Electron heat transport
in a steep temperature gradient
J. H. Rogers and J. S. De Groot
Department of Applied Science, University of California
Davis, Davis, California 95616
Z. Abou‐Assaleh,
J. P. Matte, and T. W. Johnston
INRS‐Energie, Université du Québec, Varennes, Québec J0L
2P0, Canada
M. D. Rosen
Lawrence Livermore National Laboratory, Livermore,
California 94550
ABSTRACT
Temporal and spatial measurements of electron heat transport
are made in the University of California Davis AURORA device
(J. H. Rogers, Ph.D. dissertation, University of California,
Davis, 1987). In AURORA, a microwave pulse heats a region of
underdense, collisional, plasma (n/ncr ≲1, where ncr
=1.8×1010 cm−3 is the critical density, Te0 ≊0.15 eV, and
the electron scattering mean free path λ⊥≳2 cm). In this
region, strong thermal heating (Tc ≲0.7 eV) as well as
suprathermal heating (Th≊3 eV) is observed. The strong
heating results in a steep temperature gradient that
violates the approximations of classical heat diffusion
theory (LT/λ⊥≳3 for thermal electrons, where LT=Tc(∂Tc/∂z)−1
is the cold electron temperature scale length. The time
evolution of the electron temperature profile is measured
using Langmuir probes. The measured relaxation of the
temperature gradient after the microwave pulse is compared
to calculations using the Fokker–Planck International code
[Phys. Rev. Lett. 49, 1936 (1982)] and the multigroup,
flux‐limited, target design code lasnex [Comm. Plasma Phys.
2, 51 (1975)]. The electron distribution function at the end
of the microwave pulse is used as initial conditions for
both codes. The Fokker–Planck calculations are found to
agree very well with the measurements. However, the
flux‐limited diffusion calculations do not agree with the
measurements for any value of the flux limiter.
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