Project CEEX: 2-CEx
06-11-7/25.07.2006
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RESEARCHES ON ENERGY TRANSFER
FROM THE PLASMA
TO THE RADIOFREQUENCY
ELECTROMAGNETIC FIELD
IN ELECTRICAL
GAS DISCHARGES
(PRET)
01/08/2006-30/09/2008
Thematic
fields: 11 Basic sciences
Technological platform: PT-11
Director,
Dr. Ovidiu Stoican
Contact:
e-mail: stoican@infim.ro
Tel: +40 (0)722308214
Affiliation:
National
Institute for Plasma, Lasers, Plasma Physics (INFLPR)
ATOMISTILOR Str. Nr. 409,
P.O.Box: MG-36, 077125
Tel: +40 1 457 44 89
Fax: +40 1 457 42 43
Organizations involved:
1.
National Institute for Plasma, Lasers,
Plasma
Physics (INFLPR) - Coordinator
2. University of
Bucharest
3.
University of Pitesti
4.
Horia Hulubei-National Institute of
Physics and
Nuclear Engineering (IFIN-HH)
PROJECT OBJECTIVE
The study of the energy transfer between a low temperature electrical gas discharge plasma and an external electromagnetic field.
Schedule:
01.08.2006-15.12.2006 Realization of the experimental setup aimed to study interaction the RF field-glow discharge plasma .
01.01.2006-30.07.2007 Systematic experimental studies on the interaction plasma- RF and microwave field.
01.07.2007-30.10.2007 Theoretical and experimental studies regarding the effect of the excitation electromagnetic field on plasma.
01.11.2007-01.03.2008 Studies on the global efficiency of the plasma-RF field energy transfer.
02.03.2008-30.07.2008 Studies regarding effect of the RF field frequency and geometry, respectively, on the energy transfer phenomena.
01.08.2008- 30.09.2008 Theoretical studies on the plasma-RF field interaction. Systematization of the experimental data. Conclusions.
SCIENTIFIC RESULTS
The main
scientific results
obtained in the frame of INFLPR are related to the plasma antenna
technology and
to the study of plasma-RF electromagnetic field applied to the plasma
diagnose.
Plasma antenna technology represents a novel approach in the field of
the
wireless communications. Conventional antennas employ the various
structures of
metallic conductors in order to transmit or to receive RF signals. In
the case
of the plasma antennas the metallic conductors are replaced by the
ionized gas
columns. One of the advantages of a plasma antenna is related to the
operation
in the pulsed regime. Because the gas can be ionized only during the
signal transmission,
certain transient effects (e.g. “ringing) owing to rf signal switch are
avoided. This feature is interesting for various applications,
especially in
the areas of the radar technology or digital communication. Such
studies are
important in order to perform an appropriate design for the plasma
antenna
based communication systems. Two discharge tube geometries, equivalent
of a
whip antenna and a loop antenna, respectively, have been studied.
Especially,
the dc discharges have been studied. The dc electrical discharges have
advantage to be easy obtaining and switching on/off. The researches
regarding
plasma antennas had three main objectives, namely, RF pulses forming,
study of
RF radiation due to the discharge switch and the effect of the
excitation
circuit on the plasma properties. Additionally, variations of the gain
and VSWR
for various experimental conditions have been measured. A simple, cheap
and
reliable method to obtain RF pulses is by inserting the discharge tube
in a
relaxation oscillator circuit. Thus, discharge tube operates
simultaneously as
plasma antenna, dc voltage switch and RF switch. Consequently, the RF
current
pulses carried by dc electrical discharge are generated without to use
high
voltage rated semiconductor devices. In the frame of the project, in
order to
improve RF pulses control, several relaxation oscillator topologies
have been
considered. Certain applications require the existence of two antennas,
one
operating as transmitter while the other operating as receiver for RF
pulses.
During transmission the receiver antenna operation must be inhibited.
For this
kind of applications a circuit topology based on relaxation oscillator
principle have been developed. The circuit contains two discharge tubes
acting
as transmitter and receiver antenna, respectively, being equivalent to
an
astable circuit. One disadvantage is that the shape of RF pulse is very
difficult to be controlled. The method is useful for the applications
where the
shape of the RF pulses is not critical. Another way to obtain RF pulses
is to
supply electrical discharge tube using a self oscillating flyback
converter.
