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A novel source for millimeter-wave RF is being designed at Los Alamos National Laboratory (LANL) utilizing the two-stream instability. This source has the potential for consistent output power over a large bandwidth on a single device [1]. The characteristic length of longitudinal bunching due to the two stream instability is dependent along with current, on the energy difference of the two beams[6]. The source is optimized for 1–5kV energy differential between the electron beams coupled into a single solenoid using electrostatic focusing in the electron gun region. The source will use co-axial electron beams to evaluate the longitudinal bunching of the at millimeter wavelengths.

We present a two-fluid simulation of the interaction between the powerful HF (high-frequency) electromagnetic wave and the ionosphere. The OTSI (Oscillation Two-Stream Instability) and PDI (Parametric Decay Instability), near and below the turning point of ordinary wave mode respectively, are excited. The region of coexistence of OTSI and PDI is investigated. The spectral features in OTSI, PDI and coexistence area are studied. The wave conversion from O mode to Z mode is studied by using different source intensity.

The longitudinal electric field effect on the formation of a space charge wave (SCW) with wide frequency spectrum in the helical two-stream relativistic electron beam (REB), which moves in transit section of multiharmonic two-stream superheterodyne free-electron laser, is analyzed. In the framework of cubic nonlinear approximation, it is shown that the use of the accelerating electric field makes it possible to increase the multiharmonic SCW width of the frequency spectrum. It is shown that the retarding electric field causes the increase of the amplitude level SCW harmonics, as well as the decrease of its saturation length.

The equatorial ionosphere is the most active region in the Earth's space, where the E region irregularities are a common phenomenon. The two-stream instability excited by equatorial electrojet is the main reason for the formation of E-layer irregularities. The particle-in-cell (PIC) method is used in this paper to simulate the evolution process of the two-stream instability. The energy variation curve and the growth rate curve of the two-stream instability are both analyzed. In addition, the excitation strip of the instability is simply analyzed.

We studied the wave dynamics in multiharmonic two-stream superheterodyne free-electron laser (TSFEL) amplifiers of H-ubitron type using multiharmonic input signals. TSFEL models with straight and helical relativistic electron beams were examined. We demonstrated the significant reduction of saturation lengths upon multiharmonic signal utilization compared to the monochromatic input signal. We found out that the using of helical electron beams in TSFEL allows to increase both amplification rates and frequency spectrum width of the signal wave on the system output. It was concluded that multiharmonic signal utilization allows to form powerful electromagnetic signals with broad frequency spectrum effectively in multiharmonic TSFELs.

Instability develops in a long space-charge dominated beam when it is allowed to coast in a storage ring without RF containment. The longitudinal space-charge forces in these intense beams cause it to expand axially, closing on itself and as a result wrapping the accelerator. Simulations and experimental measurements indicate that instability occurs when the leading and trailing ends of the beam spatially overlap the body of the beam. The overlapping beam segments have different velocities, which is the energy source for the instability. Two instabilities have been identified in simulations: a traditional longitudinal two-stream, and a coupled betatron, two stream instability.

We have carried out the research of plural three-wave resonances of space charge wave (SCW) harmonics in the transit section of the klystron type two-stream superheterodyne free-electron laser (TSFEL) with helical electron beam in cubic non-linear approximation. We have found out that two-stream instability critical frequency increases with increasing of two-stream electron beam input angle in the focusing longitudinal magnetic field. Due to this fact, the frequency domain in which plural three-wave parametric resonances of SCW harmonics take place increases. The two-stream instability growth rate also increases in helical electron beams with increasing of the beam input angle. Therefore, the saturation lengths in TSFELs with helical electron beams are shorter compared to TSFELs utilizing straight electron beams. We have shown that SCWs with broad frequency spectrum form in two-velocity helical relativistic electron beam due to plural three-wave parametric resonances. We have demonstrated that klystron-type TSFEL with helical electron beam can be used as a source of powerful multiharmonic electromagnetic waves in millimeter-infrared wavelength ranges.

