1. Olivier Chanrion, Torsten Neubert
NSI model for the production of runaway electrons in streamer discharges.
Olivier Chanrion, Torsten Neubert
National Space Institute / Danish Technical University

2. Outline. - Introduction : Streamer discharges
Outline Introduction : Streamer discharges Thermal runaway mechanism Terrestrial Gamma-ray Flashes - The Danish model - Result example - Plans …

3. Streamer discharge Streamers :
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’ thermal
electrons into the
runaway regime
=> Role in TGF ?

4. On the production of runaway electrons
Electric field = 3 Ek
Ionization
threshold
Friction force
X-ray -ray
thermal electrons runaway electrons
Are streamers responsible for the recently observed Terrestrial -ray Flashes ?
Numerical difficulty : Few high energy electrons % low energy ones

5. The Danish Model Chanrion&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

6. distribution function with the
The Danish Model
distribution function with the
runaway branch
Threshold for runaway
Probability
to runaway

7. 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.

8. Plans Nb of electrons 1/Probability to runaway
First runaway appears when the field in the tip is about 5 Ek
At t > 1.8 µs, 1012 electrons drift in a field > 5Ek
=> Above the precision limit a standard MCC code

9. 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 )