NSI model for the production of runaway electrons in streamer discharges .
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Transcript of NSI model for the production of runaway electrons in streamer discharges .
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Olivier Chanrion, Torsten Neubert
National Space Institute / Danish Technical University
NSI model for the production of runaway
electronsin streamer discharges.
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Outline
- Introduction : Streamer discharges Thermal runaway mechanism Terrestrial Gamma-ray Flashes
- The Danish model
- Result example
- Plans …
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Streamer discharge
Streamers : - filaments of weakly ionised plasma propagating both along and against the electric field
- present in leader tips of lightning, in mesospheric discharge ( sprites ) …
Enhancement of the field in the streamer heads
Can ‘push’ thermalelectrons into therunaway regime
=> Role in TGF ?
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On the production of runaway electrons
Friction force
Electric field = 3 EkIonization
threshold
thermal electrons runaway electrons
Are streamers responsible for the recently observed Terrestrial -ray Flashes ?
Numerical difficulty : Few high energy electrons % low energy ones
X-ray -ray
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The Danish ModelChanrion&Neubert, JGR, 115 (2010)
Physical model : Fully kinetic- movement of electrons in a background electric field- collision with neutral ( attachment, excitation, ionization, photoionization )- total cross section comes from Phelps ( BOLSIG )- extrapolation to high energies follows Murphy (LANL Rep. 2002)- scattering angle follows Okhrimovsky (PhysRevE,65,2002)- Ionisation energy partitionning follows Opal (J. Chem. Phys., 55, 1971)
Numerical model- 3D like geometry (2D cylindrical)- Based on the standard Birdshall Particle in Cell
+ Monte Carlo Collision- Advanced resampling technique for high energy electron
Features- Allow to study the acceleration of cold electron in the runaway regime- Unprecedented precision allows to calculate the probability to runaway
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The Danish Model
distribution function with the runaway branch
Threshold for runaway
Probability to runaway
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The Danish Model
In a background field of 3Ek
Estimate of runaway in agreement with Moss(JGR,111,2006) and Gurevich (Phys.Lett.A, 361, 2007) work=> lead to agreement with TGF observations.
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Plans
1/Probability to runaway
Nb of electrons
First runaway appears when the field in the tip is about 5 EkAt t > 1.8 µs, 1012 electrons drift in a field > 5Ek
=> Above the precision limit a standard MCC code
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Plans
Main goal :
-Simulate the production of X- and Gamma ray
-Understand the impact on the streamer propagation
Deniz Cinar, a PhD student will start next month
-Preliminary studies with 1D code
-Implementation of advance in the quasi-3D code
Collaboration with
CWI/TU Eindhoven (Ute Ebert, L. van Deursen)
RFNC ( Babich )