Relation between plasma plume charge and length in atmospheric pressure plasma

We present atmospheric pressure plasma generated using a quartz tube, helium gas, and copper foil electrode by applying a radio frequency high voltage. The atmospheric pressure plasma in the form of a bullet is released as a plume into the atmosphere. To study the formation of the plasma plume, the dependences of the plasma plume charge and the plasma plume length on the gas flow rate are examined. In a quartz tube with inner diameter 1.5 mm, which has more helium than air in the cross section of the flow channel, the distributions of the length and charge on the gas flow rate show similar tendencies. Consequently, when more helium gas is present than air, the travel length of the plasma plume correlates with the plasma plume charge. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Anode attachment and received heat of argon torch plasma with high lateral airflow as function of current

The torch plasma arc has useful characteristics of high energy and high current. The mode of torch plasma arcs can be flexible, even if the arc is exposed to the lateral gas. In this paper, we measured the input power, heat power, and heat efficiency of the torch plasma arc to the anode in order to determine the current effect on the anode attachment of plasma torch arc with high lateral air velocity, varying from 0 to 80 m/s at a plasma Ar flow rate of 12 slm. As a result, the input power increases with lateral gas velocity such as from about 8000 W to 16,000 W and the heat efficiency decreases with the lateral gas velocity such as from about 50% to 25% at the current I=150 A and appearance plasma length L_a=1 cm. These results could be applied to providing the electrical power from the ground to high‐speed mobiles, v.v., and to reducing an anode surface erosion by the anode spot movement. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(2): 29–35, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20479     

Novel development of an inductively coupled thermal plasma with pulse amplitude modulation of electromagnetic field

A novel system of an inductively coupled thermal plasma with a fundamental frequency of 450 kHz has been developed. This system has a capability of modulating the amplitude of the coil current periodically with a cycle on the order of 10 ms, including an inverter power supply rated with a power of 50 kW, an induction plasma torch with a 10‐turn coil, and vacuum chamber. The controlled modulation of the coil current can lead the plasma to be under various transient states intentionally. A pulse‐modulated inductively coupled plasma of Ar‐H₂ plasma was successfully generated at a plasma power of 30 kW under the atmospheric pressure condition. The on‐time and off‐time of the pulsation were set to 10 and 5 ms, respectively, for a stable pulse‐modulated plasma establishment, and the ratio of minimum to maximum of the amplitude of the coil current can be set down to 61.7%. In order to investigate the transient behavior of the plasma dynamics in such a pulsing mode, spectroscopic observations of an argon atomic spectral line at a wavelength of 751 nm were made. It was found that the pulse‐modulated plasma has a characteristic time on the order of 2 to 5 ms to rise or to decrease. The excitation temperature of the Ar atom was estimated from the spectroscopic measurement by the Boltzmann plot method, and it was found to change periodically from 5000 to 10,000 K with the pulse modulation of the amplitude of the coil current. © 2002 Scripta Technica, Electr Eng Jpn, 138(4): 26–33, 2002; DOI 10.1002/eej.1135     

Studies of the mechanism of boron nitride thin-film formation by means of nitrogen-argon gas mixture plasma jet

The mechanism of boron nitride thin-film formation using the nitrogen-argon gas mixture plasma jet, which is a new method reported in our previous paper, has been studied. The electron temperature, electron density, and magnitudes of various ion and radical species in the plasma jet have been measured by an electrostatic probe and by optical spectroscopic methods. The amount of recombination of free nitrogen atoms by three-body conversion was estimated using the emission intensity of the first positive band system from nitrogen B state vibrational level v = 11. The emission intensity from vibrational level v = 11 in the vicinity of the boron target shows a more than one order of magnitude increase than when the boron target is absent, and the peak value occurs at a gas pressure of approximately 5 Torr to 10 Torr. Experimental data are discussed in connection with the optimum discharge condition of BN synthesis in the plasma. It is concluded that enhanced recombination on the boron target and substrate surface supplies large amounts of molecular nitrogen ions and vibrationally excited nitrogen molecules in the vicinity of the substrate, and thus that the high-energy ion-rich condition makes it possible to form a cubic BN film on the substrate surface placed in the plasma jet. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(4): 1–6, 1997     

