Plasma Wave Instability Research Articles

Instability of whistler-mode waves by a relativistic kappa-loss-cone distribution in space plasmas

We investigate the growth rate of field-aligned whistler-mode waves in space plasmas by using a fully relativistic treatment, including a recently developed relativistic kappa-loss-cone (KLC) distribution and a fully relativistic growth rate formula. Numerical calculations are carried out for a direct comparison between the new KLC distribution and the current kappa distribution, respectively. It is found that, in the lower wave frequency (e.g. ω ≲ 0.1Ωe), the wave growth by the KLC distribution is generally higher than that by the kappa distribution, due to a larger fractional number of the resonant electrons ηrel (which controls the wave growth) for the KLC distribution; but is lower in the higher wave frequency. The growth rates, as expected, tend to increase with the thermal anisotropy A, and the peak wave growth increases more rapidly for the kappa distribution. The relativistic anisotropy Arel basically decreases as the thermal parameter θ2 increases; whereas the fractional number of the resonant electrons ηrel is found to be large in the case of θ2 ∼ 150 keV, and results in a large wave growth. This indicates that hot electrons with typical energies of hundreds of keV may play a dominant role on the instability of whistler-mode waves. The results above have applications to plasma wave instability in the outer radiation belts of the Earth, the Jovian inner magnetosphere and other astrophysical plasmas where relativistic electrons are present.

Non Resonant Response to Terahertz Radiation by Submicron CMOS Transistors

Experimental investigations on detection of terahertz radiation are presented. We used plasma wave instability phenomenon in nanometer Silicon field effect transistor. A 30 nm gate length transistor was illuminated by THz radiation at room temperature. We observe a maximum signal near to the threshold voltage. This result clearly demonstrates the possibility of plasma wave THz operation of these nanometer scale devices. The response was attributed to a non resonant detection. We also demonstrate the possibility to observe a resonant detection on the same devices.

Terahertz plasma wave generation in ultrashort-channel field effect transistors: The essential role of carrier drift velocity saturation

Taking into account both the carrier scattering and the velocity saturation, we examine the plasma wave instability of the high-density two-dimensional electron gas in a field effect transistor. It is shown that both the carrier scattering and the velocity saturation lead to a strong damping of the plasma wave instability. A threshold diagram of the instability is calculated. The device parameters required for a plasma wave generation are shown to be more strict than those reported in up-to-date subterahertz emission experiments.

Detection of terahertz radiation in gated two-dimensional structures governed by dc current

We present theoretical and experimental studies of the direct current effect on the detection of subterahertz and terahertz radiation in gated two-dimensional structures. We developed a theory of the current-driven detection both for resonant case, when the fundamental frequency of plasma oscillation is large compared to inverse scattering time, ${\ensuremath{\omega}}_{0}\ensuremath{\tau}⪢1$, and for the nonresonant case, ${\ensuremath{\omega}}_{0}\ensuremath{\tau}⪡1$, when the plasma oscillations are damped. We predict that, in the nonresonant case, even a very small dc current would increase the detection amplitude up to two orders of magnitude. Physically, this increase is related to an abrupt transition from the linear to saturation region near the knee of the current-voltage characteristic. When the current increases up to the saturation value, the electron concentration near the drain becomes very low and can be strongly affected by a small external field. As a consequence, the two-dimensional channel becomes extremely sensitive to external perturbations. In the resonant case, the detection amplitude has maxima when the radiation frequency is equal to fundamental plasma frequency and its harmonics. We predict that the effective linewidths of the respective resonances would decrease with the increasing current. Physically, this happens because dc current shifts the system towards the plasma wave instability. At some critical current value, the width corresponding to the fundamental frequency would turn to zero, indicating the onset of plasma waves generation. Our experimental measurements performed on $\mathrm{GaAs}$ HEMT confirm the theoretical predictions.

Terahertz Detection Related to Plasma Excitations in Nanometer Gate Length Field Effect Transistor.

ABSTRACTThe channel of nanometre field effect transistor can act as a resonant cavity for plasma waves. The frequency of these plasma waves is in the Terahertz range and can be tuned by the gate length and the gate bias. During the last few years Terahertz detection and emission related to plasma wave instabilities in nanometre size field effect transistors was demonstrated experimentally. In this work we review the recent results on sub-THz and THz detection by 50-300nm gate length III-V HEMTs and Si MOSFETs. We present experimental results on the resonant and nonresonant (overdamped) plasma wave detection and discuss possible applications of nanometre field effect transistors as new detectors of THz radiations.

