Lifetime and universal distribution of seed runaway electrons
Abstract
The lifetime of preexisting runaway electrons determines how likely the runaways will undergo avalanche multiplication. We estimate the lifetime of runaway electrons via kinetic analysis. We show that the rate of runaway decay depends on the combination of parameters α≡(Z+1)/$$\sqrt{{\bar{τ}}_{rad}}$$ (where $$τ_{rad}$$ is the synchrotron timescale normalized to the collisional timescale and Z is the ion charge) compared to the electric field. We identify two cases where the decay rate is slow enough to enable a quasisteady shape of the runaway distribution function. This distribution and its lifetime represent the eigenfunction and the lowest eigenvalue of the kinetic equation. In one case, α$$\ll$$1: the field required to sustain the preexisting runaways is barely larger than the ConnorHastie critical value. In the same manner as by Aleynikov and Breizman [Phys. Rev. Lett. 114, 155001 (2015)], we solve the kinetic equation perturbatively but extend the work to demonstrate that the lifetime grows exponentially with the field at a rate that depends on α. Finally, in the second case, α$$\gg$$1: the sustainment field is much greater than the ConnorHastie value, and the largeness of the field in this case enables us to universalize the kinetic equation via the rescaling procedure.
 Authors:

 Univ. of Texas, Austin, TX (United States). Inst. for Fusion Studies
 Publication Date:
 Research Org.:
 Univ. of Texas, Austin, TX (United States)
 Sponsoring Org.:
 USDOE Office of Science (SC)
 OSTI Identifier:
 1540126
 Alternate Identifier(s):
 OSTI ID: 1420640
 Grant/Contract Number:
 FG0204ER54742; SC0016283
 Resource Type:
 Accepted Manuscript
 Journal Name:
 Physics of Plasmas
 Additional Journal Information:
 Journal Volume: 24; Journal Issue: 11; Journal ID: ISSN 1070664X
 Publisher:
 American Institute of Physics (AIP)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Physics
Citation Formats
Fontanilla, Adrian K., and Breizman, Boris N. Lifetime and universal distribution of seed runaway electrons. United States: N. p., 2017.
Web. doi:10.1063/1.5001931.
Fontanilla, Adrian K., & Breizman, Boris N. Lifetime and universal distribution of seed runaway electrons. United States. doi:https://doi.org/10.1063/1.5001931
Fontanilla, Adrian K., and Breizman, Boris N. Tue .
"Lifetime and universal distribution of seed runaway electrons". United States. doi:https://doi.org/10.1063/1.5001931. https://www.osti.gov/servlets/purl/1540126.
@article{osti_1540126,
title = {Lifetime and universal distribution of seed runaway electrons},
author = {Fontanilla, Adrian K. and Breizman, Boris N.},
abstractNote = {The lifetime of preexisting runaway electrons determines how likely the runaways will undergo avalanche multiplication. We estimate the lifetime of runaway electrons via kinetic analysis. We show that the rate of runaway decay depends on the combination of parameters α≡(Z+1)/$\sqrt{{\bar{τ}}_{rad}}$ (where $τ_{rad}$ is the synchrotron timescale normalized to the collisional timescale and Z is the ion charge) compared to the electric field. We identify two cases where the decay rate is slow enough to enable a quasisteady shape of the runaway distribution function. This distribution and its lifetime represent the eigenfunction and the lowest eigenvalue of the kinetic equation. In one case, α$\ll$1: the field required to sustain the preexisting runaways is barely larger than the ConnorHastie critical value. In the same manner as by Aleynikov and Breizman [Phys. Rev. Lett. 114, 155001 (2015)], we solve the kinetic equation perturbatively but extend the work to demonstrate that the lifetime grows exponentially with the field at a rate that depends on α. Finally, in the second case, α$\gg$1: the sustainment field is much greater than the ConnorHastie value, and the largeness of the field in this case enables us to universalize the kinetic equation via the rescaling procedure.},
doi = {10.1063/1.5001931},
journal = {Physics of Plasmas},
number = 11,
volume = 24,
place = {United States},
year = {2017},
month = {11}
}
Web of Science
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Works referencing / citing this record:
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