Critical Drift Velocity Research Articles

The collisional study of EIC waves in a magnetized dusty plasma with the inclusion of a DC electric field

This study investigates Electrostatic Ion Cyclotron (EIC) waves and their behaviour in weakly collisional plasmas, utilizing a proposed kinetic analytical model. The findings include alterations in EIC wave dispersion characteristics due to collisions, with parameters such as dust density, collision frequency, gyro-radius, magnetic field, density ratio, and electric field influencing wave growth rate and frequency. Temperature analysis reveals that higher electron-to-ion temperature ratios lead to increased frequency and critical drift velocity, while decreasing the growth rate. In addition, the critical drift velocity is studied for the unstable mode and it is observed that the relative density ratio increases with a reduction in critical drift velocity. Electron collisions destabilize EIC waves, while ion collisions stabilize them. Furthermore, the presence of dust particles decreases the growth rate of EIC waves as dust grain density increases. These results align with observations reported in previous literature.

Terahertz radiation from the Dyakonov-Shur instability of hydrodynamic electrons in Corbino geometry

Hydrodynamic electrons flowing through a two-dimensional channel are predicted to undergo a plasma instability above a critical drift velocity. This Dyakonov-Shur (DS) instability terminates as a coherent nonlinear oscillator, which shows promise as a source of radiation that could fill the so-called terahertz gap. In this work, we study radial flow in a Corbino disk, and demonstrate how the DS instability is substantially enhanced in this geometry, both in terms of a lower critical drift velocity and a higher generated power. Interestingly, hydrodynamic electron flows were recently reported in a graphene sample of this geometry, and our results are therefore directly relevant to current efforts to detect this experimentally elusive phenomenon. The analysis is based on a hydrodynamic approach and features both linearized calculations as well as full numerical simulations of the Navier-Stokes equation.

In the existence of a transverse dc electric field, the kinetic theory of current‐driven electrostatic ion cyclotron waves excitation in a magnetized dusty plasma

AbstractThe theoretical modelling for the electrostatic ion cyclotron (EIC) waves in the existence of a transverse direct current (dc) electric field in a collisionless magnetized dusty plasma has been investigated using the kinetic theory model. It is examined that after incorporation of dc electric field with the dust grains can alter the dispersion properties of EIC waves in a magnetized dusty plasma. Our model developed accounts for the critical drift velocity, electron‐to‐ion temperature ratio, magnetic field, the number density of dust grains, relative density of negatively charged dust grains, and finite gyroradius parameter. Our investigation found that normalized growth rate and frequency increase with the relative density ratio and electric field. Moreover, the critical drift velocity for the excitation of the mode with negatively charged dust grains and electron‐to‐ion temperature ratio has been studied, and it was found that critical drift velocity decreases with the increase in negatively charged dust grains. The impact of dust grains on the low‐frequency waves has also been studied, and it was found that an increase in dust grain number density results in the reduction of growth rate. Some of our theoretical findings are consistent with the experimental observations.

Graphene\u2019s non-equilibrium fermions reveal Doppler-shifted magnetophonon resonances accompanied by Mach supersonic and Landau velocity effects

Oscillatory magnetoresistance measurements on graphene have revealed a wealth of novel physics. These phenomena are typically studied at low currents. At high currents, electrons are driven far from equilibrium with the atomic lattice vibrations so that their kinetic energy can exceed the thermal energy of the phonons. Here, we report three non-equilibrium phenomena in monolayer graphene at high currents: (i) a “Doppler-like” shift and splitting of the frequencies of the transverse acoustic (TA) phonons emitted when the electrons undergo inter-Landau level (LL) transitions; (ii) an intra-LL Mach effect with the emission of TA phonons when the electrons approach supersonic speed, and (iii) the onset of elastic inter-LL transitions at a critical carrier drift velocity, analogous to the superfluid Landau velocity. All three quantum phenomena can be unified in a single resonance equation. They offer avenues for research on out-of-equilibrium phenomena in other two-dimensional fermion systems.

Linear theory of current driven ion acoustic instability at the distance 0.3 to 1 AU from the Sun

Several kinds of instabilities are often observed in the solar wind. We studied the linear theory of the current-driven electrostatic ion acoustic instability at frequencies near the ion cyclotron frequency at distances from the Sun over 0.3 to 1 AU. The properties of current driven electrostatic ion-acoustic instability are investigated. The instability parameters, such as angular wave frequency, the critical drift velocity and the growth rate are calculated. We used the dispersion relation in hot magnetized plasma to calculate the current driven ion acoustic instability properties. To determine the critical drift velocity and the growth rate a full numerical solution of the dispersion relation equation is carried out. Since the growth rate of instability depends on the wave normal angle, the drift velocity of the electron along the magnetic field and the ion thermal cyclotron radius, the calculation is carried out for ranging of the wave normal angles, drift velocities and ion thermal cyclotron radius. The results show that the growth rate of instability increases with increasing distance from the Sun. The growth rate of instability increases with decreasing the wave normal angle, but the critical drift velocity decreases with decreasing the wave normal angle.

