Decrease In Plasma Temperature Research Articles

Spectroscopic measurement of temperatures in pulsed TIG welding arcs

Time resolved plasma temperatures in a pulsed tungsten-inert-gas (TIG) welding arc have been measured using optical emission spectroscopy. The peak and base pulse-averaged plasma temperatures both decrease with time after the arc ignition, and the plasma temperature decreases during the peak pulse period and increases during the base pulse period when the arc reaches the steady state. The decrease in the plasma temperature is associated with the increase in the cathode surface temperature and the decrease in the arc voltage and vice versa. The importance of the cathode surface temperature on the arc properties has been discussed.

Time resolved characterization of a free-burning argon arc after ignition by optical emission spectroscopy

Time resolved properties of a free-burning argon arc after ignition have been characterized using optical spectroscopic method. After ignition, when the arc current keeps constant, the plasma temperature decreases with time at any position of the arc. The decrease of the plasma temperature is associated with the increase of the arc cathode surface temperature. It is suggested that the variation of the cathode surface temperature, which changes the current density distribution over the cathode surface, leads to the decrease of the plasma temperature in the free-burning arc after ignition.

Radiation from wire arrays imploding on an axial target

Adding thin wires on the axis of cylindrical and conical wire arrays significantly affected the x-ray emission of the conical wire arrays, while having practically no effect on that of the cylindrical ones. The experimental study was performed using Al wire arrays with central Al and Cu wires on the 1 MA Zebra Z-pinch generator at the Nevada Terawatt Facility. Adding wires on the axis of cylindrical wire arrays led to a decrease in plasma temperature and produced practically no change in the total radiation yield. In contrast, for conical wire arrays, both the plasma temperature and the total radiation yield increased approximately proportional with the central wire thickness. Both effects were stronger for Cu center wires than for Al center wires. When using Cu, radiative cooling played a substantial role in the implosion dynamics, leading to a more compact pinch than for Al wires. Adding Al wires on the axis of conical arrays produced a cocoon-shaped emissivity distribution, with a minimum on axis. For the case of Cu wires, a short-lived, straight, and narrow filament emitting photons with energy greater than 2.5 keV formed on the axis of the cocoon. This hot filament is produced by a transient heating mechanism intense enough to fully ionize Al, and the cocoon represents plasma heated by a conical shock formed in the conical array.

Time-Dependent 2D Modeling of Magnetron Plasma Torch in Turbulent Flow

A theoretical model is presented to describe the electromagnetic, heat transfer and fluid flow phenomena within a magnetron plasma torch and in the resultant plume, by using a commercial computational fluid dynamics (CFD) code FLUENT. Specific calculations are presented for a pure argon system (i.e., an argon plasma discharging into an argon environment), operated in a turbulent mode. An important finding of this work is that the external axial magnetic field (AMF) may have a significant effect on the behavior of arc plasma and thus affects the resulting plume. The AMF impels the plasma to retract axially and expand radially. As a result, the plasma intensity distribution on the cross section of torch seems to be more uniform. Numerical results also show that with AMF, the highest plasma temperature decreases and the anode arc root moves upstream significantly, while the current density distribution at the anode is more concentrated with a higher peak value. In addition, the use of AMF then induces a strong backflow at the torch spout and its magnitude increases with the AMF strength but decreases with the inlet gas velocity.

Study of sub-mJ-excited laser-induced plasma combined with Raman spectroscopy under Mars atmosphere-simulated conditions

Laser-Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy are complimentary techniques. LIBS yields elemental information while Raman spectroscopy yields molecular information about a sample, and both share similar instrumentation configurations. The combination of LIBS and Raman spectroscopy in a single instrument for planetary surface exploration has been proposed, however challenges exist for developing a combined instrument. We present LIBS and Raman spectroscopy results obtained using a diode pumped, intracavity doubled, Q-switched, Nd:YLF laser operating at 523 nm, which overcomes some of the difficulties associated with a combined instrument. LIBS spectra were obtained with 170 μJ per pulse at 4 Hz repetition rate in a low pressure Mars-simulated atmosphere and Raman spectra produced with 200 mW at 100 kHz. The Nd:YLF laser is switchable between LIBS and Raman spectroscopy modes only by a change in Q-switch repetition rate. Emissions from Ca, Ca II, Fe, Fe II, Mg, Na, and O atom were identified in the μ-LIBS spectrum of oolithic hematite. Evidence was found for a change in plasma dynamics between 7 and 5 Torr that could be explained as a decrease in plasma temperature and electron density below 5 Torr. This is relevant to future Mars exploration using LIBS as the mean surface pressure on Mars varies from 3.75 to 6 Torr. LIBS plasma dynamics should be carefully evaluated at the pressures that will be encountered at the specific Mars landing site.