Propagation of charged particle beams in background plasma as a method of space charge neutralization has been shown to achieve high degrees of charge and current neutralization and therefore can enable nearly ballistic propagation and focusing of charged particle beams. Correspondingly, use of plasmas for propagation of charged particle beams has important applications for transport and focusing of intense particle beams in electric propulsion, inertial fusion and high energy density laboratory plasma physics. However, the streaming of beam ions through a background plasma can lead to development of the two-stream instability between the beam ions and the plasma electrons [1, 2]. The electric and magnetic self-fields enhanced by the two-stream instability can lead to defocusing of the ion beam and fast scattering of an electron beam. Using particle-in-cell (PIC) simulations, we study the scaling of the instability-driven selfelectromagnetic fields and consequent defocusing forces with the background plasma density and beam ion mass. We identify plasma parameters where the defocusing forces can be reduced.

A kinetic numerical simulation of an expanding current-carrying plasma plume of the explosive-emission center in the vacuum breakdown was performed. It was found that at the current density rise less than about of 109 A/cm2/s the expansion of the plasma generally has a self-similar character. At the higher current density growth rate the plasma expansion has an essentially non-stationary character. The high density current leads first to the development of ion-acoustic instability and then to the development of Buneman instability. Strong current instability leads to the rupture of the plasma and the creation of conditions for the collective (anomalous) acceleration of ions to the cathode and the anode. Anomalously accelerated ions with energies up to 80 keV create an additional powerful heat flux to the cathode, which should facilitate the reproduction of the cathode spots in the spark stage of vacuum discharge.

Plasmas in Hall thrusters are typically in regimes where the electron motion across the magnetic is strongly constrained by the Lorentz force and the ion Larmor radius is large so the ions are only weakly affected by the magnetic field. Such plasmas support lower-hybrid and ion-sound modes. In the presence of the ExB electron drift, these modes are easily destabilized by plasma and magnetic field gradients, electron collisions, ion flows, resonance and finite length effects. Interaction of these various effects create a complex picture of turbulence in such plasmas. We analyze these destabilization mechanisms in application to typical conditions of Hall thrusters and discuss their roles in anomalous transport and structure formation. The fluid model of plasma dynamics in these conditions has been developed and numerically implemented in the BOUT++ framework. Wave-particle resonant interaction effects have also been included via the kinetic closures implemented via non-Fourier representation. Results of numerical simulations with this model will be presented in this talk. It is shown that the lower-hybrid instability growth rate is maximized at the wavelength on the order of the electron Larmor radius. In the large wavelength region, formation of coherent large scale structures is observed in the simulations. The relative role of the inherent large scale instability (Simon-Hoh) and the inverse energy cascade (from small to large scales) is being investigated.

When an intense relativistic electron beam propagates through the plasma background, the electron beam can expel the plasma electrons and leave the plasma ions which can be seen as static. In this process, the ion channel can be formed and the electromagnetic radiation can be observed. This paper uses the method called particle-in-cell to study on the influence of different valence state under same particles on electromagnetic radiation in beam-plasma system.

The energy gain of an electron beam in the laser-driven plasma wave can be limited by dephasing between the accelerated electron bunch and the plasma wave. The dephasing length is defined as the length the electrons travel before it phase slip by one-half period of plasma wave. Since the velocity of the accelerated electrons is higher than the phase velocity of plasma wave, the electrons outrun the plasma wave and moves into decelerating region of the plasma wave phase space. In order to enlarge the dephasing length, the plasma wavelength should be increased by optimizing the plasma density profile. We report the measurements of dephasing length using plasma density distribution with linear, up-ramp and parabolic profile. The accelerated electron energy gain is calculated in different plasma density profiles. We observe that the plasma wavelength decreases when the plasma wave propagates from low to high-density layer. After density transition, the accelerated electron phase synchronizes with the phase of plasma wave. This increases the electron acceleration length and improves the beam quality. This may be crucial to determine the electron beam energy in LWFA.

