We present the results of experimental study of the dynamics of plasma formations originated from the high-current multiwire X-pinch (the current value up to 2.3 MA) based on the wires of different thicknesses made of different materials

The experiments were performed in the S-300 facility (2.3 MA, 0.15 �, 150 ns). The results of experimental investigations into the dynamics of plasma produced in the multiwire X pinch at currents up to 2.3 MA are presented. The materials, diameters, and the number of wires are varied. At such currents, the power of the soft x-ray radiation with the photon energy from 1 to 3 keV increases to 120 GW, and, since the size of a hot spot is less than 20 μm, it corresponds to a source brightness of ~10 W/(cm sr). The energy recorded in lines of neon-like molybdenum (in the range of 2.5–3 keV) is higher than 10 J. Hard x-ray radiation detected in experiments with tungsten and molybdenum X pinches has the photon energy > 800 keV.

At the Kurchatov Institute, the series of IFE experiments is carried out on the S-300 high-current generator (3 MA, 100 ns, 0.15 Ohm). In this talk, the experimental results on the S-300 machine are presented, related to the study of operation of co-axial magnetically self-insulated transporting line, by the linear current flow density on the inner electrode surface up to j ≈ 7 MA/cm. The specific parameters of this current-carrying line fairly correspond to those of the Sandia Laboratories’ conceptual project of IFE reactor based on the fast Z-pinch [1]. The near-electrode plasma dynamics and its effect on the current transport were studied. The cathode material effect, as well as that of gases and oil layer absorbed by its surface, on the near-electrode plasma dynamics and the current pulse transport along the short MITL segment ware studied too. With respect to the whole project, our conclusion is quite optimistic, to wit, we have found the idea of Recyclable Transporting Lines being adequate to the IFE reactor requirements.

Summary form only given. At the Kurchatov Institute, the series of ICF experiments is carried out on the S-300 pulsed power machine (3 MA, 100 ns, 0.15 Ohm). In this talk, the experimental results are presented, related to the study of operation of co-axial magnetically self- insulated transporting line (MITL), by the linear current flow density on the inner electrode surface up to j ap 7 MA/cm. The specific parameters of this current-carrying line fairly correspond to those of the Sandia Laboratories' conceptual project of IFE reactor based on the fast Z-pinch. The detailed study of the MITL reconnection has been carried out, as well as the physics of inter-gap plasmas. With respect to the whole project, we have found the idea of Recyclable Transmission Lines being adequate to the IFE reactor requirements. Investigation of fast Z-pinch implosion dynamics was carried out at the current up to 1.7 MA with the risetime 100 ns. The loads were fabricated on the base of foam as profiled cylinders of (3-5) mm in diameter and with 30 mg/cm 3 density, with the neck in its central part of about 1 mm in diameter. The goal of this series of experiments was the investigation of plasma dynamics in the Z-pinch neck and the mechanism of neutron generation accompanying the current-driven implosion. Within the frames of the Baikal program, a new superpower generator should be created aimed at the ICF experiments. It will use the multi-module multi-megaampere plasma opening switch (POS) with microsecond conduction times as the main stage of the output pulse conditioning. To achieve acceptable synchronization of multiple POS modules, operating parallel a common switch placed between the POS modules and their common load is proposed. The POS operates in the external applied magnetic field. This scheme utilizes a fraction of the generator energy during the conduction phase to ensure plasma erosion in all POS modules so that the magnetically insulated vacuum/plasma gap is formed at the switching phase.

A series of experiments has been carried out on the S-300 pulsed power machine, devoted to the study of a section of magnetically insulated vacuum transporting line (MITL). The length of MITL section was 1 cm, the current flow density up to 700 MA/cm2 by the linear current flow density being up to 7 MA/cm. These parameters fairly correspond to those of the Sandia Laboratories conceptual project of IFE reactor based on the fast Z-pinch. The goal of experiments was to study of the near-electrode plasma dynamics and its effect on the energy transfer. In most experiments, input and output current temporal behavior coincides up to some point (in our conditions, with a Ni cathode, up to 220-260 ns after the current start) corresponding to the gap fill by the relatively rare weakly-luminescent plasma, which front reconnects the gap with the maximal transverse velocity observed ~2.5times107 cm/s. At the moment of its coming, the output current becomes reduced, compared to the input current. The dynamics of both dense brightly luminescent plasma and rare plasma corona has been investigated. Absolute measurements of the HXR Bremsstrahlung show that even at the point of maximal electron current leaks, it did not exceed some dozen of kA. Such leaks cannot give any essential input into the current balance. Effect of impurities absorbed by the solid electrodes has been studied, as well as the influence of different electrode materials (Ni, Pb, Al, Au). In particular, in the case of golden or lead cathode, the insulation time was extended up to 400 ns. With respect to the whole project, our conclusion is quite optimistic, to wit, we have found the idea of recyclable transporting lines being adequate to the IFE reactor requirements.

