Characteristics of high-power radiating imploding discharge with cold start

A qualitative model of the dynamics of a multiterawatt radiating Z-pinch with cold start and high rate of current rise is proposed. The model is used to analyze discharges with currents I ～ 2–5 MA (with dI/dt > 10¹³ A/s) through uniform or structured plasma-producing loads, including wire arrays. The most important consequence of cold start is that spatially nonuniform plasma production is prolonged to almost the entire current rise time. Under these conditions, the Ampére force begins to play a dominant role in the plasma dynamics before the plasma-producing load is completely transformed into an accelerated plasma. The results of computations of wire-array vaporization are presented. A formula is proposed for estimating the highest attainable velocity of plasma flow into a heterogeneous liner driven by the Ampére force. It is shown that local imbalance between radial motion of the produced plasma and supply of the plasma-producing substance to be ionized leads to axially nonuniform breakthrough of magnetic flux into the liner, which precedes plasma collapse. The magnetic-flux breakthrough gives rise to a chaotic azimuthal-axial plasma structure consisting of radial plasma jets of relatively small diameter, which is called a radial plasma rainstorm. The breaking-through azimuthal magnetic flux obstructs further current flow in the breakthrough region. Analyses of Z-pinch implosion based on the theory of Rayleigh-Taylor instability or the snowplow model are incorrect under the plasma-rainstorm conditions. The processes taking place in a stagnant Z-pinch include conversion of the energy carried by the current-generated magnetic field into turbulent MHD flow of the ion component of the plasma, its convective mixing with magnetic field, heating, energy transfer from ions to electrons, and emission from the plasma. Under typical experimental conditions, emission plays a key role in the energy balance in an imploding pinch. Z-pinch is modeled by an electric-circuit component that has a time-dependent nonlinear impedance and consumes the magnetic energy supplied by a generator through a magnetically insulated transmission line (MITL). The peak power reached in the circuit is comparable to the peak soft X-ray power output emitted by the pinch in terms of magnitude and timing. Optimum matching conditions are formulated for the generator-MITL-pinch circuit.     

When Rank-One Convexity Meets Polyconvexity: An Algebraic Approach to Elastic Binodal

Journal of Nonlinear Science - In the variational problems involving non-convex integral functionals, finding the binodal, the boundary of validity of the quasiconvexity of the energy density, is...     

Weak variations of Lipschitz graphs and stability of phase boundaries

In the case of Lipschitz extremals of vectorial variational problems, an important class of strong variations originates from smooth deformations of the corresponding non-smooth graphs. These seemingly singular variations, which can be viewed as combinations of weak inner and outer variations, produce directions of differentiability of the functional and lead to singularity-centered necessary conditions on strong local minima: an equality, arising from stationarity, and an inequality, implying configurational stability of the singularity set. To illustrate the underlying coupling between inner and outer variations, we study in detail the case of smooth surfaces of gradient discontinuity representing, for instance, martensitic phase boundaries in non-linear elasticity.     

The flip side of buckling

Buckling of slender structures under compressive loading is a failure of infinitesimal stability due to a confluence of two factors: the energy density non-convexity and the smallness of Korn’s constant. The problem has been well understood only for bodies with simple geometries when the slenderness parameter is well defined. In this paper, we present the first rigorous analysis of buckling for bodies with complex geometry. By limiting our analysis to the “near-flip” instability, we address the universal features of the buckling phenomenon that depend on neither the shape of the domain nor the degree of constitutive nonlinearity of the elastic material.      

Low-x evolution equations in M?bius representation

The M?bius form of the BFKL kernel in the next-to-leading order (NLO) in theories containing fermions and scalars in arbitrary representations of the colour group is presented. The ambiguity of the NLO kernels permits to get agreement between the BFKL approach and the colour dipole model and to find the quasi-conformal representation of the BFKL kernel.     

铝-钨丝混编阵的Z-箍缩实验研究

利用铝丝和钨丝混合编制的丝阵作为Z箍缩的负载，在俄罗斯Kurchatov研究所的S300强流装置上对其Z箍缩过程进行了实验研究，并与纯铝丝阵和纯钨丝阵的实验结果进行了比较.不同材料组成的丝阵的Z箍缩x射线能谱之间有明显差异，混编丝阵的铝K壳层的x射线辐射强度比纯铝丝阵的弱，在纯钨丝阵Z箍缩中没有发现波长小于1.6nm的线辐射.混编丝阵Z箍缩的x射线发光区域比纯铝丝阵的小，但比纯钨丝阵的大,混编丝阵的x射线产额比纯铝丝阵的大，但比纯钨丝阵的略低.在驱动电流为2.5—2.8MA条件下，Z箍缩的径向收缩比为4—5，x射线辐射脉冲脉宽为25ns左右，峰值为0.3—0.5TW，总能量为10—20kJ.激光探针的阴影像显示了丝阵等离子体形成的细致过程，还表明了等离子体的边界面不够清晰，其不稳定性有明显的发展，内部有丰富的结构. 关键词： Z箍缩 混编丝阵 S300强流装置     

Kinetics of dimethyldioxirane decomposition in the presence of cumene

Dimethyldioxirane consumption increases considerably in the presence of cumene. The product composition (cumic alcohol, acetophenone, α-methylstyrene) and the inhibiting effect of oxygen prove a radical reaction mechanism. The kinetic order for dimethyldioxirane increases with the conversion from 1.5 to 2.     

Thermal Stability of Cyclododecylidene-1,1-bishydroperoxide in the Presence of Ferrocene

Russian Journal of General Chemistry - Thermal stability of cyclododecylidene-1,1-bishydroperoxide in xylene has been studied and activation parameters of the reaction have been determined. The...