During the disruption scenario in plasma, eddy and halo currents are considered to be the most important sources that come out as a result of this phenomenon1. The components that affects primarily are diverter, First Wall (FW) and other main components because plasma is unstable in vertical displacement. In this scenario, plasma moves upward and downward resulting into plasma disruption and as a result, halo current is generated helically. This halo current produced in SOL component and flows into the vacuum vessel through in-vessel components that may give rise to large force acting on the vessel and in-vessel components. In EAST reactor, some sensors have been installed for calculating the halo currents at different locations. In these experiments, it has been shown that the halo current first spread out on outer baffle plate then moves to dome and finally return back to plasma. In this paper, theoretical model for calculating sideways force in vacuum vessel is developed and verified by experimental data from EAST Tokamak. The proposed innovative system allows an effective way to study the interaction forces with plasma under controlled conditions. We used magnetic field transformation method to calculate the plasma energy in different cross section in different degrees that shows plasma interacting forces including vertical and horizontal2. In this paper, we approached to observe the magnitude of the maximum observed sideways forces at EAST that causes asymmetric loads during VDEs. This work attains novelty as no theoretical calculations for plasma sideways force has been reported so far and this is the first time to used theoretical approach. A Matlab program was developed that has been verified by using experimental data from EAST. The main objective of the research is to established theoretical relation with experimental results so as to precautionary evaluate the plasma behavior in any Tokamak.

When plasma interacts with a surface, a plasma sheath forms at the interface, which is typically a region of net positive space charge. Ions, accelerated by the electric field in the sheath region, and hot electrons are known to cause emission from the surface. This can have consequences for devices such as Hall thrusters as electron emissions can increase the rate of erosion of the electrodes affecting performance and longevity of the thrusters — an important concern for space-bound missions. The length-scale of sheaths is small in comparison to the undisturbed plasma (on order of the Debye length, λD) yet the sheath has a global effect on plasma and needs to be included self-consistently in computer simulations. This usually means resolving the Debye length and the plasma oscillation frequency, which makes global and complex simulations extremely demanding in terms of the computational cost.

Hall plasma devices operate in the regimes when the electrons are magnetized and ions are not. In these conditions standard drift waves due to the plasma density gradient do not exist however another mode appears as a result of the combined response of the inertia of un-magnetized ions and electron drift. This mode is destabilized by the ExB electron drift due to the equilibrium electric field: this is the collisionless Simon-Hoh instability. The local theory predicts that the condition 4ω∗ωE > k⊥2Cs2 is required for the instability, ω∗ and ωE are the electron drift frequency and frequency of the equilibrium ExB drift, respectively; k⊥ is the wave-vector perpendicular to the magnetic field, and Cs is the ion sound velocity. We investigate stability of this mode in general case with spatial profiles of ω∗ and ωE when the local theory is not applicable. The stability of nonlocal modes in slab and cylindrical geometry are investigated numerically with Chebyshev spectral method. The results of theoretical analysis are compared with experimental results from Penning and Hall thruster experiments in an attempt to identify the source of large scale structures in these discharges.

In the fluid-Maxwell theory of the two-plasmon decay instability, when Landau damping is neglected, configuration of plasma waves is described by a hyperbola-lemniscate curve in a wave vector space.1 A point on the curve is determined from density and temperature of a plasma and describes configuration of waves for maximum growth of the instability. However, when a weak Landau damping is taken into consideration, we find a significant deviation of the wave vector from the hyperbola-lemniscate curve, although the known expression for growth rate is preserved. Here we present a perturbation expansion of the growth rate from the hyperbola configuration, using the angle variable of wave vector of a plasma wave. And analysis for configuration of waves for maximum growth rate produces an implicit algebraic equation for the angle variable. An example numerical solution of the equation shows 65.5° rather than the well-known 45” inclination from the pump direction.

When the duration of laser pulse is comparable to the plasma wave period, the large-amplitude plasma wave can be driven by the laser. In the presence of a guiding magnetic field, the large-amplitude plasma wave of finite transverse extent and large phase velocity resonantly accelerates the electrons to a higher energy-level. For a small laser spot size the laser exerts an axial as well as the radial ponderomotive force on the electrons that creates a density depression on the laser axis. This electron depleted channel also creates a radial electric field (ion space-charge field). Acceleration of electrons in this channel is investigated, where the effect of ion space-charge field is considered, by solving the dynamical equations using a two-dimensional particle-in-cell code for particle acceleration. We observe that the spacecharge field plays an important role in electron energy gain during acceleration by a plasma wave in a magnetic plasma channel.

The plasma inside a Hall thruster is a complex environment full of instabilities and interesting physical phenomena such as anomalous transport. To better understand this complex plasma dynamics, a nonlinear fluid model has been developed. The model contains the effect of electron inertia, electron collisions, electron temperature and density gradients as well as nonlinearities in the ion velocity and the electron advection term that arises from the ExB drift. The model is simulated using BOUT++, a framework for plasma simulations developed at the Lawrence Livermore National Laboratory. The linear limits of the model correspond to the lower hybrid mode rendered unstable by collisions and to the density gradient drift instabilities.