Comparative study of electron density profiles in compact torus plasma merging experiments

Following two previous papers on comparative studies of the electron density distributions for a single compact torus (CT) and a spherical tokamak (ST), and for a single ST and a merged ST, a comparative study on the dynamics of the electron density profile during and after the CT and ST plasma merging process was performed. The sharpness of the peak in the electron density profile around the midplane just after the merging of CT with a low safety factor (q value) such as RFP or spheromak is found to be related to the speed of the magnetic axis during the plasma merging process. It is also found that the electron density gradient near the plasma edge in a high‐q ST is larger than that of a low‐q CT. High‐q ST is found to have a magnetic structure which is able to sustain a large thermal pressure by a strong j × B force. Despite these differences in the electron density profile between CT and ST during merging, the confinement characteristics evaluated from the number of electrons confined within the magnetic separatrix after the completion of the merging are almost similar between the merging CT and the merging ST. For all configurations, the electron density profiles after the completion of the merging are analogous to those of the corresponding single configuration produced without the merging process. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 14–21, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10312     

Inactivation property of microorganisms in water irradiated by atmospheric‐pressure plasma using dielectric barrier discharge

Microorganisms in water were inactivated by irradiating with an atmospheric‐pressure plasma generated by a dielectric barrier discharge. To understand the inactivation mechanism of microorganisms, the actions due to irradiation with plasma discharge, heating, and chemical reaction are studied. We compare the buffer gases helium and argon in generating the atmospheric‐pressure plasma. The results indicate that the inactivation with the helium as buffer gas is higher than with argon. It is found that the inactivation ratio at different reactor volumes depends on the density of microorganisms in water. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Neutron production rate and plasma characteristics of spherically convergent beam fusion

Experimental and simulation results of a spherical glow discharge for a portable neutron source are presented. The experimental device is a 45‐cm‐diameter, 31‐cm‐high stainless‐steel cylindrical chamber, in which a spherical mesh‐type anode 30 cm in diameter is installed. The spherical grid cathode consists of 2.0‐mm‐diameter stainless‐steel wire, which is made into an open spherical grid of 5‐cm diameter. The system is maintained at a constant pressure of 1 to 15 mTorr by feeding hydrogen or deuterium gas. The basic characteristics of breakdown voltages versus pressure and electrostatic potential profiles were measured for hydrogen discharge. Using deuterium, a steady‐state neutron production of 10⁴ s^–1 was observed at a discharge of 40 kV, 2 mA. Motions of ions and electrons in the device were simulated by using a particle code, which is one‐dimensional in coordinate system and two‐dimensional in velocity space. It was confirmed by both the measurement and simulation that a virtual anode is formed in the central part inside the grid cathode. © 2001 Scripta Technica, Electr Eng Jpn, 135(2): 1–8, 2001     

Three‐dimensional numerical analysis on discharge properties of microwave excited ring dielectric line surface wave processing plasma device

A three‐dimensional simulation code with the finite difference time domain (FDTD) method combined with the electron fluid model has been developed for the microwave excited surface wave plasma in the RDL‐SWP device. This code permits the three‐dimensional numerical analysis of the spatial distributions of electric field, power absorption, electron density, and electron temperature. At a low gas pressure (about 10 mTorr), the numerical results were compared with the experimental measurements that show the validity of this 3D simulation code. A simplified analysis assuming that the electron density is spatially uniform has also been studied and its applicability is evaluated by the comparison of the 3D simulation and the analytical solutions. The surface wave eigenmodes are determined by the electron density, and it is found that the structure of the device strongly influences the spatial distribution of the electric fields of surface waves in a low‐density area (n_e < 3.0 × 10¹¹ cm^?3). A method to irradiate by microwave the whole surface area of the plasma is proposed. The method is found to be effective in obtaining a high uniformity distribution of electron density. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 150(4): 1–12, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10333     

Deuterium atomic density estimation in recombining plasmas using self‐absorption spectroscopy

