Reactive Instability Research Articles

Computational investigation of chemical and non-equilibrium effects on the Richtmyer–Meshkov instability

In order to study the reactive Richtmyer–Meshkov instability (RMI) at a microscale, we have implemented a direct simulation Monte Carlo (DSMC) method which is recently developed for resolving thermal–chemical processes at the scale of molecular motions. The method allows efficient simulations of polyatomic reactions and non-equilibrium processes without violation of the detailed balance which is generically suffered by the conventional algorithms and leads to failure of local thermal equilibrium eventually. With attainment of essential accuracy, the effects of nonequilibrium and chemical reactions on the evolution of two-dimensional (2D) RMI at the microscale are investigated. The results show that the nonequilibrium effect slows down the heat release of chemical reactions and strengthens the viscous and diffusive effects for the mixture and shock conditions tested, which inhibit the growth of the RM instability. The heat release via combustion, however, can substantially increase the RMI growth due to induced baroclinic torque. Consequently, the intricate coupling of these effects nonlinearly dominates the development of RMI at the microscale. Therefore, the influence of nonequilibrium conditions where the translational energy is higher than that of the internal modes of polyatomic molecules, specifically the vibrational energy, in the post-shock region should be considered. The procedure provides a paradigm for further research in pursuit of accurate evaluation of microscopic processes and the resulted performance in supersonic combustion that plays a key role in the development of hypersonic vehicles.

Some fundamental issues associated with theoretical analyses of reactive infiltration instability in fluid‐saturated porous media

AbstractThis paper deals with three fundamental issues associated with theoretical analyses of reactive infiltration instability (RII) problems in fluid‐saturated porous media. The first fundamental issue is to determine the spatial shapes of chemical dissolution‐fronts in the limit case of the mineral dissolution ratio approaching zero in both conventional time (daily life time) and unconventional time (abstract time) domains. The chemical dissolution‐front is commonly represented by the spatial shape of the porosity profile. The second fundamental issue is to conduct theoretical analyses of the RII problems associated with the mineral dissolution ratio approaching zero through directly solving dimensional mathematical governing equations in the conventional time domain. The third fundamental issue is to carry out theoretical analyses of the RII problems associated with the mineral dissolution ratio approaching zero through solving dimensionless mathematical governing equations in the unconventional time domain. Through purely mathematical deductions, it has been proven that: (1) the spatially sharp shape of a chemical dissolution‐front, which is theoretically predicted either at a much smaller timescale than the dissolution timescale associated with the daily life time or at a much larger timescale than the dissolution timescale associated with the daily life time, can be observed in the daily life time domain; (2) the theoretical instability criterion of an RII problem can be established directly at three different length‐scales in the daily life time domain; and (3) although the spatial shape of a chemical dissolution‐front at the dissolution timescale associated with the daily life time cannot be observed in the daily life time domain, the theoretical instability criterion of an RII problem at the dissolution timescale associated with the daily life time can be established when a physically consistent mathematical transform is used in the theoretical analysis.

Analysis of Conditional Stability and Unconditional Stability and Instability for Microwave 3-Ports

A full and rigorous treatment of conditional and unconditional stability and instability for an active 3-port microwave circuit, represented at a given frequency by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -parameters, is carried out. By terminating a given port with a variable termination one may study at the input and the output of the resulting 2-port circuit the occurrence of unconditional stability and instability, as well as of special cases of conditional stability, defined as reactive unconditional stability or instability. Such conditions are especially relevant in microwave oscillator design and were exhaustively identified for the first time and treated in previous analysis by the authors. Drawing from its conclusions, one obtains in the plane of the variable termination and with a simple algorithm, a single parametric representation, providing at once, in a closed and direct form, the entire collection of boundaries of the regions, wherein the listed conditions occur at ports of the resulting 2-port circuit. Guidelines for the design of microwave amplifiers and oscillators, both in series and shunt configuration, are sketched. Numerical examples, validated by simulations, are also presented.

Anion Equilibria and Stability of Quaternary Phosphonium Chloroaluminate Ionic Liquids

The anion equilibria and thermal stability in a series of quaternary trialkyloctylphosphonium chloroaluminate ionic liquids are investigated qualitatively by Raman spectroscopy, broadband dielectric spectroscopy, and nuclear magnetic resonance spectroscopy. Results indicate that Lewis acidic chloroaluminate ionic liquids based upon the phosphonium cation are less stable than those based upon other molecular cations. A slow time-dependent drop in room-temperature dc ionic conductivity as well as a step drop at elevated temperatures is tentatively attributed to a reaction involving the Lewis acidic Al2Cl7 - anion and the phosphonium cations. This reaction results in significant changes in the 1H, 13C, and 31P NMR spectra, but only minor changes in the Raman spectra. Furthermore, extended time at elevated temperatures results in a significant quantity of neutral aluminum chloride sublimating from the liquid. These results demonstrate an unusual reactive instability of phosphonium-based Lewis acidic chloroaluminate ILs.

