STREAMER DYNAMICS IN A MEDIA CONTAINING DUST PARTICLES* Natalia Yu. Babaeva and Mark J. Kushner Iowa...
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Transcript of STREAMER DYNAMICS IN A MEDIA CONTAINING DUST PARTICLES* Natalia Yu. Babaeva and Mark J. Kushner Iowa...
STREAMER DYNAMICS IN A MEDIA CONTAINING DUST PARTICLES*
Natalia Yu. Babaeva and Mark J. Kushner
Iowa State UniversityDepartment of Electrical and Computer Engineering
Ames, IA 50011, USA [email protected] [email protected]
http://uigelz.ece.iastate.edu
July 2005
* Work supported by the National Science Foundation and Air Force Research Lab
ICPIG2005_01
Iowa State University
Optical and Discharge Physics
AGENDA
Streamer dynamics through aerosols and dust particles
Description of the model
Effect of dust particles on streamer dynamics
Dynamics before and after particles
Multiple particles
Summary
ICPIG2005_02
STREAMER DYNAMICS
Streamers are ionization waves having a high electric field at the avalanche front.
Air or other gases can be contaminated with particles or aerosols having sizes of 10s to 100s μm.
The intersection of propagating streamers with particles can significantly perturb streamer dynamics.
Iowa State UniversityOptical and Discharge Physics
• Streamer in atmospheric pressure gases.
ICPIG2005_03
Positive corona is sustained between between a rod (rc= 0.07 cm) at 15 kV and a grounded surface separated by 0.2 cm.
2-d unstructured mesh is produced with Skymesh2.
DESCRIPTION OF THE MODEL: GEOMETRY
Iowa State UniversityOptical and Discharge PhysicsICPIG2005_04
Iowa State University
Optical and Discharge Physics
• N2/O2/H2O = 79.5/19.5/1.0
DESCRIPTION OF THE MODEL: BASIC EQUATIONS
Poisson’s equation, continuity equations and surface charge are simultaneously solved using a Newton iteration technique.
j
sjjqN jj
j St
N
jjjj
s Sqt
))(()(
• Species: N2, N2(v), N2*, N2**, N2
+, N, N*, N+, N4+,
O2, O2*, O2+, O2
-, O-, O, O*, O+, O3,
H2O, H2O+, H2, H, OH, e
ICPIG2005_05
TYPICAL STREAMER PARAMETERS: POTENTIAL
Iowa State UniversityOptical and Discharge PhysicsMIN MAX
0 - 15000 (V)
Potential is compressed in front of the streamer head.
Potential drop inside the streamer is small.
Streamer is analogous to the metal rod on the axis.
ICPIG2005_06
• t = 0 – 6 ns • t = 0 – 6 ns
15000 V, 0 – 6 ns
ANIMATION SLIDE
TYPICAL STREAMER PARAMETERS: E/N
Iowa State UniversityOptical and Discharge Physics
Electric field is high at the streamer tip where ionization occurs.
Electric field is small in the conducting channel.
100 – 1000 (Td) Log scaleICPIG2005_07 MIN MAX
15000 V, 0 – 6 ns
• t = 0 – 6 ns • t = 0 – 6 ns
ANIMATION SLIDE
TYPICAL STREAMER PARAMETERS: [e], CHARGE,
Iowa State UniversityOptical and Discharge Physics
1010 - 3 x 1014 (cm-3) 1011 - 1013 (cm-3)
The electron density behind the streamer front is 1013-1014 cm-3 .
The plasma in the inner part of the streamer channel is quasi-neutral.
Positive space charge is concentrated at the streamer boundary.
[e] Space Charge
Log scale
MIN MAX
t = 5.0 ns ICPIG2005_08
15000 V, 0 – 6 ns
E/N BEFORE 20, 60 and 80 m DUST PARTICLE
Iowa State UniversityOptical and Discharge Physics
100 - 1000 (Td) Log scale
• t = 3.8 ns
Streamer velocity and electric field increase as the streamer approaches the particle.
MIN MAX ICPIG2005_09
15000 V, 0 – 6 ns
• No particle • r =20m • r =60m • r =80m
E/N
Iowa State University
Optical and Discharge Physics
E-FIELD AFTER 80m PARTICLE
• t = 0 – 5 ns • t = 0 – 5.2 ns
The conical streamer head develops into a concave tip.
A new streamer starts from the bottom side facing the grounded electrode. The two streamers eventually merge.
If the particle has sharp features , electric field enhancement launches a secondary streamer that does not merge with the primary streamer.
ICPIG2005_10
E/N
MIN MAX 100 - 1000 (Td) Log scale
ANIMATION SLIDE
Iowa State University
Optical and Discharge Physics
E-FIELD AFTER 60m PARTICLE
The conical streamer head develops into a concave tip.
The streamer compresses the E-field field between its tip and the particle surface facing the front.
Plasma envelopes smaller particles (20 µm, 60 µm).
