Numerical investigation of the theta pinch in intrinsic indiumantimonide

The electron-hole plasma in intrinsic InSb at 300 K can be compressed by electric and magnetic fields. In the theta-pinch configuration one applies, by a capacitor discharge over a one-winding coil around the sample, a magnetic field (0, 0,B _z), which induces an electric field (0,E _φ, 0); both fields cause the ambipolar motion (v _r, 0, 0) of the plasma. We describe the electron-hole plasma by means of a magnetohydrodynamical two-fluid model. The resulting system of differential equations is solved numerically under the assumptions of scalar hydrodynamic pressure and field-independent mobilities. The influence of the plasma properties on the theta pinch is studied as well as the dependence on the experimental conditions like radius of the sample, maximum value and risetime of the magnetic field.     

Experimental study of stark broadening of nitrogen ion lines in a theta pinch plasma

We have studied the Stark broadening of the 3s-3p, 3p-3d and 3d-4f emission lines of the nitrogen II, III, and IV ions emitted from a hot plasma. The plasma was created by a 60 kJ, 60 kV single turn coil theta pinch, where the fill gas was 3 torr of (49%He+51%N₂). The plasma was diagnosed by measuring the Stark-broadened profile of the He(II) 4686 Å line and by taking shadowgrams of the plasma development. It was found that the ionization stage distribution and thus the electron density departed from that predicted by Saha-Boltzmann equilibrium relations. The analysis of the plasma parameters gave an electron density of 1.4 x 10¹⁸ cm^-3. The electron temperature was measured from the relative intensities of emission lines as well as from the line-to-continuum ratio and was found to be 5.0 eV. The line profiles have been fitted to Lorentzian profiles and the thus measure line widths are compared with earlier experimental data as well as with simple theoretical calculations. We find that our line widths are broader than earlier data taken at lower densities if we assume a linear scaling of the half width with the density. A simple Lorentzian profile fits in most cases quite well to the observed line profile. The simple calculations can predict the linewidths within 20% for the low lying levels of both the singly and doubly ionized nitrogen while the predictions are far too narrow for the higher lying levels from the multiply ionized atoms.     

Experimental study of CF4 conical theta pinch plasmaexpanding into vacuum

Langmuir probe, photodiode, and optical multichannel analyzer (OMA) measurements have been made on a pulsed CF₄ conical theta-pinch plasma. A cloud of CF₄ was puffed into a conical theta-pinch coil, converted to plasma, and propelled into the vacuum region ahead of the expanding gas cloud. At a position 67 cm away from the conical theta-pinch coil, the plasma arrived in separate packets that were about 20 μs in duration. The average drift velocity of these packets corresponded to an energy of about 3 eV. The OMA measurements showed that the second packet contained neutral atomic fluorine as well as charged particles. The electron temperature and ion density in the second packet were 2.0 eV and 1.5×10¹³ cm^-3, respectively. The electron temperature and ion density in the wake plasma were 8.3 eV and 4×10¹¹ cm^-3 , respectively. This device can be used for plasma processing or as a laboratory test of numerical and analytical models of the expansion of plasma into vacuum     

Anomalous resistivity at the initial stage of a theta pinch

It is found that an anomalous resistivity exists even before the implosion phase, that is, it exists already at the so-called plasma formation stage of the theta pinch in the low-pressure regime.     

Magnetohydrodynamic instabilities of a pinch resonant streamer microwave discharge

A pulsed freely localized resonant streamer microwave discharge in air and high-pressure hydrogen in the field of a linearly polarized standing electromagnetic wave in a two-mirror open cavity is investigated. The observed characteristic features of the discharge are treated as consequences of the sausage and wriggle instabilities of the plasma channel with a longitudinal microwave current contracted by its magnetic self-field.     

Multichannel energy analysis of the ion flux from a theta pinch

The ion flux parallel to the axis of a linear theta pinch (p ₀=10–30 μ D₂) is analyzed by a new 10-channel energy spectrometer (E=1–10keV). Time resolved energy spectra were measured in each single discharge. It can be shown experimentally that neutral gas, electrons and magnetic fields considerably influence the flux distribution. The measured energy spectra (E≦15 keV) are broad and have no ion groups. At 10 μ D₂ dn/dE is proportional to exp {?E/ē} forE≧3 keV, whereē≈1 keV. For 10, 20 and 30 μ D₂ ē is about equal to thekT deduced from the neutron flux. The time developments of the neutron and ion fluxes (in the range 1–10 keV) are correlated. For the initial phase of the discharge the measuring results are incompatible with relaxation by Coulomb collisions. It seems rather, that there is anomalously fast relaxation due to a microinstability. After the anomalous relaxation the end losses, particularly of the slower ions, continue as a result of Coulomb collisions. This produces increasing distortion of theE-distribution with smallE, which leads to a second microinstability with loss of energetic ions in particular (probably a loss-cone type).     

Study of the internal structure and small-scale instabilities in the dense Z pinch

High-resolution laser diagnostics at the wavelength of 266 nm were applied for the investigation of Z pinches at the 1-MA generator. The internal structure of the stagnated Z pinches was observed in unprecedented detail. A dense pinch with strong instabilities was seen inside the column of the trailing plasma. Kink instability, disruptions, and micropinches were seen at the peak of the x-ray pulse and later in time. The three-dimensional structure of the stagnated Z pinch depends on the initial wire-array configuration and implosion scenario. Small-scale density perturbations were found in the precursor plasma and in the stagnated Z pinch. Development of instabilities is in agreement with three-dimensional magnetohydrodynamic simulations.     

