Расширение цилиндрических трубчатых заготовок на высоковольтной магнитно-импульсной установке с управляемым вакуумным разрядником

Purpose. An experimental verification of the existence of a range of values for the parameters of the capacitive energy storage of the magnetic-pulse installations with controlled vacuum discharger, in which, with a high probability, there is a «cut» of the discharge current pulses and the expansion of cylindrical thin-walled tubular workpieces using an external coil. Methodology. High voltage magnetic-pulse installation of NTU «KhPI» with controlled vacuum discharger, multiturn coil with inside dielectrical die and inside aluminum alloy workpiece are used. The capacitance and charge voltage of capacitive energy storage are changed. Discharge current pulses are measured by Rogowski coil and the oscillograph. Results. Parts of complicated shape are made by expansion of cylindrical tubular workpieces with help of external coil. Pressed metallic tubular part is removable from inner dielectric rod. Originality. The frequency of «cut» pulse is defined by negative magnetic field pressure amplitude. It is shown that we must coordinate this frequency and charge voltage with capacitive storage parameters by high probability of pulse «cut». Practical value. It is shown how to use installations with controlled vacuum dischargers in magnetic forming technology based on «cut» pulses.Мета. Метою роботи є експериментальна перевірка існування зони параметрів ємнісного нагромаджувача енергії магнітно-імпульсної устатковини з керованим вакуумним розрядником, в котрій з високою імовірністю відбувається «зріз» імпульсів розрядного струму та розширення циліндричних тонких трубчастих заготівок за допомогою зовнішнього індуктора. Методика. Використано високовольтну магнітно-імпульсну устатковину НТУ «ХПІ» з керованим вакуумним розрядником та багатовитковий індуктор, усередині котрого було розміщено діелектричну матрицю і заготівку з алюмінієвого стопу. Змінювали ємність та зарядну напругу нагромаджувача енергії. Імпульси розрядного струму вимірювали за допомогою поясу Роговського та реєстрували осцилографом. Результати. Магнітно-імпульсним розширенням циліндричних заготівок за допомогою зовнішнього індуктора отримано деталі складної форми та здійснено зняття металевої деталі, що була напресована на діелектричний стрижень. Наукова новизна. Показано, що частоту імпульсу, що «зрізається», при котрій амплітуда від’ємного тиску магнітного поля наближається до максимальної, а також зарядну напругу необхідно узгоджувати з параметрами ємнісного нагромаджувача енергії, при яких з високою імовірністю відбувається «зріз» імпульсу. Практичне значення. Результати та рекомендації, що отримано, можуть бути використано у магнітно-імпульсних технологіях на устатковинах з керованими вакуумними розрядниками

Relativistic resistive magnetohydrodynamic reconnection and plasmoid formation in merging flux tubes

We apply the general relativistic resistive magnetohydrodynamics code {\tt BHAC} to perform a 2D study of the formation and evolution of a reconnection layer in between two merging magnetic flux tubes in Minkowski spacetime. Small-scale effects in the regime of low resistivity most relevant for dilute astrophysical plasmas are resolved with very high accuracy due to the extreme resolutions obtained with adaptive mesh refinement. Numerical convergence in the highly nonlinear plasmoid-dominated regime is confirmed for a sweep of resolutions. We employ both uniform resistivity and non-uniform resistivity based on the local, instantaneous current density. For uniform resistivity we find Sweet-Parker reconnection, from $\eta = 10^{-2}$ down to $\eta = 10^{-4}$, for a reference case of magnetisation $\sigma = 3.33$ and plasma-$\beta = 0.1$. {For uniform resistivity $\eta=5\times10^{-5}$ the tearing mode is recovered, resulting in the formation of secondary plasmoids. The plasmoid instability enhances the reconnection rate to $v_{\rm rec} \sim 0.03c$ compared to $v_{\rm rec} \sim 0.01c$ for $\eta=10^{-4}$.} For non-uniform resistivity with a base level $\eta_0 = 10^{-4}$ and an enhanced current-dependent resistivity in the current sheet, we find an increased reconnection rate of $v_{\rm rec} \sim 0.1c$. The influence of the magnetisation $\sigma$ and the plasma-$\beta$ is analysed for cases with uniform resistivity $\eta=5\times10^{-5}$ and $\eta=10^{-4}$ in a range $0.5 \leq \sigma \leq 10$ and $0.01 \leq \beta \leq 1$ in regimes that are applicable for black hole accretion disks and jets. The plasmoid instability is triggered for Lundquist numbers larger than a critical value of $S_{\rm c} \approx 8000$.Comment: Matching accepted version in MNRA

