Plasma Propagation Speed Research Articles

Effect of ambient gas species on microwave breakdown pattern

The air, nitrogen, and helium breakdown caused by microwaves at atmospheric pressure are, respectively, investigated by solving the theoretical model, which consists of Maxwell’s equations and plasma fluid equations. The transport coefficients (e.g. an ionization frequency) are predicted by the Boltzmann equation solver BOLSIG+. The effective diffusion coefficient that describes properly the transition from the free diffusion to the ambipolar diffusion is introduced into the plasma fluid equations. The two-dimensional simulation results show that a filamentary plasma array is produced in the air and nitrogen breakdown, but it disappears completely in the helium breakdown. This is because the transport coefficients and wave scattering by the plasma differ from gas to gas. The simulated plasma patterns in the three different gases agree qualitatively with the experimental results. In addition, the plasma propagation speed in the nitrogen breakdown from the simulations is close to the experimental data.

Structural characteristics of internal microcavities produced in optical fiber via the fuse effect

We discuss the internal structure of microcavities in single-mode and multi-mode acrylate- and polyimide-clad optical fibers due to fusion occurring as a plasma spark propagates through the core. The calculated plasma propagation speed was 61±2cm/s. The structure of the microcavities was studied from the end and side surfaces of the fibers, and the microcavities had sizes of 2.7±0.5µm and 5.6±0.7µm, respectively, when viewed from each of these two directions. The ultimate strengths of damaged and undamaged single-mode fibers were determined via two-point bending and the axial tension method. It was experimentally determined that following the damage to the core, the flexure strength of fibers with each type of protective coating decreased by 5%–8%, while the tensile strength of the fibers with polyimide coating decreased by 72%–83%, and the tensile strength of the fibers with acrylate coating decreased by 26%–30%.

Laser heating conditions for copper sphere implantation into borosilicate glass

Implanting metals in glass can serve many different purposes, ranging from enhancing the electro-optical properties to modifying the mechanical properties of the substrate. One approach involves the use of continuous laser illumination to implant metal spheres by transferring particles from a metal foil in direct contact with one side of the glass substrate. The process, which occurs in a very short period time (in tens of milliseconds), is unidentified: due to the bright thermal emissions, it cannot be directly observed. In this study, the continuous laser heating conditions required for implanting copper spheres in borosilicate glass were investigated via spectroscopy and numerical calculations to estimate the temperature of the copper foil. Emission spectroscopy revealed that the temperature during implantation reached 5100 K, which largely exceeded the temperature threshold for laser absorption (∼2000 K). Under such conditions, the plasma forms and enables the migration of copper particles into the glass host. The plasma propagation speed increased with increasing laser power density. The copper sphere was implanted when the plasma propagation speed was 20–50 mm/s. The copper sphere could not be implanted, and fiber fuse occurred when the plasma propagation speed was higher than 50 mm/s.

Dependence of plasma structure and propagation on microwave amplitude and frequency during breakdown of atmospheric pressure air

The structure and propagation of the plasma in air breakdown driven by high-power microwave have attracted great interest. This paper focuses on the microwave amplitude and frequency dependence of plasma formation at atmospheric pressure using one two-dimensional model, which is based on Maxwell’s equations coupled with plasma fluid equations. In this model, we adopt the effective electron diffusion coefficient, which can describe well the change from free diffusion in a plasma front to ambipolar diffusion in the bulk plasma. The filamentary plasma arrays observed in experiments are well reproduced in the simulations. The density and propagation speed of the plasma from the simulations are also close to the corresponding experimental data. The size of plasma filament parallel to the electric field decreases with increasing frequency, and it increases with the electric field amplitude. The distance between adjacent plasma filaments is close to one-quarter wavelength under different frequencies and amplitudes. The plasma propagation speed shows little change with the frequency, and it increases with the amplitude. The variations of plasma structure and propagation with the amplitude and frequency are due to the change in the distribution of the electric field.

