Viacheslav I. Krauz

Progress in plasma focus research and applications

An analysis of the current state of the plasma focus (PF) research is presented. Some new opportunities for the use of PF in studies on high-energy-density physics are discussed. The main attention is paid to the results obtained on one of the worlds largest PF-type facilities PF-3 at the Kurchatov Institute. Experimental results of the studies of foam liners and the tungsten wire arrays dynamics in the PF discharge are presented. A new approach to load formation using a cloud of free fine-disperse particles of condensed matter (dust) is proposed. Being a source of additional mass, the dust particles essentially affect the development of MHD and RT instabilities. It is manifested, in particular, in an increase in MHD stability. The main tendencies in PF research, including application problems, are discussed.

Experimental study of the structure of the plasma-current sheath on the PF-1000 facility

The results of studies of the plasma-current sheath structure on the PF-1000 facility in the stage close to the instant of pinch formation are presented. The measurements were performed using various modifications of the calibrated magnetic probes. Studies of the influence of the probe shape and dimensions on the measurements accuracy were done. The current flowing in the converging sheath at a distance of 40 mm from the axis of the facility electrodes was measured. In the optimal operating modes, this current is equal to the total discharge current, which indicates the high efficiency of current transportation toward the axis. In such shots a compact high-quality sheath forms with shock wave in front of the magnetic piston. It is shown that the neutron yield depends on the current compressed onto the axis. This dependence agrees well with the known scaling, Yn ~ I4. The use of the total discharge current in constructing the current scaling, especially for facilities with a large stored energy, is unjustified.

Filippov type plasma focus as intense source of hard X-rays (E/sub x//spl sime/50 keV)

This paper evaluates the use of a plasma focus machine (Filippov type) as a pulsed intense source of hard X-rays. It is shown experimentally that discharging a capacitor bank of W=50 kJ in the new arrangement of the discharge parameters, one can deliver into the test cavity (volume of 6*10/sup 3/ cm/sup 3/) an average of /spl Phi//sub x/=8*10/sup -4/ J/cm/sup 2/. The delivered energy fluence varies in the range of 2*10/sup -4/ J/cm/sup 2//spl les//spl Phi//sub x//spl les/2.9*10/sup -3/ J/cm/sup 2/, depending on the probe position. The X-ray energy spectra were established by the differential absorption method using thermo-luminescent detectors (time-integrated spectra) or plastic scintillators (time-resolved spectra). The average energy of X-ray photons is 40 keV<E/sub x//sup av/<50 keV (20 keV/spl les/E/sub x//spl les/170 keV) and remains quasi-constant during the main part of the pulse (/spl sim/40 ns). The electron energy that can produce such bremsstrahlung radiation is in the range of 95 keV/spl les/E/sub e//spl les/170 keV. However, time-resolved experiments reveal that at each instant of time only one energy of electron beam occurs. The aforementioned radiation characteristics reveal new potentials for the plasma-focus machine for a variety of applications. Some insight into the physics behind production mechanism of quasi-monoenergetic relativistic-electron beams will be concurrently reviewed.

Dynamics of the Current Distribution in a Discharge of the PF-3 Plasma Focus Facility

In this paper, results are presented from studies of the dynamics of the plasma-current sheath and current distribution in the PF-3 facility, one of the largest plasma focus machines in the world. The experiments were done at input energy of W = 290 kJ and discharge current of I ~ 2 MA, with the chamber being stationary filled with the working gas. The current sheath parameters were measured with absolutely calibrated magnetic probes installed at different distances from the system axis and at different heights above the anode plane. The possibility is demonstrated of the formation of closed current loops due to the development of shunting breakdowns in the insulator region. The maximum residual plasma density at which the electrode gap remains magnetically self-insulated is estimated.