Rayleigh instability in non-uniform multi-ion species magnetoplasmas

We present the Rayleigh instability of low-frequency (in comparison with the ion-gyrofrequency) electrostatic waves in multi-ion species plasmas containing equilibrium density gradient and transverse ion-sheared flows caused by the dc electric field. For this purpose, multi-fluid equations are used to obtain the governing equations for two-dimensional convective cells and pseudo-three-dimensional drift waves in a non-uniform magnetoplasma. Standard procedures are then employed to study the Raleigh instability. Thresholds and growth rates are obtained. Applications to Hall thrusters are discussed.

Transit‐time mechanism of plasma instability in high electron mobility transistors

AbstractWe show that the transit‐time effects in the high‐electric‐field region near the drain edge of the channel of a field effect transistor can increase the increment of plasma wave growth in the device channel. These electron transit‐time effects might lead to the plasma wave instability in high‐electron‐mobility transistors (HEMTs) in the terahertz range of frequencies. We demonstrate that the self‐excitation of plasma oscillations is possible when the ratio of the electron velocity in the high field region, ud, and the gate length, Lg, is sufficiently large in comparison with the electron collision frequency in the gated channel, ν, i.e udLg > ν/k, where k is a constant. Hence, in contrast with the Dyakonov–Shur mechanism of plasma instability in HEMTs, the plasma instability associated with the mechanism under consideration can occur at fairly low values of the electron mobility in the gated portion of the HEMT channel. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Plasma wave resonant detection of femtosecond pulsed terahertz radiation by a nanometer field-effect transistor

We report on the room-temperature, resonant detection of femtosecond pulsed terahertz radiation obtained by optical rectification in a ZnTe crystal. The detection was realized using a 250nm gate length GaAs∕AlGaAs heterostructure field-effect transistor. We show that physical mechanism of the detection is related to the plasma waves excited in the transistor channel. The detection is strongly enhanced by increasing the drain current and driving the transistor into the plasma wave instability region. Our results clearly show that plasma wave nanometer transistors can be efficient and fast detectors for terahertz spectroscopic imaging based on the femtosecond pulsed THz sources.

Kinetic Alfvén waves in preflare plasma

Low-frequency instabilities of plasma waves in the arch structures in solar active regions have been investigated before a flare. In the framework of mechanism of “direct initiation” of instability by slowly increasing (quasi-static) large-scale electric field in a loop the dispersion relation has been studied for the perturbations which propagate almost perpendicularly to the magnetic field of the loop. The case has been considered, when amplitude of weak (“subdreicer”) electric field sharply increases before a flare, low-frequency instability develops on the background of ion-acoustic turbulence and thickness of this turbulent plasma layer plays the role of mean characteristic scale of inhomogeneity of plasma density. If the values of the main plasma parameters, i.e. temperature, density, magnetic field amplitude allow to neglect the influence of the shear of magnetic strength lines on the instability development, then two types of the waves can be generated in preflare plasma: the kinetic Alfvén waves and some new kind of the waves from the range of slowly magneto-acoustic ones. Instability of kinetic Alfvén waves has clearly expressed threshold character with respect to the amplitude of “subdreicer” electric field. This fact seems to be useful for the short-time prediction of a flare in arch structure. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

What can we learn about accelerated electrons in coronal loops from analysis of solar type IV radio bursts?

Specific type IV radio burst with fine structure – quasi-periodic broadband pulsations (BBPs) and zebra pattern (ZP), recorded by OSRA spectrograph (Potsdam) on October 25, 1994, is considered as a source of information about electrons accelerated during solar flare. The type IV bursts are generated in coronal trap-like structures (coronal loops) accumulating accelerated electrons. BBP are considered as a result of periodically repeated injections of fast electrons into the magnetic trap. The ZP is well understood as a result of plasma wave instability at the levels of double plasma resonance. Using the observed features of fine structure, we found the number of electrons and energy of electrons capable to provide the observed structure as well as the physical conditions in the coronal magnetic loop.