Evidence of Volatile‐Induced Melting in the Northeast Asian Upper Mantle

AbstractA seismic low velocity layer (LVL) above the mantle transition zone (MTZ), often thought to be caused by volatile‐induced melting, can significantly modulate planetary volatile cycles. In this work, we show that an LVL observed beneath northeast Asia is characterized by small, 0.8 0.5 vol%, average degrees of partial melting. Seismically derived P‐T conditions of the LVL indicate that slab‐derived , possibly combined with small amounts of O, is necessary to induce melting. Modeling the reactive infiltration instability of the melt in a stationary mantle above a stalled slab, we demonstrate that the volatile‐rich melt slowly rises above the stalled slab in the MTZ, with percolation velocities of 200–500 m/yr. The melt remains stable within the LVL for this geologically significant period of time, potentially transferring up to 52 Mt/yr of from the subducting slab to the mantle for an LVL similar in areal extent () to the northeast Asian LVL. Reaction between the melt channels and the LVL mantle precipitates up to 200 ppmw solid C in localized zones. Using the inferred small melt volume fraction to model trace element abundances and isotopic signatures, we show that interaction between this melt and the surrounding mantle can over the long‐term produce rocks bearing a HIMU like geochemical signature.

Perturbation-based balance assessment: Examining reactive balance control in older adults with mild cognitive impairments.

Older adults with mild cognitive impairment (OAwMCI) present subtle balance and gait deficits along with subjective memory decline. Although these presentations might not affect activities of daily living (ADLs), they attribute to a two-folded increase in falls. While changes occurring in volitional balance control during ADLs have been extensively examined among OAwMCI, reactive balance control, required to recover from external perturbations, has received little attention. Therefore, this study examined reactive balance control in OAwMCI compared to their healthy counterparts. Fifteen older adults with mild cognitive impairment (OAwMCI), fifteen cognitively intact older adults (CIOA) (>55 years), and fifteen young adults (18-30 years) were exposed to stance perturbations at three different intensities. Behavioral outcomes postural COM state stability, step length, step initiation, and step execution were computed. Postural COM state stability was the lowest in OAwMCI compared to CIOA and young adults, and it deteriorated at higher perturbation intensities (P < 0.001). Step length was the lowest among OAwMCI and was significantly different from young adults (P < 0.001) but not from CIOA. Unlike OAwMCI, CIOA and young adults increased their step length at higher perturbation intensities (P < 0.001). OAwMCI showed longer recovery step initiation times and shorter execution times compared to CIOA and young adults at higher perturbation intensities (P < 0.001). OAwMCI exhibit exacerbated reactive instability and are unable to modulate their responses as the threat to balance control altered. Thus, they are at a significantly higher risk of falls than their healthy counterparts.

Systematic LREE enrichment of mantle harzburgites: The petrogenesis of San Carlos xenoliths revisited

