Propagation of Cathode-Directed Streamer Discharges in Air

Size: px

Start display at page:

Download "Propagation of Cathode-Directed Streamer Discharges in Air"

Lorena Owen
6 years ago
Views:

1 Propagatio of Cathode-Directed Streamer Discharges i Air Yuriy Serdyuk Associate Professor High Voltage Egieerig Chalmers Uiversity of Techology SE Gotheburg, Swede yuriy.serdyuk@chalmers.se

2 Outlie Itroductio Drift-diffusio model of streamer discharges i air Model implemetatio Simulatios of positive streamers Cocludig remarks

3 Electrical gas discharges Pheomea associated with trasport of electrical charges through eutral gas due to applied electric fields. Trasport processes are usually strogly domiated by space charge effects. Examples of o-thermal discharges: electro avalaches, streamers, coroas, statioary glow discharges, dielectric barrier discharges (DBD). A streamer discharge is a self-sustaied ioizatio wave propagatig i eutral gas.

Positive streamers i air Streamers develop as thi plasma chaels sustaied by productio of electros i

4 Positive streamers i air Streamers develop as thi plasma chaels sustaied by productio of electros i the strog field regio at the head. Depedig upo coditios (pressure, legth, power iput, overvoltage, etc.) they may experiece brachig. Trasitio from glow to streamer: eedle-plae gap, legth 20mm, U app = +21 kv, exposure 5 s. T. M. P. Briels et al., Positive ad egative streamers i ambiet air: measurig diameter, velocity ad dissipated eergy, J. Phys. D: Appl. Phys., 2008, 41, T. Czech et al., Optical emissio spectroscopy of poit-plae coroa ad back-coroa discharges i air, Eur. Phys. J. D, 2011, 65,

Drift-diffusio model of air discharges Charge carriers are represeted as electroic ad ioic fluids ad are characterized by averaged properties.

5 Drift-diffusio model of air discharges Charge carriers are represeted as electroic ad ioic fluids ad are characterized by averaged properties. Mass coservatio equatios for electros ad ios: Poisso equatio for electric potetial : Appropriate (problem depedet) boudary ad iitial coditios are to be provided for all the PDEs. ) ( ) ( / ) ( ) ( / ) ( ) ( / E S D t E S D t E S D t p p p p p p e e e e e e E E E E, ) ( ) ( 0 e p q

6 Icorporatig photoioizatio i air Mechaism: e * * N 2 N 2 e N 2 N 2 h ( m) O2 h O No-local ioizatio: electros are created by photos at a distace from a source of radiatio. The photoioizatio rate is icluded as j where the terms (r) satisfy Helmholtz equatios ( * ) 2 S j ph S ph ( r) ( p j O 2 j 2 ) S ( r) A p I( r) 2 ph j O2 Two expoetial fit is used with the parameters ad A j. ( * ) A. Bourdo et al., Efficiet models for photoioizatio produced by othermal gas discharges i air based o radiative trasfer ad the Helmholtz equatios, Plasma Sources Sci. Techol., 2007, 16, j S ph( r) S ph ( r) j j e

7 Model implemetatio Set of PDEs: three drift-diffusio, Poisso s, two Helmholtz. Source term stabilizatio is implemeted for the DD PDEs. Mesh size at streamer frot is ~10 µm, withi the plasma chael ~70 µm ad larger i the rest of the domai. The mesh was refied maually. Solver: direct, segregated (two steps) with cotiues Jacobia update. Time steppig: BDF with variable order.

8 Simulatios of streamers i air Hyperbolic eedle-plae electrodes, pressure 760 Torr, temperature 293 K, voltage rise time 0.1 s. A sigle discharge is cosidered ad the model is implemeted i 2D utilizig axial symmetry. The discharge is iitiated from a seedig charge spot of Gaussia shape ( e = p = m -3, σ = 30 µm) located at 0.1 mm from the eedle tip. Drift of ios is eglected due to the short duratio of the discharge. Two study cases: - gap legth 5 mm (applied voltage +15 kv dc) - gap legth 30 mm (voltage +40 kv dc).

9 Short streamer: dyamics of electros plae eedle

10 Short streamer: electric field plae eedle

11 Log streamer: dyamics of electros plae eedle

12 Log streamer: electric field plae eedle

13 Calculated discharge curret Streamer 5 mm Streamer 30 mm

14 Calculated parameters of streamers Velocity at stable propagatio: 5 mm streamer - ~ m/s 30 mm streamer - ~ m/s Chael radius at stable propagatio : 5 mm streamer µm (strogest field) µm (strogest S ph ) 30 mm streamer µm (strogest field) µm (strogest S ph )

velocities, J. Phys. D: Appl. Phys. 41 (2008) 234005. T. M. P. Briels et al.

15 Typical parameters of streamers A. Luque et al., Positive ad egative streamers i ambiet air: modellig evolutio ad velocities, J. Phys. D: Appl. Phys. 41 (2008) T. M. P. Briels et al., Circuit depedece of the diameter of pulsed positive streamers i air, J. Phys. D: Appl. Phys. 39 (2006)

16 Cocludig remarks The drift-diffusio (fluid) model of o-thermal discharges i air has bee implemeted. Lessos leart: meshig, umerical stability, settig proper boudary coditios, optimizig solver properties, etc. Wish list : - implemetatio of a movig frame with a fie mesh for resolvig gradiets at streamer frot; - implemetatio of a high order umerical scheme or techique allowig for flux correctio; - implemetatio of fiite volume approach for drift-diffusio equatios (to preserve positivity).

17 Thak you for your attetio!!

Modeling of Plasmas and Neutrals Including Plasma-Wall Interaction for Long Term Tokamak Operation

Modeling of Plasmas and Neutrals Including Plasma-Wall Interaction for Long Term Tokamak Operation odelig of Plasmas ad Neutrals Icludig Plasma-Wall Iteractio for Log Term Tokamak Operatio Akiyoshi Hatayama 1, Kousuke Okamoto 1, Ryoko Tatsumi 1, Kazuhiro. Abe 1, ad Kazuaki Haada 2 1. Backgroud/otivatio