Order out of Randomness : Self-Organization Processes in Astrophysics

Self-organization is a property of dissipative nonlinear processes that are governed by an internal driver and a positive feedback mechanism, which creates regular geometric and/or temporal patterns and decreases the entropy, in contrast to random processes. Here we investigate for the first time a comprehensive number of 16 self-organization processes that operate in planetary physics, solar physics, stellar physics, galactic physics, and cosmology. Self-organizing systems create spontaneous {\sl order out of chaos}, during the evolution from an initially disordered system to an ordered stationary system, via quasi-periodic limit-cycle dynamics, harmonic mechanical resonances, or gyromagnetic resonances. The internal driver can be gravity, rotation, thermal pressure, or acceleration of nonthermal particles, while the positive feedback mechanism is often an instability, such as the magneto-rotational instability, the Rayleigh-B\'enard convection instability, turbulence, vortex attraction, magnetic reconnection, plasma condensation, or loss-cone instability. Physical models of astrophysical self-organization processes involve hydrodynamic, MHD, and N-body formulations of Lotka-Volterra equation systems.Comment: 61 pages, 38 Figure

The Magnetic Field in the Solar Atmosphere

This publication provides an overview of magnetic fields in the solar atmosphere with the focus lying on the corona. The solar magnetic field couples the solar interior with the visible surface of the Sun and with its atmosphere. It is also responsible for all solar activity in its numerous manifestations. Thus, dynamic phenomena such as coronal mass ejections and flares are magnetically driven. In addition, the field also plays a crucial role in heating the solar chromosphere and corona as well as in accelerating the solar wind. Our main emphasis is the magnetic field in the upper solar atmosphere so that photospheric and chromospheric magnetic structures are mainly discussed where relevant for higher solar layers. Also, the discussion of the solar atmosphere and activity is limited to those topics of direct relevance to the magnetic field. After giving a brief overview about the solar magnetic field in general and its global structure, we discuss in more detail the magnetic field in active regions, the quiet Sun and coronal holes.Comment: 109 pages, 30 Figures, to be published in A&AR

