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We computationally investigate the Richtmyer–Meshkov instability of a density interface with a single-mode perturbation in a two-fluid, ion–electron plasma with no initial magnetic field. Self-generated magnetic fields arise subsequently. We study the case where the density jump across the initial interface is due to a thermal discontinuity, and select plasma parameters for which two-fluid plasma effects are expected to be significant in order to elucidate how they alter the instability. The instability is driven via a Riemann problem generated precursor electron shock that impacts the density interface ahead of the ion shock. The resultant charge separation and motion generates electromagnetic fields that cause the electron shock to degenerate and periodically accelerate the electron and ion interfaces, driving Rayleigh–Taylor instability. This generates small-scale structures and substantially increases interfacial growth over the hydrodynamic case.

We report experimentally observed triggering criteria for Buneman instability and boundary conditions for existence of multiple double layers (MADL) in glow discharge plasma. The MADLs are generated by accelerating plasma electrons towards a positively biased electrode submerged in it. The boundary conditions for the formation and existence of MADL are obtained from the experiment in terms of electron drift velocity ( ν d ) and electron thermal velocity ( ν t e ). The MADL is found to exist within the range 3 ν t e ≥ ν d ≥ 1.3 ν t e . For the condition ν d ≥ 1.3 ν t e , rise of an instability and simultaneous formation of MADL is observed in the experiment. The analysis of fluctuations in floating potential showed that the instability has all the characteristics of Buneman instability.

As a continuation of developing multiscale method for the transport phenomena, a unified gas kinetic scheme (UGKS) for multi-scale and multi-component plasma simulation is constructed. The current scheme is a direct modeling method, where the time evolution solutions from the Vlasov-BGK equations of electron and ion and the Maxwell equations are used to construct a scale-dependent plasma simulation model. The modeling scale used in the UGKS is the mesh size scale, which can be comparable to or much larger than the local mean free path. As a result, with the variation of modeling scales in space and time through the so-called cell's Knudsen number and normalized Larmor radius, the discretized governing equations can recover a wide range of plasma evolution from the Vlasov equation in the kinetic scale to different-type of magnetohydrodynamic (MHD) equations in the hydrodynamic scale. The UGKS provides a general evolution model, which goes to the Vlasov equation in the kinetic scale and many types of MHD equations in the hydrodynamic scale, such as the two fluids model, the Hall, the resistive, and the ideal MHD equations. All current existing governing equations become the subsets of the UGKS, and the UGKS bridges these distinguishable governing equations seamlessly. The construction of UGKS is based on the implementation of physical conservation laws and the un-splitting treatment of particle collision, acceleration, and transport in the construction of a scale-dependent numerical flux across a cell interface. At the same time, the discretized plasma evolution equations are coupled with the Maxwell equations for electro-magnetic fields, which also cover a scale-dependent transition between the Ampére's law and the Ohm's law for the calculation of electric field. The time step of UGKS is not limited by the relaxation time, the cyclotron period, and the speed of light in the ideal-MHD regime. Our scheme is able to give a physically accurate solution for plasma simulation with a wide range of Knudsen number and normalized Larmor radius. It can be used to study the phenomena from the Vlasov limit to the scale of plasma skin depth for the capturing of two-fluid effect, and the phenomena in the plasma transition regime with a modest Knudsen number and Larmor radius. The UGKS is validated by numerical test cases, such as the Landau damping and two stream instability in the kinetic regime, and the Brio-Wu shock tube problem, and the Orszag-Tang MHD turbulence problem in the hydrodynamic regime. The scheme is also used to study the geospace environment modeling (GEM), such as the challenging magnetic reconnection problem in the transition regime. At the same time, the magnetic reconnection mechanism of the Sweet-Parker model and the Hall effect model can be connected smoothly through the variation of Larmor radius in the UGKS simulations. Overall, the UGKS is a physically reliable multi-scale plasma simulation method, and it provides a powerful and unified approach for the study of plasma physics.