Deuterium atomic density in the divertor region of fusion reactors is an important parameter. In this study, atomic density is estimated in the divertor simulator NAGDIS‐T by use of an absorption effect of Lyman‐β, of which the wavelength is in the vacuum ultraviolet (VUV). The calibration of the spectrometer in the VUV wavelength was performed by using a branching ratio method. The intensity ratio of Lyman‐β to Balmer‐α significantly decreased in detached plasmas because of radiation trapping. The atomic density was estimated by use of self‐absorption effect. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Characteristic measurement of discharge current injected by the air discharge of an ESD gun onto a ground

An immunity testing method for electrostatic discharge (ESD) is being specified in IEC 61000‐4‐2, in which the contact discharge of an ESD gun is being normally specified. Air discharge testing is known to be a severe immunity test compared to contact discharge testing, while the discharge current injected is not well reproduced. Grasping the behavior of the current injected by the air discharge would be helpful in establishing the worst‐case ESD immunity testing. We previously measured the discharge currents for air discharge testing onto the IEC‐recommended current transducer with a commercially available ESD gun, and showed that there exists a specific relationship of Ip·tr^ξ/V_c=constant (ξ=0.75), between rise time tr and current peak Ip. The current transducer, however, has a frequency‐dependent transfer impedance which should affect the measured current waveform. In this study, we investigated whether the above‐mentioned specific relationship can be obtained for air discharge of an ESD gun onto a ground that assumes a metal enclosure of electronic equipment under test. A method was presented for estimating the discharge current from simultaneously measured magnetic fields with two magnetic field probes regardless of the distance between the gun discharge‐point and the probe position. This method was validated for contact discharge of an ESD gun to an SMA connector. With this method, we estimated the discharge currents injected onto a ground for air discharge testing of an ESD gun with intentionally fast and slow approaches. As a result, we could confirm a specific relationship between rise time tr and current peak Ip of Ip·tr^ξ/V_c=constant with ξ=0.57 independent of charge voltages and gun approaches. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 51– 59, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20454     

Measurements of electron density profile characteristics in various kinds of plasma configurations in the TS‐3 plasma merging device

Measurements and a comparative study have been performed on electron density profiles, focusing on the electron density gradient near the magnetic separatrix in various kinds of plasma confinements such as the ST, spheromak, and RFP in the TS‐3 device. A CO₂ laser interferometer using a glass tube to clear the path for the laser was introduced in order to measure the electron density profile with time resolution. It was shown that ST with a high q value at the plasma edge (q: safety factor) has a larger electron density gradient than low‐q plasma confinements such as the spheromak and RFP. In particular, the ST with edge q value greater than about 2 showed a large electron density gradient at the edge. The idea that the j × B force profile of the higher‐q ST could sustain the higher thermal pressure supports these results. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(2): 35–41, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10158     

Oxygen radical density measurement in O2–N2 gas mixture plasma by means of a thin platinum wire

The oxygen radical density was measured in a weakly ionized plasma in an O₂–N₂ gas mixture by using a simple platinum thin‐wire sensor. The increased temperatures of the platinum wire caused by the energy released in the recombination of two oxygen radicals on the platinum surface were measured by varying the nitrogen gas mixture ratio and were compared with the oxygen radical densities theoretically calculated under the same plasma conditions. The relation between the wire temperature and the oxygen radical densities was cross‐checked by quantitative measurement of oxygen radical densities with a quadrupole mass spectrometer. All of these results made it possible to determine the oxygen radical density experimentally from the platinum wire temperature alone. The influence of the ambient gas temperature on the radical density measurement is also discussed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(4): 14–20, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20018     

Application of atmospheric pressure plasma polishing method in machining of silicon ultra-smooth surfaces