On the relaxation of heavy ion energy anisotropy in a theta pinch plasma

Line profiles from impurity ions in a small theta pinch have been analyzed. Isotropization of the distribution function is fast compared to binary collision times and occurs preferentiallly perpendicular to the magnetic field in the beginning.     

On a step-like magnetic piston in a low density theta pinch

The origin of the “step-like” characteristic in a magnetic piston of a low density theta pinch is discussed. The characteristic can be fairly well explained by an anomalous resistivity due to ion acoustic instabilities.     

A study of the VUV emission from highly ionized krypton in a theta pinch plasma

The ionization rates of Kr(IX), (X), (XI), and (XII) have been measured using a fast 60-kV-60kJ theta pinch as a plasma source. The line emission from each ion stage has been identified and the time evolution observed. A coupled set of rate equations was used along with time- and space-resolved measurements of the electron density and temperature to model the plasma light emission. The ionization rates of Kunze were adjusted by multiplying the rate for each ion stage with a constant until the peak intensity of the calculated emission agreed with the time of the observed peak intensity. The constants required for best fit were 2.5, 0.15, 3.0, and 2.0 for Kr(IX), (X), (XI), and (XII), respectively. Two successive ionization stages, Kr(X) and Kr(XI), have shown the same time dependence and possible reasons for this observation are discussed. During the course of modeling the light emission, we have also found that the rate for the excitation from the 3dⁿ to the 3p⁵3dⁿ⁺¹ level in Kr(X) (n=9) and Kr(XI) (n=8) is a factor of 5 lower than predicted by the van Regemorter excitation rate equation.     

Radiation losses of a theta pinch plasma in the wave-length range 10–200 Å

In order to measure the radiation losses of a theta pinch plasma (electron densityn _e=1?5×10¹⁶ cm^?3, electron temperatureT _e=150?350 eV), a grazing incidence spectrograph is absolutely calibrated in the range 10–200 Å. This is done in two steps: First the measured intensity ratios of lines emitted by hydrogen-like ions are compared with their calculated values thus yielding the relative sensitivity of the instrument. The result is confirmed by incorporating well known intensity ratios of lithium-like ions. Secondly absolute calibration is possible by hanging the spectrograph on an absolutely calibrated monochromator via the branching-ratios of lithium-like ions. Radiation losses from the plasma turn out to be negligible as compared with heat conduction losses and the total energy radiated is found to be small compared with the energy content of the electrons, if the impurity concentration does not exceed 0.5 percent. The radiation is found to be predominantly emitted by the resonance lines of the oxygen and carbon ions O VI, O VII, O VIII, CV, CVI whereas continuum radiation and the contribution from other ions are negligible small. However, in discharge where the oxygen concentration reaches 5 percent, radiation losses can exceed the losses by heat conduction during the early phase of the discharge. But still the final electron temperature is not significantly influenced by the impurities.     

Toroidal momentum pinch velocity due to the coriolis drift effect on small scale instabilities in a toroidal plasma

In this Letter, the influence of the "Coriolis drift" on small scale instabilities in toroidal plasmas is shown to generate a toroidal momentum pinch velocity. Such a pinch results because the Coriolis drift generates a coupling between the density and temperature perturbations on the one hand and the perturbed parallel flow velocity on the other. A simple fluid model is used to highlight the physics mechanism and gyro-kinetic calculations are performed to accurately assess the magnitude of the pinch. The derived pinch velocity leads to a radial gradient of the toroidal velocity profile even in the absence of a torque on the plasma and is predicted to generate a peaking of the toroidal velocity profile similar to the peaking of the density profile. Finally, the pinch also affects the interpretation of current experiments.     

Experimental investigation of electrohydrodynamic instabilities in micro channels

The European Physical Journal Special Topics - An electric field is applied to destabilize the interface between two Newtonian and immiscible liquids flowing in a rectangular micro channel. The...     

Experimental evidence of absolute and convective instabilities in optics

Experimental evidence of convective and absolute instabilities in a nonlinear optical system is given. In optics, the presence of spatial nonuniformities brings in additional complexity. Hence, signatures characterizing these two regimes are derived based on analytical and numerical investigations. The corresponding noise-sustained and dynamical patterns are observed experimentally in a liquid crystal layer subjected to a laser beam with tilted feedback.     

Direct proof of the mirror theorem for projective hypersurfaces up to degree 3 rational curves

In this paper, we directly derive a generalized mirror transformation of projective hypersurfaces of up to degree 3, genus 0 Gromov-Witten invariants by comparing the Kontsevich’s localization formula with residue integral representation of the virtual structure constants. We can easily generalize our method for the rational curves of arbitrary degree, except under combinatorial complexities.     

Experimental observation of anisotropic magnetic turbulence in a reversed field pinch plasma

In this Letter we report an experimental study of fully developed anisotropic magnetic turbulence in a laboratory plasma. The turbulence has broad (narrow) spectral power in the perpendicular (parallel) direction to the local mean magnetic field extending beyond the ion cyclotron frequency. Its k[see symbol] spectrum is asymmetric in the ion and electron diamagnetic directions. The wave number scaling for the short wavelength fluctuations shows exponential falloff indicative of dissipation. A standing wave structure is found for the turbulence in the minor radial direction of the toroidal plasma.