Plasma Physics Reports最新文献

The paper presents a numerical analysis of the possibility of performing local measurements of potential and plasma density fluctuations in the T-15MD tokamak using the Heavy Ion Beam Probe (HIBP) diagnostic. Four types of fluctuations are considered in the frequency range up to 500 kHz: Geodesic Acoustic Mode (GAM), Quasi-Coherent Mode (QCM), Tearing Mode (TM), and Alfvén eigenmode (AE). For each type of fluctuation, spatial measurement areas are defined for regimes with different values of average density ({{bar {n}}_{e}}) and toroidal magnetic field ({{B}_{T}}). Regimes with flat and peaked density profiles are considered. It is shown that high-Q fluctuations (GAM, AE, TM) can be measured in the peripheral region of the plasma (rho < 0.8) up to density ({{bar {n}}_{e}} leqslant 7 times {{10}^{{19}}};{{{text{m}}}^{{ - 3}}}), while low-Q QCMs can be measured up to ({{bar {n}}_{e}} leqslant 5 times {{10}^{{19}}};{{{text{m}}}^{{ - 3}}}). In the plasma gradient region (rho = 0.5{-} 0.9) the measurement of high-Q fluctuations is possible at a density of ({{bar {n}}_{e}} leqslant 5 times {{10}^{{19}}};{{{text{m}}}^{{ - 3}}}), and of the low-Q QCM at a density of ({{bar {n}}_{e}} leqslant 3 times {{10}^{{19}}};{{{text{m}}}^{{ - 3}}}).

A self-consistent model combining the kinetic Vlasov equation governing the distribution function of the resonant particles and the Ampere–Maxwell law is presented. The nonresonant particles are taken into account via the dielectric permittivity in the linear approximation. The results of numerical simulations demonstrating the nonlinear evolution of the broad spectrum of waves induced by an unstable distribution of electrons in homogeneous and inhomogeneous plasma are analyzed. The frequency–time analysis of the electric field reveals the presence of quasi-periodic elements with increasing frequency. It is demonstrated that temporal modulation of the amplitude of the electric field appears due to selection of harmonics with equally spaced wavenumbers in the initial spectrum of the waves. This choice of harmonics gives rise to spatial periodic structures of the electric field that transform into temporal modulation seen in the spectrograms upon propagation.

An algorithm for the plasma density profile reconstruction based on heavy ion beam plasma probing diagnostic data is developed. The algorithm is applied to a typical TJ-II stellarator pulse with a chord-average density varying from 0.5 × 10¹⁹ to 5.0 × 10¹⁹ m⁻³. The results of experimental data processing—the evolution of the reconstructed plasma density profile—are presented.

The experimental studies of the breakthrough phase of the leader spark discharge in 1.3 m gap are presented. A numerical model describing the dynamics of streamer zone parameters and the dynamics of leader current pulse during the breakthrough phase is developed. The dependences of leader velocity in the breakthrough phase on the reduced electric field E/N in the streamer zone are obtained. These dependences are compared with the measurement data; it is shown that the leader velocity V_L ~ (E/N)^3/2. Agreement between the calculated and measured time profiles of the leader current during the breakthrough phase is obtained. It is shown that the main origin of the sharp increase in the current at times of 1–2 μs is the growth of the reduced electric field in the streamer zone, associated with a decrease in the length of this zone as a result of the convergence of the leader heads. The growth of the field leads to an increase in the streamer velocity in the streamer zone, an increase in the leader current and the velocity of the leaders.

Linear and nonlinear processes that are related to the presence of dust and can play an important role in plasma of the Saturn’s magnetosphere are analyzed. Excitation of the lower hybrid turbulence due to the interaction of heavy ions of the Saturn’s magnetosphere with dusty plasma is described. It is demonstrated that the lower hybrid turbulence can be driven in entire region where plasma of the Saturn’s magnetosphere interacts with the charged dust. The effective collision frequency that characterizes an anomalous loss of momentum by heavy ions upon their interaction with the lower hybrid waves, along with the electric fields appearing in the system, are found. It is noted that the fields induced due to the development of the lower hybrid turbulence can influence the pattern of the electric field in the Saturn’s magnetosphere, including the field at the Enceladus orbit, despite the fact that the amplitude of the electric fields induced at the Enceladus orbit in the presence of the lower hybrid turbulence is lower than the magnitude of the electric fields at the Enceladus surface.

