Olivier Chanrion, Torsten Neubert

National Space Institute / Danish Technical University

chanrion@space.dtu.dk

NSI model for the production of runaway

electronsin streamer discharges.

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’ thermalelectrons into therunaway regime

=> Role in TGF ?

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

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

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

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

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 )