The saturation level of the low-threshold parametric two-plasmon instability of the extraordinary pump wave decay to two upper hybrid plasmons is analyzed under conditions when the only efficient saturation mechanism is the pump depletion. A closed system of differential equations describing both the instability excitation and saturation is derived. The system is solved numerically and an analytic expression is obtained for the anomalous absorption coefficient of the pump wave caused by the development of this instability. The saturation level of the two-plasmon decay instability and the related anomalous absorption efficiency are estimated from data obtained in experiments on the electron cyclotron resonance heating of the plasma by an extraordinary wave in the TEXTOR tokamak.

Jeans instability with magnetosonic perturbations is discussed in quantum dusty magnetoplasmas. The quantum and smaller thermal effects are associated only with electrons. The quantum characteristics include exchange-correlation potential, recoil effect, and Fermi degenerate pressure. The multifluid model of plasmas is used for the analytical study of this problem. The significant contribution of electron exchange is noticed on the threshold value of wave vector and Jeans instability. The presence of electron exchange and correlation effects reduce the time to stabilise the phenomenon of self-gravitational collapse of massive species. The results of Jeans instability by magnetosonic perturbations at quantum scale help to disclose the details of the self-gravitating dusty magnetoplasma systems.

The Weibel instability plays an important role in stopping hot electrons and energy deposition mechanism in fast ignition of inertial fusion process. In this paper, the ion Weibel instability in counter propagating electron-ion plasmas is investigate. The obtained results show that the growth rate of Weibel instability will be decreased about 40% with the anisotropy velocity as vxe = 2vze = 20; the ion density ratio, b = n0i1/n0i2, and density gradient, are increasing 50 and 90% respectively. The ion streaming in density gradient of dense plasma leads to increasing the Weibel instability growth rate and its amplification through ion streaming in the large wavenumber. The maximum unstable wavenumber has been decreased with decreasing the ion beam density ratio. For fixed ion density ratio, increasing 90% of the density gradient in the near of fuel plasma corona leads to reducing growth rate and unstable wavenumber about 43 and 42% respectively.

The quasi-optical approach has been used to study the linear and nonlinear stages of instability of an electron beam propagating near a flat boundary of an absorbing medium with dissipative characteristics that can be described by the Leontovich impedance boundary conditions. It has been shown that resistive instability can be used to amplify radiation in the short-wave ranges, including the terahertz range. The instability increments and the efficiency of energy transfer have been determined.

Azimuthal surface waves are eigen-electromagnetic waves which propagate in coaxial plasma-vacuum waveguides across an axial stationary magnetic field. Their excitation in the coaxial plasma layer by the flow of electrons which rotate along large Larmor orbits either around or inside the plasma layer has been well studied in the collision-less approach. The influence of weak collisions between the plasma particles on the growth rate of such waves for both cases of the electron beam placement is studied here for the frequency range above the upper-hybrid frequency and compared to the case of the electron cyclotron frequency range. Transition from the regime of beam-plasma instability to that of a beam-dissipative instability is discussed.

By using quantum hydrodynamic model, we derive a generalized dielectric response function for two stream instability (convective only) in n-type gallium arsenide semiconductor plasma. We investigate the phase and amplification profiles of two stream instability with externally applied electric field ranging from 2600 to 4000 kV m−1 in presence of non-dimensional quantum parameter-H. In this range, a significant number of electrons in satellite valley become comparable to the number of electrons in central valley. The presence of quantum corrections in plasma medium induces two novel modes; one of it has amplifying nature and propagates in forward direction. It also modifies the spectral profile of four pre-existing modes in classical plasma. The existence of two stream instability is also established analytically by deriving the real part of longitudinal electrokinetic power flow density.

An ionization wave travelling ahead of the shock wave of the plasma jet, propagating in residual gas (nitrogen) of the plasma focus discharge, is detected by the laser-interferometry method at the plasma focus. Radial and axial distributions of electron densities of the shock wave and plasma jet are measured.

