An Improved Two-Dimensional Snow-Plow Model for Plasma Acceleration in Coaxial Geometry (original) (raw)
Studies on a low energy plasma focus discharge
NUKLEONIKA, 2007
This paper is devoted to the experimental and theoretical study of plasma current sheath behavior for a low energy plasma focus device operating at a filling nitrogen gas pressure of 3.3 torr, and at a stored energy of 1.2 kJ. Axial distribution profiles of plasma current sheath (PCS) characteristics such as propagation velocity V z , acceleration a z , azimuthal magnetic field induction B θ , and magnetic force per unit volume F z /m 3 along the coaxial electrodes system was performed from a magnetic probe and miniature Rogovsky coil signals. The experimental results showed that the axial distribution of V z , a z , B θ and F z has approximately the same profile and the maximum value of these parameters was detected nearly at a mid-distance of coaxial electrodes system. Theoretical description of PCS dynamics at the axial phase, based on a snowplough, was estimated as a function of discharge time. These data were compared with the received experimental results.
Snow plow model of IPD discharge
Vacuum, 2003
A two-dimensional fluid model of snow plow type to simulate the plasma dynamics in a coaxial accelerator is described. The self-consistent model combines the description of the electric circuit with the plasma resistance and inductance, as well as the balance of magnetic and fluid pressures at the contact interface. The applicability of presented model has been proved by comparison of computational results with the high-speed photographs of plasma dynamics in the impulse plasma deposition (IPD) coaxial accelerator. r
Sheath and plasma parameters in a magnetized plasma system
Pramana, 2000
The variation of electron temperature and plasma density in a magnetized N¾ plasma is studied experimentally in presence of a grid placed at the middle of the system. Plasma leaks through the negatively biased grid from the source region into the diffused region. It is observed that the electron temperature increases with the magnetic field in the diffused region whereas it decreases in the source region of the system for a constant grid biasing voltage. Also, investigation is done to see the change of electron temperature with grid biasing voltage for a constant magnetic field. This is accompanied by the study of the variation of sheath structure across the grid for different magnetic field and grid biasing voltage as well. It reveals that with increasing magnetic field and negative grid biasing voltage, the sheath thickness expands.
Current-Voltage characteristics of nonharmonically modulated plasma boundary sheaths
mpserver.pst.qub.ac.uk
The dynamics of dual frequency capacitive RF discharges is largely dominated by the charge-voltage characteristics of the plasma boundary sheath, which in turn is dependent on the characteristcs of the modulation. This contribution focuses on the behavior of the sheath under nonharmonic excitation, such as square, sawtooth, dual frequency and pulse-like excitation. Fluid model of a collisional sheath and a PIC simulation of different complexety and computational efficiency is established and compared.
IEEE Transactions on Plasma Science, 2014
A self-consistent analytical model for a timeindependent collisional capacitively coupled plasma (CCP) sheath driven by a triple frequency (TF) RF current source is proposed. Sheath parameters are calculated using this model for some standard plasma parameters and are compared with those of a single frequency (SF) and a dual frequency (DF) capacitively coupled collisional sheath. This model estimates higher values of sheath width and potential with more oscillating behavior compared with SF and DF sheaths. By proper choice of source frequencies or phase differences in the source currents, it is possible to adjust the ion energy hitting the electrode. Use of TF source is found to facilitate better control upon sheath parameters for collisional CCP.
IEEE Transactions on Plasma Science, 2000
Using the self-consistent steady-state 2-D Kinetic Plasma Solver (KIPS-2D), thorough characterizations are performed of high-voltage cylindrical sheaths surrounding ionattracting conductive cylinders immersed in stationary as well as flowing collisionless plasmas. Analytical fits are obtained that allow for the accurate prediction of stationary sheath sizes for round-cylinder radii anywhere from one thousandth of a Debye length to five Debye lengths and for any bias potential beyond a small lower bound. Plasma flow is shown to progressively compress the sheath on its ram and lateral sides, down to a limit that closely matches the stationary frozen-ion sheath radius. Conversely, plasma flow is shown to cause a significant wake-side elongation of the sheath. The quasi-elliptical sheath-edge contours observed under flowing conditions can be characterized by their along-flow and across-flow dimensions. By normalizing these dimensions against stationary-sheath diameters, contour plots of the corresponding flow-effect correction factors can be obtained that account for plasma-flow velocity effects in a wide range of speed regimes and bias potentials. In this paper, Mach numbers up to ten and bias potentials from −10T e to −500T e (where T e is the electron temperature in units of volts) are simulated and corresponding correction factors are computed, although KiPS is capable of simulating even higher speeds and bias potentials. These correction factors appear to stabilize at high voltages, suggesting that their values at the highest simulated potential bias possibly can be used with reasonable accuracy to predict performance at even higher (but nonrelativistic) bias-potential values using analytical equations derived from stationary simulations. For example, at a Mach number of 1.1, the along-flow and across-flow sheath dimensions at high voltages are expected to be around 115% and 85% of the stationary-sheath diameter, respectively. Flow-effect correction factors for current collection are also obtained for the ram-side, wake-side, and total collected current. For the same plasma-velocity example, at high voltages, total current collection is minimized to about half of the stationary value, which would translate into a 50% reduction in power to collect the current. This example is of significance for Earth-radiation-belt remediation-system concepts using high-voltage tethers.
