1 , represents an actual current value of 10 kA. We use a trial-and-error method to integrate equations 1-4 through the sheath region of the wave. Our solutions for a range of wave speeds, and also maximum current values possible for those wave speeds, meet the expected conditions at the trailing edge of the wave ) 0
1 ( 2 2 . The following is a graph of the net electric field as a function of wave speed within the sheath region of the wave.
For return strokes, in addition to existence of large currents, we also confirm existence of a relationship between the wave speed and peak current values.
[1] V.A. Rakov. 25 th Int. Conference on Lightning Protection. (2000). 103-108. [2] C.F. Wagner. AIEE Trans. Power Appar. Syst. 1968. 82:609-17. [3] M. Hemmati, W.P. Childs, H. Shojaei and D.C. Waters. 28 th International Symposium on Shock Waves, 2011, England. 5 125 XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal Radiation study for DC and microware (mw) HID lamps A. Sahab
P 1 P , M. Hamady 2 , G. Zissis P 3 P 1 P
2 P
P
P
Narbonne, F-31062 Toulouse cedex9, France Advances in microwave and light source technology in the last decade have led to the most recent generation of highly efficient electrodeless discharge lamps. Such lamps are generally classified in the scientific literature as electrodeless HID (EHID) lamps, but currently they are often referred to as plasma lamps. The radiations of discharges sustained by a microwave (mw) electromagnetic field as well as discharges containing electrodes are discussed. The visible radiations are mainly important in light sources application while UV radiations are used extensively in water sterilisation.A 1D power balance model and ray-tracing method are both employed to calculated the radiations in these discharges. 1. General In recent years, the use of an electrodeless light source excited by microwave electric fields has been widely used in our daily life and has attracted a great interest. The absence of electrodes provides greater flexibility in lamp design and the discharge is no longer limited by the narrow gap between the electrodes. In addition, the lack of inexpensive and efficient microwave power supplies has hampered the development of these lamps for many years. Pure Hg discharges are an ideal vehicle for a fundamental study, since the physical properties of mercury atoms have been well understood for many years.
2. Models Zollweg [1] has deeply studied Hg DC
lamps in different spectral range. The corresponding (same power) mw HID lamps are studied in this work. These discharges are considered to be excited by microwave electromagnetic fields in a cylindrical TM 010
mode. A detailed theoretical analysis of these lamps was presented by Offermanns [2] and Waymouth [3]. We have already used in previous work
[4] these
analyses and
obtained a representation of the temperature profile for DC discharges as well as for mw discharges. 3. DC and MW Discharges Once the temperature profile for each lamp is known, the radiations in different spectral range are calculated using a model of radiation transport as in [4]. The obtained results for DC discharges at almost the same applied power are comparable with experimental results of Zollweg [1] as shown in Table 1.
Range (nm) 350-
390 390-
420 420-
450 535-
560 560-
590 Model (W) 12.1 5.9
10.1 8.5
11.7 Zollweg (W) 14.4 7.5
10.7 12 15.2 Table 1: Radiations of each spectral range of the lamp 3. Results We show in Figure 1 the increase in radiation as the applied electric power increases for both DC and mw discharges. The results show that the increase of radiation is almost linear with the applied power with a higher slope for DC discharge (blue line). 10 20
40 50 60 0 10 20 30 40 50 W elec
(W.cm-1) W ra d (W
.cm -1 ) DC Model mw Model
Figure 1: Variation of radiation with applied power 3. References [1] Zollweg R J, Lowke J J and Liebermann R W,1975, J. Appl. Phys. 46 3828-3838 [2] Offermanns S 1990 J. Appl. Phys.67 115. [3] Waymouth J F 1993 Microwave Discharges:
York 427. [4] M. Hamady, G. G. Lister, G. Zissis 2015
10.1177/1477153515571678. 16 126
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Flow Circulation and Ozone Concentration Generated by Plasma Actuator in a Closed Circuit Pipe
Youhwan Shin P 1 P , Heon-Su Lee P 2 P
P 1 P
P
P
Hwarangno 14-gil 5, Seongbuk-gu, Seoul 02792, Korea. yhshin@kist.re.kr
This experimental research includes the characteristics of the flow generated by dielectric barrier discharge (DBD) plasma actuators installed on the wall inside a circular pipe as a closed circuit. We compare and discuss with the flow velocities and their distributions in the closed-loop tunnel at the various excitation voltages and frequencies applied to the actuators. We also observed the variation of the ozone concentrations with various conditions supplied to the actuators. The velocity magnitude of the air in the closed pipe decreases as the ozone concentration rapidly increases at first short time. Higher voltage excited to the plasma actuator makes its increasing rate grow steeper. However as time goes, the ozone concentration is saturated in a closed pipe and consequently it is independent on the electrode excitation voltage of the plasma actuator.