The dichotomy between partial melting and metasomatism is a paradigm of mantle geochemistry since the pioneering work of Frey and Prinz (1978) on the occurrence of LREE-enriched harzburgites. However, the thermo-chemical implications of such two-stage scenarios are often poorly considered, and the latter fail to explain why trace-element enrichment and major-element depletion are often proportional. We here re-envisage the petrogenesis of the famous San Carlos peridotites based on new petrographic observations and detailed modal, major- and trace-element compositions. The lherzolites (and pyroxenites) are characterized by homogeneously fertile mineral chemistry and LREE-depleted patterns consistent with low degrees of partial melting of the lherzolitic protolith. Bulk compositions and mineral zoning suggest that opx-rich pyroxenites formed by pressure-solution creep during melt-present deformation, locally accompanied by magmatic segregations of cpx. The harzburgites are characterized by stronger mineral zoning with low-Mg# and Na-, Al- and Cr-rich cpx rims, and can be discriminated in a low-Jd and high-Jd cpx groups. The high-Jd group is interpreted as the result of local elemental redistribution in the presence of a low-degree hydrous melt, in good agreement with their wide range of LREE enrichment. In contrast, the MREE-to-HREE fractionation and increasing Cr# in spinel of the low-Jd group indicate that they experienced higher degrees of melting. Open-system melting simulations of trace-element fractionation during hydrous flux melting suggests that the high-Jd harzburgites are the result of low fluid influx producing poorly extracted melt, while higher influx led to higher melting degrees and efficient melt extraction in the low-Jd harzburgites; the lherzolites mostly remained below or near solidus during that process. The lithological and chemical heterogeneity of San Carlos mantle is thus compatible with a single-stage evolution, which is also supported by the striking consistency between Fe-Mg exchange and REE thermometric estimates (1057 and 1074 °C on average, respectively), indicating that harzburgites and lherzolites probably followed a similar P-T path and relatively little sub-solidus re-equilibration. These interpretations suggest that the development of melt extraction pathways promoted by reactive channeling instability is able to produce complex lithological heterogeneities during hydrous flux melting. This process provides a self-consistent explanation for the systematic enrichment of harzburgites observed in many mantle terranes and xenoliths worldwide. We argue that San Carlos is one of such examples where a ca 1.5-Ga continental lithosphere experienced localized flux melting and deformation during the tectonic reactivation of a Proterozoic subduction zone, providing new constraints on the mantle sources of volcanic activity in the Jemez Lineament.

Geological Carbon Sequestration by Reactive Infiltration Instability

We study carbon capture and sequestration (CCS) over time scales of 2000 years by implementing a numerical model of reactive infiltration instability caused by reactive porous flow. Our model focuses on the mineralization of CO2 dissolved in the pore water—the geological carbon sequestration phase of a CCS operation—starting 10–100 years after the injection of CO2 in the subsurface. We test the influence of three parameters: porosity, mass fraction of the Ca-rich feldspar mineral anorthite in the solid, and the chemical reaction rate, on the mode of fluid flow and efficiency of CaCO3 precipitation during geological carbon sequestration. We demonstrate that the mode of porous flow switches from propagation of a planar front at low porosities to propagation of channels at porosities exceeding 10%. The channels develop earlier for more porous aquifers. Both high anorthite mass fraction in the solid phase and high reaction rates aid greater amounts of carbonate precipitation, with the reaction rate exerting the stronger influence of the two. Our calculations indicate that an aquifer with dimensions 500 m × 2 km × 2 km can sequester over 350 Mt solid CaCO3 after 2000 years. To precipitate 50 Mt CaCO3 after 2000 years in this aquifer, we suggest selecting a target aquifer with more than 10 wt% of reactive minerals. We recommend that the aquifer porosity, abundance of reactive aluminosilicate minerals such as anorthite, and reaction rates are taken into consideration while selecting future CCS sites.

‘BAAE’ instabilities observed without fast ion drive

The instability that was previously identified (Gorelenkov 2009 Phys. Plasmas 16 056107) as a fast-ion driven beta-induced Alfvén-acoustic eigenmode (BAAE) in DIII-D was misidentified. In a dedicated experiment, low frequency modes (LFMs) with characteristic ‘Christmas light’ patterns of brief instability linked to the safety factor evolution occur in plasmas with electron temperature T e ≳ 2.1 keV but modest beta. To isolate the importance of different driving gradients on these modes, the electron cyclotron heating (ECH) power and 80 keV, sub-Alfvénic neutral beams are altered for 50–100 ms durations in reproducible discharges. Although beta-induced Alfvén eigenmodes and reversed-shear Alfvén eigenmodes stabilize when beam injection ceases (as expected for a fast-ion driven instability), the LFMs that were called BAAEs persist. Data mining reveals that characteristic LFM instabilities can occur in discharges with no beam heating but strong ECH. A large database of over 1000 discharges shows that LFMs are only unstable in plasmas with hot electrons but modest overall beta. The experimental LFMs have low frequencies (comparable to diamagnetic drift frequencies) in the plasma frame, occur near the minimum of the safety factor q min, and appear when q min is close to rational values. Theoretical analysis suggests that the LFMs are a low frequency reactive instability of predominately Alfvénic polarization.

