Download Document

NSI model for the production of
runaway electrons
in streamer discharges.
Olivier Chanrion, Torsten Neubert
National Space Institute / Danish Technical University
chanrion@space.dtu.dk
Outline
- Introduction : Streamer discharges
Thermal runaway mechanism
Terrestrial Gamma-ray Flashes
- The Danish model
- Result example
- Plans …
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 ?
On the production of runaway electrons
Electric field = 3 Ek
Ionization
threshold
Friction force
X-ray
thermal electrons
-ray
runaway electrons
Are streamers responsible for the recently observed Terrestrial -ray Flashes ?
Numerical difficulty : Few high energy electrons % low energy ones
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
The Danish Model
distribution function with the
runaway branch
Threshold for runaway
Probability
to runaway
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.
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
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 )