Study on interaction between plasma and electromagnetic field in ion source of 10cm ECR ion thruster

Through diagnosing plasma density and calculating the intensity of microwave electric field, four 10cm electron cyclotron resonance (ECR) ion sources with different magnetic field structures are studied to reveal the inside interaction between plasma, magnetic field and microwave electric field. From the diagnosing result it can be found that the plasma density distribution is controlled by the plasma generation and electron loss volumes associated with magnetic field and microwave power level. Based on the cold plasma hypothesis and diagnosing result, the microwave electric field intensity distribution in the plasma is calculated. The result shows that the plasma will significantly change the distribution of microwave electric field intensity to form a bow shape. From the boundary region of the shape to the center, the electric field intensity varies from higher to lower and the diagnosed density inversely changes. If the bow and its inside lower electric field intensity region is close to the screen grid, the performance of ion beam extracting will be better. The study can provide useful information for the creating of 10cm ECR ion source and understanding its mechanism.

Dynamical Spectra in Two-Dimensional Dusty Plasmas

Equilibrium molecular dynamics (EMD) simulation has been employed to explore the dynamical structure factors (DSFs) of two-dimensional (2D) dusty plasma systems for a wide domain of plasma parameters of Coulomb coupling (Γ) and Debye screening strength (κ). The influence of varying wave vectors (k) on plasma DSFs S (k, ω) have been reported with different combinations of plasma state points (Γ, κ). New simulations have been tested for the influence of different wave vectors on plasma density S (k, ω) in addition to different combinations of plasma state points. New results of plasma density S (k, ω) show that amplitude of oscillation and frequency will vary with increasing value of Coulomb coupling parameter (Γ) and Debye screening strength (κ). These simulation techniques show that transient behavior has been reported for frequency (ω) with various values of Debye screening strength (κ) and number of particles (N). Moreover, EMD simulation has been checked in order to investigate the behavior of plasma DSFs with increasing number of particles (N). The outcomes of EMD simulations are matched to earlier known numerical and experimental data. It has been shown that fluctuation of dynamical density increases at intermediate to higher values of coupling parameter. However, it shows less fluctuation at higher values of Debye screening strength (κ).

Post-arc current measurement and interruption performance of vacuum interrupter in DC interruption

In the DC grid, fault current rises very fast due to low impedance. Fast DC circuit breakers are needed to isolate faults and avoid a collapse of the common DC grid voltage. Based on the forced current zero (CZ) technology, the vacuum interrupter (VI) equipped with fast electromagnetic repulsion mechanism is a very promising solution of fast DC interruption. The experimental research on the DC interruption characteristics of a VI, namely by examining the post‑arc current (PAC) is presented in this paper. The dependence of the interruption capability on the PAC is analysed. What’s more, the failure modes of the VI under various experiment conditions are summarized. A former finding was that not all the arcing history which starts from the electrodes separating to the CZ has influence on the PAC but only a very short duration of several microseconds right before the CZ takes effects. New experiment results are added in this paper to support the former finding. Another former finding was that a longer electrode separation will bring about higher PAC. In this paper, both the influence of the arcing memory time and the electrodes separation are owed to a higher residual plasma density, which is verified by a model for calculating the residual plasma density and the continuous transient model (CTM) for calculating PAC.

Investigation of the plasma-wave interaction in helicon plasmas near the lower hybrid frequency

The study of the characteristics of the plasma-wave interaction in helicon plasmas near the lower hybrid frequency has been carried out. The (0D) dispersion relation is derived to analyse the properties of the wave propagation and the 1D cylindrical plasma-wave interaction model is established to investigate the power deposition and implement the parametric analysis. It is concluded that the lower hybrid resonance is the main mechanism of the power deposition in helicon plasmas when the RF frequency is near the lower hybrid frequency and the power deposition mainly concentrates a very thin layer near the boundary. Therefore, it causes that the plasma resistance has a large local peak near the lower hybrid frequency and the variation of the plasma density and the parallel wavenumber lead to the frequency shifting of the local peaks. It is found that the magnetic field is still proportional to the plasma density for the local maximum plasma resistance and the slope changes due to the transition.