The structure and dynamics of ion-acoustic waves in an unmagnetized plasma, including the case of weakly relativistic collisional plasma (when it is necessary to take into account the high energy particle flows which are observed in the magnetospheric plasma), are studied analytically and numerically on the basis of a model of the Kadomtsev-Petviashvili (KP) equation. It is shown that, if the velocity of plasma particles approaches the speed of light, the relativistic effects start to strongly influence on the wave characteristics, such as its phase velocity, amplitude, and characteristic wavelength, with the propagation of the twodimensional solitary ion-acoustic wave. The results can be used in the study of nonlinear wave processes in the magnetosphere and in laser and astrophysical plasma.

The transition to overlimiting currents directly from prelimiting regimes bypassing the limitingcurrent stage is considered for imperfect electric membranes. The hydrodynamic instability of the onedimensional equilibrium state, which is a result of the balance between diffusion and electromigration, is investigated. The influence of volume and surface effects on instability and the transition to overlimiting currents is estimated under variation of the membrane selectivity. It is found that the dominating mechanism of instability is destabilization of the residual space charge. The fact of the replacement of monotonic instability by vibratory instability with a vibration frequency of about 50−300 Hz has been discovered.

The instability behavior of moving magnetic fluid jet in the presence of a constant uniform transverse magnetic field is investigated theoretically within the framework of linear stability analysis. The corresponding dispersion relation between the wave growth rate of instability and the magnitude of its wavenumber is obtained. The dependence of the wave growth rate on the polar angle in the presence of magnetic field is found. The influence of the magnetic field on the length of undisturbed jet section and the instability wavelength is studied. The correlation with the experimental results is demonstrated.

The behavior of short-wavelength electromagnetic waves passing through a warm motional plasma is studied. The velocity and the self-magnetic field of the plasma particles are directed transversely to the direction of wave propagation. Using local approximation method, dielectric tensor and dispersion relation of perpendicular waves are derived employing the Fluid-Maxwell model. The role of temperature in propagation of EM waves, and as a result, in the instability caused by interaction between extraordinary EM waves and modified electron plasma waves is demonstrated. Moreover, the effects of self-magnetic field strength on the instability are illustrated.

The quantum hydrodynamic model is used to investigate the arbitrary degenerate electron/hole stream instabilities in ballistic semiconductors or semiconductor plasmas (semiplasmas) for a wide range of impurity doping, number density, and temperatures. It is observed that, while the instability in classical plasma regime is always of single $k$ -range type, the double-range instability can occur in degenerate plasma regime. Different types of carrier counter-streaming instabilities are classified and parametrically studied in arbitrarily doped ballistic semiconductors. The parametric study of counter-stream instability in silicon at room temperature shows that the doping scheme has fundamental effect on electron–electron and hole–hole instabilities but no effect on electron–hole instability. Other parameters, such as the electron temperature and stream speed, have significant effects on the unstable wavenumber range and the growth rate. It is remarked that the electron stream in n-type semiconductors becomes unstable at somewhat lower limit of the stream speed than that of holes in a p-type silicon semiconductors. A description based on the energy exchange between unstable modes is given for different instability types. It is found that the instability in asymmetric doped semiconductors (electron–electron and hole–hole) is of symmetric type without energy exchange between the modes, while, for symmetric doped semiconductors (electron–hole), it is of asymmetric type with the energy exchange. Finally, it is found that the electron and hole spin exchange–correlation effects enhance the two-stream instability.

The electron–electron two-stream instability has been studied in two-valley n-GaAs embedded with nanoparticle (NP) cluster. We considered polar optical phonon as the dominant intravalley scattering mechanism and drifted Maxwellian to approximate the distribution of carriers between each valley. We derived the dispersion relation for electrostatic wave using hydrodynamic model of plasmas. While investigating temporal behaviour, we found two novel modes of propagation. These two novel modes are found to be evanescent by nature and propagate with equal phase velocities, but in opposite directions. The pre-existing modes retained their profile structures even in the presence of NP cluster. On the other hand, in the case of convective instability, no new modes are obtained but the propagation and gain profiles of the preexisting modes are significantly modified by the presence of NP cluster in the host medium.