Spatio-temporal evolution of relativistic Buneman instability has been investigated in one dimension using a particle-in-cell simulation code. Starting from the excitation of the instability, its evolution has been followed numerically till its quenching and beyond. It is found that the maximum growth rate(γmax) reduces due to relativistic effects and varies with γe0 and m/M as γmax ∼ √(3/4γe0) (m/2M)1/3, where γe0 is Lorentz factor associated with the initial electron beam velocity(vo) and (m/M) is the electron to ion mass ratio. Further it is observed that in contrast to the non-relativistic results1,2 at the saturation point, ratio of electrostatic field energy density (E2/8π) to the initial drift kinetic energy density (W0) scales with γe0 as ∼1/γ2e0. These results are found to be in good agreement with that derived using fluid theory.

Operation of a number of plasma devices such as Hall thrusters for electric propulsion and magnetrons for plasma processing rely on ExB drift of electrons in crossed electric and magnetic fields. The closed drift of electrons supports plasma ionization. The magnetic field constrains electron motion in perpendicular direction, while ions can be freely accelerated and extracted by the electric field from the discharge and used for various purposes such as thrust for electric propulsion, material deposition and modification for plasma processing. The electron current is also a source of free energy resulting in a number of discharge instabilities. In all, it is important to accurately predict the electron drift velocity and electron current. Large fraction of the electron current is due to the ExB drift. In a plasma with finite temperature the contribution of diamagnetic velocity due to inhomogeneous plasma pressure becomes important and comparable (for typical parameters) to the ExB drift. The magnetic gradient and curvature drifts existing in guiding center theory do not contribute additional current unless the plasma pressure is anisotropic. The structure and various contributions to the total electron current in inhomogeneous plasma and inhomogeneous magnetic field are discussed for some typical parameters of Hall devices.

Results are presented from basic heat transport experiments and gyrokinetic simulations of multiple magnetized electron temperature filaments in close proximity. This arrangement samples cross-field transport from nonlinear drift-Alfven waves and large scale convective cells. Experiments are performed in the Large Plasma Device (LAPD) at UCLA. A biased LaB6 cathode injects low energy electrons (below ionization energy) along a strong magnetic field into a pre-existing large and cold plasma forming an electron temperature filament embedded in a colder plasma, and far from the machine walls. A car bon masking plate with several holes (each 1cm diameter, 1.5 cm apart) is used to create 3 electron temperature filaments. By covering two holes in the mask drift-Alfven and thermal waves from a single filament have been characterized and compared to previous studies with a different electron beam source1. The observed eigenmode structures also compares favor ably with recent 3D gyrokinetic simulations2. The 3-filament case exhibits a complex wave pattern and enhanced cross-field transport. Detailed mode analysis and comparison with non linear simulations is reported.

In the present work we have studied the novel nonlinear phenomenon of plasma physics - beam-plasma instability in a charged plasma in the absence of ions. We have shown the possibility of the instability development and analyzed the characteristics of physical processes taking place during the beam-plasma interaction.

It is shown theoretically that laser ablation can change the growth rate of the Rayleigh-Taylor instability. Rayleigh-Taylor instability can grow in the interface of the low density (light fluid) with density ρ 1 and the target foil (heavy fluid) with density ρ 2 . The variation of RT growth rate with the Atwood number which represents the relative density differences of the two fluids and also with the evaporated plasma velocity is studied. The results show that the growth rate for Co 2 laser is low while it is high for KrF laser. Also it is shown that the growth rate is increased by increasing the relative density differences of the two fluids and is decreased by increasing plasma normalized velocity.