A series of experiments has been carried out on the S-300 pulsed power mac hine, devoted to the study of a section of magnetically insulated vacuum transpo rting line (MITL). The length of MITL section was 1 cm, the current flow densi ty up to 500 MA/cm2 by the linear current flow density being up to 7 MA/cm. These parameters fairl y correspond to those of the Sandia Laboratories' conceptual project of IFE reac tor based on the fast Z- pinch (1,2). Except of loads with two plane parallel outer electrodes play ing the role of anode by the distance between them varied in the range of 5-12 mm, the segments of c oaxial line were used, as well; they allowed to enhance our diagnostic abilities. The spatial layout o f output device included the return conductor in form of 3 rods with the diameter 3-5 mm, made of tungsten or stainless steel and placed at the diameter 15 mm. In the experiments, the tubes made of stainless steel or nickel with the outer diameter 0.75, 1 or 1.2 mm and the wall thickness 100 or 200 µm were used as cathodes. The inner negative electrode of MITL was situated symmetrically between return conductor rods. MITL section was joined to the output unit of the S-300 generator. The experimental scheme is described in (2). Our experiments have demonstrated the efficiency of current transpor t almost independent upon the form of outer electrode; therefore, we used just th e last geometry in most shots. The current amplitude in the load was up to 1.7 MA with the rise time ~ 160 ns. The input and output current were recorded by means of calibrated mag netic loops and shunts, respectively. The signal taken from the shunt was correcte d by taking into account the field/current diffusion through the shunt wall. The data on near-electrode plasma dynamics were based on the multi-fra me shadow and Schlieren photographs in the light of second YAG:Nd laser harmonics ( = 532 nm, =

在装置“S-300”上,通过测量真空磁绝缘传输线中电极间电子流轫致辐射和负载上的电流、电压等参数,研究了磁绝缘传输线中的电流损失特性。实验中使用了阻抗特性不同的3种负载,结果表明,磁绝缘传输线中的电流损失特性显著地取决于负载。当负载为丝阵靶时,电流损失出现在丝阵等离子体最大箍缩时刻,且其值不超过负载总电流的5%。

A series of experiments has been carried out on the S-300 pulsed power machine (3 MA, 0.15 Ohm, 100 ns), devoted to the study of a section of magnetically insulated vacuum transporting line (MITL), by the current flow density up to 500 MA/cm(2), by the linear current flow density being up to 6 MA/cm. These parameters fairly correspond to those of the Sandia Laboratories' conceptual project of IFE reactor based on the fast Z-pinch [1]. The goals of experiments were as follows: 1) study of the near-electrode plasma and its effect on the energy transfer; 2) testing the 2-temperature MHD code NPINCH modeling the behavior of near-electrode plasmas. As a result, the conditions of plasma formation and reconnection of the MITL gap have been determined.

On the S-300 pulsed power machine at the Kurchatov Institute, some experimental activity is devoted to the prospects of Inertial Fusion Energy (IFE) program [1]. The results of experiments devoted to the study of operation of magnetically insulated transporting line (MITL), by the linear current flow density on the inner electrode surface up to j ≈ 7 MA/cm on S-300 are presented. The specific parameters of this current-carrying line correspond to those of the conceptual project of IFE reactor based on the fast Z -pinch. The duration of efficient functioning for such a line has been measured and possible reasons for broken isolation have been studied. Instability of expanding plasma sheath inside this line were recorded, probably it was of MHD origin. The processes of electrode explosion and subsequent dynamics of the dense plasma turn out to be in a good agreement with results of 1-D numerical modeling based on the NPINCH code, by taking into account equilibrium of state for both metal and plasma. A series of SXR and HXR measurements have been carried out clarifying the dynamics and parameters of rare plasmas inside the MITL gap.

The dynamics of radiation spectra of fast Z-pinch plasmas was studied on the S—300 machine. By means of the polychromator APCH—10, X-ray spectra of imploding wire arrays were measured in the range of 50~1 500 eV. The main part of the radiation power falls at the spectral interval 60~220 eV. The radiation spectrum is described by the Planckian-spectrum with the “black-body” temperature of 40~50 eV. For the part of radiation with more than 500 eV energy of quanta, remarkable deviation from the Planckian-spectrum is observed. The deviation seems to be the result of the appearance of hot plasma spots, existence of characteristic spectral lines in the range of 1.5~2 keV, and bremsstrahlung losses of the accelerated electrons.

