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1

Studies of plasma interactions with tungsten targets in PF-1000U facility

Ladygina M. S., Skladnik-Sadowska E., Zaloga D. R., Sadowski M. J., Kubkowska M., Kowalska-Strzeciwilk E., Krawczyk N., Paduch M., Miklaszewski R., Garkusha I. E.

Nukleonika

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2016

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Vol. 61, No. 2

149--153

EN

This paper presents results of experimental studies of tungsten samples of 99.95% purity, which were irradiated by intense plasma-ion streams. The behaviour of tungsten, and particularly its structural change induced by high plasma loads, is of great importance for fusion technology. The reported measurements were performed within a modifi ed PF-1000U plasma-focus facility operated at the IFPiLM in Warsaw, Poland. The working gas was pure deuterium. In order to determine the main plasma parameters and to study the behaviour of impurities at different instants of the plasma discharge, the optical emission spectroscopy was used. The dependence of plasma parameters on the initial charging voltage (16, 19 and 21 kV) was studied. Detailed optical measurements were performed during interactions of a plasma stream with the tungsten samples placed at the z-axis of the facility, at a distance of 6 cm from the electrode outlets. The recorded spectra showed distinct WI and WII spectral lines. Investigation of a target surface morphology, after its irradiation by intense plasma streams, was performed by means of an optical microscope. The observations revealed that some amounts of the electrodes material (mainly copper) were deposited upon the irradiated sample surface. In all the cases, melted zones were observed upon the irradiated target surface, and in experiments performed at the highest charging voltage there were formed some cracks.

2

Measurements of fast electron beams and soft X-ray emission from plasma-focus experiments

Surała W., Sadowski M. J., Kwiatkowski R., Jakubowski L., Żebrowski J.

Nukleonika

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2016

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Vol. 61, No. 2

161--167

EN

The paper reports results of the recent experimental studies of pulsed electron beams and soft X-rays in plasma-focus (PF) experiments carried out within a modifi ed PF-360U facility at the NCBJ, Poland. Particular attention was focused on time-resolved measurements of the fast electron beams by means of two different magnetic analyzers, which could record electrons of energy ranging from about 41 keV to about 715 keV in several (6 or 8) measuring channels. For discharges performed with the pure deuterium fi lling, many strong electron signals were recorded in all the measuring channels. Those signals were well correlated with the fi rst hard X-ray pulse detected by an external scintillation neutron-counter. In some of the analyzer channels, electron spikes (lasting about dozens of nanoseconds) and appearing in different instants after the current peculiarity (so-called current dip) were also recorded. For several discharges, fast ion beams, which were emitted along the z-axis and recorded with nuclear track detectors, were also investigated. Those measurements confi rmed a multibeam character of the ion emission. The time-integrated soft X-ray images, which were taken side-on by means of a pinhole camera and sensitive X-ray fi lms, showed the appearance of some fi lamentary structures and so-called hot spots. The application of small amounts of admixtures of different heavy noble gases, i.e. of argon (4.8% volumetric), krypton (1.6% volumetric), or xenon (0.8% volumetric), decreased intensity of the recorded electron beams, but increased intensity of the soft X-ray emission and showed more distinct and numerous hot spots. The recorded electron spikes have been explained as signals produced by quasi-mono-energetic microbeams emitted from tiny sources (probably plasma diodes), which can be formed near the observed hot spots.

3

Experiments and simulations on the possibility of radiative contraction/collapse in the PF-1000 plasma focus

Akel M., Cikhardt J., Kubes P., Kunze H.-J., Lee S., Paduch M., Saw S. H.

Nukleonika

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2016

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Vol. 61, No. 2

145--148

EN

Experimental studies of discharges in the plasma focus facility with neon filling and respective numerical simulations employing the radiative Lee code are reported. The pinch currents exceed the Pease-Braginskii current, which indicates that radiative losses are larger than heating and that contraction of the formed plasma should occur. Both of these effects were indeed observed. Parallel numerical simulations were crucial for the identifi cation of such an effect.

4

Diagnostic systems for the nuclear fusion and plasma research in the PF-24 plasma focus laboratory at the IFJ PAN

Marciniak Ł., Wójcik-Gargula A., Kulińska A., Bielecki J., Wiącek U.