Effects of charge exchange in the tail of the heliosphere

Physical processes in the tail of the solar wind interaction region with the partially ionized local interstellar medium are investigated in the framework of a self-consistent kinetic-gas dynamic model. It is shown that the charge exchange process of the hydrogen atoms with the plasma protons results in disappearance of the contact discontinuity at sufficiently large distances from the Sun. The solar wind plasma temperature decreases and, ultimately, the parameters of the plasma and hydrogen atoms approach the corresponding parameters of the unperturbed interstellar medium at large heliocentric distances.

Charge separation effects in magnetized electron–ion plasma expansion into a vacuum

Charge separation effects in the expansion of magnetized relativistic electron–ion plasmas into a vacuum are examined using 212-dimensional particle-in-cell plasma simulations. The electrostatic field at the plasma surface decelerates electrons and accelerates ions. A fraction of the surface electrons is trapped and accelerated by the pondermotive force of the propagating electromagnetic pulse, a mechanism we call the diamagnetic relativistic pulse accelerator. This charge separation is enhanced as the initial plasma temperature is decreased. The overall energy gain of the plasma particles through the expansion strongly depends on the initial plasma temperature. Moreover, the electrons become relatively less energized and the ions more energized as the plasma temperature decreases.

Energy Dependence of Emission Intensity and Temperature in a LIBS Plasma Using Femtosecond Excitation

In this paper, we investigate the effect of laser energy on laser-induced breakdown emission intensity and average temperature in a short-pulse plasma generated by using 140 fs laser excitation. Both line emission and continuum background intensity and plasma temperature decrease very rapidly after excitation compared to the more conventional nanosecond pulse excitation. Both emission intensity and plasma temperature increase with increasing laser energy. However, the intensity increase appears to be mostly related to the amount of material ablated. Also, nongated laser-induced breakdown spectroscopy (LIBS) is demonstrated using a high-pulse (1 kHz) pulse repetition rate.

高周波支援マグネトロンスパッタリング法におけるＡｒ｀＋´及びＴｉ｀＋´のエネルギー分布のＡｒ圧力依存性

Effects of Ar pressure on the number of the 48Ti+ ions incident to the substrate have been investigated in inductively coupled rf plasma enhanced magnetron sputtering. The energy distributions of the 40Ar+ and 48Ti+ ions incident to the substrate were measured by an energy-resolved mass spectrometer. In addition to the energy distribution measurements, plasma conditions have been measured by a Langmuir probe technique to investigate the effects of Ar pressure on plasma. The experimental results of the ion energy distribution measurements show that the number of 48Ti+ ions arriving at the substrate increased as Ar partial pressure increased and that the number of 40Ar+ ions arriving at the substrate increased to an Ar pressure of 1.0 Pa and decreased for further increase in Ar pressure. From electron temperature measurement results, it was found that electron temperature decreased with increasing Ar pressure. The main process of Ti ionization is ascribed to the Penning effect, the ionization of Ti by the excited neutral Ar, resulting in a decrease of plasma temperature. It is concluded that an increase in Ar pressure enhances the ionization probability of Ti sputtered atoms.

Investigation of Saha-Boltzmann equilibrium in the analyte zone of a two-jet plasma generator

Relative populations of the excited levels for Cr(I), Cr(II), Fe(I) and Fe(II) in the argon plasma flow of an arc two-jet plasma generator used in spectrochemical analysis were measured. The range of the total energy E of excitation and ionization was 4.5–8.0 and 12.5–16.0 eV, respectively. It is shown that the populations of atom and ion levels are linear with respect to energy lower than E∼15 eV. For ionic lines with energy close to 15.5–16.0 eV the line intensities behave anomalously against equilibrium values. This can be associated with charge transfer between the analyte and argon ions. Deviation of I from LTE values increases in the plasma zones below and above the site of jet confluence, where the plasma temperature decreases.

UV radiation of the GTA welding plasma versus shielding gas composition

UV radiation during gas tungsten arc (GTA) welding in argon/helium shielding gas mixtures versus gas composition and arc length has been investigated experimentally and theoretically. UV radiation was found to increase with an increase of argon concentration in the mixture. A physical model describing this phenomenon has been developed. The model predicts an increase in the total amount of ions in the mixture with an increase of argon concentration despite a decrease in plasma temperature. The result of calculations using the model is in satisfactory agreement with the experimental data.