In this work, the propagation characters of an intense Gaussian laser beam through warm collisional plasma are investigated by considering the ponderomotive force nonlinearity, upward electron density and complex eikonal function. The ponderomotive force (PF) on the plasma electrons causes periodic self-focusing of the Gaussian laser beam. The PF mechanism changes the dielectric permittivity of plasma (refractive index) by expelling the electrons from the high intensity region (axial region) when the laser intensity is strong enough1. In our previous work2, we studied the thermal self-focusing of a laser beam in homogeneous warm collisional plasma. In the present work, propagation characters of Gaussian laser beam in warm collisional plasma under density ramp have been studied. By introducing the dielectric permittivity of warm unmagnetized plasma according to the Boltzmann equation3, the coupled differential equations defining the variations of laser beam parameters are obtained and solved numerically. The variation of beam width parameter with respect to dimensionless distance of propagation is investigated for different values of initial laser intensity, electron temperature and collision frequency. The results show that, there is a temperature interval in which the self-focusing can occur, while the beam diverges outside of this region. In addition, the results represent the existence of a “turning point temperature” in the mentioned interval in which the self-focusing has the strongest strength. And it is shown that, the collision frequency strongly affects the beam width parameter due to the energy attenuation. Moreover, the effect of the upward plasma density profile on the beam width parameter is studied. Results also show that, using the plasma density ramp-up, the self-focusing temperature range expands and its strength increases.

It is important to know basis of plasma turbulence induced by different wave instabilities in order to reduce the turbulent transport. There are many developed theories in which processes of plasma turbulence suppression by sheared flows are widely presented. In agreement with experiments theoretical researches1, 2 say that shearing effects lead to tilting or breaking of eddy structures. These effects were also compared with certain turbulent processes in fluid. But these researches mainly considered developed turbulence and slightly showed evolution of the plasma turbulence.

The effect of finite Larmor radius correction of ion to the pressure tensor (FLR) and pressure anisotropy is studied on the Jeans instability of self-gravitating quantum magnetohydrodynamic (QMHD) plasma considering linear approximation. The effect of FLR and pressure anisotropy is incorporated in the Fermi degenerate quantum plasma and basic Chew-Goldberger and Low (CGL) equations are modified. The linear QMHD equations including the quantum Bohm potential in the momentum transfer equation of anisotropic plasma, continuity equation and the energy equations are linearized. A linear analytical dispersion relation is obtained using the normal mode analysis. The non-gravitating magnetized mode is obtained which provides the hose instability and it is independent of quantum corrections. The gravitating mode modified due to the quantum corrections is obtained separately. The Jeans criterion of instability is examined and it is found that due to increase in quantum correction parameter the critical Jeans wave number and unstable region decreases. Hence it has destabilizing influence on the growth rate of Jeans instability of self gravitating anisotropic pressure quantum plasma.

Convective transport of plasma at edge and Scrape-off-layer (SOL) of plasma is an important issue in all the fusion machines needs to be addressed [1-6] for future fusion machines. Moreover, it is observed in all the fusion devices that the edge and SOL region where plasma detachment region is observed is having higher base pressure and the electron temperature of plasma is very low ∼ 1 eV [4-6]. Here the effect of base/ambient pressure on plasma parameters is reported. Electron density profile of plasma is calculated using Langmuir probe. Langmuir probe measurement at ∼ 8cm away from Gun mouth shows high density fluctuations. The FFT of density fluctuations shows a peak at ∼25 kHz. Detail analysis suggests R-T instability at this region. Variation of electron temperature of argon plasma with base pressure is estimated using emission spectroscopy data. It is observed that the electron temperature of plasma is ∼ 0.3–1 eV. However, at higher base pressure ∼ 1 mb or above a number of prominent argon lines are observed unlike that at lower base pressure. This indicates formation of more fast neutrals inside bulk plasma. Fast imaging results (∼9100 fps) shows blob formation and transport from main plasma column at base pressure 1 mb and above. The velocity of blob is ∼ 213 m/s, calculated using time of flight technique. For these experimental findings it can be proposed that the asymmetry force due to fast neutrals inside bulk plasma and slow neutrals outside main plasma column is responsible for blob formation at higher base pressure [7]. The detail mechanism is presented in this communication.

In the present research, collimated plasma jets form from Joule heating and ablation of a radial foil (Al 20 μm thin disk) using a pulsed power generator (COBRA) with 1 MA peak current and 100 ns rise time. Plasma dynamics of the jet are diagnosed with and without an applied uniform external magnetic field (∼1 T axial Bz) and under a change of current polarities, which correspond to current moving either radially outward or inward from the foil's central axis. Experimental results are compared with predictions made by numerical simulations (PERSEUS)1. The influence of the Hall effect on the jet development is observed under opposite current polarities. Before jet formation, initial plasma on top of the foil surface develops discrete narrow current path channels (tendrils) that display characteristics of electrothermal-filamentation plasma instability. A disruption of the tendrils and subsequent jet is noticed after a modest increase in the applied field strength from 1 to 1.5 T, which is not predicted by the 2D (r-z) simulations.