Temperature-drift instabilities of plasma waves in preflare plasma of solar active regions

A preflare situation in a loop structure for stability to the development of plasma waves at the chromosphere part of a current circuit of a loop is investigated. We consider the situation when plasma has the spatial gradients of the density and temperature. In accordance with Heyvarts-Priest-Rust theory such a preflare situation would typically exist when the amplitude of weak electric field in the circuit of an “old” loop in an active region begins to increase as “new” magnetic flux emerges from under the photosphere (Heyvaerts, Priest & Rust (1977)). To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Millimeter wave emission from GaN high electron mobility transistor

We report on millimeter wave electromagnetic radiation from a GaN high electron mobility transistor with the gate length of 1.5 μm at 8 K. The emission takes place at gate and drain voltages in the linear regime of operation but close to the saturation voltage with the principal emission peak at approximately 75 GHz, which is much higher than the device cut-off frequency. An explanation of this effect involves the “shallow water” plasma wave instability, with the frequency of the plasma waves decreased by the ungated regions of the device.

Solar type IV burst spectral fine structures

We discuss a source model for the origin of solar type IV burst fine structures (FS) using the data of an event in AR 7792 on 25 October 1994. After giving a comprehensive observational treatment of FS (Paper I), here we repeat the main observed facts to construct a simplified radio source model. It consists of two interacting loops (named LS1 and EL) with one spatial order of magnitude scale difference (turning heights 70 and 7 Mm). We consider the implications of this model for physical mechanisms of broad band pulsations (BBP) and zebra patterns (ZP). Our analysis leads to the conclusion that meter wave BBP and ZP originate from a common magnetic source structure – a large asymmetric coronal loop. It is shown that the BBP result from periodically repeated injections of fast electrons into the asymmetric magnetic trap. The excitation of plasma waves is due to the stream instability when these electrons are propagating along the loop. We demonstrate that a two percent quasi-periodic modulation of a magnetic field component in EL is sufficient for it to act as a periodic electron accelerator. The ZP is due to a plasma wave instability at the levels of double plasma resonance (DPR) in an inhomogeneous source distributed along the loop axis of LS1. The DPR frequencies appear at those height levels where the upper hybrid frequency is equal to a harmonic of the gyrofrequency. Two Appendices review theoretical details needed to understand the given ZP interpretation. The gyrofrequency as a function of height was derived from a force-free extrapolated field line that passes the coronal radio source. After knowing the loop turning height and the magnetic field strength we identified for a fixed observing time the harmonic number of each zebra stripe. The comparison of the calculated DPR levels with the observed zebra stripe peak frequencies yields a density law for the ZP source volume. It turns out that this is a barometric law with a temperature near 106 K. We demonstrate that the drift of the whole ZP to higher frequencies can be explained as a signature of magnetic field decrease and/or plasma cooling in the ZP source. The time delay between BBP and ZP was found to be due to the higher fast particle threshold of the DPR versus the beam instability. The present analysis confirms the double plasma resonance model for the ZP fine structure, and underlines the significance of force-free extrapolated photospheric fields for coronal magnetic field modelling.

Low-frequency wave instabilities in a plasma with a quasistatic electric field and weak spatial inhomogeneity

A specific type of plasma-wave instability in a hot magnetoactive collisional plasma due to a weak external electric field and weak spatial inhomogeneity is considered for the cases of kinetic Alfvén-like waves. These low-frequency waves with ω [Lt ] Ωi (where Ωi is the ion gyrofrequency) are solutions of the corresponding dispersion relation. The model integral of Bhatnagar, Gross, and Krook is used for the description of collisions. The quasistatic time variation of the electric field amplitude makes it possible to use the ‘direct initiation’ mechanism to describe instability development. An expression for the growth rate is obtained in the framework of linear theory. The instability in question occurs for a certain equation of state of the plasma. For this equation of state, a numerical analysis of the obtained instabilities is performed.

Modulational instability of short-wavelength ion waves in strongly coupled dusty plasmas.

Modulational instability of electrostatic short-wavelength ion waves in plasmas containing strongly coupled dusts with variable charge is considered. The evolution equations for the ion waves modulated by slow dust motion are obtained. The instability behavior differs considerably from that of plasmas with weakly coupled dust grains and depends strongly on the Coulomb coupling parameter as well as the dust-charge relaxation rate.

