"Cold start" Stage of Wire Explosion
Experimental Investigation and Mathematical Simulation of “Cold start” of Metal Wire Explosion by High-Power Current Pulse (Dynamics, Transport Properties, and Equation of State of Metastable Phases)
Tech Area / Field
- FUS-PLA/Plasma Physics/Fusion
- PHY-PLS/Plasma Physics/Physics
8 Project completed
Senior Project Manager
Malakhov Yu I
FIAN Lebedev, Russia, Moscow
- VNIITF, Russia, Chelyabinsk reg., Snezhinsk
- Sandia National Laboratories / Energetic Experiments and System Instrumentation Department, USA, NM, Albuquerque\nCornell University, USA, NY, Ithaca\nCNRS / Ecole Polytechnique / Laboratore de Physique et Technologie des Plasmas, France, Palaiseau\nImperial College of Science, Technology and Medicine / Blackett Laboratory, UK, London
Project summaryA goal of the proposed Project is the experimental and theoretical study of an initial stage of explosion of a thin wire by a high-power current pulse ("cold start" of a discharge). The main problem is to study the dynamics of formation and the properties of a metastable state of matter at this stage. Basing on these results one will develop a model of formation and evolution of a dense central part of a discharge (core). This should be a substantial contribution to the existing mathematical programs, which have not so far considered a formation of a cold core and its interaction with an ambient current-carrying hot plasma. As an important part of a research plan, a series of new experiments will be carried out on optical and X-ray investigation of an initial stage of a wire explosion. The experimental and theoretical results will be treated on the basis of a numerical simulation, including a description of a radiative magnetic hydrodynamics, radiative-collisional atomic kinetics, radiative transfer, and a equation of state.
A "cold start" discharge is a problem of major importance proposed today by large-scale exploding wires experiments. Such experiments are very important in studies of soft X-ray emission by high-power current pulses, which are being actively performed, in particular, in the interests of a controlled nuclear fusion (CNF) problem. The properties of a pinch-produced dense hot plasma of high-charged ions are close to those of a laser produced plasma. This permitted Sandia Labs (USA) to obtain the record power of X-ray radiation above 200 TW, using Z-facility of the electrical power of 40 TW and the peak current of 20 MA. In Russia, such investigations are being carried out on the Angara, S-300, and SNOP-5 facilities. The results obtained have taken the high-power pinches to the class of most promising drivers for the inertial nuclear fusion. An evidence has been obtained of a long-time existence of a dense cold liquid core surrounded by a plasma corona, which was optically observed in the form of a plasma column generated by a shunt breakdown of evaporation products from a metal surface. Both media have been separated by about a 100-fold density jump induced by a liquid-vapor transition. Such a structure appears due to an initial electrical current explosion of wire, but the whole process remains unclear for undestanding, and the nature of explosion itself is contradictory. The currently available diagnostic means have demonstrated a strong evaporation from surface of a metal, a sharp growth of impedance, breakdown of a "steam jacket", formation of a current-carrying plasma corona, and volume boiling of a liquid metal. Mass of the corona and velocity of the core expansion are determined by ohmic heat during the explosion.
Thus, the evolution of a liquid phase, evaporation, and the vapor ejection determine the dynamics of explosion of wires. Moreover, metastable states in a nanosecond discharge can be expected. These processes taking place during a wire explosion, in a phase coexistence region between the binodal and spinodal states, have not yet been sufficiently studied.It is still impossible to develop an adequate model for simulation of an initial stage of a wire explosion, which is important for understanding of subsequent stages of the process.
In the framework of proposed project the experimental studies will be performed on the available BIN-facility of the LPI-FIAN Modern Accelerators' Problem Laboratory that can generate current pulses of 270 kA amplitude and 100-150 ns duration. It is proposed that the facility will operate as an X-pinch driver of the X-ray radiation, and as a current source for a fast explosion of wires.
