Зондовые измерения в источнике трубчатой плазмы для плазменного релятивистского СВЧ-усилителя

To overcome the discontinuity between the axial phase and the radial phase in the plasma focus, a new model (the Masoud model) has been developed. It is assumed that, according to the snowplough model, the radial phase moves in the angular direction with continuity between the axial and the radial phases. This model is based on the introduction of an angle of motion in all equations of motion and circuit. Then, the plasma sheath position and velocity were calculated numerically from the previous equations. A slug model has been used to calculate the shock wave velocity, and hence the electron temperature. Values of the discharge current, the axial speed, the axial position, the spike voltage, the radial piston speed, the radial piston position, the plasma column length and the plasma temperature have been obtained using the new model. The values calculated by using this model show good agreement with the published experimental results. Keywords: Plasma focusLee modelSnowplough modelSlug model

The first direct experimental measurements of electron current due to rotating spokes in a modern highpower Hall thruster are presented. A segmented anode consisting of 12 equally spaced azimuthal sections has been retrofitted onto the H6 6-kW class Hall thruster and operated at power levels up to 3 kilowatts. Independent discharge current measurements on each anode segment at 1 MHz and synchronous high-speed video of the discharge at 87,500 frames per second reveal that visible rotating spoke structures in the thruster channel correspond to local electron current oscillations with amplitude approximately 30% of the mean local discharge current through each segment. Discrete Fourier transforms of discharge current oscillations on each segment reveal peaks at spoke rotation frequencies an order of magnitude larger than at the well-known breathing mode frequency. The apparent dominance of the breathing mode in traditional Hall thruster discharge current frequency spectra is revealed to be an artifact of the use of a contiguous ring-shaped anode. Based on the magnitude of local discharge current oscillations on each segment, the magnitude of plasma density oscillations are inferred to be of the order of the mean plasma density and the net discharge current carried by the spoke mechanism is calculated to be up to 50% of the total thruster discharge current.

The electron temperature and the density of argon arc plasma plume injected into water were observed through optical emission spectroscopic measurement. Argon arc plasma jets were generated with a DC arc current of 40–200 A by a non‐transferred arc discharge plasma torch under atmospheric pressure, and ejected through a nozzle on the anode into water or gas‐phase argon. The electron temperature of the plasma plume was determined by the Boltzmann plot with line intensity measurement of atomic argon lines, while the electron density is examined with the Stark broadening measurement of Hα line. It was found that the electron temperature increased from approximately 6500–8000 K, and the electron density also increased up to the order of 1016cm−3, as the discharge current increased for the underwater argon arc plasma plume, both of which were observed at 20 mm in the downward direction from the plasma generator nozzle. In addition, the electron temperature of the underwater plasma plume was slightly lower than that of the gas‐phase argon plasma plume, while the electron density of the underwater plasma was slightly higher than that of the gas‐phase plume. Longitudinal variation of the electron temperature and density of the underwater plasma plume was also observed, and the lowering rate was found to depend on the arc discharge current. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Summary form only given. In low pressure Ar-Hg discharges, the cathode thermionic hot-spot is heated primarily by Hg-ion impact. Recent work (Garner and Li, 1997) has resulted in a combined cathode/negative glow model which predicts (among other things) the Hg-ion energy flux incident on the hot spot and the resulting hot-spot temperature. The model requires input data on: electron and ion temperatures, Ar and Hg densities, discharge current, lamp diameter, thermionic work function and hot spot size. However, since only steady state fluid equations are used in the model, the model fails if discharge current and voltage change too fast. This paper will explore the temporal response of the negative glow-hot-spot system to sudden changes in discharge voltage and current. Time resolved observations of the negative glow and cathode hot-spot have been performed. After equilibrium conditions were established, a fast risetime voltage pulse was applied across a few Torr, Ar-Hg discharge. The resulting discharge current pulse was recorded as were the 398.4 nm Hg-ion line emission from the negative glow, the IR radiation from the thermionic hot-spot and the cathode-plus-anode fall voltage (inferred from a movable anode technique).

Summary form only given. A THz interferometer has been constructed with the goal of directly measuring plasma electron densities in HID lamp plasmas. The system utilizes a 600 GHz source, capable of measuring plasma densities up to 4times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . Due to the short wavelength of 600 GHz radiation, the focal spot size can be less than a millimeter in diameter. These advantages will allow a THz interferometer to measure electron densities in plasmas previously unavailable to interferometric methods. In addition to the use of THz radiation for interferometry, a significant departure from typical microwave measurement will be made in the elimination of heterodyning from the system. Due to the high density and AC nature of HID lamp plasmas, the plasma is expected to recombine twice per cycle when the discharge current is equal to zero. The effect on the beam will change over time as the discharge current passes through its full AC range, allowing calculation of the density as a function of time with zero-points contained within the measurement itself. The only limitation of such a method is the bandwidth of the detector, in that the bandwidth must be higher than the frequency of the AC current in the plasma. Sensors with bandwidths of 1 kHz or greater are available and should prove sufficient for a self-heterodyning interferometer. This self-heterodyning system can eliminate the complexity associated with traditional heterodyne systems, while simultaneously providing time-dependent information on the behavior of electrons in HID plasmas, and eliminating the need for separate measurements of zero-density points for calibration.

