DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Lifetime and universal distribution of seed runaway electrons

Journal Article · · Physics of Plasmas
DOI: https://doi.org/10.1063/1.5001931 · OSTI ID:1540126
 [1];  [2]
  1. Univ. of Texas, Austin, TX (United States). Inst. for Fusion Studies; DOE/OSTI
  2. Univ. of Texas, Austin, TX (United States). Inst. for Fusion Studies

The lifetime of pre-existing 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 quasi-steady 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 pre-existing runaways is barely larger than the Connor-Hastie 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 Connor-Hastie value, and the largeness of the field in this case enables us to universalize the kinetic equation via the re-scaling procedure.

Research Organization:
Univ. of Texas, Austin, TX (United States)
Sponsoring Organization:
USDOE Office of Science (SC)
Grant/Contract Number:
FG02-04ER54742; SC0016283
OSTI ID:
1540126
Alternate ID(s):
OSTI ID: 1420640
Journal Information:
Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 11 Vol. 24; ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)Copyright Statement
Country of Publication:
United States
Language:
English

References (11)

Disruption generated runaway electrons in TEXTOR and ITER journal March 1996
Phase-space dynamics of runaway electrons in magnetic fields journal February 2017
Theory for avalanche of runaway electrons in tokamaks journal October 1997
Relativistic limitations on runaway electrons journal June 1975
Damping of relativistic electron beams by synchrotron radiation journal December 2001
Zur Theorie des Durchgangs schneller Elektronen durch Materie journal January 1932
Electron and Ion Runaway in a Fully Ionized Gas. II journal January 1960
Marginal stability model for the decay of runaway electron current journal April 2014
Theory of Two Threshold Fields for Relativistic Runaway Electrons journal April 2015
Electron and Ion Runaway in a Fully Ionized Gas. I journal July 1959
Momentum–space structure of relativistic runaway electrons journal June 1998

Cited By (2)

Physics of runaway electrons in tokamaks journal June 2019
Spatial transport of runaway electrons in axisymmetric tokamak plasmas journal January 2019