7,967 research outputs found
Large area space solar cell assemblies
Development of a large area space solar cell assembly is presented. The assembly consists of an ion implanted silicon cell and glass cover. The important attributes of fabrication are (1) use of a back surface field which is compatible with a back surface reflector, and (2) integration of coverglass application and call fabrication
Further research on high open circuit voltage in silicon solar cells
The results of a new research on the use of controlled dopant profiles and oxide passivation to achieve high open circuit voltage V sub oc in silicon solar cells is presented. Ion implantation has been used to obtain nearly optimal values of surface dopant concentration. The concentrations are selected so as to minimize heavy doping effects and thereby provide both high blue response and high V sub oc ion implantation technique has been successfully applied to fabrication of both n-type and p-type emitters. V sub oc of up to 660 mV is reported and AMO efficiency of 16.1% has been obtained
Processing technology for high efficiency silicon solar cells
Recent advances in silicon solar cell processing have led to attainment of conversion efficiency approaching 20%. The basic cell design is investigated and features of greatest importance to achievement of 20% efficiency are indicated. Experiments to separately optimize high efficiency design features in test structures are discussed. The integration of these features in a high efficiency cell is examined. Ion implantation has been used to achieve optimal concentrations of emitter dopant and junction depth. The optimization reflects the trade-off between high sheet conductivity, necessary for high fill factor, and heavy doping effects, which must be minimized for high open circuit voltage. A second important aspect of the design experiments is the development of a passivation process to minimize front surface recombination velocity. The manner in which a thin SiO2 layer may be used for this purpose is indicated without increasing reflection losses, if the antireflection coating is properly designed. Details are presented of processing intended to reduce recombination at the contact/Si interface. Data on cell performance (including CZ and ribbon) and analysis of loss mechanisms are also presented
Conformal field theory correlations in the Abelian sandpile mode
We calculate all multipoint correlation functions of all local bond
modifications in the two-dimensional Abelian sandpile model, both at the
critical point, and in the model with dissipation. The set of local bond
modifications includes, as the most physically interesting case, all weakly
allowed cluster variables. The correlation functions show that all local bond
modifications have scaling dimension two, and can be written as linear
combinations of operators in the central charge -2 logarithmic conformal field
theory, in agreement with a form conjectured earlier by Mahieu and Ruelle in
Phys. Rev. E 64, 066130 (2001). We find closed form expressions for the
coefficients of the operators, and describe methods that allow their rapid
calculation. We determine the fields associated with adding or removing bonds,
both in the bulk, and along open and closed boundaries; some bond defects have
scaling dimension two, while others have scaling dimension four. We also
determine the corrections to bulk probabilities for local bond modifications
near open and closed boundaries.Comment: 13 pages, 5 figures; referee comments incorporated; Accepted by Phys.
Rev.
A flowing plasma model to describe drift waves in a cylindrical helicon discharge
A two-fluid model developed originally to describe wave oscillations in the
vacuum arc centrifuge, a cylindrical, rapidly rotating, low temperature and
confined plasma column, is applied to interpret plasma oscillations in a RF
generated linear magnetised plasma (WOMBAT), with similar density and field
strength. Compared to typical centrifuge plasmas, WOMBAT plasmas have slower
normalised rotation frequency, lower temperature and lower axial velocity.
Despite these differences, the two-fluid model provides a consistent
description of the WOMBAT plasma configuration and yields qualitative agreement
between measured and predicted wave oscillation frequencies with axial field
strength. In addition, the radial profile of the density perturbation predicted
by this model is consistent with the data. Parameter scans show that the
dispersion curve is sensitive to the axial field strength and the electron
temperature, and the dependence of oscillation frequency with electron
temperature matches the experiment. These results consolidate earlier claims
that the density and floating potential oscillations are a resistive drift
mode, driven by the density gradient. To our knowledge, this is the first
detailed physics model of flowing plasmas in the diffusion region away from the
RF source. Possible extensions to the model, including temperature
non-uniformity and magnetic field oscillations, are also discussed
Dynamics of a disordered, driven zero range process in one dimension
We study a driven zero range process which models a closed system of
attractive particles that hop with site-dependent rates and whose steady state
shows a condensation transition with increasing density. We characterise the
dynamical properties of the mass fluctuations in the steady state in one
dimension both analytically and numerically and show that the transport
properties are anomalous in certain regions of the density-disorder plane. We
also determine the form of the scaling function which describes the growth of
the condensate as a function of time, starting from a uniform density
distribution.Comment: Revtex4, 5 pages including 2 figures; Revised version; To appear in
Phys. Rev. Let
Evolution of the Dark Matter Distribution at the Galactic Center
Annihilation radiation from neutralino dark matter at the Galactic center
(GC) would be greatly enhanced if the dark matter were strongly clustered
around the supermassive black hole (SBH). The existence of a dark-matter
"spike" is made plausible by the observed, steeply-rising stellar density near
the GC SBH. Here the time-dependent equations describing gravitational
interaction of the dark matter particles with the stars are solved. Scattering
of dark matter particles by stars would substantially lower the dark matter
density near the GC SBH over 10^10 yr, due both to kinetic heating, and to
capture of dark matter particles by the SBH. This result suggests that
enhancements in the dark matter density around a SBH would be modest whether or
not the host galaxy had experienced the scouring effects of a binary SBH.Comment: 5 pages, 3 figures. Submitted to Physical Review Letter
Electron Temperature of Ultracold Plasmas
We study the evolution of ultracold plasmas by measuring the electron
temperature. Shortly after plasma formation, competition between heating and
cooling mechanisms drives the electron temperature to a value within a narrow
range regardless of the initial energy imparted to the electrons. In agreement
with theory predictions, plasmas exhibit values of the Coulomb coupling
parameter less than 1.Comment: 4 pages, plus four figure
Suppression of energetic electron transport in flares by double layers
During flares and coronal mass ejections, energetic electrons from coronal
sources typically have very long lifetimes compared to the transit times across
the systems, suggesting confinement in the source region. Particle-in-cell
simulations are carried out to explore the mechanisms of energetic electron
transport from the corona to the chromosphere and possible confinement. We set
up an initial system of pre-accelerated hot electrons in contact with ambient
cold electrons along the local magnetic field, and let it evolve over time.
Suppression of transport by a nonlinear, highly localized electrostatic
electric field (in the form of a double layer) is observed after a short phase
of free-streaming by hot electrons. The double layer (DL) emerges at the
contact of the two electron populations. It is driven by an ion-electron
streaming instability due to the drift of the back-streaming return current
electrons interacting with the ions. The DL grows over time and supports a
significant drop in temperature and hence reduces heat flux between the two
regions that is sustained for the duration of the simulation. This study shows
transport suppression begins when the energetic electrons start to propagate
away from a coronal acceleration site. It also implies confinement of energetic
electrons with kinetic energies less than the electrostatic energy of the DL
for the DL lifetime, which is much longer than the electron transit time
through the source region
Information-theoretic determination of ponderomotive forces
From the equilibrium condition applied to an isolated
thermodynamic system of electrically charged particles and the fundamental
equation of thermodynamics () subject
to a new procedure, it is obtained the Lorentz's force together with
non-inertial terms of mechanical nature. Other well known ponderomotive forces,
like the Stern-Gerlach's force and a force term related to the Einstein-de
Haas's effect are also obtained. In addition, a new force term appears,
possibly related to a change in weight when a system of charged particles is
accelerated.Comment: 10 page
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