Resistive MHD modes in hollow cathodes external plasma

2021 ◽  
Author(s):  
Giulia Becatti ◽  
Francesco Burgalassi ◽  
Fabrizio Paganucci ◽  
Matteo Zuin ◽  
Dan M Goebel
Keyword(s):  
Magnetic Field ◽  
Hollow Cathode ◽  
Electric Propulsion ◽  
Axial Magnetic Field ◽  
Mhd Equations ◽  
Linear Perturbation ◽  
Plasma Parameters ◽  
Hollow Cathodes ◽  
Plume Region ◽  
Helical Mode

Abstract A significant number of plasma instabilities occur in the region just outside of hollow cathodes, depending on the injected gas flow, the current level and the application of an external magnetic field. In particular, the presence of an axial magnetic field induces a helical mode, affecting all the plasma parameters and the total current transported by the plasma. To explore the onset and behavior of this helical mode, the fluctuations in the plasma parameters in the current-carrying plume outside of a hollow cathode discharge have been investigated. The hollow cathode was operated at a current of 25 A, and at variable levels of propellant flow rate and applied magnetic fields. Electromagnetic probes were used to measure the electromagnetic fluctuations, and correlation analysis between each of the probe signals provided spatial-temporal characterization of the generated waves. Time-averaged plasma parameters, such as plasma potential and ion energy distribution function, were also collected in the near-cathode plume region by means of scanning emissive probe and retarding potential analyzer. The results show that the helical mode exists in the cathode plume at sufficiently high applied magnetic field, and is characterized by the presence of a finite electromagnetic component in the axial direction, detectable at discharge currents $\geq$ 25 A. A theoretical analysis of this mode reveals that one possible explanation is consistent with the hypotheses of resistive magnetohydrodynamics, which predicts the presence of helical modes in the forms of resistive kink. The analysis has been carried out by linear perturbation of the resistive MHD equations, from which it is possible to obtain the dispersion relation of the mode and find the $k-\omega$ unstable branch associated with the instability. These findings provided the basis for more detailed investigation of resistive MHD modes and their effect in the plume of hollow cathodes developed for electric propulsion application.

Characterization of hollow cathode vacuum arc with axial magnetic field as a concentrated heat source

Vacuum ◽  
2019 ◽  
Vol 160 ◽  
pp. 70-74 ◽  
Author(s):  
Jianping Xu ◽  
Xiubo Tian ◽  
Haiqun Qi ◽  
Jiajie Wang ◽  
Chunzhi Gong ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Heat Source ◽  
Hollow Cathode ◽  
Axial Magnetic Field ◽  
Vacuum Arc

Parametric instabilities of finite-amplitude, circularly polarized Alfvén waves in an anisotropic plasma

1993 ◽  
Vol 49 (1) ◽  
pp. 29-39 ◽  
Author(s):  
Hiromitsu Hamabata
Keyword(s):  
Finite Amplitude ◽  
Alfven Waves ◽  
Mhd Equations ◽  
Alfvén Waves ◽  
Linear Perturbation ◽  
Plasma Parameters ◽  
Circularly Polarized ◽  
Pressure Anisotropy ◽  
Parametric Instabilities ◽  
Fifth Order

A class of parametric instabilities of finite-amplitude, circularly polarized Alfvén waves in a plasma with pressure anisotropy is studied by application of the CGL equations. A linear perturbation analysis is used to find the dispersion relation governing the instabilities, which is a fifth-order polynomial and is solved numerically. A large-amplitude, circularly polarized wave is unstable with respect to decay into three waves: one sound-like wave and two side-band Alfvén-like waves. It is found that, in addition to the decay instability, two new instabilities that are absent in the framework of the MHD equations can occur, depending on the plasma parameters.

A mechanism for Taylor relaxation in Z-pinches. Part 1. Dynamo mechanism

1986 ◽  
Vol 35 (2) ◽  
pp. 295-310 ◽  
Author(s):  
S. K. H. Auluck
Keyword(s):  
Magnetic Field ◽  
Experimental Data ◽  
Axial Magnetic Field ◽  
Positive Definite ◽  
Low Energy ◽  
Toroidal Field ◽  
Mhd Equations ◽  
Larmor Radius ◽  
Electron Mass ◽  
Dynamo Mechanism

The dynamo mechanism in an RFP is explained on the basis of new terms in the MHD equations which are proportional to the electron mass and are traditionally neglected. A new azimuthal dynamo current is obtained which is shown to be positive definite. Sustained, spontaneous self-reversal of the toroidal field naturally follows from this. The (F, Θ) curve calculated from this theory under certain assumptions agrees well with experimental data. The theory predicts the presence of large-Larmor-radius particles in the RFP. It also predicts a spontaneous axial magnetic field in linear Z-pinches. Preliminary experiments on low-energy Z-pinches corroborate this prediction.

scholarly journals Measurement of Some Argon Plasma Parameters Glow Discharge Under Axial Magnetic Field

2019 ◽  
Vol 7 (4) ◽  
pp. 158-166
Author(s):  
Pshtiwan M.A. Karim ◽  
Diyar S. Mayi ◽  
Shamo Kh. Al-Hakary
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Glow Discharge ◽  
Electron Temperature ◽  
Breakdown Voltage ◽  
Axial Magnetic Field ◽  
Argon Plasma ◽  
Emission Lines ◽  
Plasma Parameters ◽  
Gas Pressures