Flow phenomena such as a separation on the surface wall or the leakage flow on the gas turbine blade tips normally cause flow losses. Therefore in order to increase some efficiencies related on the aerodynamic flow, they are needed to be depressed by the flow control. Plasma actuator can be used as one effective choice of the methods for active flow control, which has many advantages such as simple structure without moving parts and so on [1]. DBD plasma actuator induces parallel flow on the wall surface of the actuator by the interaction between plasma and neutral air particles. As shown in Fig. 1, an experimental setup was arranged with single and multiple DBD actuators installed on a circular tube wall. The electrode is connected to high-voltage power amplifier (TREK 20/20C) excited by a function generator generating sine waves. The voltage and frequency ranges are 10~16 kV and 0.5~1.0 kHz respectively. Ozone concentrations were measured by USB New iStar ICCD Camera (Andor Technology) and analyzed by S/W, Andor Solis. Flow velocities were also measured at several radial positions inside the pipe by hotwire anemometry. Ozone concentrations were measured for 20 minutes in a closed circular pipe under the operation of the plasma actuator as shown in Fig. 2. Firstly they dramatically increase for a short time, 300 seconds. Subsequently they gradually decrease to be saturated conditions. Higher excitation voltage applied to the actuators generates higher growing rate of them. The velocity magnitude in the pipe steeply decreases as the ozone concentration rapidly increases. References [1]
G. Pechlivanoglou, C.N. Nayeri and C.O. Paschereit, Performance Optimization of Wind Turbine Rotors with Active Flow Control, Proceedings of ASME Turbo Expo. (2011) GT2011-45493. [2]
Parisse, A. Chakir and J. Brion, Ozone UV spectroscopy. II. Absorption cross-sections and temperature dependence, Journal of Atmospheric Chemistry V.21 (1995) 263. Figure 1 Schematic half view of a DBD plasma actuator on inner wall of a circular pipe Figure 2 Ozone concentrations with different electrode voltages of DBD plasma actuators (1 kHz) 17 127
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Optical measurement of meter-scale microwave line plasma under atmospheric pressure
H. Suzuki, Y. Tamura, Y. Inomata, and H. Toyoda Graduate School of Engineering, Nagoya University, Nagoya, Japan
Meter-scale microwave line plasma is produced under atmospheric pressure using a loop-waveguide with a microwave circulator to suppress ununiformity of electromagnetic field inside the waveguide, and is investigated by an optical emission spectroscopy. Gas temperature and electron density of argon plasma are ~600 K and ~10 20 m
, respectively, and are spatially-uniform in 80 cm in length.
Recently, large-area surface treatment using atmospheric-pressure (AP) plasma attracts much attention due to its cost benefit and a variety of possibilities for industrial applications. As a new AP plasma source for large area processing, we have proposed a one-dimensionally long-scale AP microwave plasma source using a loop-waveguide system, where plasma uniformity is realized by suppression of standing wave inside the waveguide. Using this plasma source, spatially-uniform line plasma of 40 cm in length has been realized with helium gas and cw microwave power of 1.0 kW [1]. Furthermore, production of pure molecular gas line plasma inside a slot of 50 cm in length has been realized by improving the waveguide structure to increase power efficiency [2]. To apply this plasma source to industrial processing, understanding of the plasma characteristics such as spatial uniformity, gas temperature, plasma density and plasma-sustainment mechanism are important. In this study, plasma parameters are investigated by optical emission spectroscopy (OES).