Plasma in magnetic field configuration of alternating-sign curvature — with appropriate combination of the convex and concave field line parts, exhibits specific stability features against convective (flute-interchange) modes1,2. This results in the internally peaked stable pressure profiles that has been predicted from theory with taking into account necessary and sufficient ‘kinetic’ criterion of plasma convective stability. Simplest magnetic confinement system that is required for such a peaking — tandem of a mirror and cusp device, having minimum of second adiabatic invariant J = ∫ v dl in a middle of confinement volume. Compact magnetic confinement system Magnetor3,4 with 2.45 ECR plasma has been improved by adding additional current coil to satisfy alternating-sign curvature requirements for a plasma pressure peaking. First experimental measurements of the ion saturation current transverse profiles (see figure 1) demonstrate a maximum in ion saturation current at the region of low but alternating-sign curvature.

Study of kinetic instabilities of non-equilibrium plasma produced in an open magnetic trap by powerful microwave radiation under electron cyclotron resonance (ECR) conditions is of fundamental interest including prospects to simulate physical processes in the solar corona, in the magnetospheres of the Earth and other planets. For example, plasma instabilities in magnetic traps on the Sun are the sources of powerful broadband radio emission (the so-called type IV bursts) which is interpreted as the excitation of plasma waves by fast electrons in the upper hybrid resonance frequency followed by transformation in electromagnetic waves, for example, as a result of scattering by thermal ions. In the case of double plasma resonance condition when the frequency of the upper hybrid resonance coincides with one of the electron gyrofrequency harmonics the instability increment of plasma waves is greatly increased. This leads to the appearance of bright narrow-band radio emission near the harmonics of the electron gyrofrequency - the so-called zebra patterns. It should be noted that the possible manifestations of double plasma resonance effect are not rare in astrophysical plasmas. The phenomenon of zebra pattern is observed not only on the Sun, but in the decametric radiation of the Jupiter, kilometric radiation of the Earth and even in the radio emissions of pulsars. In connection with the above, verification of the effect of double plasma resonance in a laboratory plasma experiments is a very relevant task.

We have investigated the E x B instability in presence of sheared magnetic field, found in the internal transport barrier of fusion machines. The response of electric potential with respect to an important parameter y/θ, where y is the direction along which the magnetic shear acts and θ is the angle of magnetic shear of ions, is estimated which results in some critical outcomes.

The Z-pinch phase of a dense plasma focus (DPF) emits multiple-MeV ions from a ∼cm length interaction. The mechanisms through which these physically simple devices generate such high-energy beams in a relatively short distance are not fully understood. We are exploring the mechanisms behind these large accelerating gradients using fully kinetic simulations of a DPF Z-pinch and ion probe beam measurements. Our particle-in-cell simulations have successfully predicted ion beams and neutron yield from kJ-scale DPFs1, which past fluid simulations have not reproduced. To access the regime of MJ-scale devices within computational resources, we have developed a handoff simulation starting from a fluid calculation near the end of rundown and continuing fully kinetic through the pinch. To probe the accelerating fields in our tabletop experiment, we inject a 4 MeV deuteron beam along the z-axis. For the first time, we have directly measured the gradients in the DPF and the acceleration of an injected ion beam. We observe > 50 MV/m acceleration gradients during 800 J operation using a fast capacitive driver2. In addition, we have now experimentally measured and observed in simulations for the first time, electric field oscillations near the lower hybrid frequency. This is suggestive that the lower hybrid drift instability, long speculated to be the cause of the anomalous plasma resistivity that produces large DPF gradients, is playing an important role. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability for accelerator and neutron source applications.