Pulsar radio emission mechanisms: a critique

ABSTRACT We consider critically the three most widely favoured pulsar radio emission mechanisms: coherent curvature emission (CCE), beam-driven relativistic plasma emission (RPE), and anomalous Doppler emission (ADE). We assume that the pulsar plasma is 1D, streaming outwards with a bulk Lorentz factor γs ≫ 〈γ〉 − 1 ≳ 1, where 〈γ〉 is the intrinsic spread in the rest frame of the plasma. We argue that the formation of beams in a multicloud model is ineffective in the intrinsically relativistic case for plausible parameters because the overtaking takes too long. We argue that the default choice for the particle distribution in the rest frame is a Jüttner distribution and that relativistic streaming should be included by applying a Lorentz transformation to the rest-frame distribution, rather than the widely assumed relativistically streaming Gaussian distribution. We find that beam-driven wave growth is severely restricted by (a) the wave properties in pulsar plasma, (b) a separation condition between beam and background, and (c) the inhomogeneity of the plasma in the pulsar frame. The growth rate for the kinetic instability is much smaller and the bandwidth of the growing waves is much larger for a Jüttner distribution than for a relativistically streaming Gaussian distribution. No reactive instability occurs at all for a Jüttner distribution. We conclude that none of CCE, RPE, and ADE is tenable as the generic pulsar radio emission mechanism for ‘plausible’ assumptions about the pulsar plasma.

A semianalytical approach for solving first‐order perturbation equations of dissolution‐timescale reactive infiltration instability problems in fluid‐saturated rocks

SummaryThis paper presents a semianalytical approach for solving first‐order perturbation (FOP) equations, which are used to describe dissolution‐timescale reactive infiltration instability (RII) problems in fluid‐saturated rocks. The proposed approach contains two parts because the chemical dissolution reaction divides the whole problem domain into two subdomains. In the first part, the interface‐condition substitution strategy is used to derive the analytical expressions of purely mathematical solutions for the FOP equations in the upstream subdomain, where the dissolution chemical reaction is ceased and the FOP equations are weakly coupled. In the second part, the finite element method (FEM) is used to derive the analytical expressions of numerical solutions for the FOP equations in the downstream subdomain, where the dissolution chemical reaction needs to be considered and the FOP equations are strongly coupled so that it is impossible to derive purely mathematical solutions for them. Particular attention is paid to the development of the element‐by‐element forward marching strategy, which is associated with the use of the FEM for solving this new kind of scientific problem. The related analytical results demonstrated that (1) both the dynamic characteristic of a reactive infiltration system and the dimensionless wavenumber can have pronounced influences on the distribution of the FOP dimensionless acid concentration within the entire domain of the dissolution‐timescale RII problems in fluid‐saturated rocks and (2) the FOP dimensionless acid concentration distribution exhibits two significantly different patterns in the upstream and downstream subdomains of the dissolution‐timescale RII system.

Water is a biomarker of changes in the cellular environment in live animals

The biological processes that are associated with the physiological fitness state of a cell comprise a diverse set of molecular events. Reactive oxygen species (ROS), mitochondrial dysfunction, telomere shortening, genomic instability, epigenetic changes, protein aggregation, and down-regulation of quality control mechanisms are all hallmarks of cellular decline. Stress-related and decline-related changes can be assayed, but usually through means that are highly disruptive to living cells and tissues. Biomarkers for organismal decline and aging are urgently needed for diagnostic and drug development. Our goal in this study is to provide a proof-of-concept for a non-invasive assay of global molecular events in the cytoplasm of living animals. We show that Microwave Dielectric Spectroscopy (MDS) can be used to determine the hydration state of the intracellular environment in live C. elegans worms. MDS spectra were correlative with altered states in the cellular protein folding environment known to be associated with previously described mutations in the C. elegans lifespan and stress-response pathways.

Reactive instabilities in linear acidizing on carbonates

Acid injection, reactive instabilities and wormholing in carbonate reservoirs is investigated through the analysis of the linear acidizing problem theoretically and experimentally. Theoretically acidizing was analyzed by formulating the problem as a reactive moving boundary Stefan type problem. Wormholing is viewed as a reactive infiltration instability to the trivial solution of uniform dissolution. A linear stability analysis from the equilibrium state is performed and the critical wavenumber below which instabilities have a positive growth rate is identified. When applied to the scale of the experiment, an optimum injection velocity is identified for a given formation and injection concentration, for the growth for a single wormhole. This optimum injection velocity scales with the inverse of the specimen diameter. Experimentally, linear acidizing tests were performed in Mons chalk, a high porosity analogue of North Sea reservoir chalk. In the experiments the critical injection velocity for wormhole formation at minimum acid injection was obtained and the results were compared with the theoretical predictions.