A model is constructed allowing computer simulations of the near-wall area of a planar plasma sheet in conditions where the steady state of the plasma is supported by the production of charged particles in a region removed from the wall. Calculations have revealed variation in the energy distribution of the electrons in both time and spatially over the sheet width (cooling the electronic component) due to absorption of fast electrons at the walls bounding the plasma volume. It is shown that the plasma density profile across the sheet width has an abrupt decrease at the boundary of the region of plasma regulation. Thus the standard concepts of the potential and plasma density distributions in the sheath and presheath based on the assumption of a stable energy distribution for the electrons in the presheath yields inaccurate results for the plasma sheet where the ionization source is remote from the wall.

In this contribution we have presented two techniques for determination of plasma equilibrium position in IR-T1 tokamak: Relaxation and optical techniques. An analysis method of tokamak plasma equilibrium by a relaxation method with specified magnetic axis was presented. The degrees of freedom due to designated positions of the magnetic axis are possible by using poloidal field coil currents. Stable steady state tokamak plasma equilibria are calculated along with the Magnetohydrodynamic (MHD) potential energy. The plasma generates a plasma current which partially or fully cancels the magnetic field from the poloidal field coils. For low-temperature plasmas, the plasma current distribution is centrally peaked; for high-temperature plasmas, the plasma current has a hole. A centrally peaked current distribution in a low-temperature plasma is evolved into a current distribution with a hole by increasing the plasma pressure by Ohmic heating, RF heating, or by neutral beam injection heating. In the second technique, an image processing technique is used for the output signal of CCD camera. Then, plasma emission intensity profile and plasma position were obtained. Results were compared and discussed.

Processes occurring near the boundary between three-component plasma with negative ions and two-component electron−ion plasma are considered. The excited waves and instability are described. Stability condition at the boundary is determined.

Experimental conditions under which the low-threshold absolute parametric decay instability of an electromagnetic wave with extraordinary polarization at the electron cyclotron resonance heating of a plasma at the second harmonic resonance in toroidal devices are analyzed. A new mechanism is proposed for the localization of a daughter electrostatic wave in the toroidal direction in the region of a high-power pump beam. This mechanism, along with the two-dimensional localization of the daughter wave because of a nonmonotonic radial profile of the plasma density and the poloidal inhomogeneity of the magnetic field, can be responsible for the parametric excitation of a three-dimensional cavity for this wave and, as a result, low-threshold absolute decay instability of the pump wave.

In the long pulse RF source the plasma drift caused by the magnetic filter field leads to different plasma parameters close to the top and bottom halves of the plasma. In order to investigate the effect of the plasma density on the extracted currents, the bottom grid halve was covered and the direction of the drift was converted by changing the polarity of the magnets. The asymmetry of the plasma density was measured by Hβ spectroscopy. By biasing the plasma grid the asymmetry could be enlarged, but the current of co‐extracted electrons could be minimized in a similar way for both polarities. The extracted currents of H− ions as well as of the electrons, however, depend only weakly on the direction of the drift i. e. on the plasma densities. The results indicate that the source performance is determined to a greater degree by the plasma sheath close to the plasma grid which is not yet accessible by diagnostics.

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.

Ion acceleration in electrostatic collisionless shocks is driven by the interaction of the high-power laser with specially tailored near-relativistic critical density plasma. 2D EPOCH particle-in-cell simulations show that the ion acceleration is dependent on the target material used. In materials with low charge-to-mass ratio.

Мета роботи – встановлення основних фізичних закономірностей, що пов’язані з формуванням у мультигармонічних двопотокових та плазмово-пучкових СЛВЕ з гвинтовими РЕП потужного електромагнітного випромінювання з широким частотним спектром в міліметровому-інфрачервоному діапазонах довжин хвиль.

