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Modeling the relativistic runaway electron avalanche and the feedback mechanism with GEANT4.

Skeltved AB, Østgaard N, Carlson B, Gjesteland T, Celestin S - J Geophys Res Space Phys (2014)

Bottom Line: Our results indicate that the multiplication of electrons during the development of RREAs and under the influence of feedback are consistent with previous estimates.This comparison shows that the choice of physics list used in GEANT4 simulations has a significant effect on the results.Testing the feedback mechanism with GEANT4Validating the GEANT4 programming toolkitStudy the ratio of bremsstrahlung photons to electrons at TGF source altitude.

View Article: PubMed Central - PubMed

Affiliation: Birkeland Centre for Space Science, Institute of Physics and Technology, University of Bergen Bergen, Norway.

ABSTRACT

: This paper presents the first study that uses the GEometry ANd Tracking 4 (GEANT4) toolkit to do quantitative comparisons with other modeling results related to the production of terrestrial gamma ray flashes and high-energy particle emission from thunderstorms. We will study the relativistic runaway electron avalanche (RREA) and the relativistic feedback process, as well as the production of bremsstrahlung photons from runaway electrons. The Monte Carlo simulations take into account the effects of electron ionization, electron by electron (Møller), and electron by positron (Bhabha) scattering as well as the bremsstrahlung process and pair production, in the 250 eV to 100 GeV energy range. Our results indicate that the multiplication of electrons during the development of RREAs and under the influence of feedback are consistent with previous estimates. This is important to validate GEANT4 as a tool to model RREAs and feedback in homogeneous electric fields. We also determine the ratio of bremsstrahlung photons to energetic electrons N γ /N e . We then show that the ratio has a dependence on the electric field, which can be expressed by the avalanche time τ(E) and the bremsstrahlung coefficient α(ε). In addition, we present comparisons of GEANT4 simulations performed with a "standard" and a "low-energy" physics list both validated in the 1 keV to 100 GeV energy range. This comparison shows that the choice of physics list used in GEANT4 simulations has a significant effect on the results.

Key points: Testing the feedback mechanism with GEANT4Validating the GEANT4 programming toolkitStudy the ratio of bremsstrahlung photons to electrons at TGF source altitude.

No MeSH data available.


Related in: MedlinePlus

The friction force experienced by electrons in air at sea level with respect to their kinetic energy (solid black line). The dotted red line indicates the conventional breakdown field, Ecb=3200 kV/m. The dashed red line show the effective minimum threshold force experienced by runaway electrons and corresponds to Eth=284 kV/m [Dwyer, 2003]. The dashed blue line shows the upper threshold for thermal runaway to occur, and the lower dotted blue line indicates the minimum ionization threshold. The data set was obtained from International Commission on Radiation Units and Measurements [1984].
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fig01: The friction force experienced by electrons in air at sea level with respect to their kinetic energy (solid black line). The dotted red line indicates the conventional breakdown field, Ecb=3200 kV/m. The dashed red line show the effective minimum threshold force experienced by runaway electrons and corresponds to Eth=284 kV/m [Dwyer, 2003]. The dashed blue line shows the upper threshold for thermal runaway to occur, and the lower dotted blue line indicates the minimum ionization threshold. The data set was obtained from International Commission on Radiation Units and Measurements [1984].

Mentions: Wilson [1925], based on observations of the tracks of energetic electrons in a cloud chamber, suggested a theory to explain the behavior of energetic electrons in a thundercloud. Wilson proposed that energetic electrons in air, such as can be produced from cosmic rays, can be accelerated to large energies by the strong electric fields produced in thunderclouds. These electric fields must be sufficiently strong to oppose the effective friction force resulting from electron interactions with air molecules. Electrons that continue to be accelerated then become runaway electrons (REs). The effective frictional force in air at sea level pressure and density, with respect to the kinetic energy of the electron, is shown in Figure 1. The minimum friction force for REs is experienced by electrons with a kinetic energy of ≈1 MeV. Monte Carlo simulations show that in order for REs to propagate large distances, the electric field threshold Eth is approximately 30% larger than the minimum ionization threshold and is equal to 284 kV/m (dashed red line) [Dwyer, 2003]. This is due to the effect of elastic scattering, which causes electrons to scatter out of alignment of the electric field. The upper limit, where local ionization can occur and which will cause streamers and subsequent lightning discharges to form, is called the conventional breakdown field, Ecb≈3200 kV/m (dotted red line). Thermal runaway occurs at approximately 10Ecb. The average energy gained dε by runaway electrons traveling a given distance dz through a thundercloud can be expressed as a function of the electric field E and the opposing friction force Fd


Modeling the relativistic runaway electron avalanche and the feedback mechanism with GEANT4.