Implantation-free edge termination structures in vertical GaN power diodes

Gallium nitride (GaN) is a promising candidate for power applications, due to its superior electrical properties such as high critical breakdown field and saturation drift velocity. The recent emergence of GaN substrates with low defect densities has made it feasible to develop efficient vertical GaN power diodes. However, the breakdown voltage of these diodes is far from the theoretical value, due to the lack of suitable edge termination techniques in GaN such as junction termination extension (JTE). This is attributed to the processing challenges in fabricating GaN power diodes where it is difficult to form p-type regions through implantation. This work addresses this challenge and proposes the design, optimization, and a comprehensive design methodology for implantation-free, edge termination techniques such as field plate (FP), single and multi-etch JTE, and a hybrid FP-JTE structure, suitable for vertical GaN diodes. The proposed approaches demonstrate that close to theoretical breakdown voltages (>80%) are achievable, with greater area efficiency, simple processing, and high tolerance in process variation.

Dust-ion-acoustic modes at comet 67P/Churyumov-Gerasimenko

The dynamics of dust-ion-acoustic (DIA) modes at Comet 67P/Churyumov-Gerasimenko, where H2O+ ions with warm and cold electrons as well as dust grains were detected, are investigated within the two-electron-temperature dusty plasmas model by the kinetic theory. In terms of current-driven DIA waves, the bulk electron drift is assumed to overcome Landau damping due to resonance interaction of DIA waves with cometary ions. The results show that the presence of charged dust grains lowers the critical drift velocity of bulk electrons and the Landau damping rates, and inversely enhances the growth rates of DIA instabilities. Consequently, the presented dust grains make the DIA modes more easily excited. The present results indicate that the DIA wave may be a possible candidate to interpret the wave observation of the European Space Agency's spacecraft “Rosetta” at comet 67P/Churyumov-Gerasimenko.

Counter-Doped Multizone Junction Termination Extension Structures in Vertical GaN Diodes

GaN is an attractive wide bandgap semiconductor for power applications, owing to its superior electrical properties, such as high critical electric field and saturation drift velocity. Recent advancements in developing native GaN substrates has drawn attention toward exploring vertical GaN power diodes with high breakdown voltages (VBR). In practice, effective edge terminations techniques, such as junction termination extension (JTE) structures, play a crucial role in realizing high-voltage devices. Though certain challenges in fabricating GaN diodes, such as difficulty in forming p-type region, makes it difficult to realize edge termination, hence impeding the development and adoption of such devices. This paper aims to address these challenges by presenting the design and methodology of forming multi-zone, counter-doped JTE structures in vertical GaN diodes, which attains close to theoretical breakdown voltage for a wide range of tolerance in implant dose variation. Extensive device simulations using experimental data and including the effects of surface charges and implant profiles, are performed to present realistic results. The results suggest that >80% of ideal VBR is achievable for a wide range of doping concentration ( $2.4\times 10^{17}$ cm $^{-3}$ ) with a maximum VBR reaching 96% of the ideal value. This paper serves as the first step toward leveraging the current challenges in the fabrication of GaN diodes, by proposing optimum design techniques for realizing vertical GaN diodes with high breakdown voltages.

Current-Driven Low-Frequency Electrostatic Waves in a Collisional Strongly Coupled Magnetized Dusty Plasma

Current-driven low-frequency electrostatic waves are studied in a collisional strongly coupled magnetized dusty plasma. The theoretical model for the longitudinal and transverse modes is developed in the regime $\omega \tau _{m} \ll 1$ for the collisional strongly coupled magnetized dusty plasma in the presence of drifting currents. It is observed that the dispersion properties of low-frequency electrostatic waves are modified under the effect of magnetic field-aligned drifting ion currents in a strongly coupled collisional magnetized dusty plasma. The frequency rate and growth rate of longitudinal and transverse modes increase with normalized wave number. Moreover, the growth rate of unstable waves is destabilized with normalized drift velocity of ions for both longitudinal and transverse modes. The critical drift velocity of ions decreases with normalized wave number but increases with increase in the strong correlation parameter $\Gamma $ . The effect of strong coupling parameter on the frequency and growth rate of low-frequency electrostatic modes in the presence of current drift and collisions is also investigated.