Computer simulation of the sheath and the adjacent plasma in the presence of a plasma source
Vacuum, 2017
A model is constructed allowing computer simulations of the near-wall area of a planar plasma sheet in conditions where the steady state of the plasma is supported by the production of charged particles in a region removed from the wall. Calculations have revealed variation in the energy distribution of the electrons in both time and spatially over the sheet width (cooling the electronic component) due to absorption of fast electrons at the walls bounding the plasma volume. It is shown that the plasma density profile across the sheet width has an abrupt decrease at the boundary of the region of plasma regulation. Thus the standard concepts of the potential and plasma density distributions in the sheath and presheath based on the assumption of a stable energy distribution for the electrons in the presheath yields inaccurate results for the plasma sheet where the ionization source is remote from the wall.
Physics of Plasmas
A double plasma device has two regions: Source region and target region. These two regions are divided by a magnetic filter field. A grid is placed coplanar to the magnetic filter. To study the sheath structure in the target region, a metallic plate is placed at the center, which can be biased with respect to the chamber (ground) potential. Plasma is created in the source region by filament discharge technique. Plasma diffusing from the source region to the target region is subjected to the magnetic filter field and also an electric field applied on the grid. Plasma thus obtained in the target region forms a sheath on the biased plate. The influence of both the magnetic filter field and the electric field, applied between the grid and the chamber wall, on the sheath structure formed on the biased plate is studied. It is found that the magnetic filter field and the electric field change the sheath structure in different ways. V
Amrit research journal, 2022
Ion and electron densities, potential, electric field and space charge density in magnetized plasma sheath for various permittivity of plasma medium are studied using the Kinetic trajectory simulation method. • The plasma parameters in magnetized plasma sheath regime may be controlled by controlling the permittivity in plasma medium. • The results are qualitatively more accurate and provide a better understanding of the plasma-wall transition phenomena.
Dynamic model of the electrode sheaths in symmetrically driven rf discharges
Physical Review A - PHYS REV A, 1990
A self-consistent dynamic model for rf sheaths in the frequency range between the ion and electron plasma frequencies is developed and solved for arbitrary collision parameters and arbitrary rf sheath voltages. For floating dc sheaths with no rf voltage, and for collisionless and highly collisional rf sheaths at high rf voltages, the obtained solutions for the dc sheath voltage and the capacitive sheath width converge to the known limits. However, for rf voltages of tens and hundreds of volts, usually encountered in rf discharge applications, our results differ from those obtained using high voltage approximations and are in good agreement with the experiment. The found relations between the sheath characteristics show that the rf sheath capacitance and the equivalent sheath resistance, corresponding to ion acceleration losses, are practically independent of the rf voltage and the discharge current.
Keywords Langmuirprobe, electron temperature, density,longitudinal magnetic field. PACS 52.25.Xz, 52.80.Hc, 52.70.Ds Thev ariations of plasma parameters of ad cd ischarge in an on-uniform magnetized plasma were measured usingf ast floatingd oubleL angmuirp robes. As olenoidi su sed to produce au niform magnetic field parallel to thed ischarge axis. Thea xial changes of thep lasma parameters are presented in ther ange of longitudinal magnetic fields 200 to 600 Gauss at thepressure range 0 . 3 to 2 . 1 Torr and discharge currents 5 and 15 mA in argon gas. Theexperimental results indicatethat,asaconsequence of theaxial magnetic field and thevariations in thedischarge tube radii, theplasma parameters at smallradius exhibitobvious changes in theirdistributions along theaxiscompared to thesituationofunmagnetized plasma.