Correlation of magnetic probe and neutron signals with interferometry figures on the plasma focus discharge

In this paper the results of temporally resolved measurements using calibrated azimuthal and axial magnetic probes are presented, together with interferometry and neutron diagnostics performed on the PF-1000 (IPPLM, Warsaw, 2 MA) device with a deuterium filling and 1011 neutron yield. The probes located in the anode front at three different radial positions allow determination of the dominant part of the discharge current flows behind the imploding dense plasma layer. The current sheath is composed of both the axial and azimuthal components of the magnetic field. After reaching the minimum diameter, the current sheath continues in a radial motion to the axis and then penetrates into the dense plasma column. At the final phase of stagnation, the dominant current passes through the dense column. The probes located on the axis of the anode front registered an increase and a decrease in the pulse of the axial component of the magnetic field in correlation with the formation and decay of the dense plasmoidal structure. The estimated values of the axial component of the magnetic field at the center of the plasmoids in the first neutron pulse and close before its decay and dominant neutron production can reach 2 and 10 T; it is 10–30% of the value of the azimuthal magnetic field of the dense column boundary.

Transformation of axial magnetic field during neutron production on the MA plasma focus with deuterium filling

Summary form only given. In this contribution we present the results of experimental studies of the pinch evolution on the PF-1000. The calibrated magnetic probes in different radial positions were correlated with neutron production and with interferometry images. The characteristics of probe measurement of azimutal magnetic field on the PF-1000 were published in [1]. The transformations of the pinched column during different types of neutron production on this device were published in [2]. In this presentation the new results are presented using measurement of axial (Bz) and azimutal (Bϕ) component of magnetic field. The current layer imploding the dense plasma sheath is 2–3 cm thick with dominant part of the current out of the dense plasma sheath. This layer is composed from Bϕ and Bz component, Bz component is roughly 4 – 6 times lower. After achieving the minimal diameter of the plasma column the current layer penetrates into the dense plasma and at the start of explosion the total current layer is absorbed in the dense column. The formation and evolution of m=0 instability correlates with axial fluctuation of Bz. The Bz in the imploding necks decreases and in the expanding dense disks and plasmoids between them increases. The values of Bz reached 1–2 T, about 20% of the Bϕ values on the dense plasma column boundary. During the first neutron pulse the Bz field in the axis increases and during the dominant neutron production the Bz decreases.

D(d,n) neutrons induced by ions from explosive evaporation of Ta anode deuterium occluded. X-ray mode of plasma focus discharges

Summary form only given. Neutron yield, Y/sub n/=10/sup 7/-10/sup 8/ was observed when PF at SRRC (Filippov-type; 0.3 Torr of Ar; 50 kJ; 12 kV) was fired in the X-ray mode. Before the experiment, the Ta anode was immersed in D/sub 2/ and due to occlusion, the atomic ratio 2(Ta):1(D) was obtained. After a few shots in pure Ar, neutrons do appear and hold their yield during the entire experiment. Y/sub n/ was detected with Ag-activation counters (end-off; 0/spl deg/) and Time-of-Flight, ToF, [X(E/sub x//spl ges/0.2 MeV) and n(E/sub n/=2.45 MeV)] was measured with fast plastic detectors (/spl les/2 ns), behind collimators aimed for the chamber roof (side-off; 90/spl deg/) and Pb-shield (5 cm). Ion energy, E/sub D+/, was defined from measured delay, T, between X and n signals to be: T=ToF(D/sup +/)+ToF(n)-ToF(X) Experiments were done for different combinations of ion bases and neutron bases.

Intense hard X-ray radiation source based on the plasma focus facility

Summary form only given. The physical principles of hard X-ray (HXR) production at a facility of the plasma focus type with plane geometry of electrodes are represented. An internal selfgeneration of the accelerating field, as a result of sharp power peaking for the times/spl sim/1O**8 s, occurs in the given device. The transformation of practically the whole discharge current into the electron beam-the energy of the main part of electrons does not exceed 100-150 KeV-is attained by the corresponding regime selection. The results of studying the X-ray radiation field and its spectral and time characteristics are reported.