The following results are expected :
- new experimental and theoretical data in the field of physics of an initial explosion of a current carrying conductor, including a magnetic hydrodynamics of matter, phase transitions, and a breakdown of evaporation products;
- new experimental and theoretical data on the metastable states in a liquid-vapor system;
- a radiative MHD model of the exploding wires throughout a wide range of processes from a discharge start to hot dense plasma generation and compression;
- numerical simulation of the dense Z-pinch dynamics of a wire explosion experiment.
The proposed fundamental researches of the exploding wires will extend knowledge of the physics of discharges and will help to develop a sufficiently complete computational model of the physical processes occurring in them. As the result, the methods of control of the "cold start" processes will be elaborate to optimize the conditions for high-power soft X-ray pulse generation and to decrease rather high cost of experiments on large-scale high-current facilities. The application value of the "cold start" investigations is beyond the scope of the X-ray pulse generation problem. For example, using more complicated configuration of wires, one can initiate an acceleration of a small part of a matter along the axis of a discharge. Or, using a pair of crossed thin wires of different metals, it is possible to create a thermodynamically non-equilibrium conditions of the liquid phases' mixing to the create new alloys. Such a combination of possibilities would allow one both the creation of new materials and their separation from other substances by removing them from the discharge area.
The experimental group engaged in the Project has more than a two-decade experience of work in the field of X-ray diagnostics of hot plasma, and its achievements are acknowledged by the world scientific community. During the recent years the investigations have been performed in close cooperation with Cornell University and Sandia National Laboratories (USA). The theoretical group of the Project participants has also a great experience in the research of plasma physics, high-current electric discharges, and inertial nuclear fusion, and has at its disposal a set of necessary numerical codes. The group of mathematical modeling and computations has great experience in numerical simulation of the liner compression. The group has a set of 1D and 2D numerical codes, which take into account a great number of physical processes, and allow one to solve a wide class of problems in high-temperature plasma research.
Now, the collaborators of the project are the Plasma Study Laboratory of the Cornell University, USA (the head, Prof. B. Kass), a group of magnetized high energy density plasma from the Laboratory plasma physics and Technology of Ecole Polytechnique (France) (the head, Dr. A. Chuvatin), a plasma physics group from Blackett Lab of the Imperial College (UK) (the head, Dr. G. Chittenden). The first of the collaborators presents a well-known American laboratory engaged in scientific provision of the experiments with exploded wires performed with Z facility at Sandia Lab. (USA). In this Laboratory the experimental research is carried out with the help of a powerful current pulsed generator XP (the current up to 500 kA, the voltage, 250 kV, pulse duration, 100 ns).The second collaborator of the Project is one of the leading European scientific teams engaged in the field of plasma implosion of the exploding multi-wire liners. The research is performed in close cooperation with the experiments at different facilities, including high-power generator LION with the parameters close to the XP. The third collaborator is known for its research in the field of X-ray emitting compressed discharges through the wires. The experiments make use of the facility with the current up to 1 MA and the pulse duration of 500 ns. The experimental and theoretical investigations of the mentioned laboratories involve the problem of creation of radiative magneto-hydrodynamic codes destined for the calculation of the discharge plasma compression via the wire loads of different types, as well as physics of the equation of state and transport properties of the substance in such discharges. The role of collaborators will consist in the discussions on the formulation of the problems in particular areas of the Project research, as well as the exchange of scientific information, the discussion of the results obtained during the work on the Project, participation in the joint experiments with Russian Project participants and numerical simulations.
The innovations of the Project are to as follows:
- new knowledge in the field of physics of the initial state ("cold start") of the electrical explosion of a thin wires during a powerful current pulse;
- new knowledge in the field of equation of multi-phase state of matter;
- the methods to control the dynamics of a "cold start" of the electrical explosion of a thin wires aimed at optimizing of soft X-ray emission from pinch-produced plasma and other technological applications;
the development of radiative MHD model and numerical code for simulation of the electrical explosion of a thin wires including the “cold start”.
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