Joule Energy Dissipation Research Articles

The Phenomenon of a Cathode Spot in an Electrical Arc: The Current Understanding of the Mechanism of Cathode Heating and Plasma Generation

A vacuum arc is an electrical discharge, in which the current is supported by localized cathode heating and plasma generation in minute regions at the cathode surface called cathode spots. Cathode spots produce a metallic plasma jet used in many applications (microelectronics, space thrusters, film deposition, etc.). Nevertheless, the cathode spot is a problematic and unique subject. For a long time, the mechanisms of spot initiation, time development, instability, high mobility, and behavior in magnetic fields have been described by approaches that caused some controversy. These spot characteristics were discussed in numerous publications over many years. The obscurity and confusion of different studies created the impression that the cathode spot is a mysterious phenomenon. In the present work, a number of typical representative publications are reviewed with the intention of clarifying problems and contradictions. Two main theories of cathodic arcs are presented along with an analysis of the experimental data. One of the approaches illustrates the cathode heating by Joule energy dissipation (volume heat source, a sharp rise in current density, etc.), nearly constant cathode potential drop, and other certain initial conditions. On the other hand, a study using a mathematically closed approach shows that the spot initiation and development are determined not by electron emission current rise but by a rise in arc power density, affecting heat sources including the energy of ion flux to the cathode (surface heat source).

Magnetoplasmadynamic acceleration of solid body in a railgun

A physical model and a mathematical approach were developed to describe ponderomotive acceleration a body pushed by plasma column of high-current arc in a railgun. In contrast to the previously published studies, the arc plasma generation was considered by taking into account kinetics of heavy particle fluxes in a non-equilibrium layer near the vaporizating (ablating) rails and the phenomena of heat and mass transfer and electric sheath at rail surfaces. The self-consistent numerical analysis has been conducted for a wide range of arc currents (up to 2MA). It has been shown that the electron temperature was determined mainly by the Joule energy dissipation supporting high degree of ionization. It has been determined that the arc voltage is about 102 V. The rails temperatures are relatively low (~ 3000 K) and therefore, the electron flux emitted from the cathode manly due to thermionic emission enhanced by Schottky effect is lower than the flux of ions from the plasma, which supported the current continuity at the cathode region. The calculated velocity vs of the plasma-solid body increased with the arc current (I) showing tendency to saturation. In range of I = 0.5–2 MA the vs slightly increased from 5 × 105 to 10 × 105 cm/s when the rail length increased from 1 to 3 m respectively. The dependence of the velocity on the arc current and the calculated plasma parameters are in range of those values observed experimentally. The nature of the velocity with arc current saturation is explained by presence of the dynamic pressure resulting in predicted velocity dependence on the arc current as 4-th root.

JT-60SA TF coil quench model and Analysis: Joule energy estimation with SuperMagnet and STREAM

In the framework of JT-60SA Tokamak commissioning (Japan, 2021), all coils have to be cooled with supercritical helium forced-flow at the temperature of 4.5 K in order to reach superconducting state before energization. An important issue is to predict the Joule energy dissipated in Cable-In-Conduit Conductors (CICC) and the maximal temperature reached in case of an incidental quench occurrence. Therefore, quench simulations were performed on the Toroidal Field Coil (TFC) with the STREAM (Superconductor Thermal hydraulic and Resistive Electrical Analytical Model) code and with the SuperMagnet code (CryoSoft), coupling THEA (thermal hydraulic and electrical 1-D CICC model) and Flower (thermal hydraulic network model). The quench event was simulated for one TFC at nominal conditions of tokamak operation. External energy deposition over each pancake’s first turn of the coil at the peak magnetic field location was applied for initiating the resistive transition. This way, the computed Joule energy dissipated by one TFC is conservatively evaluated to be 5.65 MJ. The Joule energy dissipation depends strongly on quench initiation conditions and on the number of fully and rapidly quenched pancakes (maximal quench propagation velocity of 19.5 m/s). Some further analyses were performed on the acceptance quench test realized at the Cold Test Facility (CEA Saclay, 2018) on TFC02. The different calculation results (helium temperature, mass flow rate in upstream and downstream manifolds, normal length propagation) are presented in the following study and are consistent with the measurements. This analysis brings information on the limits and the ability of STREAM code to model quench behaviour in CICC coils cooled by forced flow of supercritical helium. This tool could be useful for tokamak magnets protection during quench event and safe operation, notably thanks to its fast computing time.

Features of the thermal stabilization theory of composite superconductors: The nonlinear description of the dissipative states

The features of the Joule's energy dissipation in a composite high-temperature superconductor with a power equation of the voltage-current characteristic cooled by liquid helium or hydrogen are discussed. It is shown that the non-standard thermal stabilization conditions of composite superconductors can exist if the nonlinear temperature dependences of the electrical resistivity of the stabilizing matrix and heat flux to liquid refrigerant are considered. First, there may be no minimum currents of the existence and propagation of a normal zone. Second, the intensive cooling of a composite superconductor by liquid refrigerant significantly increases the range of the stable currents, which leads to the existence of the supercritical applied currents. Third, an increase in the temperature of a composite superconductor may occur under the conditions close to adiabatic during irreversible propagation of the thermal instability despite its intensive cooling by liquid refrigerant. This effect must be considered when determining the burnout conditions of a composite superconductor. The performed numerical experiments are compared with the results obtained from the existing thermal stabilization theory of the composite superconductors, which is based on the linear temperature dependence of the critical current density of superconductor and jump-like transition from the superconducting state to the normal.

