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High-Speed Plasma Fluxes


Formation and Application of High-Speed Dense Plasma Fluxes, Generated in High-Current Electric Discharges

Tech Area / Field

  • FUS-OTH/Other/Fusion

3 Approved without Funding

Дата регистрации

Ведущий институт
VNIIEF, Russia, N. Novgorod reg., Sarov

Краткое описание проекта

Facilities with electric discharges of Z-pinch type [1] represent neutron and X-ray radiation sources [2], [3] as well as high-speed plasma fluxes [4]. Generation of radiation and high-speed fluxes occurs in high-current plasma channel with the diameter of the order of 1 millimeter, compressed to high densities under the effect of magnetic forces of the intrinsic electric current. For the purpose of the channel formation there is usually employed cumulating current plasma collapsing towards the axis under the effect of ponderomotive forces. This method of channel formation has got a disadvantage, related to the necessity of timing the energy source operation with the dynamics of current plasma for ensuring maximum current at its collapse. When operating with plasma of light elements and currents of the order of several megaampers the above disadvantage places strict constraints on the current rise velocity, dI/dt>1014 A/s, which can be observed in reality at the working voltages of the order of several megavolts. Such electrical characteristics are achieved at the use of high-power energy systems, such as SATURN [5], BLACKJACK-5 [6], PITHON [7], ANGARA-5-1 [8] etc. The facilities specified are rather bulky; thus, further progress in plasma parameters only through the increase of the energy system power requires extremely high expenses.

In VNIIEF there is being developed a plasma electrodischarge device of the new type [9]. Its distinctive property consists in the fact that there is no cumulating current plasma in it. The electric discharge passes through the narrow channel, about 1 mm in diameter, where magnetic pressure equilibrates with the plasma one from the very beginning of the discharge. The narrow gas channel with sufficiently high concentration of particles is formed before the discharge beginning at the axis between the electrodes of the discharge chamber, pumped out up to high vacuum. In the self-compressed channel the heating of ions at the initial electric discharge stage progresses less intensively as compared to electrons.

This limits the growth of magnetohydrodynamic disturbances; owing to this fact there increases t time, during which the plasma channel holds its initial configuration, t value, estimated as a rough approximation by the velocity of energy exchange between the components, constitutes ~ 1ms for plasma of light elements at typical concentrations equal to 1018...1019 cm-3. Owing to this fact, at microsecond front of current pulse, the plasma channel will retain its configuration within the time of current rise. Thus, it may be therefore concluded that the constraints towards the velocity of current rise in such facilities can be considerably less strict as compared to the facilities with cumulating current plasma in which the required front of current pulse is less than 100 nanoseconds. It would appear reasonable that this must assist in realization of sufficiently high plasma parameters at the use of the available energy systems.

The problem of preliminary gas channel formation (1 mm diameter) is solved through the use unsteady outflow of the gas flux into vacuum; moreover, the leading part of the flux represents cool gas accelerated along the axis up to the velocity, which exceeds the sonic speed several times. The basic possibility of this way formation of 1 mm gas channel with further discharge of high-voltage capacitor storage into it is confirmed by the series of plasma experiments held in VNIIEF. The mode of unsteady gas motion was ensured by the fact that the valve operating time in the system of gas bleeding in constituted less than one percent of the time of gas flux front motion towards the interelectrode gap. As a fast-acting valve the membrane of thin metal foil was used; the foil was destroyed by the auxiliary electric discharge within approximately 1 microsecond time period. The gas entered the interelectrode gap through the central axial channel in the anode. The high-voltage capacitor storage ensured the current amplitude in the discharge chamber up to 0.7 MA at the stored energy equal to 24 kJ and charging voltage equal to 100 kV. As a result of the investigations performed it was demonstrated that in the given facility the processes related to neutron and X-ray radiation as well as to the generation of high-speed plasma flux in the high-current channel are similar to those which take place in the facilities with cumulating current plasma.

The work on the project will represent the continuation of the investigations started. It is suggested that the energy of capacitor storage should be increased twice and owing to this the maximum current in the discharge chamber should be raised up to 1 MA. Basic attention is planned to be paid to the problems, connected with the generation of high-speed axial plasma flux in the high-current channel. The created design of the discharge chamber is very convenient for such investigations. The plasma flux with the following parameters: axial velocity ~ 108 cmґs-1, concentration of particles - 1017...1018 cm-3, goes beyond the limits of interelectrode gap through the central hole in the grounded cathode. This makes it possible to work with high-speed plasma flux at a minimum distance from the place of its generation.

The goal of the project is to study the mechanism of high-speed flux generation in the high-current plasma channel, and to investigate the problems of high-speed plasma flux dynamics and its interaction with the obstacle material. The basic results obtained in the course of the project execution are planned to be published.


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