Amygdala Resting State Connectivity Differences between Bipolar II and Borderline Personality Disorders

Background: Borderline personality disorder (BPD) and bipolar II disorder (BD II) have significant clinical overlap, leaving the potential for diagnostic inaccuracies and inadequate treatment recommendations. However, few studies have probed for clinical and neurobiological differences between the two disorders. Clinically, some prior studies have linked BPD with greater impulsivity and more frequent negative affective shifts than BD II, whereas previous neuroimaging studies have highlighted both similar and distinct neural abnormalities in BPD and BD II. Notably, no prior study has specifically targeted cortico-limbic neural differences, which have been hypothesized to underlie these core clinical differences. Methods: Individuals with BPD (n = 14) and BD II (n = 15) completed various clinical measures and a resting state functional imaging scan at 3T. Whole-brain amygdala resting state functional connectivity (RSFC) was compared between the two groups. Results: Relative to the BD II group, BPD participants reported significantly higher levels of impulsivity, trait anxiety, more frequent negative affective shifts, greater interpersonally reactive affective instability, lower overall functioning, and were characterized by lower amygdala-middle frontal gyrus RSFC. Lower amygdala-middle frontal gyrus RSFC was associated with greater impulsivity, trait anxiety, affective shifts, interpersonal affective reactivity, and functional impairment. Limitations: The current study consisted of small sample sizes and lacked a control group. Conclusions: This preliminary study suggests that amygdala-frontal RSFC may distinguish BPD from BD II. These results may guide future work aimed at identifying neural markers that can help disentangle these two disorders, leading to greater diagnostic accuracy and appropriate treatment implementation.

Supervisory Control for Wireless Networked Power Converters in Residential Applications

This paper presents a methodology to design and utilize a supervisory controller for networked power converters in residential applications. Wireless networks have been interfaced to multiple power factor correction (PFC) converters which are proposed to support reactive power. Unregulated reactive power support from PFC converters could cause reactive power deficiency and instability. Therefore, a supervisory controller is necessary to govern the operation of PFC converters. WiFi and WirelessHART networks have been used to implement the supervisory controller. Different nodes of the power network are connected by wireless communication links to the supervisory controller. Asynchronous communication links latency and uncertain states affect the control and response of the PFC converters. To overcome these issues, the supervisory controller design method has been proposed based on the system identification and the Ziegler-Nichols rule. The proposed supervisory controller has been validated by using a hardware-in-the-loop (HIL) test bed. The HIL testbed consisted of an OP4510 simulator, a server computer, Texas Instrument-Digital Signal Controllers (TI-DSCs), WiFi and WirelessHART modules. Experimental results show that the proposed supervisory controller can help to support and govern reactive power flow in a residential power network. The proposed method of controller design will be useful for different small-scale power and wireless network integration.

An interface‐condition substitution strategy for theoretical study of dissolution‐timescale reactive infiltration instability in fluid‐saturated porous rocks

SummaryA theoretical study of reactive infiltration instability is conducted on the dissolution timescale. In the present theoretical study, the transient behavior of a dissolution‐timescale reactive infiltration system needs to be considered, so that the upstream region of the chemical dissolution front should be finite. In addition, the chemical dissolution front of finite thickness should be considered on the dissolution timescale. Owing to these different considerations, it is very difficult, even in some special cases, to derive the first‐order perturbation solutions of the reactive infiltration system on the dissolution timescale. To overcome this difficulty, an interface‐condition substitution strategy is proposed in this paper. The basic idea behind the proposed strategy is that although the first‐order perturbation equations in the downstream region cannot be directly solved in a purely mathematical manner, they should hold at the planar reference front, which is the interface between the upstream region and the downstream region. This can lead to two new equations at the interface. The main advantage of using the proposed interface‐condition substitution strategy is that through using the original interface conditions as a bridge, the perturbation solutions for the dimensionless acid concentration, dimensionless Darcy velocity, and their derivatives involved in the two new equations at the interface can be evaluated just by using the obtained analytical solutions in the upstream region. The proposed strategy has been successfully used to derive the dimensionless growth rate, which is the key issue associated with the theoretical study of dissolution‐timescale reactive infiltration instability in fluid‐saturated porous rocks.