Nukleonika

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2016

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Vol. 61, No. 4

413--418

EN

This paper presents a set of diagnostics dedicated to PF-24 – new medium size – plasma focus (PF) device built and operated at the Institute of Nuclear Physics Polish Academy of Sciences (IFJ PAN). The PF-24 can operate at energy level up to 93 kJ and charging voltage up to 40 kV. Each condenser is connected with a specially designed spark gap with a very small jitter, which ensures a high efficiency and a low current rise time. The working parameters of PF-24 generator make it a suitable tool for testing new detection systems to be used in fusion research. Four types of such detection systems are presented in this article: three diagnostic systems used to measure electric quantities (Rogowski coil, magnetic probe, capacitance probe), neutron counter based on beryllium activation, fast neutron pinhole camera based on small-area BCF-12 plastic scintillation detectors and high-speed four-frame soft X-ray camera with microchannel plate.

5

Recent measurements of soft X-ray emission from the DPF-1000U facility

Surała W., Sadowski M. J., Paduch M., Zielinska E., Tomaszewski K.

Nukleonika

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2015

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Vol. 60, No. 2

303--308

EN

Soft X-ray imaging is a very useful diagnostic technique in plasma-focus (PF) experiments. This paper reports results of four experimental sessions which were carried out at the DPF-1000U plasma-focus facility in 2013 and 2014. Over 200 discharges were performed at various experimental conditions. Measurements were taken using two X-ray pinhole cameras with a line of sight perpendicular to the z-axis, at different azimuthal angles (about 20° and 200°), and looking towards the centre of the PF-pinch column. They were equipped with diaphragms 1000 μm or 200–300 μm in diameter and coated with filters of 500 μm Al foil and 10 μm Be foil, respectively. Data on the neutron emission were collected with silver activation counters. For time-resolved measurements the use was made of four PIN diodes equipped with various fi lters and oriented towards the centre of the PF-column, in the direction perpendicular to the electrode axis. The recorded X-ray images revealed that when the additional gas-puff system is activated during the discharge, the stability of the discharge is improved. The data collected in these experiments confi rmed the appearance of a filamentary fi ne structure in the PF discharges. In the past years the formation of such fi laments was observed in many Z-pinch type experiments. Some of the recorded X-ray images have also revealed the appearance of the so-called hot- -spots, i.e. small plasma regions of a very intense X-ray emission. Such a phenomenon was observed before in many PF experiments, e.g. in the MAJA-PF device, but it has not been investigated so far in a large facility such as the DPF-1000U. The time-resolved measurements provided the evidence of a time lapse between the X-ray emission from plasma regions located at different distance from the anode surface. The formation of distinct ‘hot-spots’ in different instants of the DPF-1000U discharge was also observed.

6

Comparison of optical spectra recorded during DPF-1000U plasma experiments with gas-puffing

Zaloga D. R., Skladnik-Sadowska E., Kubkowska M., Ladygina M. S., Malinowski K., Kwiatkowski R., Sadowski M. J., Paduch M., Zielinska E., Makhlaj V. A.

Nukleonika

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2015

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Vol. 60, No. 2

309--314

EN

The results are presented of the optical spectra measurements for free plasma streams generated with the use of the modifi ed DPF-1000U machine. This facility was recently equipped with a gas injection system (the so-called gas-puff) placed on the symmetry axis behind the central opening in the inner electrode. The DPF-1000U experimental chamber was fi lled up with pure deuterium at the initial pressure of 1.6 or 2.4 mbar. Additionally, when the use was made of the gas-puff system about 1 cm3 of pure deuterium was injected at the pressure of 2 bars. The gas injection was initiated 1.5 or 2 ms before the triggering of the main discharge. The investigated plasma discharges were powered from a condenser bank charged initially to 23 kV (corresponding to the energy of 352 kJ), and the maximum discharge current amounted to about 1.8 MA. In order to investigate properties of a dense plasma column formed during DPF-1000U discharges the use was made of the optical emission spectroscopy. The optical spectra were recorded along the line of sight perpendicular to the vacuum chamber, using a Mechelle®900 spectrometer. The recent analysis of all the recorded spectra made it possible to compare the temporal changes in the electron density of a freely propagating plasma stream for discharges without and with the gas-puffing. Using this data an appropriate mode of operation of the DPF-1000U facility could be determined.