The modern optics industry demands rigorous surface quality with minimum defects, which presents challenges to optics machining technologies. There are always certain defects on the final surfaces of the components formed in conventional contacting machining processes, such as micro-cracks, lattice disturbances, etc. It is especially serious for hard-brittle functional materials, such as crystals, glass and ceramics because of their special characteristics. To solve these problems, the atmospheric pressure plasma polishing (APPP) method is developed. It utilizes chemical reactions between reactive plasma and surface atoms to perform atom-scale material removal. Since the machining process is chemical in nature, APPP avoids the surface/subsurface defects mentioned above. As the key component, a capacitance coupled radio-frequency plasma torch is first introduced. In initial operations, silicon wafers were machined as samples. Before applying operations, both the temperature distribution on the work-piece surface and the spatial gas diffusion in the machining process were studied qualitatively by finite element analysis. Then the following temperature measurement experiments demonstrate the formation of the temperature gradient on the wafer surface predicted by the theoretical analysis and indicated a peak temperature about 90°C in the center. By using commercialized form talysurf, the machined surface was detected and the result shows regular removal profile that corresponds well to the flow field model. Moreover, the removal profile also indicates a 32 mm³/min removal rate. By using atomic force microscopy (AFM), the surface roughness was also measured and the result demonstrates an Ra 0.6 nm surface roughness. Then the element composition of the machined surface was detected and analyzed by X-ray photoelectron spectroscopy (XPS) technology. The results also demonstrate the occurrence of the anticipated main reactions. All the experiments have proved that this atmospheric pressure plasma polishing method has the potential to achieve the manufacture of high quality optical surfaces. __________ Translated from Optics and Precision Engineering, 2007, 15(11): 1749–1755 [译自: 光学精密工程]     

Study on grounding in the vicinity of the work site on 1000-kV power transmission line. Part 2. Electromagnetic induction and its protection

In order to clarify the grounding conditions for protecting workers on a de-energized circuit from induction from a live circuit and to determine the required current capacity of the grounding conductor for a 1,000 kV double-circuit power transmission line, the phenomena caused by electromagnetic induction resulting from a live circuit are discussed. The electromagnetic induction current I_g flowing through the body of a worker and the electromagnetic induction current I_gO flowing through the grounding conductor can be analyzed by dividing the various power line conditions into three main factors, and using electromagnetic induction current calculations for a power line of infinite length. The zone where I_g does not exceed 1 mA is within 1 km of the grounding point on the de-energized circuit owing to the grounding resistance (0.1 Ω) of the substations at the ends of the line and the difference in the phase configurations on the line when the current I₁ of the live circuit is a constant 1 kA through the line. Similarly the value of I_gO is determined by the grounding resistance of the substations at the ends of the line and the difference in the phase configurations on the line. I_gO is approximately 10 A per 1 kA of I₁. The currents I_g and I_gO produced by electromagnetic induction are additive, allowing I_g and I_gO in the actual power line to be evaluated by summation.     

Dielectric properties of nanocrystalline TiO2 prepared using spark plasma sintering

Ultra fine rutile powders (below 50 nm) were prepared via the sol-gel process and bulk type TiO₂ specimens were fabricated using spark plasma sintering (SPS). The TiO₂ specimen sintered at a low temperature (720^∘C) exhibited a highly relative density (97%) and a nano-sized grain structure (200 nm). Dielectric properties of spark plasma sintered TiO₂ specimens including dielectric constants (k) and losses (tan δ) were measured. The TiO₂ specimen, obtained by SPS, showed a high dielectric constant (∼780) and a low tan δ (∼0.005), and a relaxation behavior at 1 MHz. After the subsequent annealing process of the TiO₂ specimen in O₂ flow, the dielectric constants remarkably decreased (k = 100s). These dielectric properties of nanocrystalline TiO₂ specimens prepared by SPS were discussed in terms of space charges produced by the reduction of Ti⁴⁺ ions and crystallographic orientations of grains.     

Highly elongated,low‐aspect‐ratio tokamak produced by negative‐biased theta pinch

Ultra Low Aspect Ratio Tokamaks (ULART) are produced by using a negative‐biased theta‐pinch device. A slender conducting rod which serves as a toroidal field coil is newly installed along a geometrical center axis of the theta‐pinch coil. The ULART is quickly formed for about 10 μs by applying programmed current flows from three sets of fast banks and a slow bank to these coils and is sustained for about 100 μs. The plasma diagnosed from a magnetic probe array has a low aspect ratio A = 1.1 and a poloidal surface with a high elongation ratio κ = 10. The safety factor reaches about 30 near the separatrix edge when I_p = 280 kA flows in the plasma and I_tfc = 30 kA in the conducting rod. A preliminary result on global MHD characteristics of the ULART is also given. The plasma is unstable with respect to a vertical displacement and a toroidal n = 1 mode. The amplitudes of these modes depend on the values of I_tfc and κ. © 2001 Scripta Technica, Electr Eng Jpn, 134(4): 19–27, 2001     