Magnetic-field enhancement of the current instability in field-effect transistors

A theoretical investigation, within the framework of hydrodynamics, is made of the plasma-wave instability mechanism in a two-dimensional electron fluid in a field-effect transistor in the presence of a perpendicular magnetic field B. Scattering by impurities and/or phonons, termed external friction, is accounted for by adding a damping term to the equation of motion. The treatment is valid for a nondegenerate electron fluid in which the mean free path for interelectronic collisions is much smaller than the device length and the mean free path due to impurities and/or phonons. We show that a relatively low DC current should be unstable because of magnetoplasma-wave amplification due to reflection from the device boundaries. As in the absence of the field B, the instability occurs for 0< v 0< s and v 0<− s, where v 0 is the local electron velocity and s the plasma wave velocity. The field B enhances this instability considerably, as the imaginary part of the wave increases with B, and can outbalance the stabilizing role of the external friction.

Influence of a magnetic field on the current instability in a ballistic field-effect transistor

A theoretical investigation is made of the plasma-wave instability mechanism in a two-dimensional (2D) electron fluid in a ballistic field-effect transistor (FET) in the presence of a perpendicular magnetic field. The 2D electron fluid in the FET channel has been treated within the framework of hydrodynamics applicable to the shallow water waves. We show that a relatively low dc current should be unstable because of magnetoplasma-wave amplification due to the reflection of the wave from the device boundaries. Just as in the absence of the magnetic field the instability occurs for $0l{\ensuremath{\upsilon}}_{0}ls$ and ${\ensuremath{\upsilon}}_{0}l\ensuremath{-}s,$ where ${\ensuremath{\upsilon}}_{0}$ is the local electron velocity and s the plasma-wave velocity. The external field B enhances this instability considerably as the imaginary part of the wave increases with B. Accordingly, the magnetic field can be used to compensate or overcome the stabilizing role of the external and/or internal friction on plasma-wave generation. Such a ballistic FET channel is a promising device for the generation of tunable electromagnetic radiation in the terahertz frequency range.

Plasma wave instability in gated collisionless two-dimensional electron gas

We present the solution of the Boltzmann equation for relatively low density gated two-dimensional electron gas where electron–electron collisions are not significant. This solution describes the plasma waves with the same dispersion law as for a high electron sheet density. In both cases, the plasma waves become instable in a short channel field effect transistor with asymmetric boundary conditions at small channel currents (provided that the scattering by phonons and impurity is sufficiently small). Our analysis also shows that for realistic values of the device parameters, the Landau damping is small.

Instability of dusty plasma waves in the presence of elongated and rotating charged particulates

A new dispersion relation for low-frequency waves in an unmagnetized dusty plasma is obtained when the plasma contains electrons, ions and non-spherical (elongated) rotating charged dust grains. Since the dipole moments of the latter are non-zero, significant modifications of the dusty plasma wave spectra emerge. Analyses of the newly found dispersion relation reveals instabilities of both the electromagnetic and electrostatic waves. Specifically, waves with frequencies close to the angular rotation frequency of the dust grains are found to be unstable. The relevance of our investigation to enhanced fluctuations in space and laboratory dusty plasmas has been pointed out.

Application of Thomson scattering to identify ion acoustic waves stimulated by the Langmuir decay instability

In this article, we present how ion acoustic waves can be unambiguously identified and can be used to definitely demonstrate the existence of the Langmuir decay instability (LDI) of electron plasma waves associated with stimulated Raman scattering. This observation is very important in the context of inertial confinement fusion because the LDI is a mechanism that may influence the stimulated Raman scattering saturation and growth. The experimental identification of those waves relies on Thomson scattering of a short wavelength probe beam. The Thomson scattered light was analyzed by two sets of spectrometer and streak camera providing information on the density fluctuations associated with the electron plasma waves and ion acoustic waves with temporal and spectral resolutions. Selection of a narrow range of angles (4° of aperture) inside the probe and scattered light apertures provided necessary resolution in wave vector. The method used for the design of the Thomson scattering diagnostic is described as well as the technique used to clearly identify the observed ion acoustic waves as one of the Langmuir decay instability products.