Analytical study of effects of positron density and temperature anisotropy on electrostatic ion cyclotron instability

The effects of the positron concentration and ion temperature anisotropy on the electrostatic ion cyclotron instability are studied analytically, in a magnetized electron-positron-ion plasma with temperature anisotropy, using the linear kinetic theory. Positrons and electrons are supposed to drift either in the same direction or in opposite directions relative to singly ionized stationary ions and parallel to the magnetic field. The dispersion relation of the electrostatic ion cyclotron waves is derived, and then the conditions for exciting the instability of the waves are investigated. Moreover, the condition for the marginally stable state is also studied. It is found that as the positron concentration and perpendicular ion temperature increase, the growth rate of the electrostatic ion cyclotron instability decreases, whereas the critical drift velocity increases. It is also found that for the chosen set of parameters, with electrons and positrons drifting in the same direction, the instability in the plasma is stronger than when the electrons and positrons drift in opposite directions. In addition, a comparison is made to the normal electron-ion plasma.

Electrostatic ion cyclotron instability in a plasma with q-nonextensive distributions

The general dispersion relation for electrostatic waves in magnetized plasmas is derived using the standard linear Vlasov theory and the q-distribution of Tsallis statistics. The dispersion relation is solved for a plasma that has nonextensive electrons drifting with respect to stationary ions, and satisfies the other conditions for the excitation of electrostatic ion cyclotron waves. The frequency spectrum and growth rate are obtained for the electrostatic ion cyclotron waves. The marginally stable state is investigated for the onset of instability. It is shown that decreasing the non-extensivity parameter of electrons strengthens the instability and decreases the minimum value of the critical drift velocity, whereas larger temperature anisotropy of ions weakens the instability and increases the minimum value of the critical drift velocity.

Numerical analysis of electrostatic ion cyclotron instability in an electron-positron-ion plasma

This paper presents a theoretical study of the effects of positron density on the electrostatic ion cyclotron instability in an electron-positron-ion plasma using the kinetic theory approach. It is supposed that positrons and electrons can drift parallel to the magnetic field either in the same or the opposite directions. The dispersion relation for the electrostatic ion cyclotron waves in an electron-positron-ion plasma is derived, and the numerical results are investigated. It is found that an increase in positron concentration increases the critical drift velocity for excitation of the instability in both configurations. It is also found that as the positron concentration increases the growth rate of instability decreases. In addition, it is shown that at low velocities the maximum instability growth rate for the unidirectional case is higher than the counter-streaming case; however, after a certain velocity, the maximum growth rate in the counter-streaming case dominates that of the unidirectional case.

THE MULTI-SPECIES FARLEY-BUNEMAN INSTABILITY IN THE SOLAR CHROMOSPHERE

Empirical models of the solar chromosphere show intense electron heating immediately above its temperature minimum. Mechanisms such as resistive dissipation and shock waves appear insufficient to account for the persistence and uniformity of this heating as inferred from both UV lines and continuum measurements. This paper further develops the theory of the Farley-Buneman Instability (FBI) which could contribute substantially to this heating. It expands upon the single ion theory presented by Fontenla (2005) by developing a multiple ion species approach that better models the diverse, metal-dominated ion plasma of the solar chromosphere. This analysis generates a linear dispersion relationship that predicts the critical electron drift velocity needed to trigger the instability. Using careful estimates of collision frequencies and a one-dimensional, semi-empirical model of the chromosphere, this new theory predicts that the instability may be triggered by velocities as low as 4 km s^-1, well below the neutral acoustic speed. In the Earth's ionosphere, the FBI occurs frequently in situations where the instability trigger speed significantly exceeds the neutral acoustic speed. From this, we expect neutral flows rising from the photosphere to have enough energy to easily create electric fields and electron Hall drifts with sufficient amplitude to make the FBI common in the chromosphere. If so, this process will provide a mechanism to convert neutral flow and turbulence energy into electron thermal energy in the quiet Sun.

Аналитическая зависимость критической по заносу скорости быстроходной гусеничной машины от ее колебаний

Аналитическая зависимость критической по заносу скорости быстроходной гусеничной машины от ее колебаний

Kinetic theory of electrostatic ion cyclotron waves (QPESIC) in multicomponent plasmas with negative ions

The instabilities of the quasi-perpendicular electrostatic (?B = 0) ioncyclotron waves (QPESIC) are investigated. The kinetic theory with BGK model collision integrals is used to estimate the critical electron drift velocity in the presence of positively or negatively charged resonant ions in multi-component plasma. Analytical evaluation for the ion-cyclotron modes and instabilities in the long-wave range in a weakly-ionized Maxwellian plasma with two positive ion species, one negative ion species and with electrons, drifting along magnetic lines of force is demonstrated. The spectrum in these situations is also given. It is shown that the critical drift decreases as the state of plasma approaches the isothermic state.