On the S-300 pulsed power machine at the Kurchatov Institute, some experimental activity is devoted to the prospects of Inertial Fusion Energy (IFE) program. Experiments are gone on aimed at the energy transfer into the high-current tiny wire array with the typical radius R à 1 mm, as well as study of its dynamics and analysis of the tiny Hohlraum heating. The results of experiments, devoted to the study of operation of magnetically selfinsulated transporting line (MITL), by the linear current flow density on the inner electrode surface up to j à 0.7 MA/mm are also presented. The specific parameters of this currentcarrying line correspond to those of the conceptual project of IFE reactor based on the fast Z-pinch [1, 2]. An investigation of output devices similar to the plasma flow switch but operating in the nanosecond range of pulse duration was carried out [3]. The plasma bridge between the inner and outer cylinders is accelerated along the axis by means of the current pulse of generator (FIG.1-A). When it is flying through the break of the inner cylinder, the circuit breaks, as a result, the magnetic flux enters the central cavity where the load is situated.

Fast implosion of Z-pinches is considered as possible way to the generation of X-ray pulse on the level of some dozens MJ aimed at IFE. In this talk, experiments on the S-300 pulsed power machine are presented on the current-driven implosion of wire arrays composed of different fractions of Al and W. In the case of nested arrays, the effect of “pass” the outer liner, while imploding, through the inner one was first discovered on the base of X-ray spectral analysis. Another experimental series was carried out on sharpening the pulse by the plasma flow switches operating in nanosecond range with typical space scales ~ 1 mm. The reproducible regime of switching on the level of 750 kA is achieved, with the consequent damping rate ~100 ns. The radiative temperature of the inner wall of Hohlraum turns out to be as high as 40–50 eV. Besides, the prospects of application plasma opening switches as output cascades of pulsed power generators of megajoule range is studied on base of RS-20 machine. By using the programmed fill the diode gap by plasma, the suppression of pre-pulse has been achieved and shortening the pulse from 40 μs to 100 ns has been obtained. Implosion of Nested Wire Arrays On the “S-300” generator (3 MA, 100 ns, 0.15 Ohm) at the Kurchatov Institute, the experimental studies with multi-material wire array units are carried on aimed at investigation of the wire array chemical composition effect on the implosion dynamics and stability. The experiments were performed on various fashions of loads distinct from each other by the geometry and materials, including nested arrays fabricated from wires of different substances (Al, W). The following set of diagnostics was used: optical streak-camera photography, scintillator power recorder operating in the range of 50-500 eV, time-integrated three pinhole cameras, and X-ray spectrograph on convex mica crystal. As an active diagnostics in the visible range, the five-frame laser shadowgraphy with 0.3 ns time resolution was used. One of the features in some shadow pictures is an appearance of transparency space for the probing laser light. Such an effect may be treated as “filamentation” effect in the plasma of neighbor current-carrying conductors, carrying tens of kilo-amperes. Detailed description of all the experimental results is presented in the joint Sino-Russian paper [1]. The most interesting result is related to the implosion of nested arrays made of different wires: 1) Inner: W(6 μm), N=20, r = 2–3 mm; outer: Al(15 μm), N=30, r = 6 mm; h = 10 mm. 2) Inner: Al(15 μm), N=20, r = 2 mm; outer: W(6 μm), N=30, r = 6 mm; h = 10 mm. By the liner loads listed above, the output current value of the “S-300” machine was in the range of 2.5–3 MA. While imploding aluminum wire array, spectral lines of the hydrogen-like and helium-like aluminum ions were recorded by means of an X-ray spectrograph (FIG.1). One may conclude from the electric measurements that the inner almost immovable tungsten array intercepts an

On the S-300 pulsed power generator (4.5 MA, 70 ns, 0.15 Ohm), within the frames of ICF program based on fast high-current Z-pinches, experiments are being carried out studying promising schemes of output units. In particular, a device similar to the plasma flow switch is being investigated aimed at sharpening the pulse. In the experiments with such a device, by means of variation the geometry of the inner electrode of a coaxial, as well as the acceleration of a cascade of plasma "washers", the switching of the current up to 750 kA has been obtained, with the rise time /spl sim/ 5-7 ns and subsequent decrease being in accordance with that of the net current (/spl sim/ 100 ns). Thereby the opportunity of switching of much more amount of energy onto the load has been demonstrated compared to our preliminary experiments (2.5 MA/2.5 ns). Soft X-ray radiation from the cavity was recorded by means of vacuum diodes with a nickel cathode and especially selected filters. The radiative temperature of the cavity walls estimated from the ratio of diode signals was close to 50 eV.