HELicon Experiment for Negative ion source (HELEN-I) with a single driver is developed with a focus on the production of negative hydrogen ions. In the Helicon wave heated plasmas, very high plasma densities (1018–1019 m−3) can be attained with electron temperatures as low as ∼1 eV in the downstream region. These conditions favor the production of negative hydrogen ions. In HELEN-I device at IPR, helicon plasma is produced using Hydrogen gas by applying a RF power (PRF) of 800–1000 W at 13.56 MHz frequency. A Nagoya-III antenna is used to excite m = 1 helicon mode in the plasma. A permanent ring magnet creates the required axial magnetic field. The plasma is confined by a multi-cusp field configuration in the expansion chamber. The transition from inductively coupled mode to Helicon mode is observed near PRF ∼ 700 W with plasma density ∼1018 m−3 and electron temperature ∼5 eV in the driver and ∼1 eV in the expansion volume. Negative hydrogen ion density, averaged over the line of sight, is measured in the expansion chamber by employing an optical emission spectroscopy diagnostic technique using Hα/Hβ ratio and a laser photodetachment based cavity ring down spectroscopic diagnostic technique. The measured value of negative hydrogen ion density is in the order of 1016 m−3 at 6 m Torr pressure and does not vary significantly with power, pressure and downstream axial magnetic field variation in the helicon mode. The negative ion density measurements are compared with theoretically estimated values calculated using a particle balance method considering different reaction rates responsible for negative hydrogen ion creation and destruction. It is to be noted that, at present, cesium is not injected in the plasma discharge to enhance H− ion density.

An electrical method is proposed to measure the dielectric film thickness, electron temperature, and plasma density for deposition plasmas. In this method, a square voltage is applied to a flat probe coated with a dielectric film, and the transient voltage of a series capacitor connected to the probe is measured. The thickness of the dielectric film is obtained from the transient voltage because the applied voltage is divided across the dielectric film and the series capacitor. The deposited dielectric film causes a change in transient voltage of the series capacitor. A circuit model with a nonlinear sheath, a series capacitor, and the dielectric films is suggested to obtain plasma density and electron temperature. The time response of transient voltage is related to plasma density, electron temperature and total capacitance of the series capacitor and the dielectric film. Two square voltages with different amplitudes were applied to measure plasma density and electron temperature. Experiments were conducted in inductively coupled plasma. Various capacitors were used to replace the dielectric films, and a flat probe coated with Al2O3 was used to verify the measurement of dielectric film thickness, showing the high accuracy of our method. In addition, the electron temperature from our method is in good agreement with that from electron energy distribution functions, and the plasma density is in good agreement with that from orbital motion limited theory. Therefore, this method would be useful for monitoring plasma parameters and deposited film thickness in industrial plasma processing.

A self-consistent fluid model is developed to investigate the radial distributions of dusty plasma parameters in a DC glow discharge, in which the extended fluid approach of plasma particles and the transport equations of dust particles are coupled. The electrical interaction between charged dust particles is considered in the model. The time evolution of radial distributions of dust density, plasma density, the radial component of electric field and the forces acting on dust particles when dust density tends to be stable, are obtained and analyzed under different discharge currents and dust particle radii. It is shown that the dust density structure is determined mainly by the radial electrostatic force, thermophoretic force and ion drag force in the discharge tube, and both discharge current and dust particle radius have an obvious effect on the transport processes of dust particles. The dust particles gather in the central region of the discharge tube for low discharge current and small dust radius, then dust voids are formed and become wider when the discharge current and dust radius increase. The plasma parameters in the dust gathering region are obviously affected by the dust particles due to the charging processes of electrons and ions to the dust surface.

Mode transition of power dissipation and plasma parameters in an asymmetric capacitive discharge

The traditional way of relativistic electron beam (REB) injection in the experiments on REB- plasma interaction is the injection through an anode foil that separates vacuum diode from plasma chamber. The presence of separating foil leads to the following: (1) replacement of destroyed foil is required after each shot, and (2) the beam angular characteristics making worse. A beam with low angular spread can be obtained from foilless diode placed into strong guiding magnetic field; the problem is how to avoid the diode shortening in the presence of a dense plasma from the interaction chamber. In the experiments on studying of Langmuir turbulence, carrying out on GOL-M device it becomes possible to avoid a separating foil and to obtain a foilless injection of REB into a dense (<EQ 1016 cm-3) plasma, utilizing a special drift pipe as an anode of the foilless axially symmetric magnetized diode.