MAGNETIC FIELD DYNAMICS IN PLASMA OPENING SWITCH

Computer simulations for magnetic field penetration into plasma of plasma opening switch (POS), and current loop formation in it are presented for various initial plasma densities, currents, and POS geometries. It is shown that the current loop dynamics in the POS is determined by the fast magnetic field penetration in plasma due to the Hall effect. The strong dependence of the current loop longitudinal velocity on the transverse coordinate, together with the influence of the boundary conditions at the POS cathode and anode, lead to the formation of the narrow S-shaped current loop even in a homogeneous plasma. It is shown that the control parameters influencing the dynam-ics of the magnetic field and the motion of the current loop in the POS are the initial plasma density, driving current and cathode radius. The POS resistance is calculated for wide range of initial plasma densities, currents, and cath-ode radiuses. It is shown, that POS resistance is proportional to the total current, inversely proportional to plasma density, and is in the range 10-3…1 Ω for plasma densities 1012…1015 cm-3.

Distributed ferromagnetic enhanced inductive plasma source for plasma processing

New experimental data on the plasma density profiles have been obtained for a low-frequency (100 kHz) distributed ferromagnetic enhanced inductive plasma source at different locations of inductive discharges. An ability to control the plasma density profiles in a large gas discharge chamber in order to achieve a uniform treatment of a substrate is demonstrated. The differences between the obtained results and literature data for a distributed ferromagnetic enhanced inductive plasma source combined with a radio-frequency inductive discharge are discussed.

Daily Variations of Plasma Density in the Solar Streamer Belt

Improved space weather diagnostics depend critically on improving our understanding of the evolution of the slow solar wind in the streamer belts near the Sun. Recent innovations in tomography techniques are opening a new window on this complex environment. In this work, a new time-dependent technique is applied to COR2A/Solar Terrestrial Relations Observatory observations from a period near solar minimum (2018 November 11) for heliocentric distances of 4–8 R ⊙. For the first time, we find density variations of large amplitude throughout the quiescent streamer belt, ranging between 50% and 150% of the mean density, on timescales of tens of hours to days. Good agreement is found with Parker Solar Probe measurements at perihelion; thus, the variations revealed by tomography must form a major component of the slow solar wind variability, distinct from coronal mass ejections or smaller transients. A comparison of time series at different heights reveals a consistent time lag, so that changes at 4 R ⊙ occur later at increasing height, corresponding to an outward propagation speed of around 100 km s−1. This speed may correspond to either the plasma sound speed or the bulk outflow speed depending on an important question: are the density variations caused by the spatial movement of a narrow streamer belt (moving magnetic field, constant plasma density), or changes in plasma density within a nonmoving streamer belt (rigid magnetic field, variable density), or a combination of both?

Simulation of nonlinear standing wave excitation in very-high-frequency asymmetric capacitive discharges: roles of radial plasma density profile and rf power

It is recognized that in large-area, very-high-frequency capacitively coupled plasma (VHF CCP) reactors, the higher harmonics generated by nonlinear sheath motion can lead to enhanced standing wave excitation. In this work, a self-consistent electromagnetic model, which couples a one-dimensional, radial nonlinear transmission line model with a bulk plasma fluid model, is employed to investigate the nonlinear standing wave excitation in a VHF driven, geometrically asymmetric capacitive argon discharge operated at low pressure. By considering a radially nonuniform plasma density profile (case I ) calculated self-consistently by the nonlinear electromagnetic model and the corresponding radially-averaged, uniform plasma density profile (case II ), we first examine the effect of the plasma density nonuniformity on the propagation of electromagnetic surface waves in a 3 Pa argon discharge driven at 100MHz and 90W. Compared to case II, the higher plasma density at the radial center in case I determines a higher plasma series resonance frequency, yielding stronger high-order harmonic excitations and more significant central peak in the harmonic current density Jz,n and the harmonic electron power absorption pn profiles. Therefore, under the assumption of the radially uniform plasma density in a CCP discharge, the self-excitation of higher harmonics at the radial center should be underestimated. Second, using the self-consistent electromagnetic model, the effect of the rf power on the excitation of nonlinear standing waves is investigated in a 3 Pa argon discharge driven at 100MHz. At a low power of 30W, the discharge is dominated by the first two harmonics. The higher harmonic excitations and the nonlinear standing waves are observed to be enhanced with increasing the rf power, resulting in a more pronounced central peak in the radial profiles of the total electron power absorption density pe, the electron temperature Te, and the electron density ne. For all rf powers, the calculated radial profiles of ne show good agreement with the experimental data obtained by a floating double probe.