7

Progress in MJ plasma focus research at IPPLM

Scholz M., Karpinski L., Krauz V. I., Kubeš P., Paduch M., Sadowski M. J.

Nukleonika

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2012

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Vol. 57, No. 2

183-188

EN

The results of studies of the plasma dynamics and neutron emission on a PF-1000 facility in the stage of pinch formation are presented. The measurements were performed using various modifications of the calibrated magnetic probes, 16 frame interferometry, silver activation counters and photomultiplier tube (PMT) neutron probes. The current measurements at a distance of 40 mm from the axis of the electrodes was measured. This dependence agrees well with the known scaling, Yn similar to I4. The evolution plasma density during pinch formation and a neutron emission were study.

8

Preliminary determination of angular distribution of neutrons emitted from PF-1000 facility by indium activation

Jednoróg S., Szydłowski A., Scholz M., Paduch M., Bienkowska B.

Nukleonika

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2012

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Vol. 57, No. 4

563-568

EN

This paper presents a new method applied to measure the angular neutron emission from Plasma Focus (PF) - type deuterium discharges performed within the PF-1000 facility. Neutrons were recorded by activation of especially optimized (mass and shape) indium samples with subsequent gamma spectrometry to measure the induced activity of the samples. The neutron fluence rate on every indium sample used was determined using neutron transport calculation and measured activity of the samples.

9

Diagnostics and scaling of fusion-produced neutrons in PF experiments

Schmidt H.

Nukleonika

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2011

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Vol. 56, No. 2

107-112

EN

Neutrons from a plasma focus (PF) device operated in a deuterium gas, measured as a function of time, location and direction of emission, reveal quite a number of important parameters on fusion reactions occurring in the dense high-current phase of the experiment. In addition the determination of the energy spectra of the emitted neutrons is important for understanding the mechanisms taking place for the neutron production. Results of neutron measurements in large experiments such as the former POSEIDON experiment in Stuttgart and the PF-1000 experiment in Warsaw are presented. The neutron diagnostic methods that had been utilized include nuclear track detectors, plastic scintillators coupled to photomultipliers, activation measurements, time-of-flight methods as well as pinholes for spatial resolution of the neutron source. The well known scaling law according to which the neutron yield scales roughly as the square of the energy input or the fourth power of the current is discussed. Reasons for strong deviation from this law for high energies - known as the saturation effect - are still a subject of debate.

10

Experimental investigation of current pinch behavior and hard X-ray signals by APF plasma focus facility

Habibi M., Amrollahi R.

Journal of Technical Physics

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2009

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Vol. 50, no 3

283-289

EN

In this paper, design and construction of APF Mather-type plasma focus device (16 kV, 36 μF, and 115 nH) is reported. The design of the system is based on the three-phase theory of the plasma focus formation presented by J.H. Lee. Results of some important experiments to obtain optimum working pressures result in high intensity current pinch at various applied voltages, dependence between the pinch current and the applied voltage at the optimum pressure, and also the focusing time proportional to the gas pressure investigated in this paper. For hollow anode tube, the intensity of HXR shows highly anisotropic behavior. When Al target is installed at the anode tip, the HXR intensity increases and the data shows a large anisotropy, with a maximum intensity between 22.5μ and -22.5μ.

11

Damage and modification of materials produced by pulsed ion and plasma streams in Dense Plasma Focus device

Pimenov V. N., Demina E. V., Ivanov L. I., Gribkov V. A., Dubrovsky A. V., Ugaste U., Laas T., Scholz M., Miklaszewski R., Kolman B., Tartari A.

Nukleonika

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2008

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Vol. 53, No. 3

111-121

EN

The Dense Plasma Focus (DPF) devices PF-1000, PF-6 and PF-5M working with different gases and in dissimilar irradiation modes were used to carry out experimental investigations of irradiation of a number of materials by powerful pulsed ion and high-temperature plasma streams. The materials under test were designed for application in structural and functional components of thermonuclear fusion devices with magnetic (MPC) and inertial (IPC) plasma confinement, as well as for working chambers of plasma and accelerator devices. The main features of the materials are low-activation and radiation-resistant properties. On the basis of the investigations a significant progress was achieved in understanding of dynamics of high-energy nano- and micro-second pulsed streams in DPF from one side as well as on the mechanisms of their influence upon materials under irradiation from the other one. We demonstrated that this approach can be useful for certain tests of plasma-facing materials (e.g. W for MPC and stainless steels for IPC) and of structural (construction) elements of the above-mentioned devices subjected to pulsed high-energy radiation streams. The results obtained suggest also that DPF devices can be used in new pulse technologies for material treatment by means of powerful nanosecond and microsecond pulses of plasma and ion streams.