This paper investigates the characteristics some of argon plasma parameters of glow discharge under axial magnetic field. The DC power supply of range (0-6000) V is used as a breakdown voltage to obtain the discharge of argon gas. The discharge voltage-current (V-I) characteristic curves and Paschen’s curves as well as the electrical conductivity were studied with the presents of magnetic field confinement at different gas pressures. The magnetic field up to 25 mT was obtained using four coils of radius 6 cm and 320 turn by passing A.C current up to 5 Amperes. Spectroscopic measurements are employed for purpose of estimating two main plasma parameters electron temperature (Te) and electron density (ne). Emission spectra from positive column (PC) zone of the discharge have been studies at different values of magnetic field and pressures at constant discharge currents of 1.5 mA. Electron temperature (Te) and its density are calculated from the ratio of the intensity of two emission lines of the same lower energy levels. Experimental results show the abnormal glow region characteristics (positive resistance). Breakdown voltage versus pressure curves near the curves of paschen and decrease as magnetic field increases due to magnetic field confinement of plasma charged particles. Also the electrical conductivity increases due to enhancing magnetic field at different gas pressures. Both temperature density of electron and the intensities of two selected emission lines decrease with increasing pressure due decreasing of mean free path of electron. Electron density increase according to enhancing magnetic field, while the intensity of emitting lines tends to decrease.

The HelCat basic plasma science device

2014 ◽  
Vol 81 (1) ◽  
Author(s):  
M. Gilmore ◽  
A. G. Lynn ◽  
T. R. Desjardins ◽  
Y. Zhang ◽  
C. Watts ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Axial Magnetic Field ◽  
Medium Size ◽  
Plasma Parameters ◽  
Plasma Sources ◽  
Plasma Gun ◽  
Background Magnetic Field ◽  
Wide Range ◽  
Plasma Science ◽  
Helicon Source

TheHelicon-Cathode(HelCat) device is a medium-size linear experiment suitable for a wide range of basic plasma science experiments in areas such as electrostatic turbulence and transport, magnetic relaxation, and high power microwave (HPM)-plasma interactions. The HelCat device is based on dual plasma sources located at opposite ends of the 4 m long vacuum chamber – an RF helicon source at one end and a thermionic cathode at the other. Thirteen coils provide an axial magnetic fieldB⩾ 0.220 T that can be configured individually to give various magnetic configurations (e.g. solenoid, mirror, cusp). Additional plasma sources, such as a compact coaxial plasma gun, are also utilized in some experiments, and can be located either along the chamber for perpendicular (to the background magnetic field) plasma injection, or at one of the ends for parallel injection. Using the multiple plasma sources, a wide range of plasma parameters can be obtained. Here, the HelCat device is described in detail and some examples of results from previous and ongoing experiments are given. Additionally, examples of planned experiments and device modifications are also discussed.

Combined Effects of Magnetic Field and Thermal Radiation on Fluid Flow and Heat Transfer of Mixed Convection in a Vertical Cylindrical Annulus

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Ben-Wen Li ◽  
Wei Wang ◽  
Jing-Kui Zhang
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Fluid Flow ◽  
Mixed Convection ◽  
Axial Magnetic Field ◽  
Outer Cylinder ◽  
Mhd Equations ◽  
Temperature Fields ◽  
Flow And Heat Transfer ◽  
Cylindrical Annulus

Magnetohydrodynamic (MHD, also for magnetohydrodynamics) mixed convection of electrically conducting and radiative participating fluid is studied in a differentially heated vertical annulus. The outer cylinder is stationary, and the inner cylinder is rotating at a constant angular speed around its axis. The temperature difference between the two cylindrical walls creates buoyancy force, due to the density variation. A constant axial magnetic field is also imposed to resist the fluid motion. The nonlinear integro-differential equation, which characterizes the radiation transfer, is solved by the discrete ordinates method (DOM). The MHD equations, which describe the magnetic and transport phenomena, are solved by the collocation spectral method (CSM). Detailed numerical results of heat transfer rate, velocity, and temperature fields are presented for 0≤Ha≤100, 0.1≤τL≤10, 0≤ω≤1, and 0.2≤εW≤1. The computational results reveal that the fluid flow and heat transfer are effectively suppressed by the magnetic field as expected. Substantial changes occur in flow patterns as well as in isotherms, when the optical thickness and emissivity of the walls vary in the specified ranges. However, the flow structure and the temperature distribution change slightly when the scattering albedo increases from 0 to 0.5, but a substantial change is observed when it increases to 1.

Experimental study of fast hydromagnetic waves in an argon plasma

1964 ◽  
Vol 278 (1373) ◽  
pp. 243-255 ◽  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Axial Magnetic Field ◽  
Argon Plasma ◽  
Wave Number ◽  
Axially Symmetric ◽  
Plasma Parameters ◽  
Quantitative Evidence ◽  
Hydromagnetic Waves

In these experiments fast hydromagnetic waves are excited by discharging a capacitor through a single turn coil surrounding a cylindrical column of magnetized argon plasma. The plasma column is 200 cm long and 22 cm in diameter, and the axial magnetic field strength is varied in the range from 1 to 6 kG. The wave amplitude is typically 10 G, and the frequency is varied between 1.2 and 6 times the ion cyclotron frequency. Measurement of the radial variation and the relative amplitudes of the three components of the wave magnetic field shows that the oscillation is the lowest axially-symmetric mode. As predicted by the theory, the wave is elliptically polarized in the rθ plane with the magnetic vector rotating in the same sense as the electron cyclotron rotation. The experimental results demonstrate the cut-off of this mode both as the frequency is decreased and as the axial magnetic field strength is increased. Measurements of the axial wave number and absorption coefficient are in good numerical agreement with theoretical dispersion curves computed from the measured plasma parameters. This work provides quantitative evidence to support the theories currently used in treating hydromagnetic oscillations, both stable and unstable, of magnetized plasmas.

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