On the S-300 pulsed power generator (4.5 MA, 70 ns, 0.15 Ohm), within the frames of ICF program based on fast high-current Z-pinches, experiments are being carried out studying promising schemes of output units. In particular, a nanosecond-range plasma flow switch is being investigated aimed at sharpening the pulse. As a result, the switching rate as high as 2.5 MA / 2.5 ns has been achieved. The numerical simulation of such a device has been carried out. The results of experiments on the extrinsic magnetic field influence on high-impedance plasma opening switch (POS) operation are reported. It has been demonstrated that the POS output voltage could be increased by the factor of 1.5 compared to the POS free of an extrinsic field. Also the possibility of the expansion of POS conduction phase duration up to 40 µs has been presented. The development of more new laser and nuclear diagnostic methods will definitely contribute to attain new data which could help in understanding the POS operation physics.

On the S-300 pulsed power generator, within the frames of ICF program based on fast highcurrent Z-pinches, promising schemes of output units are studied. In particular, a device similar to the plasma flow switch is being investigated aimed at sharpening the pulse. The switching rate as high as 2.5 MA / 2.5 ns has been achieved. Numerical simulations of the plasma “washer” acceleration have been carried out. The experiments on the extrinsic magnetic field influence on the high-impedance plasma opening switch (POS) operation are reported. Also the possibility of the expansion of POS conduction phase duration by means of programmed fill of the gap has been presented. The study of the wire array implosion on the Angara-5-1 machine is reported. Magnetic probes and the X-ray backlighting technique were used to investigate a current and mass distribution during the implosion. The experimental data confirm the concept of prolonged plasma production.

On the S-300 pulsed power generator (4.5 MA, 70 ns, 0.15 Ohm), within the frames of ICF program based on fast high-current Z-pinches, experiments axe being carried out studying promising schemes of output units. In particular, a device similar to the plasma flow switch is being investigated aimed to sharpening the pulse. As a result, the switching rate as high as 2.5 MA / 2.5 ns has been achieved. The results of experiments on the extrinsic magnetic field influence on high-impedance plasma opening switch (POS) operation are reported. It has been demonstrated that the POS output voltage could be increased by the factor of 1.5 compared to the POS free of an extrinsic field. Also the possibility of the expansion of POS conduction phase duration up to 40 mus has been presented. The development of more new diagnostic methods will definitely contribute to attain new data which could help in understanding the physics of POS operation.

Fast compression of liners is under consideration as a possible approach to electric energy conversion into X-ray pulse at the energy scale of dozens of megajoules. Scientific cooperation including TRINITI, Kurchatov institute, Efremov institute, and VNIITF develops the "Baikal" project in which an inductive storage has to be used which in the case of successive transformation procedure could produce an electric pulse with parameters adequate for these purposes. On the S-300 pulsed power generator, experiments is being carried out studying promising schemes of output devices for the next generation of machines. In particular, a device similar to the plasma flow switch is being investigated aimed to sharpening the current ns. The results of experiments on a current implosion of multi-wire arrays on Angara-5-1 facility are presented. There are given experimental proofs that the formation of Z-pinch takes place at temporally spread plasma production. The phenomena of temporally spread plasma production determines mode and quality of final stage of a pinch. The temporally spread plasma formation is not a hindrance to obtain high power of X-radiation output at compression and heating of a Z-pinch.

The successful experiment carried out the last years on “Z” and “ANGARA-5” facilities on soft X-ray generation in wire-arrays implosion attract much attention. On “S-300” generator (700 kV, 4 MA, 70 ns) the experimental studies are also carried on with wire-array output units to create a powerful X-ray source. The development of more new diagnostic methods will definitely contribute to attain new data which could help in explanation of a X-ray emission mechanism of imploding multi-wire arrays that is not yet well understood.

Experimental results of the micro-liner implosion study on S-300 and “Angara-5” machines have been presented as well as some theoretical results. Our investigations were carried out in a broad range of liner constructions, masses, and chemical compositions. On the S-300 machine with a current value up to 3.5 MA, 1.5 TW X-ray pulse was obtained as a result of multi-wire liner implosion. The measurements of X-ray spectra have been presented. Theoretical investigations and 2.5-d simulations were devoted to some critical points. Double liner implosion approach for X-ray production and distinction between gas-puff and wire array implosions on “Angara-5” have been described. The test-bed for multi MJ X-ray generator “Baikal” named as “MOL” is presented. 1. Study of Imploding Plasmas on the S-300 Machine. The goal of our experiments on S-300 machine (4 MA, 100 ns) [1] was to study and to model various schemes of generation of sharp powerful X-ray pulses aimed to the inertial fusion and some other applications. 1.5 TW of the soft X-ray radiation ( ≥ ω 100 eV) was achieved as a result of implosion of the multiwire tungsten liner. The total energy of the pulse was ~ 20 kJ. The spectrum of X-rays was recorded in the range of 50 – 500 eV by the 10-channel polychromator.