Дисертаційна робота присвячена теоретичному дослідженню динаміки електромагнітних хвиль у мультигармонічних двопотокових супергетеродинних лазерах на вільних електронах Н-убітронного типу з гвинтовими електронними пучками з урахуванням множинних трихвильових параметричних взаємодій різного типу. Запропоновано використовувати гвинтові електронні пучки у мультигармонічних двопотокових супергетеродинних лазерах на вільних електронах (ДСЛВЕ), призначених для одержання потужного електромагнітного сигналу з широким частотним спектром. З’ясовано, що такі пристрої мають менші поздовжні габарити та здатні формувати мультигармонічні електромагнітні хвилі з більш широким частотним спектром порівняно з ДСЛВЕ, які використовують прямолінійні електронні пучки. У кубічному нелінійному наближенні одержано самоузгоджену систему диференціальних рівнянь для амплітуд гармонік електромагнітних хвиль у мультигармонічних двопотокових супергетеродинних лазерах на вільних електронах Н-убітронного типу з гвинтовими релятивістськими електронними пучками (РЕП). Виявлені та враховані трихвильові резонансні взаємодії різного типу, зокрема й пов’язані з обертальним рухом електронів у фокусувальному магнітному полі. Показано, що множинні взаємодії хвиль у таких системах є визначальними для формування електромагнітного сигналу з широким частотним спектром. З’ясовано, що завдяки використанню гвинтових двопотокових РЕП у ДСЛВЕ вдається збільшити інкременти зростання хвиль за умови збільшення кута вльоту електронного пучка відносно фокусувального магнітного поля. Показано, що у гвинтових двопотокових РЕП критична частота двопотокової нестійкості також зростає зі збільшенням кута вльоту. Це дозволяє збільшити ширину частотного спектра електромагнітних хвиль, що формується мультигармонічними ДСЛВЕ. Завдяки використанню гвинтових двопотокових РЕП у ДСЛВЕ вдається сформувати мультигармонічну електромагнітну хвилю з більш широким частотним спектром та на менших відстанях порівняно з ДСЛВЕ, що використовують прямолінійні РЕП. Продемонстровано, що в разі використання мультигармонічного вхідного сигналу з вузьким частотним спектром у мультигармонічних ДСЛВЕ-підсилювачах з гвинтовими РЕП формування потужної мультигармонічної електромагнітної хвилі відбувається на довжинах, у два і більше разів менших порівняно із системами, на вхід яких подається монохроматичний вхідний сигнал. Диссертация посвящена теоретическому исследованию динамики электромагнитных волн в мультигармонических двухпотоковых супергетеродинных лазерах на свободных электронах Н-убитронного типа с винтовыми электронными пучками с учетом множественных трёхволновых параметрических взаимодействий разного типа. Предложено использовать винтовые электронные пучки в мультигармонических двухпотоковых супергетеродинных лазерах на свободных электронах (ДСЛСЭ), предназначенных для получения мощного электромагнитного сигнала с широким частотным спектром. Установлено, что такие устройства имеют меньшие продольные габариты и способны формировать мультигармонические электромагнитные волны с более широким частотным спектром по сравнению с ДСЛСЭ, использующими прямолинейные электронные пучки. В кубическом нелинейном приближении получена самосогласованная система дифференциальных уравнений для амплитуд гармоник электромагнитных волн в мультигармонических двухпотоковых супергетеродинных лазерах на свободных электронах Н-убитронного типа с винтовыми релятивистскими электронными пучками (РЭП). Выявлены и учтены трёхволновые резонансные взаимодействия различного типа, в том числе и связанные с вращательным движением электронов в фокусирующем магнитном поле. Показано, что множественные взаимодействия волн в таких системах являются определяющими для формирования электромагнитного сигнала с широким частотным спектром. Выяснено, что благодаря использованию винтовых двухпотоковых РЭП в ДСЛСЭ удается увеличить инкременты нарастания волн при условии увеличения угла влета электронного пучка относительно фокусирующего магнитного поля. Показано, что в винтовых двухпотоковых РЭП критическая частота двухпотоковой неустойчивости также вырастает с увеличением угла влета. Это позволяет увеличить ширину частотного спектра электромагнитных