E.Yu. Klimenko

Experimental observation of space magnetic anisotropy

Abstract It has been experimentally discovered that there exist certain regions in strong magnetic fields of solenoids where the substance is subjected to a force which is different from the magnetic one. The angular arrangement of this region in the solenoid aperture depends on the time of day and the season. This indicates space magnetic anisotropy.

Computations of voltage-current characteristics for a stabilized inhomogeneous superconductor with thermal resistance across the boundary between the superconducting wire and the substrate

Abstract A quench in modern multifilament conductors with voltage-current characteristics, broadened due to a longitudinal inhomogeneity of a critical current, occurs at electric fields high enough to be easily registered. It provides an opportunity to control superconducting solenoids made of such conductors, even in the case when steady-state stabilization is absent. Use of a semiempirical relationship for voltage-current characteristics of multifilament wires permits the computation of the main characteristics of a combined conductor consisting of such wires and of a stabilizing substrate. Presence of a thermal resistance across the boundary between the wire and the substrate decreases the quench current insignificantly, but causes a considerable drop in the electric field at which the quench occurs.

The next step in the development of a negative ion beam plasma neutralizer for ITER NBI

Deuterium atom beam injectors developed for ITER plasma heating and current drive are based on negative ion acceleration and further neutralization with a gas target. The maximal efficiency of the gas stripping process is 60%. The replacement of the gas neutralizer by a plasma one must increase the neutral yield to 80%. An overview of experimental studies of microwave discharges in a multicusp magnetic system chosen as the base device for plasma neutralizer (PN) realization and design development of PNs for ITER neutral beam injectors (NBIs) is presented. The experimental results achieved with the PN model PNX-U are discussed. Plasma confinement, gas flows and ionization degree were investigated. High density plasmas with ne ~1018 m-3 with low electron and ion temperatures ( ≈ 5-6 eV) and a high ionization degree (not less than 40%) at its centre have been generated in operation with argon.

Resistance-current curves of high pinning superconductors

The lack of universal phenomenological approaches to calculation of the spatiotemporal distributions of vector fields in superconducting materials with high anisotropic pinning hinders the analysis of accumulated empirical data. The development of such phenomenology is impeded by the tradition of inadequate description of the transition characteristics of superconductors. Based on a detailed investigation of the current-dependent transitions in commercial niobium-titanium wire, it has been found that, in contrast to the commonly accepted approach, the transition characteristics are conveniently described as the dependences of the resistance on the current, by analogy with the dependences on the temperature and magnetic field. Investigations in the range of magnetic fields from 0 to Bc2 showed that it is the resistance that exhibits exponential variation with the field. The values of resistances determined by extrapolation of the transition curves to a zero current obey the exponential dependence on the magnetic field. The experimental results are consistent with predictions of the statistical model explaining the shape of the transition characteristic as determined by the bulk inhomogeneity of the superconductor.

Analyses of conductor behaviour in the superconducting toroidal magnet system of the tokamak T-15 installation

Abstract Results from analyses of T-15 conductor performance in different situations are reported. Some features of the conductor are thoroughly considered and methods to take these features into account based on real transition characteristic (RTC) stability theory have been developed. Evaluation results are discussed and compared with experiments.

Superconducting magnet for high speed ground transportation

This paper presents the design of a superconducting magnet intended to propel, levitate and guide a magnetically levitated vehicle by means of combined ground propelling circuits. It also describes the on-board cryostat with an indirect immersion cooling system which enables both longitudinal sides of the vertical superconducting magnet to create an electrodynamic force. During coil testing a magnetomotive force of 450 kA was achieved with the maximum induction of 3.5 T at the winding surface.

Applicability of the normal distribution for calculating voltage-current characteristics of superconductors

Abstract On the basis of the longitudinally inhomogeneous multifilament superconductor model the normal distribution function for the critical current values along a conductor is considered. A conclusion has been made that it is correct to apply the normal distribution for calculating voltage-current characteristics (VCC) within a wide range of inhomogeneities.

Closed flux winding for smes

To all appearances the projects of huge energy storage SC magnets are not being pursued. However SC magnets storing 10–1000 MJ could be useful today both as power controlling devices for transport needs and urban locations and as power transformers for powerful (1–10 GW) pulse generation for a lot of applications. It is important to exclude stray magnetic fields in the most of the DC and pulse applications, and optimization of closed flux windings is a topical question. Some modification of a toroidal coil (called Φ-shape coil) allows energy storage with uniform density and reduces well-known structural problems of toroidal coils to a design close to an ordinary solenoid. An adhesive bonding technique developed in RRC “Kurchatov Institute” combines mechanical and electrical strengths of the winding and provides thermal conductivity of the structure sufficient for use of indirect cooling, high current density and reliable protection.

Losses and stability in superconducting wire in a.c. fields with frequencies up to 2.5 kHz

Abstract Results are presented of losses and stability measurements in a small superconducting (SC) coil with an alternating current at frequencies up to 2.5 kHz. The mutual influence of losses and instability on the maximum attainable current is studied and discussed. It is shown that there are different modes of quench. SC wire can go to the normal state due to the development of instability with almost no overheating over the ambient temperature. In another mode, overheating over the current sharing temperature occurs due to losses under stable conditions. The experimental results agree with a recently developed stability theory for composite wires, taking into account the smoothness of the transition characteristic and its influence on stability. This theory explains why cryogenically unstable SC wires work at currents close to the critical current, why SC wires are more stable at lower rates of field change and current charge rate and why wires with a smoother transitional characteristic are generally more stable than SC wires with sharp transitions to the normal state. The theory thus allows us to approach the problem of the relationship between losses and stability.

Anisotropic pinning in macroscopic electrodynamics of superconductors

Anisotropy of critical currents and electric fields in superconductors with strong pinning has been ascribed in the macroscopic model to features of the material equation system relating the electric field to the current density in a superconductor. The anisotropy of the pinning proper is described by an operator relating the pinning force density to the vectors of magnetic induction and Lorentz force. In the approximation of an extended critical state model, a feasible expression of this operator is given in the form of an algorithm based on the concept of a collective anisotropic potential well containing fluxoids. The current-carrying capacity of a strongly anisotropic niobium-titanium foil as a function of the orientation of the current density and applied field with respect to the principal axes of the material has been investigated in detail. Given measurements of the transverse electric fields in the foil under magnetic fields normal to the foil plane, we can plot cross sections of surfaces describing the pinning force density in the space of magnetic induction and Lorentz force.