Skeltved AB, Østgaard N, Carlson B, Gjesteland T, Celestin S - J Geophys Res Space Phys (2014)

The friction force experienced by electrons in air at sea level with respect to their kinetic energy (solid black line). The dotted red line indicates the conventional breakdown field, Ecb=3200 kV/m. The dashed red line show the effective minimum threshold force experienced by runaway electrons and corresponds to Eth=284 kV/m [Dwyer, 2003]. The dashed blue line shows the upper threshold for thermal runaway to occur, and the lower dotted blue line indicates the minimum ionization threshold. The data set was obtained from International Commission on Radiation Units and Measurements [1984].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4497459&req=5

fig01: The friction force experienced by electrons in air at sea level with respect to their kinetic energy (solid black line). The dotted red line indicates the conventional breakdown field, Ecb=3200 kV/m. The dashed red line show the effective minimum threshold force experienced by runaway electrons and corresponds to Eth=284 kV/m [Dwyer, 2003]. The dashed blue line shows the upper threshold for thermal runaway to occur, and the lower dotted blue line indicates the minimum ionization threshold. The data set was obtained from International Commission on Radiation Units and Measurements [1984].
Mentions: Wilson [1925], based on observations of the tracks of energetic electrons in a cloud chamber, suggested a theory to explain the behavior of energetic electrons in a thundercloud. Wilson proposed that energetic electrons in air, such as can be produced from cosmic rays, can be accelerated to large energies by the strong electric fields produced in thunderclouds. These electric fields must be sufficiently strong to oppose the effective friction force resulting from electron interactions with air molecules. Electrons that continue to be accelerated then become runaway electrons (REs). The effective frictional force in air at sea level pressure and density, with respect to the kinetic energy of the electron, is shown in Figure 1. The minimum friction force for REs is experienced by electrons with a kinetic energy of ≈1 MeV. Monte Carlo simulations show that in order for REs to propagate large distances, the electric field threshold Eth is approximately 30% larger than the minimum ionization threshold and is equal to 284 kV/m (dashed red line) [Dwyer, 2003]. This is due to the effect of elastic scattering, which causes electrons to scatter out of alignment of the electric field. The upper limit, where local ionization can occur and which will cause streamers and subsequent lightning discharges to form, is called the conventional breakdown field, Ecb≈3200 kV/m (dotted red line). Thermal runaway occurs at approximately 10Ecb. The average energy gained dε by runaway electrons traveling a given distance dz through a thundercloud can be expressed as a function of the electric field E and the opposing friction force Fd

Bottom Line: Our results indicate that the multiplication of electrons during the development of RREAs and under the influence of feedback are consistent with previous estimates.This comparison shows that the choice of physics list used in GEANT4 simulations has a significant effect on the results.Testing the feedback mechanism with GEANT4Validating the GEANT4 programming toolkitStudy the ratio of bremsstrahlung photons to electrons at TGF source altitude.

View Article: PubMed Central - PubMed

Affiliation: Birkeland Centre for Space Science, Institute of Physics and Technology, University of Bergen Bergen, Norway.

ABSTRACT

: This paper presents the first study that uses the GEometry ANd Tracking 4 (GEANT4) toolkit to do quantitative comparisons with other modeling results related to the production of terrestrial gamma ray flashes and high-energy particle emission from thunderstorms. We will study the relativistic runaway electron avalanche (RREA) and the relativistic feedback process, as well as the production of bremsstrahlung photons from runaway electrons. The Monte Carlo simulations take into account the effects of electron ionization, electron by electron (Møller), and electron by positron (Bhabha) scattering as well as the bremsstrahlung process and pair production, in the 250 eV to 100 GeV energy range. Our results indicate that the multiplication of electrons during the development of RREAs and under the influence of feedback are consistent with previous estimates. This is important to validate GEANT4 as a tool to model RREAs and feedback in homogeneous electric fields. We also determine the ratio of bremsstrahlung photons to energetic electrons N γ /N e . We then show that the ratio has a dependence on the electric field, which can be expressed by the avalanche time τ(E) and the bremsstrahlung coefficient α(ε). In addition, we present comparisons of GEANT4 simulations performed with a "standard" and a "low-energy" physics list both validated in the 1 keV to 100 GeV energy range. This comparison shows that the choice of physics list used in GEANT4 simulations has a significant effect on the results.

Key points: Testing the feedback mechanism with GEANT4Validating the GEANT4 programming toolkitStudy the ratio of bremsstrahlung photons to electrons at TGF source altitude.

No MeSH data available.


Related in: MedlinePlus