Simulation of Plasma Focus Devices with Hemisphere Electrodes
Journal of Fusion Energy, 2009
A magneto-hydrodynamic simulation of a plasma focus device with hemisphere electrodes is constructed. The snowplow model is used with help of the momentum conservation equation to describe the motion of the plasma sheath between the two concentric hemispheres. The model simulates various plasma parameters like plasma temperature and plasma sheath velocity. The circuit equation is used to calculate the discharge current and electrodes voltage across the two hemisphere terminals. A comparison between the cylindrical and spherical devices is built. The results show that the current dip and the spike voltage is expected to be much pronounced in the spherical devices. It is found also that the plasma sheath velocity and temperature in the case of the cylindrical system are higher than that in the spherical one.
Sheath propagation along the cathode of a plasma opening switch
IEEE Transactions on Plasma Science, 1999
A model is proposed for sheath propagation along the cathode of a plasma opening switch that is valid for switch conditions intermediate to the erosion-dominated and MHDdominated regimes. The model assumes that the sheath propagates due to erosion of the plasma that conducts the current. The calculated velocity of propagation agrees with particle-incell simulation results much better than do velocities calculated by previous models that assumed magnetic pressure opens a vacuum gap along the cathode.
MHD Simulation of Hemisphere Plasma Focus Using Snowplow Model
Fusion Science and Technology, 2020
The Hemisphere Plasma Focus (HSPF) device is a new construction of plasma focus (PF) devices wherein the discharge takes place between the inner and outer concentric hemispherical electrodes with total energy up to 3.4 kJ. The pinch effect appears in the shape of a sharp crevice in the discharge current signal. HSPF is simulated by utilizing the Snowplow Model depending on the circuit equation incorporated with the momentum equation. Some modifications were added to the model to improve the theoretical data in order to be consistent with the experimental results. The code includes a rundown phase starting from the equator point toward the antipodal point and the reflected shock phase at the axis. The model results are compared with experimental results, and the effect of discharge parameters such as the discharge voltage and helium gas pressure on the plasma parameters is studied. The total system inductance is about 285 nH with a resistance of about 23 mΩ. Furthermore, the plasma inductance has a maximum value at the pinch time, which is decreased by increasing the charging voltage or decreasing the gas pressure. The mass factor in the HSPF device is found to be relatively low compared to that of the coaxial PF device. The shock front and current sheath velocities are increased by increasing the drive factor while the pinch time is decreased. Also, the minimum pinch radius and the plasma inductance have a reverse trend as a function of the drive factor.
Case Study: On Most General Exact Solution of Plasma Sheath Model for a Negatively Biased Probe
m-hikari.com
Plasma characteristics have been identified with the aid of an insulated probe analysis immersed in the plasma. An Exact solution approach coupled with initial values for the sheath thickness and wall potential can predict the overall relation between the distance from the wall and wall potential based on a positive space charge near the vicinity of the probe. The I-V plasma characteristics of the probe can identify the position of the point or potential where the total current drawn by the probe is zero, i.e. floating potential.
Two-dimensional Fluid Model of DC and RF Plasma Discharges in Magnetic Field
36th AIAA Plasmadynamics and Lasers Conference, 2005
The hydrodynamic equations of continuity and momentum for electrons and ions along with the electrostatic field equation are solved numerically using a self-consistent finite-element algorithm in the low-pressure, high frequency regime. The plasma formation over a flat plate is investigated for three different cases. The twodimensional numerical algorithm is first benchmarked with published literature for plasma formed between symmetric electrodes in nitrogen gas. Discharge characteristics of plasma for an electrode-insulator configuration are then analyzed under steady and transient conditions using argon as a working gas. The effect of magnetic field on electric potential and charge difference is studied for an infinitesimally thin electrode. The magnetic field distorts the stream-wise distribution because of strong y-momentum v×B coupling. Finally, the shape effects of insulator-conductor edge for an electrode of finite thickness have been compared using a 90 o shoulder and a 45 o chamfer. The 90 o chamfer displays a stronger body force created due to plasma in the downward and forward directions.
Isentropic plasma sheath model for improved fidelity
Physics of Plasmas, 2022
A model is developed for a collisionless plasma sheath assuming isentropic electrons in contrast to the standard isothermal electron assumption. This approach is enabled by the approximation of a Maxwellian electron velocity distribution function across the sheath, which is justified by near wall measurements. The conservation of entropy leads to a modified Boltzmann relation and a modified Bohm criterion. The predicted floating sheath potential is in excellent agreement with experimental data. Takamura's model for a space-charge limited plasma sheath near an emissive surface is also modified for isentropic electrons and with that modification agrees well with numerical results from a full fluid plasma model.