The operating point of a flyback converter is self-adjusting so that
the output
voltage is matched to the operating regime of the discharge and no
ballast
resistor is necessary. This device can be also used in order to detect
the
discharge changes. It is known that electrical parameters of a self
oscillating
flyback converter (supply current, duty cycle, operating frequency)
depend on
the electrical characteristics of the load. By monitoring these
parameters the
variation of the discharge electrical characteristics can be detected.
Another
effect studied was the influence of the excitation RF field on the dc
discharge
properties. It was investigated the drift of a discharge tube
relaxation
oscillator period placed in a low intensity microwave field. A
significant
variation of the relaxation oscillator period has been observed. The
experiments led to the conclusion that even RF fields much smaller than
dc
field can modify the discharge breakdown voltage. A simple method to
detect the
microwave fields using discharge tube represents a side application of
this
work. To be equal to performance the ionized gas acting as plasma
antenna must
exhibit the same properties as a metallic conductor, e.g. an uniform
electrical
conductivity. To obtain homogenous plasma it is necessary to employ
special
electrodes configurations. On the other hand it is known that in
certain conditions
electrical discharge plasma can radiate RF energy. The experimental
study on
the RF field characteristics due to the short current pulses flowing
through a
hollow cathode discharge tube has been performed. It has been
demonstrated that
such as electrical discharge act as RF signal sources. Experiments
shown that
RF field consists of a train of RF pulses associated to each current
pulse
through the discharge tube. The waveform of the voltage corresponding
to these
pulses is similar to that of an underdamped harmonic oscillation in a
coupled
inductive circuit. Several frequency peaks were found in the spectrum
of the
perturbation generated by the electrical discharge. The spectrum of
such kind
of perturbation has been acquired. As a rule only the region of the dc
electrical discharge called positive column is appropriate to be used
as a
conductive element in a plasma antenna. The positive column is
characterized by
a high and spatial homogeneous electrical conductivity and also by a
space
charge equal to zero, similar to the metallic conductors. Most of
experimental
arrangements employ metallic sleeves in order to perform RF excitation
of a
plasma antenna. These sleeves slide along the discharge tube in order
to be
positioned over the positive column. Usually, to obtain a good coupling
between
RF excitation signal and plasma column, the two sleeves have a large
surface
being similar to a capacitor armature. Because at low frequencies the
RF
excitation circuit is equivalent to a short cut to the ground, it was
evaluated
the RF excitation circuit effect on the characteristics of the
discharge
plasma. The modifications of the plasma properties when the external
electrode
is connected to the ground are evidenced. The effect was detected using
a
relaxation oscillator circuit. The oscillations frequency for various
operating
conditions has been measured. The external electrode induces a
significant
drift of the oscillation frequency. Based on this experimental
observation a
method to switch a plasma antenna has been proposed. The study of the
RF
field-plasma interaction represents an important tool for plasma
diagnosis. A
simple and practical method aimed to investigate the spatial
distribution of
the RF field absorption by a plasma column in a wide frequency band has
been
developed. The method is based on the measurement of the amplitude
variation of
the RF field harmonics components due to the presence of a plasma
volume. As a
signal source is used a noise generator which generates a broadband RF
field.
The effect of the plasma on the RF field amplitude at different
frequencies for
various experimental conditions is observed by means of a spectrum
analyzer.
Compared to a RF sweep generator the noise generator is able to deliver
a
signal containing simultaneously all harmonics components. The RF sweep
generator output has a well defined frequency, varying in time. This
method has
been tested using a dc electrical discharge as a plasma source. A
modified
version of the experimental setup intended to investigate the
excitation of the
RF harmonics in plasmas was performed. The major experimental results
are
summarized as follows: observation of the presence of RF absorption
dips,
variations of RF absorption dips as a function on discharge region and
effect
of the external supply circuit on the RF absorption dips magnitude.
