1Beam & Plasma Technologies Inc., 328 Bingham Circle, Mundelein, IL ... 3Robert Morris College, 1507 South Waukegan Road, Waukegan, IL 60085, USA.
THE NANOSECOND GENERATORS OF AIR PLASMA S. Korenev1, V. Efanov2, I. Korenev3 1
Beam & Plasma Technologies Inc., 328 Bingham Circle, Mundelein, IL 60060, USA 2 FID GmbH, 28 Carl-Benz-Strasse, D-57299, Burbach, Germany 3 Robert Morris College, 1507 South Waukegan Road, Waukegan, IL 60085, USA
Abstract The new nanosecond pulsed air plasma generators with nanosecond pulsed high voltage generators on the basis of new type of semiconductor switch Fast Ionization Device (FID) with high repetition are considered in the paper. This type of switches leads to design of compact high voltage nanosecond generators with short pulse rise on the level of few nanosecond and high repetition. The experimental results of generation for air nanosecond plasma with pulsed high voltage generators on the basis of combined capacitor-induction storage energy are given in this report. The two pulsed generators with pulse duration about 10 nsec and time rise of pulse about 1 nsec were used for generation of air plasma. The voltage was regulated from 5 to till 60 kV. The repetition was changed from 0.01- 10 kHz. The design of pulsed air plasma generators with applications is considered.
II. CONCEPT OF PULSED PLASMA GENERATOR The main concept of suggested air plasma generator consists in the forming of plasma by electrical discharges with nanosecond pulsed high voltage generator and high repetition. The main concept of pulsed high voltage generator consists in the using of combined capacitorinductor (C-L) energy storage with solid state closing and opening switches. The physical characteristics of these solid state switches allows to form the nanoseconds voltage pulses with nanosecond rise front and high repetition. Closing switches (Fast Ionization Devices (FID)) and opening switches (Drift Recovery Diodes (DRD)) are used as the main switches in the pulsed high voltage generators. Both switches are produced by FID GmbH. The diagram of plasma generator is given in Figure1. SWITCHES
I. INTRODUCTION Air plasma generators found large number of applications in the industry and research [1]. These generators also use for produce of ozone and free radicals for plasma chemistry processes. In spite on the progress in the technology and engineering of plasma generation, the problem of effective air plasma generator has place. So, the new approaches for air plasma generators are very important. The typical air plasma generator consists of pulsed high voltage generator and discharge unit. The type of pulsed high voltage generator is very critical, especially for nanosecond pulse duration. The typical electrical circuit for high voltage generator presents the capacitor storage energy and switch. The hydrogen thyratrons or gas sparks typically use as switches for nanosecond pulsed generators [2]. However, the progress with solid state switches, such as a FID [3], allows considering this type of switches for high voltage generators for supply of discharge unit of plasma generator. The nanosecond generators of air plasma with high repetition are considered in the paper. 0-7803-9189-6/05/$20.00 ©2005 IEEE.
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Figure 1. The diagram of plasma generator. The three types of electrical discharge we use for generation of plasma: • corona discharge; • glow discharge; • barrier dielectric discharge. The generation of air plasma realizes in the glow and barrier dielectric discharges between 2 electrodes in the air or flow air. The corona discharge forms on the pin electrodes. The flow air plasma has gas line connected with dry air cylinder. The wet air plasma forms in wet air, 860
which produces by ultrasound evaporator with heating or heating evaporation of water.
III. DESIGN OF PLASMA GENERATORS
SWITCH
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The few nanosecond plasma generators were designed with plasma discharge panel and flow air plasma nozzles. The design of plasma panel determines by applications of plasma generator. The panel with corona discharge uses for produce of ozone and free radicals. The example the electrical circuit of such plasma generator is presented in Figure 2.
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Figure 4. The glow plasma generator.
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The nozzle electrical discharge uses for local surface treatment and sterilization. The examples of these systems are given in Figure 5 and Figure 6.
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Figure 2. The plasma generator with corona discharge. FLANGE
The plasma generator panel with barrier dielectric discharge panel is given in Figure 3. The new approach consists in the using of metal grid on the surface of dielectric. The detail consideration of this system for plasma cathode is given in [4].
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Figure 5. The nozzle plasma generator.
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Figure 3. The plasma generator with barrier dielectric discharge.
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The plasma generator with pin electrodes discharge unit for forming of glow discharge between 2 electrodes is presented in Figure 4. This plasma generator uses for surface etching and surface sterilization.
