Modeling a plasma photoelectric converter of the focused optical radiation.

Nikolay A. Gorbunov and Aleksei Kopitov
Physics Institute of St.-Petersburg State University, Ulianovskaya 1, 198904 St.-Petersburg, Russia (e-mail:
gorbunov@paloma.spbu.ru)
Abstract. A model is considered of the plasma photoelectric converter, which can be designed on the basis of a heat pipe
filled with alkali metal vapor and buffer inert gas. The efficiency of direct transformation of the focused light into electricity
is estimated.
Keywords: Photoplasma, Photovoltaic effect.
PACS: 84.60.Jt, 52.65.-y.
Conversion of the concentrated solar radiation is an effective
means of reducing the photoelectricity production
costs. Studies of the feasibility of using an ambipolar field
in photoplasma for direct conversion of focused light radiation
into electricity were initiated in [1, 2]. In these
works a photovoltaic (PV) effect in sodium vapor photoplasma
has been observed. The resonance laser radiation
was used to produce photoplasma. High photo EMF values
in one converting plasma cell (about 4 Volts) were
demonstrated that are unachievable with other technologies.
The intensified values of EMF resulted from high
values of the electron temperatures achieved in the photoresonant
plasma [3]. It has been shown that photo-EMF
was generated at a nonuniform ionization of the vapor inside
a plasma volume [4]. Conversion efficiency of light
to electricity in the range 15-30 % was estimated in alkali
plasma [5].
Development of a plasma photovoltaic cell may be
considered as a new plasma application to renewable solutions.
The starting point in the development of a plasma
photoelectric converter can be the heat pipe [2]. This device
makes it possible to maintain constant and stable alkali
metal vapor density over a closed cycle comprising
evaporation, condensation and the return of the condensate
to the evaporation zone as a result of surface tension
forces. The alkali vapor is confined by inert gas, which
eliminates the destructive effect of the vapors on optical
windows. The existence of spatially separated zones of
alkali vapors and the buffer gas is also affecting the diffusion
of charged particles. As an alkali ion is transiting
from the alkali vapor zone to the buffer gas zone a significant
rise of the diffusion coefficient takes place.
A model of photovoltaic effect in alkali photoplasma
under the action of the focused optical radiation is considered.
A configuration with plane electrodes, which is the
simplest from the standpoint of describing the ambipolar
field in plasma, is analyzed. Current-voltage characteristics
and the output power are calculated as a function of
a set of parameters (the spot position, the mixture composition)
describing the converter operating regimes. A
model of photoplasma under diffusion conditions is developed.
Estimations of the energy losses in the photoelectric
converter are obtained. The influence of plasma
parameters on the efficiency of direct transformation of
light into electricity is analyzed. It is shown that the spatial
separation of the alkali vapors and the buffer gas
over the converter volume occurring in the heat pipe enhances
the conversion efficiency significantly. Thus, spatial
nonuniformities (as in the case of p-n junctions or heterostructures
in semiconductor photoconverters) are just
the means to achieve the maximum conversion efficiency
of the plasma photoelectric converter.
REFERENCES
1. Gorbunov N. A., and Stacewicz T., Tech. Phys. Lett., 26, 654 (2000).
2. Gorbunov N. A., and Stacewicz T., High Temperature , 39, 623 (2001).
3. Gorbunov N. A., Grochola A., Kruk P., Pietruczuk A., Stacewicz T., Plasma Sources Sci and Techn., 11, 492 (2002).
4. Gorbunov N. A., and Flamant G., Tech. Phys., 49, 1491 (2004).
5. Gorbunov N. A., Stepanov S. V., and Flamant G., IEEE Trans. Plasma Sci., 33, 1346 (2005).

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