12

Studies on a low energy plasma focus discharge

Allam T. M., Abd El-Latif S. T., Soliman H. M.

Nukleonika

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2007

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Vol. 52, nr 3

87-91

EN

This paper is devoted to the experimental and theoretical study of plasma current sheath behavior for a low energy plasma focus device operating at a filling nitrogen gas pressure of 3.3 torr, and at a stored energy of 1.2 kJ. Axial distribution profiles of plasma current sheath (PCS) characteristics such as propagation velocity Vz, acceleration az, azimuthal magnetic field induction Btheta, and magnetic force per unit volume Fz/m3 along the coaxial electrodes system was performed from a magnetic probe and miniature Rogovsky coil signals. The experimental results showed that the axial distribution of Vz, az, Btheta and Fz has approximately the same profile and the maximum value of these parameters was detected nearly at a mid-distance of coaxial electrodes system. Theoretical description of PCS dynamics at the axial phase, based on a snowplough, was estimated as a function of discharge time. These data were compared with the received experimental results.

13

Surface and bulk processes in materials induced by pulsed ion and plasma beams at Dense Plasma Focus devices

Pimenov V., Maslyaev S., Ivanov L., Dyomina E., Gribkov V., Dubrovsky A., Scholz M., Miklaszewski R., Ugaste U., Kolman B.

Nukleonika

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2006

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Vol. 51, nr 1

71-78

EN

A review of results and new data on the interaction of pulsed ion and dense plasma beams with metals in different Dense Plasma Focus (DPF) devices are presented. Different irradiation conditions with microsecond pulses of the power density in the range of 105 109 W/cm2 were applied. The most interesting thermal and radiation effects observed in both surface and bulk of the material positioned at the cathode part of the DPF device have been considered. Advanced directions of DPF use for scientific and applied problems of radiation material science were determined.

14

Status of a mega-joule scale Plasma-Focus experiments

Scholz M., Bieńkowska B., Borowiecki M., Ivanova-Stanik I., Karpiński L., Stępniewski W., Paduch M., Tomaszewski K., Sadowski M., Szydłowski A., Kubeš P., Kravárik J.

Nukleonika

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2006

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Vol. 51, nr 1

79-84

EN

This paper presents results of the recent plasma-focus (PF) experiments carried out with PF facilities, which was operated at energies ranging from 0.5 MJ to about 1 MJ. Particular attention has been paid to pinch evolution, the emission of pulsed X-ray, fast electron beams, and fusion produced neutrons. Some theoretical models of the initial breakdown, which occurs at the insulator surface, are compared. It is pointed out that modeling of the breakdown is sensitive to kinetics of ionization processes and transport coefficients. Progress in experimental studies of the axial acceleration phase is unsatisfactory. Important experimental data have been collected, but new measurements are still needed. For the radial collapse phase, it was shown that the MHD modeling is efficient until the maximum compression, but plasma instabilities require more sophisticated approaches. The pinch phase was investigated by means of different diagnostics. Fusion neutron yields were measured in different experiments, but some discrepancies in scaling must still be explained. The conclusions concern directions for further studies and optimization of large-scale high-current PF facilities.

15

Development of diagnostic tools for Plasma Focus derived X-ray source

Angeli E., Bonifazzi C., Da Re A., Marziani M., Tartari A., Frignani M., Mannucci S., Mostacci D., Rocchi F., Sumini M.

Nukleonika

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2006

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Vol. 51, nr 1

15-20

EN

The energy spectra of X-rays generated by the impact of electron beams on high- and medium-Z targets following the pinch implosion of Plasma Focus (PF) devices are discussed in terms of the possible mechanisms of X-ray production following electron impact ionization. In addition, the temperature measurement of the PF inner electrode is reported and some results have been proved useful in order to optimize the device functionalities.

16

D(3He,p)4He and D(d,p)3H fusion in a small plasma focus operated in a deuterium helium-3 gas mixture

Springham S., Sim T., Rawat T., Lee P., Patran A., Shutler P., Tan T., Lee S.