The Generation of Langmuir Waves by Thick Target Electron Beams in Solar Flares

Hard X-rays, observed during the impulsive phase of solar flares, are commonly believed to be produced by the bremsstrahlung of collimated beams of electrons, which lose their energy collisionally in the dense chromosphere. This thesis is concerned with the generation of Langmuir waves by such beams. In Chapter 1 we review observations of solar flares across the electromagnetic spectrum. Particular emphasis is given to the impulsive phase, and to those observations which provide strong evidence for the existence of electron beams. Solar flare theory, insofar as it is pertinent to the original work of this thesis, is reviewed in Chapter 2. After briefly discussing models of primary energy release and particle acceleration, we consider in detail the theoretical interpretation of hard X-ray and microwave observations. Emissions at these wavelengths are believed to contain the most direct information on the electron distribution function in the flaring region. In Chapter 3 we use the quasi-linear theory to determine the conditions required for the stability of a steady state electron beam propagating in the solar corona. The growth rate for electron plasma waves in a magnetized plasma is evaluated, with the electron distribution being given by an analytic solution of the linearized Fokker-Planck equation. A stability boundary in parameter space is determined, indicating that electron beams must be highly collimated at injection to be Langmuir unstable at any point in space. The implications of this result for alternative models of hard X-ray emission are discussed and it is argued that Langmuir instability will not occur in either the trap model or the dissipative thermal model. Such models would therefore be refuted by the detection of a large flux of plasma microwave emission associated with hard X-ray emission. In Chapters 4 and 5 we investigate the quasi-linear dynamics of thick target electron beams, using a combination of analytical and numerical techniques. In Chapter 4, one dimensional quasi-linear equations are derived from the general three dimensional equations for an axisymmetric beam in a magnetized collisional plasma. Asymptotic analytical solutions are discussed, and it is shown that the energy density of Langmuir waves excited by a steady state thick target beam is negligible compared with the beam energy density, although the waves heat the plasma at a rate which is comparable to that of the fast electrons. We also describe an approximate method of incorporating quasi-linear interactions into the collisional treatment of thick target beam evolution, based on the assumption that the asymptotic state is a plateau distribution. Numerical computations of the thick target electron distribution and the associated Langmuir wavelevel are presented in Chapter 5. It is shown that the energy deposition rate and bremsstrahlung X-ray signature of a thick target beam are essentially unaffected by the presence of Langmuir turbulence. We also show that reverse current energy losses can reduce the wavelevel by as much as a factor of 2, depending on the beam and plasma parameters. Finally, we consider the possible plasma radiation signature of a relaxed beam, and show that an observable flux of 2nd harmonic radiation will be produced if the Langmuir waves are close to being isotropic. In Chapter 6 we consider Langmuir wave generation by a time dependent beam. It is shown that the steady state model remains valid if the electrons are injected on a timescale greater than about Is. If the injection timescale is as short as 100ms, however, the energy density of Langmuir waves produced by a given instantaneous flux of electrons may be amplified by as much as an order of magnitude. We argue that the wavelevel is nevertheless unlikely to exceed the threshold for strong turbulence (i.e. the modulational instability), and that the propagation of thick target beams can therefore be adequately described using the quasi-linear theory. In Chapter 7 we briefly discuss two possible ways of extending the work described in previous chapters. Specifically, we consider thick target beam relaxation in an inhomogeneous plasma, and the induced scattering of Langmuir waves on thermal ions

Conceptual mechanization studies for a horizon definition spacecraft attitude control subsystem, phase A, part II, 10 October 1966 - 29 May 1967

Attitude control subsystem for spin stabilized spacecraft for mapping earths infrared horizon radiance profiles in 15 micron carbon dioxide absorption ban

Rapid Fluctuations in Solar Flares

Topics addressed include: X-rays; radio and microwaves; thermal response; plasma physics; and future plans

Proceedings of the Conference on the Design of Leak-tight Fluid Connectors

Aerospace technology and design considerations for leak-tight separable, semipermanent, and permanent fluid connectors - conferenc

The FIP and Inverse FIP Effects in Solar and Stellar Coronae

We review our state of knowledge of coronal element abundance anomalies in the Sun and stars. We concentrate on the first ionization potential (FIP) effect observed in the solar corona and slow-speed wind, and in the coronae of solar-like dwarf stars, and the "inverse FIP" effect seen in the corona of stars of later spectral type; specifically M dwarfs. These effects relate to the enhancement or depletion, respectively, in coronal abundance with respect to photospheric values of elements with FIP below about 10~eV. They are interpreted in terms of the ponderomotive force due to the propagation and/or reflection of magnetohydrodynamic waves in the chromosphere. This acts on chromospheric ions, but not neutrals, and so can lead to ion-neutral fractionation. A detailed description of the model applied to closed magnetic loops, and to open field regions is given, accounting for the observed difference in solar FIP fractionation between the slow and fast wind. It is shown that such a model can also account for the observed depletion of helium in the solar wind. The helium depletion is sensitive to the chromospheric altitude where ion-neutral separation occurs, and the behavior of the helium abundance in the closed magnetic loop strongly suggests that the waves have a coronal origin. This, and other similar inferences may be expected to have a strong bearing on theories of solar coronal heating. Chromospheric waves originating from below as acoustic waves mode convert, mainly to fast mode waves, can also give rise to ion-neutral separation. Depending on the geometry of the magnetic field, this can result in FIP or Inverse FIP effects. We argue that such configurations are more likely to occur in later-type stars (known to have stronger field in any case), and that this explains the occurrence of the Inverse FIP effect in M dwarfs.Comment: Review paper submitted to Living Reviews in Solar Physics. 74 pages. Some material revised and updated from astro-ph/0405230, arXiv:0901.3350, arXiv:1110.435