Helicon plasma sources are typically associated with a core, a radially localized central area of strong light emission. Here we describe new experimental results that clearly distinguish between the capacitive to helicon mode transition in an rf heated, argon plasma and the formation of the classic “blue” helicon core. We find that for certain source parameters, helicon plasma (discrete jump to high densities ∼ 1019 m−3 with increasing power and magnetic field, strong Ar - II dominated emission etc.) occur without the formation of the core. For such conditions, the plasma is dominated by resistive drift wave [RDW] instabilities driven by the radial density gradient rotating in the electron diamagnetic drift direction. The resulting particle flux is radially outwards for all radii. For controlled changes in the source parameters, we are able to trigger the formation of the core. A new global equilibrium state is achieved where we find the simultaneous existence of three radially separated plasma instabilities. The density gradient region, still dominated by RDWs, separates the plasma radially into the edge region and the core region. The edge region is dominated by strong, turbulent, shear driven Kelvin - Helmholtz [KH] instabilities, while the core region shows coherent Rayleigh - Taylor [RT] modes driven by azimuthal rotation. The RT modes rotate in the ion diamagnetic drift direction and are associated with enhanced light emission. The particle flux is directed outward for small radii and inward for large radii, thus forming a radial particle transport barrier which leads to a slight increase in the core plasma density. Simultaneously the Ar - II emission from the core region increases by an order of magnitude. The radial extent of the inner RT mode and radial location of the particle transport barrier is the same as the radius of the blue core. This new equilibrium with the RT - RDW - KH instabilities leads to the formation of a very strong enhanced blue core. For a range of operating parameters, just prior to this new global equilibrium state with the enhanced blue core, the system undergoes incomplete intermittent transitions between the two equilibrium states, leading to the visual perception of the “helicon core” in a time averaged sense. This is the first time that the development of the helicon core is shown to be associated with changes in radial transport driven by inherent plasma instabilities.

The interaction of relativistic charged particle bunches with plasmas can be characterized by comparing the longitudinal (σ z ) and transverse (σ r ) bunch size to the cold plasma collisionless skindepth c/ω pe or equivalently to the corresponding wavenumber k pe =1/(c/ω pe ).

We describe a novel algorithm for the generation of cathode plasma expansion in particle-in-cell codes, and have applied the algorithm to investigate cathode plasma expansion in magnetically-insulated transmission lines (MITLs) in the particle-in-cell code LSP. The steady-state MITL electron current is modeled by a fully-kinetic electron species. Neutral particles are then desorbed from the cathode surface at a fixed rate and are allowed to fragment into electron-ion pairs as they propagate over a short distance, generally one or two cell widths, normal to the surface. These electron-ion pairs, modeled as fluid species, form the seed cathode plasma. Energetic plasma electron particles can be converted to kinetic electrons to resupply the electron flux at the plasma edge (the “effective” cathode). Using this model, we compare results for the time evolution of the cathode plasma and MITL electron flow with a simplified (isothermal) ambipolar diffusion model. We find good agreement between the two approaches for the time evolution of the coupled system of cathode plasma and MITL electrons.

Exploiting the two-stream instability to amplify radio frequency signals is an attractive concept because the interaction is extremely broadband and co-propagating beams of different energies make the instability convective instead of absolute, thus enabling operation as an amplifier. This holds out the possibility of bandwidth performance that rivals that of helical traveling wave tubes (helix TWT's) at much higher powers. Previous attempts1 at two-stream amplifiers were abandoned due to poor efficiency compared to helix TWTs. More recent work2 3 has indicated that the use of relativistic beams can increase the efficiency, perhaps as high as 50%.

Turbulence at length scales on the order of the electron Debye length has been shown to be a possible contributor to anomalous electron transport in the Hall thruster. Simulations1 and coherent Thomson scattering experiments2 have identified an azimuthal instability of megahertz frequency and millimeter wavelength which is associated with increased electron current.

Plasma instabilities in Hall thruster (HT) deteriorate the performance of the thruster and its compatibility with the electronic equipment of the spacecraft. Therefore, a development of effective methods of suppressing the instabilities is an actual problem. Among the plasma instabilities in HT, large scale electron instability holds one of the main positions. Its arising brings about redistribution of electrical field in the acceleration layer that can increase losses of ions on the walls of the thruster. In Ref (1, 2), the theoretical model of the electron instability, based on Rayleigh mechanism of its arising, was developed. The application of a feedback system is a versatile method of suppressing the large scale plasma instabilities. Two kinds of the feedback system are possible: volume and boundary (surface) ones. At conditions of the HT, the boundary feedback system (BFS) is more preferable. At an application of the BFS, sensors and controlling electrodes are placed on the plasma boundary, which is parallel to the magnetic field, that is, on an anode3. For the correct choice of the BFS parameters, a theoretical model of the electron instability suppression by the BFS was first developed. It is a subject of the presentation.