GAS FLOW CABLE POLYMER INSULATOR
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Figure 6. The flow nozzle plasma generator. The ground electrode can be same with pipe, which connected with fitting connector (Figure 6). In the case of plastic (dielectric) pipe we have automatically barrier dielectric discharge system. The two pulsed high voltage generators for supply of plasma discharge units produced by FID GmbH. The voltage regulates from 5 to till 60 kV for generator. The voltage is 16 kV in the second generator. The rise time in the both generators is about 1nsec. The pulse duration is about 10 nsec and repetition was regulated from 0.01-10 kHz. The discharge unit has cable connection with generator. The photograph of one generator is shown in Figure 7.
30 nsec and pulse duration was about 10 microseconds. The repetition was 1-100 Hz. Polarity of voltage was negative. HIGH VOLTAGE POWER SUPPLY
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Figure 8. The plasma generator. HIGH VOLTAGE POWER SUPPLY
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Figure 7. The nanosecond pulsed generator manufacturing by FID GmbH.
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IV. EXPERIMENT
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The main goal of experiments is study of generation for air plasma with nanosecond pulsed generators on the basis of combined capacitor-induction storage energy (C-L) with closing and opening semiconductor switches. The pulsed high voltage generator with hydrogen thyratron and gas spark was used for comparison. The electrical circuits of plasma devices with this generator are given in Figure 8 and Figure 9. The HVD is high voltage divider of voltage for measurement of voltage. The electrical circuit of discharge unit with pin electrodes and L-C generator is presented in Figure 10. The picture of pin electrodes with current reducing resistors is presented in Figure 11. The plasma with pin electrode according Figure 8 presents the multi-points discharge (see Figure 12). The using of current reducing resistors in the circuits of pin electrodes leads to forming homogeneous discharge for dissipated of energy density about 0.001-0.007 J/cm2. The increasing of energy density leads to multi-points discharge from pin electrodes. The two current transformers in the circuits allow to correct understand the level of dissipated energy in the discharge. The rise time for hydrogen thyratron in our experiments was about 25-
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Figure 9. The plasma generator with current reducing resistors in pin electrodes. SWITCH
HVD
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Figure10. The plasma generator.
Figure14. The waveform on pin electrodes for corona discharge with reflection. Figure11. The pin electrodes discharge panel.
Figure 12. The picture of light of plasma in cross section. The using of L-C high voltage generators for supply of plasma units leads to homogenous plasma in cross section. The explanation of this effect consists in the nanosecond pulse duration and short rise front. The time of forming for discharge is short in compared with forming of streamer or spark discharge. The plasma parameter, such as a temperature of plasma electrons is low in compared for discharge with microsecond generator and 25- 30 nsec of rise time. The semiconductors have high repetition and maximum repetition for described plasma generators is 10 kHz. The voltage waveform of generator with pin electrodes (Figure 10) is presented in Figure 13. The voltage waveform with pin electrodes for corona discharge (Figure 2) is given in Figure 14.
The few nanoseconds pulse duration allows solving these problems. The time characteristics for current discharge are stable for 100% humanity of wet air. The efficiency of produce for ozone is same for dry and for wet air. The plasma has homogeneous structure in cross section (see Figure15).
Figure 15. The picture of light of plasma in cross section.
V. CONCLUSIONS The main conclusions are following: 1. The nanosecond range of pulse duration and rise time for voltage allows forming the stable and homogeneous plasma in dry and wet air. 2. The nanosecond pulsed generators on the basis of combined C-L storage energies with fast ionization devices as switches are acceptable for plasma generators with high efficiency and high repetition. 3. The few variants for design of nanosecond plasma generators were considered. 4. The applications of these high repetition plasma nanosecond generators are very broad: plasma-chemistry, semiconductors, materials, environmental, medical and etc.
VI. REFERENCES
Figure 13. The waveform of voltage on the pin electrodes discharge panel for glow discharge. The non-stability of discharge for wet air was observed for thyratron generator. The variation of time delay between voltage and current discharge was 60-200 nsec on dependence of humanity. The concentration of ozone decreases to 40-75% for 100% humanity of wet air.
[1] J.R. Roth. Industrial Plasma Engineering, AOP, 2001. [2] G.A. Mesyatc. Generation of nanosecond pulses. Sovetskoe Radio, Moscow, 1974. [3] V.M. Efanov, et. al. “Fast ionization dynistors (FID) – a new semiconductor superpower closing switch”. Proc. XI IEEE International Pulsed Power Conference, pp. 988991, 1997. [4] S A. Korenev. "The forming of electron beams in the high current diode". Communication of JINR No: 9-81573, JINR, Dubna, 1981. 863