During project progress it was necessary to build certain equipments
and
devices related to the applied electronics field which cannot be
acquired from
commercial providers. The most important were: various gate dip meter
and
autodyne circuits, system for the RF pulses frequency measurement,
system based
on optical and laser beams used to isolate galvanically the various
equipment
stages, high voltage power supplies. In order to explain some of
experimental
results, the team belonging with IFIN-HH performed theoretical studies
regarding wave propagation through inhomogeneous media. An approximate
method
was devised for estimating scalar waves diffracted on various
obstacles. The
method can be applied to a semi-infinite circular pipe, a small
aperture in an
infinite screen and a semi-infinite plane screen. The method is based
upon
approximating the effect of the boundary conditions with surface
distribution
of sources. A theoretical model based on the investigation of an
analogy
between magnetic field and fluids equations has been also achieved. The
researches focused on the Helmholtz vorticial solution which has been
expressed
using a given vorticial the analogy between the electromagnetism
equations
which provide magnetic field distribution as a function of currents
distributions (Biot-Savart and Ampere laws) and vorticial motions of a
fluid
has been deeply studied. At
At
PAPERS
International conferences:
O. S. Stoican, Characteristics of a marginal oscillator in the stabilized frequency regime, 6th International Conference of the Balkan Physical Union-BPU-6, August 22-26, 2006, Istanbul, Turkey, Book of Abstracts, p.1203 (19-P-03).
O. S. Stoican, Feedback loop circuit of a programmable current source using a laser diode, The International Conference on Industrial Applications of Lasers, INDLAS 2007, May, 23-25,2007, Bran, Romania, Programme, p.14.
B. Oprescu, S. Anghel, S. Fianu, Two Channels of Self-Organization of Ionized Gaseous Media, The International Conference on Industrial Applications of Lasers, INDLAS 2007, May, 23-25,2007, Bran, Romania, Programme, p11
O. S. Stoican, Frequency shift of
a relaxation oscillator due to an external electrode, 8th
International Workshop on Applied Physics, IBWAP, July 5-7, 2007,
O. S. Stoican,
Study of a
switched dc electrical discharge operating as plasma antenna, 18th
International Conference on Phenomena in Ionized Gases, ICPIG 2007,
July 15-20,
2007,
O.
S. Stoican, Study
of a dc glow discharge supplied by a flyback converter, 6th
International Conference of the Balkan Physical Union-BPU-6, August
22-26,
2006,
O. S. Stoican,
Gate dip oscillator circuit used for
plasma diagnosis, 19th Europhysics Conference on
the
Atomic and Molecular Physics of Ionized Gases (ESCAMPIG-19),
O.S. Stoican, The period variation of a relaxation oscillator due to a low intensity microwave field, 35th IEEE International Conference on Plasma Science, June 15 - 19, 2008 (ICOPS2008) Karlsruhe, Germany.
O.S. Stoican, Study of the plasma rf absorption
using a noise generator, 35th European Physical Society
Conference on Plasma Physics (EPS35) Hersonissos Crete
B. Oprescu, S. Fianu, D. Giosanu, Two Channels of Self-Organization of Ionized Gaseous Media, 23rd Symposium on Plasma Physics and Technology (SPPT2008), June,16-19 2008, Praga.
O. S. Stoican, Study of rf perturbations due to a
hollow-cathode discharge, 9th International Workshop on
Applied
Physics, IBWAP, July 7-9, 2008,
O.
S. Stoican, Effect
of an external electrode on the characteristics of a low frequency
discharge,
14th International Congress on Plasma Physics ICPP2008,
September
8-12, 2008,
Proposed patent:
O. S. Stoican, Metodă şi circuit pentru emisia si recepţia undelor electromagnetice sub formă de pulsuri folosind tuburi de descărcare alimentate īn curent continuu, brevet depus la OSIM pe data de 19.10.2007.
Journals:
M. Apostol, Fluids, Fluid Vortices and the Theory of electricity and Magnetism, Journal of Theoretical Physics, 8, 135 (2007).
O. S. Stoican, L. C. Dinca, G. Visan, S. Radan, Acoustic detection of the parametrical resonance effect for a one-component microplasma, JOAM,10, 1988 (2008)
O. S. Stoican, Period shift of a discharge tube relaxation oscillator due to a weak microwave field, Jpn. J. Appl. Phys., 48, 070218 (2009)
O. S. Stoican, Frequency shift of a relaxation oscillator due to an external electrode, Rom. Journ. Phys., 54, 385 (2009)
O. S. Stoican, Effect
of an external electrode on the characteristics of a low frequency
discharge,
J. Plasma Fusion Res. Series, 8, 804 (2009)
O. S. Stoican, Frequency measurement of a pulsed rf oscillator, sent to Romanian Reports in Physics
O. S. Stoican, Study of rf perturbations due to a hollow-cathode discharge, sent to Romanian Journal of Physics
M. Apostol, On some diffraction problems for a scalar wave, Journal of Theoretical Physics, jan 2008, 162.