Micro-cathode arc thruster using segmented insulated anode with a slit for micro-satellite propulsion

Micro-cathode arc thruster (µCAT) is an electric propulsion device that uses metal cathode material as propellent to create plasma and ultimately produce thrust, which is suitable to serve as a propulsion system for microsatellites. In order to improve propulsion performance of the µCAT, a structure using a segmented insulated anode with a slit (SISA-µCAT), which mainly consists of a truncated-cone-shaped cathode, an insulating sleeve, a segmented anode including proximal anode and distant anode, and an anodic insulation layer with a slit, is proposed in this paper. We compare and analyze the differences in discharge characteristics, plasma generation characteristics and propulsion performance among the SISA-µCAT, a segmented exposed anode µCAT (SEA-µCAT) and the known non-segmented exposed anode µCAT (NSEA-µCAT). Study results show that when adopting the SISA-µCAT, plasma ejection performance is effectively improved by utilizing the special spatial electric field formed between segmented anode and the slit structure on the anodic insulation layer, thus improving the propulsion performance of the µCAT. During a single shot, compared with the NSEA-µCAT, peak values of generated thrust and thrust-to-power ratio are increased by 11.4 times and 10.4 times, respectively, by using the SISA-µCAT. Plasma parameters indicate that peak plasma density and propagation speed are increased by 8.2 times and 2.93 times, respectively.

Performance study on a metal ion plasma thruster using a trumpet-shaped insulated anode with double micropores

A metal ion plasma thruster (MIPT) structure using a trumpet-shaped insulated anode with double micropores (TsIADM), which consists of a frustum-cone-shaped cathode, insulating sleeve, trumpet-shaped anode and anodic insulating layer with double micropores, is proposed. The differences in discharge characteristics and propulsion performance of the TsIADM-MIPT and two other structures, a trumpet-shaped semi-insulated anode MIPT and a conventional trumpet-shaped exposed anode (TsEA) MIPT, are compared and analyzed. Furthermore, the influence that the position of the double micropores has on the MIPT performance is discussed. The results show that the thrust and thrust-to-power ratio are all largest when the double micropores are set at the top end of the inner insulating layer of the trumpet-shaped anode (TsIADM(T)-MIPT). When compared with the TsEA-MIPT, the TsIADM(T)-MIPT demonstrates thrust and thrust-to-power ratios that are improved by 11.6 and 9.5 times respectively. The discharge parameters show that the number of charged particles flowing into the anode in a single shot decreases obviously when adopting the TsIADM(T). The discharge phenomena indicate that compared with the TsEA-MIPT, the luminescence intensity and ejection performance of the plasma plume using the TsIADM(T)-MIPT increases significantly. When the capacitor energy of the system is 5 J, Langmuir probe data show that the plasma density and plasma propagation speed are increased by 16.5 and 4.6 times respectively. These results are believed to be fundamental to the physical mechanisms behind the increased thrust and thruster-to-power ratio of the TsIADM(T)-MIPT.

Ionization wave propagation characteristics under different polarity of pulse waveforms in micro-DBD device driven by bipolar nanosecond pulse waveform

Different spatiotemporal modes of ionization wave propagation at opposite polarity of bipolar pulses in a micro-dielectric barrier discharge structure device are investigated. The device is fabricated on a heavily doped n-type silicon substrate, and a 1 cm × 1 cm square cavity is formed on the 180 μm-thick polyimide film. Different modes of ionization wave propagation determined by the polarity of bipolar pulses are observed, and the details of streamerlike mode and wavelike mode under positive and negative half cycles of pulses are investigated, respectively. The propagation speeds of streamerlike ionization waves and wavelike ionization waves are ∼120 km/s and ∼40 km/s on average and ∼150 km/s and ∼70 km/s in maximum, respectively. Different parameters of bipolar pulses, especially the rising time of pulses, are applied to the proposed device to explore the variation of ionization wave propagation properties. The results show that the modes of the ionization wave propagation are barely changed when the device is driven by different rising time pulses. However, the initial plasma generation time and propagation speed are greatly changed. With a decrease in the rising time from 400 ns to 50 ns, the initial plasma generation time is brought forward over 200 ns, and the ionization wave propagation speed is improved over 30% for both cases. The results imply great significance in the exploration of the dynamics of plasma discharge evolution and regulation of plasma discharge properties through manipulating the pulse parameters.

