Hybrid MHD/PIC simulation of a metallic gas-puff z pinch implosion

We present the hybrid MHD/PIC simulations of the time evolution of a bismuth metallic gas-puff z pinch in external axial magnetic field (AMF). Recent experiments with IMRI-5 generator (450 kA, 450 ns) [1] show the certain effect of an axial magnetic field on radiation energy produced during z pinch implosion. In order to perform the numerical simulation of gas puff z pinch a hybrid model was developed. The hybrid model treats the electrons as a massless fluid and ions as macroparticles. The macroparticle dynamic is calculated with the use of PIC method. Ion-ion Coulomb collision is considered with the use of MC method. The radiation transfer of bismuth plasma was accounted in the framework of P1 method. The interelectrode gap pumping by plasma of 8 μs 80 kA bismuth arc with the following plasma implosion by 450 kA / 450 ns current pulse in different external AMF was modelled. The obtained results are in a reasonable agreement with the experimental results. © Published under licence by IOP Publishing Ltd.The work was supported by Russian Science Foundation (project No. 16-19-10142)

On Hybrid Type of Cathode Attachment in High Current Vacuum Arcs

This paper discusses the issues of a possible change of the type of cathode attachment of high-current vacuum arcs (HCVA) with an average cathode current density of more than 105 A/cm2. This type of HCVA is used as pumping plasma gun in experiments with plasma puff z-pinches. These experiments showed that the measured linear mass of the HCVA plasma jet is much higher (by a factor of 10 or more) than the expected mass, which can be obtained from the assumption that cathode attachment occurs only through a multitude of cathode spots emitting supersonic plasma jets. It is shown that in HCVA of the type under consideration, at some time instant there are two types of cathode attachments - cathode spots and thermionic erosion attachment (TEA). It can be said that HCVA of this type have a hybrid cathodic attachment. Unlike cathode spots, TEA produces a subsonic plasma flow, which contributes to an increase in the linear mass of the HCVA plasma jet. © 2021 Institute of Physics Publishing. All rights reserved

On possible reasons of positive near-anode voltage drop in high-current vacuum arc

In this paper we consider some reasons for the occurrence of a positive near-anode potential drop during current constriction in high-current vacuum arc. It is shown that if the radius of constriction is much larger than the electron mean free path, then a positive voltage drop in the near-anode plasma sheath does not occur, but an additional drop may occur in the near-anode plasma layer due to the anomalous resistance. If the current constriction radius is much less than the electron mean free path, then a positive voltage drop in the sheath arises under the usual condition, and the kinetic instabilities in the near-anode plasma do not develop. © 2019 IOP Publishing Ltd. All rights reserved.Russian Foundation for Basic Research, RFBR: 17-02-00346, 18-08-00547Russian Academy of Sciences, RASNational Natural Science Foundation of China, NSFC: 5191153011318-2-2-16This work was supported in part by RFBR(grant Nos. 17-02-00346, 18-08-00547, 19-08-00783, 19-58-53006), by RAS Program (project No. 11) and UB RAS Program (project No. 18-2-2-16), as well as by National Natural Science Foundation of China (project No. 51911530113)

Formation of double shell during implosion of plasma metal puff Z-pinches

This work presents the results of experimental and theoretical research of impact of tailored density profile and application of external axial magnetic field on initial spatial distribution of the plasma density in the plasma metal puff Z-pinch and on its implosion dynamics. It has been discovered that upon implosion of the plasma metal puff Z-pinch some stripes interpreted as the system of two coaxial shells appear on the optical images. With the help of numerical simulation, the formation of the plasma liner consisting of a mixture of carbon and bismuth ions and formed by the expansion of the plasma jet of the arc burning on the bismuth electrode has been considered in this work. It has been shown that the lightweight carbon ions facilitate formation of the density distribution smoothly decreasing with the increase in radius, that, in turn, leads to suppression of the Rayleigh-Taylor instability in the current sheath upon further implosion. It has also been demonstrated that availability of the two types of ions in plasma considerably different in mass leads to formation (in the compression phase) of a double shell with externally located heavy ions. It has also been revealed that the application of the external axial magnetic field leads to reduction in the plasma metal puff Z-pinch initial diameter. © 2020 Author(s).This work was funded by Russian Science Foundation. Project No. 19–19-00127

A transverse current rectification in graphene superlattice

A model for energy spectrum of superlattice on the base of graphene placed on the striped dielectric substrate is proposed. A direct current component which appears in that structure perpendicularly to pulling electric field under the influence of elliptically polarized electromagnetic wave was derived. A transverse current density dependence on pulling field magnitude and on magnitude of component of elliptically polarized wave directed along the axis of a superlattice is analyzed.Comment: 12 pages, 6 figure