The Gas Dynamic Trap (GDT) facility is an open magnetic trap for plasma confinement. It is a variation of the Budker–Post mirror machine (probkotron), with the distance between the mirrors exceeding the characteristic path length of ions before scattering into the loss cone, and with a high mirror ratio. Under these conditions, the plasma particle confinement mechanism is similar to that of a collisionless gas in a vessel with a small opening, and the plasma confinement time depends linearly on its length and mirror ratio. These systems have potential for several applications in controlled nuclear fusion, the most immediate of which is the D–T neutron fusion source, capable of producing a neutron flux with a power density of several megawatts per square meter. This is required for the materials science research necessary for the design of the first wall of future fusion reactors. The experimental program of the GDT facility includes the study of kinetic and magnetohydrodynamic plasma instabilities, investigation of the behavior of sloshing ions, additional methods for heating and maintaining the material balance in the trap, and the study of the energy balance of the plasma. The paper describes in detail the GDT facility, its Diagnostic Complex, and control system, which is relevant today.

The energy of hydrogen atoms penetrating into the plasma after being desorbed from the vacuum chamber wall of the L-2M stellarator in the ohmic heating regime was measured based on the Doppler broadening of the H_α line; this energy turned out to be equal to 4.1 eV. Penetration of hydrogen atoms with the energy measured into the plasma was simulated, and energy spectra of the flow of neutrals escaping from the plasma were calculated. The results obtained were compared with the results of similar calculations performed at the 2-eV-energy of atoms penetrating into the plasma. The 2-eV-energy is conventionally used in such simulations. It was shown that changing the energy of neutrals coming from the vacuum chamber wall strongly affects penetration of neutral particles into the central plasma regions. Simulations showed that at a particle energy of 4.1 eV, the number of neutral particles penetrating into the central plasma regions increases by one and a half or two times, as compared to the case of using 2-eV-energy of particles.

The dependences of the kinetic and transport coefficients of electrons in argon are calculated using the Monte Carlo method over a wide range of reduced field strengths E/N from 30 to 2000 Td. The obtained results are compared with experimental data available in the literature. It is shown that for argon, the drift-diffusion approximation for calculating the spatiotemporal evolution of the electron density becomes inapplicable in fields larger than ≈1000 Td. The results of numerical calculations of electron transport in argon in uniform and inhomogeneous electric fields performed using the Monte Carlo method are also compared with the results of calculations using a previously developed multigroup model.

A plasma-chemical process resulting from a microwave discharge initiated in metal–dielectric powder mixtures was used to produce luminescent materials based on Al₅O₆N doped with Ce³⁺ ions. The self-non-selfsustained discharge was initiated by microwave radiation pulses with a frequency of 75 GHz, power of 400 kW, and duration of 8 ms in Al/γ-Al₂O₃/melamine powder mixtures, cerium was introduced in the form of CeO₂ and Ce(acac)₃·H₂O, and by preliminary doping of γ-Al₂O₃ with Ce³⁺ ions. Kinetic parameters of the plasma-chemical process were determined, microscopic and X-ray diffraction analyses of the products were conducted, and pulsed cathodoluminescence spectra were recorded. It was shown that the rate of the plasma-chemical process and the efficiency of Ce³⁺ ions introduction into the produced Al₅O₆N aluminum oxynitride phase are determined to a large extent by the form of cerium present in the reaction mixture.

The possibility of using the PIV (particle image velocimetry) method as an alternative to the existing methods used to analyze the dynamics of solar plasma during a coronal mass ejection is considered. P-IVLab software was used to perform a comprehensive analysis of a coronal mass ejection dynamics. The linear speed and the velocity field of the coronal mass ejection were calculated. The study showed that the software is capable of measuring changes in the coronal structure and record the processes that lead to the observed changes.