First plasma experiment on spherical tokamak device UTST

The UTST (University of Tokyo Spherical Tokamak) device was constructed for the purpose of exploring the formation of ultrahigh‐beta ST (spherical tokamak) plasma using the double null plasma merging method. When two plasmas merge together to form a single plasma, magnetic field lines reconnect, and magnetic field energy is converted to plasma kinetic energy, increasing the plasma beta. Merging start‐up has been demonstrated in the TS‐3/4, START, and MAST devices using coils inside the vacuum vessel, and the TS‐3 plasma obtained a 50% beta. In order to demonstrate start‐up in a more reactor‐relevant situation, UTST has all poloidal field (PF) coils outside the vacuum vessel. The first plasma experiment on the UTST was begun in December 2007. In the results, the plasma obtained 10 kA by using only the outer PF coils and a single ST was generated in the lower area (z = –0.3 to –1.0 m) close to a washer gun. This result suggests that another washer gun on the top of the UTST can allow the generation of ST in the upper area and merging start‐up by using outer PF coils. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 20–26, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21216     

Discussion on population kinetics and number densities of excited species of low‐pressure discharge nitrogen plasma

A numerical model is constructed to calculate the number densities of some excited species of nitrogen in low‐pressure discharge nitrogen plasma, together with simultaneous solution of the self‐consistent electron energy distribution function and N₂‐vibration distribution function. We consider species N₂(X), N₂(A), N₂(B), N₂(C), N₂(a), N₂(a′), N2+, N4+, N(⁴S) ande⁻. In addition to electron collisional reactions, diffusion losses and molecular relations are included. It is found that the ratio of number densities of N₂(B) and N₂(C) states can be a good measure of the electron kinetic temperature. The N₂(C) state is found to be almost in a corona equilibrium, whereas the N₂(B) state becomes mainly populated by N₂(X,v≥6) + N₂(A) reaction and depopulated by collisional relaxation by the ground‐state N₂(X) molecule. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Basic characteristics of Ar/N2 atmospheric pressure nonequilibrium microwave discharge plasma jets

To understand the mechanism of surface processing by atmospheric pressure nonequilibrium microwave discharge plasma jets of coaxial type without a resonator, we measured the vibrational and rotational temperatures in plasmas using optical emission spectroscopy. The plasma was excited by a microwave power supply, using a gas mixture of Ar and N₂ as the plasma gas, and changing the flow rate of N₂ gas. We also measured the change in the contact angle of a PET film before and after the plasma processing. It decreased as the plasma rotational temperature increased, indicating that the hydrophilicity of the PET surface was improved as the plasma rotational temperature became higher. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Measurement of flow velocity for hydrogen introduced into a wall‐stabilized argon arc

Small solid particles are usually used as tracers for the measurement of flow velocity of a fluid. In the case of a high‐temperature thermal plasma, sometimes it is difficult to use solid tracers due to the loss by vaporization caused by strong heat transfer from the plasma. If gaseous tracers could be used, it would compensate for the difficulty in using conventional solid particle tracers. To investigate the feasibility of gaseous tracers, hydrogen was used as a gaseous tracer for flow velocity measurement of a well‐stabilized argon arc plasma. Propagation of Hα line emission along the arc axis was observed by high speed photography using a CCD camera with bandpass filters. The propagation velocity was 30 to 100 m/s which was influenced by the flow rate of argon. The Peclét number was calculated for the experimental condition. The result shows that the effect of the diffusion on the mass transport is smaller than that of the flow. This means that the propagating velocity of the Hα line emission closely corresponds to the flow velocity of the argon arc plasma with the added hydrogen. The measured velocity and the estimated average flow velocity of argon arc plasma were in good agreement. The principle of the gaseous tracer was confirmed, although further work will be needed for practical use. © 2001 Scripta Technica, Electr Eng Jpn, 135(1): 15–23, 2001