волн, формирующегося мультигармоническими ДСЛСЭ. Благодаря использованию винтовых двухпотоковых РЭП в ДСЛСЭ удается сформировать мультигармоническую электромагнитную волну с более широким частотным спектром и на меньших расстояниях по сравнению с ДСЛСЭ, использующими прямолинейные РЭП. Продемонстрировано, что в случае использования мультигармонического входного сигнала с узким частотным спектром в мультигармонических ДСЛСЭ-усилителях с винтовыми РЭП формирование мощной мультигармонической электромагнитной волны происходит на длинах, в два и более раз меньших по сравнению с системами, на вход которых подается монохроматический входной сигнал. The thesis is devoted to the theoretical study of the electromagnetic waves dynamics in multiharmonic two-stream superheterodyne free-electron lasers of the H-ubitron type with helical electron beams, considering multiple three-wave parametric interactions of different types. It has been proposed to use helical electron beams in multiharmonic two-stream superheterodyne free-electron lasers (TSFELs), which are designed to produce a powerful electromagnetic signal with a wide frequency spectrum. It has been found that such devices have smaller longitudinal dimensions and are capable of forming multiharmonic electromagnetic waves with wider frequency spectrum compared to TSFELs that use straight electron beams. A self-consistent system of differential equations has been obtained in the cubic nonlinear approximation for the harmonics amplitudes of electromagnetic waves in multiharmonic two-stream superheterodyne free-electron lasers of H-ubitron type with helical relativistic electron beams (REBs). Three-wave resonant interactions of various types, including those associated with the rotational motion of electrons in a focusing magnetic field, have been identified and considered. It has been shown that multiple interactions of waves in such systems are decisive for the formation of an electromagnetic signal with wide frequency spectrum. It has been found that due to the use of two-stream helical REBs in TSFEL, it is possible to increase the wave growth rates under the condition of increasing the electron beam input angle relative to the focusing magnetic field. It has been also shown that in helical two-stream REBs, the critical frequency of two-stream instability also increases with an angle. This allows to increase the frequency spectrum width of electromagnetic waves formed by multiharmonic TSFEL. Using two-stream helical REB in TSFEL, it is possible to form a multiharmonic electromagnetic wave with wide frequency spectrum and at smaller distances compared to TSFELs that use straight REBs. It has been demonstrated that in the case of multiharmonic input signal with a narrow frequency spectrum in multiharmonic TSFEL amplifiers with helical REB, the formation of powerful multiharmonic electromagnetic wave occurs at lengths two and more times smaller than the systems using monochromatic input signal.

The “Vlasov-Maxwell system” is a groundbreaking differential procedure to visualize, model, simulate and further analyze the vigorous performance of plasma (collisionless) in the presence of the different fields (electromagnetic). In this frame of reference, the analysis of “Vlasov-Maxwell system” with the deep conceptions of (time-fractional) calculus is a novel benchmark and also the key intentions of this study. For this purpose, (1D + 1P) dimensional semi-relativistic time-fractional Vlasov-Maxwell system is formulated with the physical significances of the geometry. Furthermore, to fabricate the numerical consequences, we suggest (and also implement) an innovative algorithm which based on spectral and finite-difference estimations. The spatial and temporal variables are handled by using sifted Gegenbauer polynomials and finite-difference calculations respectively. Numerous simulations are executed to validate the reliability and accuracy of anticipated method. Error bound convergence and stability of the method is inspected numerically. Moreover, the established technique can be used conveniently to observe the numerical result of other multi-dimensional fraction (variable) order problems of physical nature.