Wireless Sensor Network Energy Efficiency with Fuzzy Improved Heuristic A-Star Method

Energy is a major factor in designing wireless sensor networks (WSNs). In order to extend the network lifetime, researchers should consider energy consumption in routing protocols of WSNs. Routing will serve to facilitate a number of sensors on the technology of WSNs to identify the optimal path and manage energy consumption saving at the time of transmitting data. Current Wireless Sensor Networks efficiency system uses node selection as the main parameter without applying path finding routing. It will not complete the optimization of energy. This research was designed to address the problem of energy optimization by using fuzzy-improved heuristic A-Star. A new algorithm named improved heuristic A-Star was developed from previous A-Star algorithm. The result of fuzzy-improved heuristic A-Star indicated node sensor to sink destination saved 0.3698 joule energy dissipation which resulted in longer lifetime.

Magnetohydrodynamic Phenomena and Heat Transfer Near a Rotating Disk

We propose an approach that permits constructing an analytical solution of the problem of flow and heat transfer in a viscous compressible conducting medium near an infinite dielectric disk rotating in a homogeneous magnetic field. The influence of the magnetic field on the process of heat transfer near the disk surface has been investigated. It has been shown that Joule energy dissipation prevails over viscous dissipation at moderate magnetic fields.

Features of power engineering in a dynamic electrically conductive medium

A new approach to power engineering modeling in a weak electrically conductive dynamic medium with induction fields was developed. The optimum induction field energy for moving liquid-gas systems in which chemical transformations takes place was estimated. For these systems, the dynamics of Joule energy dissipation and pondermotive action distributions was found to depend on the induction field frequency and movement velocity.

Formation of Intensive Magnetic Flux Tubes in a Converging Flow of Partially Ionized Solar Photospheric Plasma

Theoretical model, explaining a phenomenon of formation of Intensive Magnetic Flux Tube (IMFT) in a converging flow of partially ionized solar photospheric plasma is considered. Special attention is paid to the fact of weak ionization (n/nn ∼ 10-4) of plasma in the photosphere. The cases of 2D magnetic slab and cylindric magnetic tube are considered. It was shown that in a converging flow of photospheric plasma thin magnetic tubes, or slabs with the characteristic scale L0 ∼ (1 ÷ 5) ċ 107 cm and magnetic field 1000 ÷ 2000 G can be generated. By this 2D magnetic slabs could be unstable with respect to an exchange instability and appear as an intermediate step during IMFT formation on the boundary of two supergranulation cells. Formation of compact strong magnetic field structures, and their energy balance are discussed. Stationary Joule energy dissipation taking place on the photospheric levels in the models of magnetic slab or IMFT under consideration increases towards the periphery of these objects and can exceed radiation looses. This can cause the occurrence of magnetic tubes with hot external envelopes, and modification of plasma temperature and density distribution, with respect to ones in a quiet atmosphere.

Self-propagating high-temperature synthesis as a means of obtaining composites under conditions of joule energy dissipation

Self-propagating high-temperature synthesis as a means of obtaining composites under conditions of joule energy dissipation

Rocket and ground-based study of an auroral breakup event

On 27 January, 1979 the Substorm-GEOS rocket S23H was launched from ESRANGE, Kiruna, shortly after the onset of an intense magnetospheric substorm over northern Scandinavia. Rocket electric field and particle observations have been used to calculate ionospheric currents and heating rates. These results are generally consistent with the ground magnetic (SMA ∗) and optical (all-sky, TV) observations. An important finding emerging from a comparison of this event with a pre-breakup event earlier on this day (Marklund et al., 1982) is that the ionospheric substorm-related electric field could be split up into two parts, namely: 1. (1) an ambient LT dependent field, probably of magnetospheric origin; 2. (2) superimposed on this a small-scale electric field associated with the bright auroral structures, being southward for both events. This is shown to have important consequences on the location of the ionospheric currents and the Joule energy dissipation relative to the auroral forms. For example, in the pre-breakup arc, Joule energy dissipation and particle energy flux were found to be anti-correlated, while in the breakup case correlated.

Heating of a medium as a result of Joule energy dissipation

It is well known that when a magnetic field is present and electric currents flow through a gas, terms over and above those present in the case of ordinary thermal conductivity appear in the heat flux density vector. If the gas is dense enough and the magnetic field not over large, then the anisotropy caused by the magnetic field may be neglected. However, for a sufficiently large electric current a term proportional to the temperature and to the current density vector remains in the heat flux density vector. This effect explains, for example, the asymmetry of heat fluxes in the electrodes of a continuously operated electromagnetic accelerator (1).