Anomalous resistivity in non‐Maxwellian plasmas

Vlasov simulations of the current‐driven ion‐acoustic instability produced in Maxwellian and non‐Maxwellian (Lorentzian, κ = 2) electron‐ion plasma with number density 7 × 106 cm−3, reduced mass ratio mi/me = 25, and electron to ion temperature ratio Te/Ti = 1 are presented and compared. A concise stability analysis of current‐driven ion‐acoustic waves in Maxwellian and non‐Maxwellian plasmas modeled by generalized Lorentzian distribution function with index 2 ≤ κ ≤ 7 and electron to ion temperature ratio 1 ≤ Te/Ti ≤ 100 is also presented. The ion‐acoustic instability is excited in low temperature ratio Lorentzian (κ = 2) plasma for lower absolute electron drift velocity (up to half the critical electron drift velocity of a Maxwellian). The anomalous resistivity resulting from ion acoustic waves in a Lorentzian plasma is a strong function of the electron drift velocity and in the work presented here varies by a factor of ∼100 for a 1.5 increase in the electron drift velocity. Furthermore, ion‐acoustic anomalous resistivity is excited for electron drift velocities that would be stable for Maxwellian plasmas. The magnitude of resistivity which can be generated by unstable ion‐acoustic waves may be important for magnetic reconnection at the magnetopause.

Ion acoustic instability of HPT particles, FAC density, anomalous resistivity and parallel electric field in the auroral region

During the magnetic storm of 21st March 1990, the DE-1 spacecraft encountered the auroral region at high invariant latitude at altitudes ranging from a few thousand kilometers in the ionosphere to many earth radii in the magnetosphere. The magnetic field perturbations interpretable as field aligned current (FAC) layers and the electrostatic turbulence possibly due to electrostatic ion acoustic instability driven by these currents are shown. The critical drift velocity of Hot Plasma Torus (HPT) electrons and the growth rate of ion acoustic wave as a function of electron to ion temperature ratio (T e/Ti) for low and high current densities and energy of HPT electrons are found out. The intense FAC destabilizes the ion acoustic wave and the resultant electrostatic turbulence creates an anomalous resistivity. The current driven resistivity produces parallel electric field and high power dissipation. The anomalous resistivityη, potential difference along the auroral field lines Vt|, intensity of electric field turbulenceE t| and power produced per unit volumeP are computed. It is found that the change in westward magnetic perturbation increasesJ t|, η, Vt|, Et| andP. Hence HPT electrons are heated and accelerated due to power dissipation during magnetically active periods in the auroral region. Concerning, applications, such HPT electrons can be used in particle accelerators like electron ring accelerator, smokatron etc.

Theory of negative energy holes in current carrying plasmas

The theory of hole structures or phase-space vortices in a one-dimensional current-carrying plasma is extended, focusing on the energy of trapped-particle modes in comparison to a homogeneous plasma. It is shown how the energy expression presented in [J.-M. Grießmeier and H. Schamel, Phys. Plasmas 9, 2462 (2002)] is obtained for small amplitude structures. Parameter regimes admitting negative energy solutions are given. It is demonstrated how negative energy structures can be found analytically for the case of a generalized solitary electron hole (where ion trapping is shown to further lower the critical drift velocity), for a generalized solitary ion hole (where the influence of electron trapping increases the critical drift velocity) and for a harmonic (monochromatic) structure. Consequently, a plasma may become nonlinearly unstable well below linear threshold already for infinitesimal wave amplitudes.

Excitation of ion-acoustic-like waves by subcritical currents in a plasma having equal electron and ion temperatures.

The effect of a magnetic-field-aligned plasma flow with a transverse velocity gradient on the excitation of current-driven ion-acoustic-like waves in a plasma having equal electron and ion temperatures (T(e) = T(i)) was investigated experimentally. In agreement with theoretical predictions, the presence of sheared plasma flow substantially reduces the critical electron drift velocity needed to produce the ion-acoustic instability.

Instabilities of steps induced by the drift of adatoms and effect of the step permeability

We theoretically study step wandering and step bunching induced by the drift of adatoms with attention to the permeability of steps. The critical drift velocity to induce the instability is calculated, and Monte Carlo simulation is performed to test the linear analysis. In sublimation, when the step distance is small in comparison with the surface diffusion length, the wandering and bunching of steps can occur simultaneously with the step-down drift if steps are impermeable. The instabilities do not occur simultaneously if steps are permeable: the bunching occurs with the step-up drift, and the wandering with the step-down drift. In growth, when the step distance is small, the bunching occurs with the step-down drift and the step wandering occurs with the step-up drift irrespective of the permeability, in agreement with M\'etois and Stoyanov [Surf. Sci. 440, 407 (1999)]. The change of the permeability with increasing temperature can explain the instabilities observed in Si(111) vicinal face [M. Degawa et al., Jpn. J. Appl. Phys 38, L308 (1999)].