Arc Plasma Propagation and Arc Current Profiles

When electrical arcs occur in space, a plasma expands away from the arc-site, neutralizing adjacent surfaces (a current), and causing a current to be produced at the arc-site (source of neutralization current). The speed of this plasma expansion depends on the plasma species, which in turn depend on the ionizable materials near the initial electrostatic discharge (ESD) site. Based on laboratory experiments undertaken as part of the U.S. round-robin experiments on plasma propagation speed, a scenario for arc plasma propagation and arc current profiles is presented. It is found that the complex arc current profiles invariably seen in laboratory arcs are due to a multicomponent plasma, where each plasma species expands away from the arc-site supersonically and with approximately constant velocity. Apparent slowing of the arc plasma seen in high-speed video cameras is caused by the density depletion of the lightest (most rapid) plasma component first and heavier (slower) plasma components later. Electron currents onto surfaces originate at the arc-site, and the conductive arc plasma is a conduit for these currents. Sudden, simultaneous onset of arc currents at all distances from the arc-site is the result of blowoff currents, making all surfaces more positive, which then attract ambient electrons. Sudden, simultaneous cutoff of arc currents at all distances from the arc-site is the result of collapse of the plasma due to conditions at the arc-site. The ionization at the arc-site during the arc is seen to be rapidly variable, with variations on the nanosecond timescale. This model not only makes the varied plasma velocities reported in the literature understandable, but it also makes predictions about the arc radio-frequency interference (RFI), contamination produced by the arcs, and the total charge in an arc possible. Arc-site materials are suggested which, being hard to ionize and with massive ions, minimize arc currents and maximize arc current rise times.

Discharge and metallic plasma generation characteristics of an insulated anode with a micropore

An insulated-anode electrode structure with a micropore (IAESM) is proposed in this paper. The aim of this study is to examine the effect that the micropore structure has on the discharge characteristics and plasma generation characteristics of the electrode in pulsed vacuum discharge. In this study, currents flowing through the cathode and the anode of the discharge electrode are simultaneously measured by two identical Rogowski coils, and plasma density and the plasma propagation speed are measured by using an improved Langmuir probe method. First, the differences in discharge characteristics and plasma generation characteristics among the IAESM and two known electrode structures, the non-insulated-anode electrode structure (NIAES) and the insulated-anode electrode structure (IAES), were compared and analyzed. Then, based on the IAESM, the effect of the micropore size on discharge characteristics and plasma generation characteristics is discussed. The results show that the IAESM discharge current flowed through the cathode with the same amplitude as in the NIAES, and the peak plasma density and the plasma propagation speed were significantly larger. The data obtained from Langmuir probes indicate that when the cross-sectional area of the micropore was reduced from 0.60 mm2 to 0.04 mm2, the peak plasma density and the plasma propagation speed are increased by 2.30 times and 2.56 times, respectively.

Considerations of Flashover Propagation

Flashover propagation of plasma on a solar panel is considered from a physics standpoint. Although useful as a first attempt to describe the flashover phenomenon, the previous perimeter theory is shown to have many areas in need of improvement before it can be used as a guide for spacecraft solar array design. A new, more physical picture is developed here. Results from the U.S. Round-Robin Experiments on Plasma Propagation Speed are used to elaborate the physical principles. The new model explains simultaneous current onset, peaks, and cutoffs at all distances; multiple peaks moving at different velocities; and nonthermal directed velocities. Further elaboration is needed before such a model can be used as a reliable guide to flashover pulse peaks, widths, and electrostatic discharge; but, as it stands, the model corrects many of the perimeter theory’s deficiencies.

Bullet-to-streamer transition on the liquid surface of a plasma jet in atmospheric pressure

This study investigated the transition of the plasma shape from a ring-shaped bullet to a pin-like streamer adjacent to the electrolyte surface in a kHz-driven helium atmospheric pressure plasma jet. The transition was observed by synchronized fast images, plasma propagation speed, time-resolved emission profile of Hβ, and spatially and temporally resolved helium metastable density. The transition height increased when electrolyte evaporation was enhanced. The plasma continued to discharge on the electrolyte surface even in the absence of metastable species, i.e., the discharge mechanism changed from Penning ionization between helium metastable and ambient nitrogen to electron collision on evaporated water.

Plasma Propagation Speed and Electron Temperature in Slow Electron Energy Non-thermal Atmospheric Pressure Indirect-Plasma Jet

Space- and time-resolved discharge-images from a nonthermal atmospheric-pressure indirect-plasma jet have been observed using a high-speed single-frame camera to investigate the electron temperature. The propagation velocity of the indirect Ar-plasma along the plasma column has been shown to be on the order of $10^{\mathrm {\mathbf {4}}}$ m/s, and that corresponds to an ion acoustic velocity on the order of $10^{\mathrm {\mathbf {2}}}$ m/s. Plasma has been generated by varying input discharge voltages from 2.0 to 4.0 kV at a driving frequency of 40 kHz. Particularly, the average electron temperature in slow electron energy nonthermal atmospheric-pressure indirect-plasma jet has been found to be about 0.3 eV.