The Raptor kJ class 1053 nm Nd:Glass laser in the Phoenix laser laboratory at UCLA is used to ablate a dense debris plasma from a carbon or plastic target, which is embedded in a relatively tenuous, uniform, and quiescent ambient magnetized plasma in the Large Plasma Device (LAPD). The LAPD provides a peak plasma density of n i ∼ 1013cm−3, with a background magnetic field that can vary between 200 to 1200G. Debris ions from laser produced plasma expand out conically with super-Alfvenic speed (M A ∼2) to expel the background magnetic field and ambient ions to form a diamagnetic cavity. The interaction of the debris plasma with the ambient plasma and the magnetic field acts as a piston which can create collisionless shocks. Two dimensional hybrid simulations are used to compare to experimental data. The effect of different electron pressure models will be studied and compared to experimental results.

Axi-symmetric mirror machines are the simplest magnetic confinement devices, and as such could be attractive for fusion machines, ions separation, and more. However, mirror machines suffer from particle loss due to the violent flute instability. We demonstrates for the first time the stabilization of fast growing, slowly rotating flute instability by multi-input, multi-output active feedback system.

Atmospheric-pressure plasma jets formed by dielectric barrier discharges and injected into ambient air are effective sources for production of chemically active non-thermal plasmas [1]. The jets are repetitively pulsed and so are composed of a sequence of ionization waves with speeds up to 108 cm/s. The luminous plume of the plasma jets can be longer than 10 cm. With typical applied voltages of a few kV, the mean electric field in the plume can be less than 1 kV/cm which is less than the avalanche field in air or in He. As a result, a conventional ionization wave (the bullet) cannot be sustained for such long distances. However, for repetition frequencies of a few to tens of kHz, each new plasma bullet propagates in a gas excited and preionized by the previous plasma bullet. The pulse-periodic plasma jet then must develop from the initially unionized (and unexcited gas) having a short extent to a preionized channel having a longer extent.

Intense electron or ion beams propagating in plasmas are subject to the two-stream instability, which leads to a slowing down of the beam particles, acceleration of the plasma particles, and transfer of the beam energy to the plasma particles and wave excitations. Making use of the particle-in-cell codes EDIPIC and LSP, we have simulated two-stream instability interactions over a wide range of beam and plasma parameters. Typically, the instability saturates due to nonlinear wave-trapping effects of either the beam particles or plasma electrons. The saturation due to nonlinear wave-trapping effects limits the “mixing” in phase-space and may produce coherent structures in the electron velocity distribution function. For the case of an electron beam, simulations show that the two-stream instability is intermittent, with quiet and active periods. In case of two dimensional simulations, considerable scattering of beam particles is observed for both electron and ion beams.

At naturally occurring plasma boundaries in the near-Earth space environment, such as the magnetopause and the plasma sheet boundary layer, strong sheared plasma flows are often observed. As plasma boundary layers begin to relax from a compressed state, the ratio of the ion gyro-radius to the shear scale length decreases. At these layers, broadband electrostatic noise has been observed where the frequency ranges from well below the ion cyclotron frequency to the electron plasma frequency. Simulations have confirmed that the free energy in the sheared plasma flows can excite Kelvin Helmholtz instabilities, ion cyclotron-like instabilities, and lower hybrid modes. Kinetic theory described by G. Ganguli (G. Ganguli, M. Keskinen et. al., J. Geophys. Res., A5, 8873, 1994) discusses the three distinct instability regimes in the context of the ion gyro-radius and the shear scale length. The ratio of the ion gyro-radius to the shear scale length acts as a surrogate for the magnitude of stress that a plasma layer is subjected to and determines which mode is dominant.

The linear Electron-Ion Hybrid (EIH) instability, a transverse velocity shear-driven instability with frequency near the lower hybrid frequency, was previously predicted theoretically to explain the observation of lower hybrid waves in applications from the plasma sheet boundary layer to laser produced plasmas. The linear EIH instability has also been observed in the laboratory in scaled magnetospheric plasma conditions and in laser produced plasma expansion experiments across magnetic fields. PIC simulations have shown that a key feature of the nonlinear evolution of the EIH mode is that it leads to the formation of coherent, closed potential contours in the fluctuating electrostatic potential.