Study of the ion plasma flow generated by a high-current vacuum arc

The vacuum arc discharge is intensively explored for a long time. It acts as a source of multiply charged plasma. The results of the special type plasma gun (5-10 kA, 12 μs) ion flow study with high temporal resolution and the electrode erosion dependences on the amplitude of the current pulse are presented in the research. The ion flow intensity had good reproducibility from series to series, while the values of total mass erosion differ significantly for different series of experiments under the same conditions. The ion erosion was measured to be significantly higher than that for arc sources with currents up to 1 kA. © 2019 IOP Publishing Ltd. All rights reserved.Russian Foundation for Basic Research, RFBR: 17-02-00346, 18-08-00547Russian Academy of Sciences, RAS18-2-2-16This work was supported in part by RFBR (grant Nos. 17-02-00346, 18-08-00547, 19-08-00783, 19-58-53006), by RAS Program (project No. 11) and UB RAS Program (project No. 18-2-2-16)

Reorganization of a 2D disordered granular medium due to a small local cyclic perturbation

We measure experimentally the rearrangements due to a small localized cyclic displacement applied to a packing of rigid grains under gravity in a 2D geometry. We analyze the evolution of the response to this perturbation by considering the individual particle displacement and the coarse grained displacement field, as well as the mean packing fraction and coordination number. We find that the displacement response is rather long ranged, and evolves considerably with the number of cycles. We show that a small difference in the preparation method (induced by tapping the container) leads to a significant modification in the response though the packing fraction changes are minute. Not only the initial response but also its further evolution change with preparation, demonstrating that the system still retains a memory of the initial preparation after many cycles. Nevertheless, after a sufficient number of cycles, the displacement response for both preparation methods converges to a nearly radial field with a 1/r decay from the perturbation source. The observed differences between the preparation methods seem to be related to the changes in the coordination number (which is more sensitive to the evolution of the packing than the packing fraction). Specifically, it may be understood as an effect of the breaking of local arches, which affects the lateral transmission of forces.Comment: 13 pages, revised and resubmitted to J. Stat. Mech.: Theory and Exp. (JSTAT

Microbial and Geochemical Evidence of Permafrost Formation at Mamontova Gora and Syrdakh, Central Yakutia

Biotracers marking the geologic history and permafrost evolution in Central Yakutia, including Yedoma Ice Complex (IC) deposits, were identified in a multiproxy analysis of water chemistry, isotopic signatures, and microbial datasets. The key study sections were the Mamontova Gora and Syrdakh exposures, well covered in the literature. In the Mamontova Gora section, two distinct IC strata with massive ice wedges were described and sampled, the upper and lower IC strata, while previously published studies focused only on the lower IC horizon. Our results suggest that these two IC horizons differ in water origin of wedge ice and in their cryogenic evolution, evidenced by the differences in their chemistry, water isotopic signatures and the microbial community compositions. Microbial community similarity between ground ice and host deposits is shown to be a proxy for syngenetic deposition and freezing. High community similarity indicates syngenetic formation of ice wedges and host deposits of the lower IC horizon at the Mamontova Gora exposure. The upper IC horizon in this exposure has much lower similarity metrics between ice wedge and host sediments, and we suggest epigenetic ice wedge development in this stratum. We found a certain correspondence between the water origin and the degree of evaporative transformation in ice wedges and the microbial community composition, notably, the presence of Chloroflexia bacteria, represented by Gitt-GS-136 and KD4-96 classes. These bacteria are absent at the ice wedges of lower IC stratum at Mamontova Gora originating from snowmelt, but are abundant in the Syrdakh ice wedges, where the meltwater underwent evaporative isotopical fractionation. Minor evaporative transformation of water in the upper IC horizon of Mamontova Gora, whose ice wedges formed by meltwater that was additionally fractionated corresponds with moderate abundance of these classes in its bacterial community. © Copyright © 2021 Cherbunina, Karaevskaya, Vasil’chuk, Tananaev, Shmelev, Budantseva, Merkel, Rakitin, Mardanov, Brouchkov and Bulat.We thank Samsonova Vera, Karzhavin Vladimir, Pankov Alexander, Andreevskaya Maya and Alexander Osipov for their for their invaluable assistance in field work

Economic Ideas and Institutional Change: Evidence from Soviet Economic Discourse 1987-1991

In recent years, institutional and evolutionary economists have become increasingly aware that ideas play an important role in economic development. In the current literature, the problem is usually elaborated upon in purely theoretical terms. In the present paper it is argued that ideas are always also shaped by historical and cultural factors. Due to this historical and cultural specificity theoretical research must be supplemented by historical case studies. The paper analyses the shift in ideas that took place in Soviet economic thought between 1987 and 1991. This case study, it is argued, may contribute to our understanding of the links between ideas and institutions. More specifically, it sheds new light on the issue of whether the evolution of economic ideas is pathdependent, so that they change only incrementally, or whether their development takes place in a discontinuous way that can best be compared with revolutions