A microwave source (2.45 GHz, power: <5.0 kW) is connected to the circulator through an impedance matcher. A slot antenna of 0.1 mm in gap width is cut along the modified ridge waveguide wall. Discharge gas (Ar: 14 slm) is introduced into the waveguide through small holes and is released through the slot. Plasma is produced inside the slot by applying microwave power. Spatiotemporal distribution of the plasma is investigated by a digital still camera and an optical multi-channel analyzer through an optical fiber. Gas temperature and electron density are measured from N 2 second positive band profile and Stark broadening of H spectrum, respectively. Microwave powers at the upstream and downstream of the slotted waveguide
are monitored by crystal mounts. 3. Results and discussion Firstly, the line plasma is produced with an input microwave-power of 500 W to a slot of 1.1 m in length. The emission intensity monitored by the digital camera is quite uniform and its spatial fluctuation is less than 8% in 80 cm around the slot center. Spatial profiles of the gas temperature and electron density are shown in Figure 1 and are uniform at ~600 K and ~10 20 m -3 , respectively. These results suggest that meter-scale almost uniform plasma with low temperature and high plasma density is realized by using the plasma source.
This work was supported by JSPS KAKENHI Grant number JP16H03893.
[1] H. Suzuki et al.: Appl. Phys. Express 8 (2015) 036001. [2] H. Suzuki et al.: 69 th Gaseous Electronics Conference, 2016, NW3.7 Topic number10 Fig. 1. Spatial distributions of (a) N 2 rotational temperature and (b) electron density along the slot. 128
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal Electronic response of a plasma-facing dielectric solid F. X. Bronold, H. Fehske P
Based on the Poisson equation for the electric potential and two sets of spatially separated Boltzmann equations, one for the conduction band electrons and valence band holes inside the dielectric and one for the electrons and ions inside the plasma, we present a kinetic theory for the electronic response of a plasma-facing dielectric solid. It enables us to determine the quasi- stationary density and potential profiles of the electric double layer formed at the interface as well as the electron and ion fluxes maintaining it. To demonstrate the feasibility and the potential of our approach we present numerical results for collisionless double layers at silicon and silicon dioxide surfaces in contact with a hydrogen plasma. The basic electronic response of a plasma- facing solid is the formation of the plasma sheath. It is the positive part of an electric double layer whose negative part is inside the solid. A stationary sheath develops if electron-ion generation in the plasma is balanced by electron and ion losses at or inside the wall. A complete kinetic modelling of the sheath has thus to contain not only the plasma physics of the positive part of the double layer but also the solid state physics of the negative part. For a dielectric wall we developed such a synergetic approach [1] which we expect to be particularly useful for integrated microdischarges [2,3], in particular, when their miniaturization continues making thereby the length and time scales of the gaseous discharge comparable with the scales of the confining wall. Our approach is based on the Poisson equation and two sets of Boltzmann equations operating in disjunct half- spaces separated by a planar interface. One set is for electrons and ions inside the plasma and the other is for conduction band electrons and valence band holes inside the wall. The two sets are connected by quantum-mechanical matching conditions for the electron distribution functions, a semi-empirical model for hole injection due to neutralization of ions at the interface, and the matching conditions for the electric potential. Essential for the modelling is the merging of the space charge region with the neutral bulk plasma and the intrinsic or extrinsic bulk of the wall as well as the ambipolarity inside the wall leading to an electron-hole recombination condition. The overall picture emerging from our kinetic modelling is a double layer whose positive space charge on the plasma side is balanced by a thermalized/trapped negative space charge inside the wall while the quasi-stationary electron and ion fluxes maintaining the double layer are limited by electron-hole recombination inside the wall. Numerical results for collisionless double layers formed at intrinsic and extrinsic silicon and silicon dioxide surfaces exposed to a hydrogen plasma (see Fig. 1 for the plasma-induced band bending in intrinsic silicon dioxide and silicon) show the feasibility and potential of our approach. Issues to be resolved before it can become quantitative for realistic interfaces will be discussed. – Supported by DFG through CRC/Transregio TRR24. FIG. 1: Band edges for intrinsic silicon dioxide (left panel) and intrinsic silicon (right panel) in contact with a hydrogen plasma [1]. Inside the wall solid red (blue) curves are the edges of the conduction (valence) band while in front of it the curves give the potential energy of the electrons (ions). Dashed blue curves indicate the edges for the valence band holes. The distances from the interface at z=0 are measured in units of the wall's (plasma's) electron Debye screening length. The profiles inside the light grey regions have no direct physical meaning. They arise from implementing technically the physical boundary conditions for the double layer responsible for the band bending. The electron (ion) temperature of the plasma is 2 eV (0.2 eV). Download 9.74 Mb. Do'stlaringiz bilan baham: 
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