First Preliminary Results From U.S. Round-Robin Tests

The first preliminary results are reported from the U.S. Round-Robin Test on Plasma Expansion Speed. The tests were performed at the NASA Glenn Research Center on two coupons (six strings) of International Space Station (ISS) solar cell arrays, with a separate small array to obtain arcs (because it is so difficult to get ISS arrays to arc). ISS arrays were used because they have no exposed interconnects to act as bare current collectors and confuse the experimental results. The preconstructed ISS strings were laid out approximately parallel to the plasma expansion velocity to allow for the best test of the simple plasma expansion front current waveform model. Several Langmuir probes were arranged above and to the sides of the sample to allow for measurement of the plasma propagation speed. In the initial set of tests, primary arcs and the consequent current waveforms were measured in a Low Earth Orbit-type plasma. In a second set of tests, two electron guns with diffusers were used to provide an approximately uniform Geosynchronous Earth Orbit-type environment, and primary arcs and current waveforms were obtained. The objective of this and other round-robin tests is to characterize primary arc waveforms in terms of speed and degree of discharge of arc plasmas produced by primary arcs, and their dependences on environment, capacitance per unit area, arc voltage, temperature, and so on. The final goal is to allow engineering estimates of arc current peaks and half-widths to allow confident design and construction of space solar arrays, and to allow mitigation techniques to be evaluated. This is the first in an extended series of tests to be performed at six different U.S. facilities, and with participation from ten different U.S. organizations.

On the velocity variation in atmospheric pressure plasma plumes driven by positive and negative pulses

To better understand the variation in the “plasma bullet” velocity, the dynamics of an atmospheric pressure plasma plume driven by positive and negative pulses are investigated in detail. It is found that, before the plasma exits the nozzle, the plasma propagates at a speed of about 30 km/s for both positive and negative pulses. As soon as the plasma exits the nozzle, the plasma propagation speed increases dramatically for both cases. The peak velocity for the case of the positive pulse is much higher than that of the negative pulse, it is approximately 150 km/s and 70 km/s, respectively. According to the optical emission spectra, the acceleration behavior of the plasma bullet when it exits the nozzle is due to the increase in the N2+ concentration.

Electrostatic Discharge Plasma Propagation Speed on Solar Panel in Simulated Geosynchronous Environment

An international project has started to establish an International organization for standardization standard for the electrostatic discharge (ESD) on the solar array panel. For the ESD ground test of satellite solar panel, it is important to understand the characteristics of a primary arc discharge. A solar array coupon made of triple-junction cells is used to understand the primary arc characteristics. In particular, the experiment focuses on the measurement of the propagation speed of plasma generated by the primary arc. The plasma propagation is analyzed using images captured by a high-speed video camera and an image intensified camera. The plasma propagation speed derived from discharge images decreases in proportion to the inverse of the square root of time. The arc current waveform assuming the decreasing speed agreed with the experiment waveform very well.

P-84: Electron Plasma Propagation in the External Electrode Fluorescent Lamps

The plasma propagation has been investigated by observing the optical signal along the tube of the EEFL for 32″ LCD backlight unit. The light starting from the electrode of high voltage moves toward the other side of electrode grounded electrically with the electron plasma propagation speed about 4×105 m/s.

Plasma Propagation Speed and Electron Temperature in Surface-Discharged Alternating-Current Plasma Display Panels

Space and time resolved discharge images from an alternating-current plasma display panel have been observed by a high-speed single-frame camera to investigate the electron temperatures. The plasma propagation speed on the cathode was measured to be 0.9 mm/µs and 1.3 mm/µs, respectively, and that on the anode was measured to be 1.8 mm/µs and 2.7 mm/µs, respectively, at driving frequencies of 50 kHz and 100 kHz. This finding indicates that the electron mobility on the anode is approximately two times the ion mobility on the cathode. Particularly, the electron temperatures in alternating-current plasma display panels (AC-PDP) were found to be 1.2 eV and 2.5 eV at driving frequencies of 50 kHz and 100 kHz, respectively, in this experiment, which are in good agreement with those obtained by a micro-Langmuir probe and the laser Thomson scattering method.

共有結合性セラミックスのレーザ加工に関する研究 （第１報） 蒸気圧とプラズマの生成挙動

This paper describes the dynamic behavior of the vapor pressure and plasma potential to investigate the metallic phase formation mechanism in laser-processing of the covalent bondceramics. The vapor pressure was measured with a high sensitivity acceleration sensor. The plasma potential was detected with electrical probes, which have been newly developed. The vapor pressure increases linearly with the peak power to about 39.2 MPa. The plasma propagation speed is higher than the velocity of sound nearby the target.