Equatorial plasma fountain and its effects over three locations: Evidence for an additional layer, the F3 layer

The equatorial plasma fountain and equatorial anomaly in the ionospheres over Jicamarca (77°W), Trivandrum (77°E), and Fortaleza (38°W) are presented using the Sheffield University plasmasphere‐ionosphere model under magnetically quiet equinoctial conditions at high solar activity. The daytime plasma fountain and its effects in the regions outside the fountain lead to the formation of an additional layer, the F3 layer, at latitudes within about plus or minus 10° of the magnetic equator in each ionosphere. The maximum plasma concentration of the F3 layer, which occurs at about 550 km altitude, becomes greater than that of the F2 layer for a short period of time before noon when the vertical E × B drift is large. Within the F3 layer the plasma temperature decreases by as much as 100 K. The ionograms recorded at Fortaleza on January 15, 1995, provide observational evidence for the development and decay of an F3 layer before noon. The neutral wind, which causes large north–south asymmetries in the plasma fountain in each ionosphere during both daytime and nighttime, becomes least effective during the prereversal strengthening of the upward drift. During this time the plasma fountain is symmetrical with respect to the magnetic equator and rises to over 1200 km altitude at the equator, with accompanying plasma density depletions in the bottomside of the underlying F region. The north–south asymmetries of the equatorial plasma fountain and equatorial anomaly are more strongly dependent upon the displacement of the geomagnetic and geographic equators (Jicamarca and Trivandrum) than on the magnetic declination angle (Fortaleza).

Analysis of solid propellant combustion behavior under electrothermal plasma injection for ETC launchers

Enhanced burn rates of solid propellants through plasma erosion has been studied showing evidence of increased burn rate with injection of electrothermal plasmas into the propellant. These experiments are designed to evaluate the effectiveness of maximizing energy versus momentum transport, and the influence of geometry on the burn rates of the JA-2 solid granular propellant. A series of experiments has shown evidence of enhanced burn rate at pressures between 55 and 90 MPa (8,000 and 12,000 psi, respectively) over 400 ps pulse length. A 20 to 40% enhancement in the burn rates has been observed when plasma is injected parallel to the surface of the propellant. When plasma is injected normal to the surface, the burn rate increases by about a factor of three. A set of experiments has been designed to measure the burn rates when the electrothermal plasma is injected at various angles, from 0/spl deg/ to 90/spl deg/, to the surface of the propellant. Experiments were conducted at a constant input energy of 5 kJ/spl plusmn/2% to the electrothermal plasma source and constant base pressure of 15 Torr, which provides a 12,300 psi plasma pressure at the source exit close to the surface of the propellant. Results indicate increased burn rates with increased angle of injection. Optical emission spectroscopy measurements revealed a decrease in plasma temperature, at the plasma-propellant interface, with increased angle of injection.

On the sources of interplanetary shocks at 0.72 AU

In order to understand the solar cycle variation of interplanetary shocks and their driving source at 0.72 AU, a survey of Pioneer Venus Orbiter (PVO) magnetometer and plasma data from 1979‐1988 has been conducted. Known shock drivers at 1.0 AU include coronal mass ejections (CMEs) and fast/slow stream interactions. In our analysis, CMEs were identified by a decrease in plasma temperature to background or below accompanied by an increase in plasma density and dynamic pressure. It was also required that the magnetic field exhibit a coherent rotation over about a day and an increase and decline in magnitude on a timescale of hours to days. Stream interactions were identified by a characteristic increase in ion temperature and velocity coincident with a decrease in density and a coincident increase in the total magnetic field magnitude. These signatures were usually preceded within 24 hours by a change in flow angle. In all, 45 shocks were identified: 36 driven by CMEs, 6 resulting from fast/slow stream interactions, and 3 with sources that could not be defined. The shocks driven by CMEs show a solar cycle variation that roughly follows the sunspot number. These shocks all have normals consistent with radial propagation of the shock fronts from the sun. In contrast, the few stream interaction related shocks show a tendency to occur later in the solar cycle and have a broader distribution of shock normals.

Einfluß von Säuren in der ICP-AES

The influence of concentration and nature of the acid, type and tuning of RF-generator, method of solution introduction (flow injection or two-nebulizer method) are investigated to understand the nature of acid matrix interferences in ICP-AES. Sixteen elements and nine different spectrometers wer used to study the matrix interferences caused by HCl, HNO3, HClO4, H2SO4, H3PO4. There are two effects connected with acid: depression of the analyte emission signals and irregular signal changes for different elements. The values of these effects depend on the RF-generator type. The obvious results of introducing acid in the plasma are a decrease in plasma temperature and departures from LTE.

