Fluctuations Of Plasma Parameters Research Articles

Self-consistent hydrodynamic two-fluid model of vortex plasma

We propose the system of self-consistent equations for vortex plasma in the framework of hydrodynamic two-fluid model. These equations describe both longitudinal flows and the rotation and twisting of vortex tubes taking into account internal electric and magnetic fields generated by fluctuations of plasma parameters. The main peculiarities of the proposed equations are illustrated with the analysis of electron and ion sound waves.

Study of plasma parameters in a pulsed plasma accelerator using triple Langmuir probe

A Triple Langmuir Probe (TLP) has been used to study plasma parameters of a transient plasma produced in a newly developed Pulsed Plasma Accelerator system. In this experiment, a TLP with a capacitor based current mode biasing circuit was used that instantaneously gives voltage traces in an oscilloscope which are directly proportional to the plasma electron temperature and density. The electron temperature (Te) and plasma density (ne) of the plasma are measured with the help of this probe and found to be 24.13 eV and 3.34 × 1021/m3 at the maximum energy (−15 kV) of the system, respectively. An attempt was also made to analyse the time-dependent fluctuations in plasma parameters detected by the highly sensitive triple probe. In addition to this, the variation of these parameters under different discharge voltages was studied. The information obtained from these parameters is the initial diagnostics of a new device which is to be dedicated to study the impact of high heat flux plasma stream upon material surfaces inside an ITER like tokamak.

Ionization balance of impurities in turbulent scrape-off layer plasmas I: local ionization-recombination equilibrium

In magnetized fusion devices, cross field impurity transport is often dominated by turbulence, in particular in the scrape-off layer. In these outer regions of the plasma, fluctuations of plasma parameters can be comparable to mean values, and the way ionization and recombination sources are treated in transport codes becomes questionnable. In fact, sources are calculated using the mean density and temperature values, with no account of fluctuations. In this work we investigate the modeling uncertainties introduced by this approximation, both qualitatively and quantitatively for the local ionization equilibrium. As a first step transport effects are neglected, and their role will be discussed in a companion paper. We show that temperature fluctuations shift the ionization balance towards lower temperatures, essentially because of the very steep temperature dependence of the ionization rate coefficients near the threshold. To reach this conclusion, a thorough analysis of the time scales involved is carried out, in order to devise a proper way of averaging over fluctuations. The effects are found to be substantial only for fairly large relative fluctuation levels for temperature, that is of the order of a few tens of percents.

DO COROTATING INTERACTION REGION ASSOCIATED SHOCKS SURVIVE WHEN THEY PROPAGATE INTO THE HELIOSHEATH?

During the solar minimum at the distance of 42-52 AU from the Sun, Voyager 2 observed recurrent sharp, shock-like increases in the solar wind speed that look very much like forward shocks (Lazarus et al.). The shocks were produced by corotating interaction regions (CIRs) that originated near the Sun. After the termination shock (TS) crossing in 2007, Voyager 2 entered the heliosheath and has been observing the plasma emanated during the recent solar minima. Measurements show high variable flow, but there were no shocks detected in the heliosheath. When CIR-driven shocks propagate to the outer heliosphere, their structure changes due to collision and merging processes of CIRs. In this Letter, we explore an effect of the merging of CIRs on the structure of CIR-associated shocks. We use a three-dimensional MHD model to study the outward propagation of the shocks with characteristics similar to those observed by Voyager 2 at ~45 AU (Lazarus et al. 1999). We show that due to merging of CIRs (1) reverse shocks disappear, (2) forward shocks become weaker due to interaction with rarefaction regions from preceding CIRs, and (3) forward shocks significantly weaken in the heliosheath. Merged CIRs produce compression regions in the heliosheath with small fluctuations of plasma parameters. Amplitudes of the fluctuations diminish as they propagate deeper in the sheath. We conclude that interaction of shocks and rarefaction regions could be one of the explanations, why shocks produced by CIRs are not observed in the heliosheath by Voyager 2 while they were frequently observed upstream the TS.

Drift wave instability in the presheath of a fully ionized collisional plasma

It is shown that a presheath near a wall in fully ionized collisional plasma is unstable due to resistive excitation of electrostatic drift waves. The instability depends on the plasma inhomogeneity and resistivity but is independent of the particle flows to the wall. The wave spectrum and growth rate were calculated using a fluid model of the plasma and the Wentzel–Kramers–Brillouin approximation. The electron-wave collision frequency and the additional diffusion flux of the particles were calculated. The resistive instability may be a cause of the fluctuations in plasma parameters observed in transporting vacuum arc plasma beams through magnetized ducts.

Formation of the flank LLBL: A case study

A formation of the low-latitude boundary layer (LLBL) on open field lines during intervals of southward oriented interplanetary magnetic field is now understood in terms of dayside reconnection. However, observations of counterstreaming particles suggest that the LLBL can exist on closed field lines over some portion of the magnetopause. The fluctuations of plasma parameters inside a layer are attributed either to a transient nature of the processes forming a layer or to sweeping of deformations of the magnetopause or inner edge of the LLBL surfaces along the spacecraft. The INTERBALL-1 and MAGION-4 crossed the LLBL near the terminator during intervals of disturbed solar wind conditions. Two-point observations allow us to distinguish the temporal and spatial changes, to estimate the LLBL thickness and its variations and to find the sources of observed plasma populations. Observations suggest that the flank LLBL is supplied by high-latitude reconnection near the cusp and that it lies on open field lines.

On Feasibility of Absolute Measurements of Ion Temperature in D–3He Fusion Plasma

We investigate a possibility of using γ-ray-generating nuclear reactions for absolute measurements of bulk ion temperature in D– 3 He fusion plasma. Radiative capture processes between fuel ions and specific γ-ray modes of nuclear reactions induced by a small admixture of 6 Li are examined for such an application. It is shown that ion temperature can be determined by comparative measurements of the respective γ-ray yields. An essential point of the method proposed is that any fluctuations of plasma parameters during the measurements do not affect accuracy of temperature probe. Nuclear reactions 3 He( 3 He,γ) 6 Be and 6 Li( 3 He,γp) 8 Be are suggested for diagnostics for the first time. Necessary data on reaction cross sections and Maxwellian rate parameters are calculated.

Ionizational instability in an ionized inert gas flowing in a magnetic field.

We discuss the evolution of ionization instability, which gives rise to the formation of regular structures in plasma. The experiment was conducted in a disk magnetohydrodynamic channel in Xe. The evolution of luminous inhomogeneities, and changes in the luminosities of individual inhomogeneities, are traced. Electron concentrations and temperatures in fluctuations are measured. Average values of the electron concentration and temperature, plasma conductivity, and the Hall parameter are estimated. The average conductivity and Hall parameter are compared with the effective values. The influence of positive and negative fluctuations in plasma parameters on the enhancement of ionization oscillations and average current is analyzed. Based on experimental data, a mechanism is suggested that is responsible for the increase in the effective conductivity of ionizationally unstable inert gas plasma with increasing magnetic induction.