High-speed camera imaging is a powerful tool to probe the spatiotemporal features of unsteady processes in plasmas, usually assuming light fluctuations to be a proxy for the plasma density fluctuations. In this article, we systematically compare high-speed camera imaging with simultaneous measurements of the plasma parameters—plasma density, electron temperature, and floating potential—in a modestly magnetized Argon plasma column at low pressure (1 mTorr, magnetic fields ranging from 160 to 640 G). The light emission was filtered around 488 ± 5, 750 ± 5, and 810 ± 5 nm. We show that the light intensity cannot be interpreted as a proxy for the plasma density, and that the electron temperature cannot be ignored when interpreting high-speed imaging, both for the time-averaged profiles and for the fluctuations. The features of plasma parameter fluctuations are investigated, with a focus on ion acoustic waves (at frequency around 70 kHz) at low magnetic field and low-frequency azimuthal waves (around a few kHz) at larger magnetic fields. An excellent match is found between the high-speed images fluctuations and an Arrhenius law functional form, which incorporates fluctuations of the plasma density and of the electron temperature. These results explain the discrepancies between ion saturation current and narrow-band imaging measurements previously reported in the literature.

An algorithm for diagnosing the electron density and temperature of helium plasma at atmospheric pressure has been developed based on a revised helium collisional-radiative (CR) model. Atomic collision processes are included, and part of the atomic data of electron collision processes in the conventional CR model has been updated to expand its valid pressure. The algorithm uses eight emission lines in the visible-wavelength range as inputs to determine the electron density, electron temperature, and number density of the two metastable states by fitting the number density of the states corresponding to the emission lines. The algorithm has a considerably small theoretical error. In the microwave-discharged low-pressure helium plasma experiment, the results obtained with the algorithm agreed well with the results obtained with the probe method. The electron density and temperature of the atmospheric-pressure helium plasma obtained with the algorithm agreed well with the results of the continuum spectrum analysis.

Recent quantitative experiments on the ionization potential depression (IPD) in dense plasma show that the observational results are difficult to explain with the widely used analytical models for plasma screening. Here, we investigate the effect of plasma screening on the IPD and ionization balance of dense carbon plasma under solar and stellar interior conditions using our developed consistent nonanalytical model. The screening potential can be primarily attributed to the free electrons in the plasma and is determined by the microspace distribution of these free electrons. The ionization balance is determined by solving the Saha equation, including the effect of IPD. The predicted IPD and average ionization degree are larger than those obtained using the Stewart–Pyatt model for mass densities that are greater than 3.0 g cm−3. Under solar interior conditions, our results are in better agreement with the Ecker–Kröll model at electron temperatures and densities lower than 250 eV and 2.1 × 1023 cm−3 and in the best agreement with the ion-sphere model at 303 eV and 4.3 × 1023 cm−3. Finally, our results are compared with those obtained via a recent experiment on a CH-mixture plasma that has been compressed six times. The predicted average ionization degree of C in a CH mixture agrees better with the experiment than the Stewart–Pyatt and Thomas–Fermi models when the screening from free electrons contributed by hydrogen atoms is included. Our results provide useful information concerning the ionization balance and can be applied to investigate the opacity and equations of state for dense plasma under the solar and stellar interior conditions.

Optical emission measurements have been made on the plasmas generated in conventional, planar magnetrons used for high-rate sputtering of metals. The measurements were made as a function of distance from the 20-cm-diam cathode for Al, Cu, and Ti cathodes in Ne, Ar, and Kr plasmas. The emission from the plasma was coupled through a movable collimator and window assembly to a monochromator and diode array detector. The emission intensity was strongly peaked near the sheath, a few millimeters from the cathode. The intensity of the emission of the neutral rare-gas atoms was approximately linear with discharge current at low discharge power, and proportional to the square root of current at high power. This is consistent with previously observed gas rarefaction effects caused by heating by the sputtered atoms. The emission intensity from the sputtered atoms depended on discharge current to approximately the second power at low discharge current, falling to the 1.4 power in some cases at high power levels. The emission intensity for the ionized, sputtered atoms was observed to depend on the discharge power to the 2.6–3.0 power. These latter observations are consistent with a simple model of excitation dependent on the species density and the electron density, coupled with predicted changes in the electron density and temperature as a function of increasing discharge power.

Modeling of a hemispherical inductively coupled plasma using neural network