260 research outputs found
Secondary electron emission yield in the limit of low electron energy
Secondary electron emission (SEE) from solids plays an important role in many
areas of science and technology.1 In recent years, there has been renewed
interest in the experimental and theoretical studies of SEE. A recent study
proposed that the reflectivity of very low energy electrons from solid surface
approaches unity in the limit of zero electron energy2,3,4, If this was indeed
the case, this effect would have profound implications on the formation of
electron clouds in particle accelerators,2-4 plasma measurements with
electrostatic Langmuir probes, and operation of Hall plasma thrusters for
spacecraft propulsion5,6. It appears that, the proposed high electron
reflectivity at low electron energies contradicts to numerous previous
experimental studies of the secondary electron emission7. The goal of this note
is to discuss possible causes of these contradictions.Comment: 3 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Ital
Effect of Electron Energy Distribution Function on Power Deposition and Plasma Density in an Inductively Coupled Discharge at Very Low Pressures
A self-consistent 1-D model was developed to study the effect of the electron
energy distribution function (EEDF) on power deposition and plasma density
profiles in a planar inductively coupled plasma (ICP) in the non-local regime
(pressure < 10 mTorr). The model consisted of three modules: (1) an electron
energy distribution function (EEDF) module to compute the non-Maxwellian EEDF,
(2) a non-local electron kinetics module to predict the non-local electron
conductivity, RF current, electric field and power deposition profiles in the
non-uniform plasma, and (3) a heavy species transport module to solve for the
ion density and velocity profiles as well as the metastable density. Results
using the non-Maxwellian EEDF model were compared with predictions using a
Maxwellian EEDF, under otherwise identical conditions. The RF electric field,
current, and power deposition profiles were different, especially at 1mTorr,
for which the electron effective mean free path was larger than the skin depth.
The plasma density predicted by the Maxwellian EEDF was up to 93% larger for
the conditions examined. Thus, the non-Maxwellian EEDF must be accounted for in
modeling ICPs at very low pressures.Comment: 19 pages submitted to Plasma Sources Sci. Techno
Exotic Low Density Fermion States in the Two Measures Field Theory: Neutrino Dark Energy
We study a new field theory effect in the cosmological context in the Two
Measures Field Theory (TMT). TMT is an alternative gravity and matter field
theory where the gravitational interaction of fermionic matter is reduced to
that of General Relativity when the energy density of the fermion matter is
much larger than the dark energy density. In this case also the 5-th force
problem is solved automatically. In the opposite limit, where the magnitudes of
fermionic energy density and scalar field dark energy density become
comparable, nonrelativistic fermions can participate in the cosmological
expansion in a very unusual manner. Some of the features of such states in a
toy model of the late time universe filled with homogeneous scalar field and
uniformly distributed nonrelativistic neutrinos: neutrino mass increases as m ~
a^{3/2}; the neutrino gas equation-of-state approaches w=-1, i.e. neutrinos
behave as a sort of dark energy; the total (scalar field + neutrino)
equation-of-state also approaches w=-1; the total energy density of such
universe is less than it would be in the universe filled with the scalar field
alone. An analytic solution is presented. A domain structure of the dark energy
seems to be possible. We speculate that decays of the CLEP state neutrinos may
be both an origin of cosmic rays and responsible for a late super-acceleration
of the universe. In this sense the CLEP states exhibit simultaneously new
physics at very low densities and for very high particle masses.Comment: 47 pages, accepted for publication in Int.J.Mod.Phys.
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