The effect of a meridional E × B drift on the thermal plasma at L = 1.4

A fully time dependent mathematical model of the thermal plasma at L = 1.4 is described. In the mathematical model account is taken of a quiet-time E × B drift in the meridional plane. Atmospheric conditions appropriate to equinox at sunspot minimum and at sunspot maximum are considered. Results of the model calculations are presented. Emphasis is placed on the effects on the thermal plasma of a quiet-time E × B drift in the meridional plane. A comparison of the model calculations which include an E × B drift with those in which there is no E × B drift shows than an E × B drift significantly affects the plasma concentration and temperature distributions during the day at both sunspot minimum and sunspot maximum; the effects at night are very small. An upward E × B drift during the day increases both NmF2 and hmF2 and decreases the plasma temperature. The decrease in plasma temperature is due primarily to the increase in plasma concentration. It is more pronounced in the electron temperature than in the ion temperature and it varies considerably with altitude, time and atmospheric conditions. The changes in plasma concentration and temperature brought about by an E × B drift also change the O +-H + transition height and the O + and H + tube contents. For the E × B drifts considered the O +-H + transition height is raised during the morning and lowered during the afternoon. The changes in O + tube content roughly follow the changes in NmF2. The changes in H + tube content, however, are small since the H + tube content is controlled by the H + concentration at the higher altitudes of the tube of plasma and these concentration values are only slightly affected by the E × B drifts considered.

Extreme Ultraviolet Observations from Voyager 2 Encounter with Jupiter

Extreme ultraviolet spectral observations of the Jovian planetary system made during the Voyager 2 encounter have extended our knowledge of many of the phenomena and physical processes discovered by the Voyager 1 ultraviolet spectrometer. In the 4 months between encounters, the radiation from Io's plasma torus has increased in intensity by a factor of about 2. This change was accompanied by a decrease in plasma temperature of about 30 percent. The high-latitude auroral zones have been positively associated with the magnetic projection of the plasma torus onto the planet. Emission in molecular hydrogen bands has been detected from the equatorial regions of Jupiter, indicating planetwide electron precipitation. Hydrogen Lyman alpha from the dark side of the planet has been measured at an intensity of about 1 kilorayleigh. An observation of the occultation of alpha Leonis by Jupiter was carried out successfully and the data are being analyzed in detail.

Nonlinear oscillations of rarified plasma

The paper basically is a review of a number of studies devoted to the theory of nonlinear motions of plasma under conditions where collisions between particles do not play a determining role.The problem is formulated in the introduction. It concerns the evolution in time of an initial perturbation of finite amplitude. The resulting physical picture will depend on these competing processes: nonlinear increase of wave steepness, dispersion, absorption and instability. In a number of cases where adsorption and instability are insignificant, it is possible to obtain an idea of the character of the nonlinear motions by applying the appropriate linear “dispersion law”.The second Section presents certain specific types of nonstationary nonlinear motions permitting exact mathematical solution, namely: nonlinear oscillations of electrons at zero temperature, nonlinear motion of plasma across a strong magnetic field, and ion waves of finite amplitude in non-isothermal plasma where pi ≪ pe. In a number of instances, evolution of the initial perturbation leads to the formation of a multi-component current, some peculiarities of which are discussed in the third Section. In the next Section stationary nonlinear waves are described, i.e. waves not changing their form with time. In a particular case they are the so-called “solitary waves”, similar to waves on the surface of heavy liquid in a channel of finite depth. The possibility of the existence of such waves requires linear laws of dispersion of a specific character. The possibility of “solitary” waves of rarefaction is pointed out.The question of absorption of waves in rarified plasma is then discussed. An approximate “quasi-linear” method is developed which permits the kinetic considerations in the absorption of waves of finite amplitude to be simplified. The method consists in the representation of the distribution function f(r, v, t) as a sum of rapidly and slowly varying terms. In the equation for the slowly varying term a quadratic average effect of fast oscillations is taken into consideration. This method is applied to two particular problems: the absorption of Langmuir electronic oscillations (in the limit of very small amplitude the equation for wave-damping goes over into the well-known formula for the so-called “Landau-damping”), and the cyclotronic absorption of transversely polarized waves which propagate along the constant magnetic field.In the last section some types of instabilities of non-linear motions are shown. In addition to the instabilities associated with the multi-component motion, it is shown that waves in a magnetic field (in particular, solitary waves) are unstable if their amplitude exceeds a certain critical value which decreases as the plasma temperature decreases.