Evolution of planar fractures in limestone: The role of flow rate, mineral heterogeneity and local transport processes

The processes that affect the evolution of fracture geometry and reactive transport in limestone fractures were evaluated using an integrated experimental and modeling approach. Flow-through experiments were performed to investigate the alteration of three artificially made planar limestone fractures, which were exposed to HCl-acidified water flow (pH 3.8 ± 0.1) at three different rates. Reactive infiltration instability developed in the fractures because of small fracture aperture variations and naturally occurring heterogeneity in the rock, i.e., the presence of clay spots of higher porosity. The dissolution regime changed from conical to dominant and ramified wormhole with increasing flow rate, i.e., Péclet number. Maps of fracture aperture obtained from X-ray micro-tomography imaging, together with measurements of permeability and analyses of fluid chemistry, provided experimental constraints for modeling. Numerical simulations were performed using a 2.5D continuum reactive transport model to examine the development of flow patterns and the reactivity and permeability evolution over time, and to interrogate the impacts of fluid reactivity, mineral heterogeneity and diffusive boundary layer. The modeling results showed that fracture alteration is very sensitive to initial fluid reactivity and mineralogical heterogeneity, in addition to flow rate. The changes of local transport processes during fracture opening also affected the reactivity of the fractured samples.

Reply to comment on “validity of using large-density asymptotics for studying reaction-infiltration instability in fluid-saturated rocks”

In this reply we further demonstrate and confirm that the main conclusion (namely, that the asymptotic limit of the acid dissolution capacity can lead to sharp dissolution fronts) in our recent publication in this journal is correct and valid. The basis of the incorrect critique in the comment is whether or not a physically-consistent velocity scale should be used in deriving the dimensionless partial differential equations of the reactive infiltration instability problem in fluid-saturated rocks. In addition, there is confusion in the comment between the conclusions drawn from results obtained using different time scales (such as a dissolution time scale and a much larger time scale than the dissolution time scale) in the process of describing the reactive infiltration instability problem, and using different mathematical transforms (such as a physically-consistent mathematical transform and a physically-inconsistent one) in the nondimensionalization of dimensional partial differential equations.

Non-resonant Alfvénic instability activated by high temperature of ion beams in compensated-current astrophysical plasmas

Context. Compensated-current systems are established in response to hot ion beams in terrestrial foreshock regions, around supernova remnants, and in other space and astrophysical plasmas. Aims. We study a non-resonant reactive instability of Alfvén waves propagating quasi-parallel to the background magnetic field B0 in such systems. Methods. The instability is investigated analytically in the framework of kinetic theory applied to the hydrogen plasmas penetrated by hot proton beams. Results. The instability arises at parallel wavenumbers kz that are sufficiently large to demagnetize the beam ions, kzVTb/ωBi ≳ 1 (here VTb is the beam thermal speed along B0 and ωBi is the ion-cyclotron frequency). The Alfvén mode is then made unstable by the imbalance of perturbed currents carried by the magnetized background electrons and partially demagnetized beam ions. The destabilizing effects of the beam temperature and the temperature dependence of the instability threshold and growth rate are demonstrated for the first time. The beam temperature, density, and bulk speed are all destabilizing and can be combined in a single destabilizing factor αb triggering the instability at αb &gt; αbthr, where the threshold value varies in a narrow range 2.43 ≤ αbthr ≤ 4.87. New analytical expressions for the instability growth rate and its boundary in the parameter space are obtained and can be directly compared with observations. Two applications to terrestrial foreshocks and foreshocks around supernova remnants are briefly discussed. In particular, our results suggest that the ions reflected by the shocks around supernova remnants can drive stronger instability than the cosmic rays.

Excitation of Ion Cyclotron Waves by Ion and Electron Beams in Compensated-current System

Abstract Ion cyclotron waves (ICWs) can play important roles in the energization of plasma particles. Charged particle beams are ubiquitous in space, and astrophysical plasmas and can effectively lead to the generation of ICWs. Based on linear kinetic theory, we consider the excitation of ICWs by ion and electron beams in a compensated-current system. We also investigate the competition between reactive and kinetic instabilities. The results show that ion and electron beams both are capable of generating ICWs. For ICWs driven by ion beams, there is a critical beam velocity, v bi c , and critical wavenumber, k z c , for a fixed beam density; the reactive instability dominates the growth of ICWs when the ion-beam velocity and the wavenumber , and the maximal growth rate is reached at for a given . For the slow ion beams with , the kinetic instability can provide important growth rates of ICWs. On the other hand, ICWs driven by electron beams are excited only by the reactive instability, but require a critical velocity, (the Alfvén velocity). In addition, the comparison between the approximate analytical results based on the kinetic theory and the exact numerical calculation based on the fluid model demonstrates that the reactive instabilities can well agree quantitatively with the numerical results by the fluid model. Finally, some possible applications of the present results to ICWs observed in the solar wind are briefly discussed.