E/N
MIN MAX 100 - 1000 (Td) Log scale
ICPIG2005_11
• t = 4.15 • t = 4.7 • t = 4.15 • t = 4.7 ns
Iowa State University
Optical and Discharge Physics
SURFACE AND SPACE CHARGE FOR 80m PARTICLE
Streamer delivers a substantial positive charge to top of particle.
Charging of particle occurs within 1 ns.
In a repetitively pulsed system, the charge accumulated on a particle can influence subsequent streamers.
1012 to 1013 (cm-3) Log scale
• t = 4.5 ns
MIN MAX
ICPIG2005_12
Iowa State University
Optical and Discharge Physics
ELECTRIC FIELD NEAR SPHERE IN EXTERNAL E-FIELD
Solution of Laplace’s equation outside a conducting particle of radius a in an external electric field.
-40 -30 -20 -10 0 10 20 30 40
Z axis, m icrom eters
-40
-30
-20
-10
0
10
20
30
40
Z' a
xis,
mic
rom
eter
s
• E = 5000 V/cm
arforr
aE
r
UEr
,cos213
3
0
arforr
aE
r
U
rE
,sin11
3
3
0
E
r
Near the particle
arforEEr ,cos3 0
arforE ,0
ICPIG2005_13
POTENTIAL: DIELECTRIC PARTICLES (r = 80m)
Iowa State UniversityOptical and Discharge Physics
• t = 0 - 5.2 ns
5 5 5 25
ICPIG2005_14 MIN MAX 100 - 1000 (Td) Log scale
ANIMATION SLIDE
ELECTRIC FIELD: DIELECTRIC PARTICLES (r = 80m)
Iowa State UniversityOptical and Discharge Physics
• t = 0 – 5.2 ns
5 5 5 25
ICPIG2005_15 MIN MAX 100 - 1000 (Td) Log scale
ANIMATION SLIDE
Iowa State University
Optical and Discharge Physics
Streamer dynamics for the upper particle are similar to a single isolated particle.
A second streamer is launched from the bottom of the first particle. A third streamer is launched from the lower surface of the second particle.
This process is repetitive for particles of the same size and evenly spaced.
STREAMER INTERACTION: TWO PARTICLES (r = 80m)
• t = 0 – 5.2 ns
100 - 1000 (Td) Log Scale
E/N
MIN MAX ICPIG2005_16
Iowa State University
Optical and Discharge Physics
Launching of secondary and tertiary streamers with three particles is the same as for two particles.
STREAMER INTERACTION: THREE PARTICLES (r = 80m)
100 - 1000 (Td) Log Scale MIN MAX
E/N
ICPIG2005_17
• t = 0 – 5.2 ns
Iowa State University
Optical and Discharge Physics
The initial process for 60 m particle is the same as for 80 m.
The secondary streamers can merge sooner than with the larger particles.
STREAMER INTERACTION: THREE PARTICLES (r = 60m)
• t = 3.75 • t = 4.25 • t = 4.6 • t = 3.75 • t = 4.25 • t = 4.6
100 - 1000 (Td) Log Scale MIN MAX
E/N
ICPIG2005_18
1012 - 6 x 1014 (cm-3) Log Scale
Electron flow envelopes the particles.
Plasma density is larger near the particle surfaces.
A wake of smaller electron density above the particle is due to electron flow around the particle.
Iowa State UniversityOptical and Discharge Physics
ELECTRON DENSITY FOR THREE 80 m PARTICLES
MIN MAX
• t = 3.45 • t = 4.2 • t = 4.75 ns
ICPIG2005_19
Iowa State University
Optical and Discharge Physics
PHOTOIONIZATION SOURCE FOR THREE 80 m PARTICLES
109 - 7x1022 (/cm3-s) Log Scale
Photoionization is enhanced in regions of high electric field.
For two or more particles there are bursts of photoelectrons.
A relay-like process results in which streamer is handed off between particles.
MIN MAX
• t = 2.95 • t = 3.95 • t = 4.25 • t = 4.8 ns
ICPIG2005_20
STREAMER VELOCITY VS PARTICLE NUMBER AND SIZE
Iowa State UniversityOptical and Discharge PhysicsICPIG2005_21
Streamer velocity increases in the presence of dust particles.
There exist an optimum for particle size and particle separation at which the streamer velocity is maximal.
Particles are separated by gaps of 3 particle diameter
CONCLUDING REMARKS
The intersection of propagating streamers with particles not only charges the particles but can also significantly perturb the streamer dynamics:
Loss of charge Electric field enhancement Secondary processes.
The interaction between the streamer electric field and the local (surface) electric field dominates the dynamics.
The particle size and dielectric constant (capacitance) and conductivity modify interaction due to charge accumulation and shorting of field.
Streamer–particle interactions are more complex for more random assemblies of particles having different sizes.
Iowa State UniversityOptical and Discharge PhysicsICPIG2005_22