Nukleonika

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2006

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Vol. 51, nr 1

47-53

EN

Abstract A 3 kJ plasma focus was operated with a 3He-D2 gas mixture, with partial pressures in the ratio of 2:1, corresponding to an atomic number ratio of 1:1 for 3He and D atoms. The fusion reactions D(3He,p)4He and D(d,p)3H were measured simultaneously using CR-39 polymer nuclear track detectors placed inside a pinhole camera positioned on the forward plasma focus axis. A sandwich arrangement of two 1000 mi m thick CR-39 detectors enabled the simultaneous registration of two groups of protons with approximate energies of 16 MeV and 3 MeV arising from the D(3He,p)4He and D(d,p)3H reactions, respectively. Radial track density distributions were obtained from each CR-39 detector and per-shot average distributions were calculated for the two groups of protons. It is found that the D(3He,p)4He and D(d,p)3H proton yields are of similar magnitude. Comparing the experimental distributions with results from a Monte Carlo simulation, it was deduced that the D(3He,p)4He fusion is concentrated close to the plasma focus pinch column, while the D(d,p)3H fusion occurs relatively far from the pinch. The relative absence of D(d,p)3H fusion in the pinch is one significant reason for concluding that the D(3He,p)4He fusion occurring in the plasma focus pinch is not thermonuclear in origin. It is argued that the bulk of the D(3He,p)4He fusion is due to energetic 3He2+ ions incident on a deuterium target. Possible explanations for differing spatial distributions of D(3He,p)4He and D(d,p)3H fusion in the plasma focus are discussed.

17

Results of large scale Plasma-Focus experiments and prospects for neutron yield optimization

Sadowski M., Scholz M.

Nukleonika

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2002

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Vol. 47, nr 1

31-37

EN

This paper summarizes results of the recent Plasma-Focus (PF) studies carried out with different PF facilities in Poland, which were operated at energies ranging from 100 kJ to about 1000 kJ. Particular attention has been paid to currentsheath (CS) dynamics, the emission of pulsed X-rays, fast electron beams, energetic ion beams, and fusion-produced neutrons. Some efforts, undertaken in order to increase the neutron emission, have been described. In particular, nuclear targets made of D2O-ice layers, which were deposited upon special cryogenic devices, have been applied in the PF-360 machine. An increase in the neutron yield from 2.4×1010 up to 3.8×1010 neutrons per shot has been achieved in 130-kJ discharges. With the PF-1000 machine, for the first time the well-formed plasma pinch columns were obtained in PF discharges performed at 1 MJ, and the neutron yield of 2×1011 neutrons per shot was achieved.

18

Energy transformation in Plasma Focus discharge with wire and liner as a load

Kubeš P., Kravárik J., Klír D., Scholz M., Paduch M., Tomaszewski K., Karpinski L., Ryc L., Juha L., Krása J., Szydlowski A., Romanova V.

Nukleonika

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2002

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Vol. 47, nr 4

151-153

EN

We present the results of experiments focused on energy transformations during the implosion of the hydrogen current sheath towards an Al wire (120 ěm in diameter) positioned on the top of the inner electrode of the PF-1000 plasma focus facility at the IPPLM in Warsaw. A wire corona is formed at the current sheath impact and ~60 ns after the impact a soft X-ray pulse is emitted. Its spectrum contains AlVI-XII lines accompanied by their satellites. The amount of emitted energy is recorded by two filtered PIN diodes and thermoluminescent dosimeters and depends on symmetry of the current sheath and quality of the current sheath focus. The mean value of energy of keV photons emitted in the runs done without the wire (~1 J) is higher than the energy obtained with the wire (~0.4 J). A time delay between the impact of the current sheath and X-ray pulse, the plasma focus dynamics and soft X-ray emission are interpreted by an axial magnetic field generation and transformations.

19

Ultrafast X-ray introspective imaging of metallic objects using a Plasma Focus

Moreno C. H., Clausse A., Martínez J. F., Llovera R., Tartaglione A.

Nukleonika

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2001

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Vol. 46, suppl. 1

33--34

EN

A compact-chamber 4.7 kJ, 30 kV, Plasma Focus operated in deuterium was used as a ultrafast high intensity radiation source for introspective radiographic imaging of metallic objects. The samples to be imaged were located outside the Plasma Focus chamber, about 1 m away from the chamber wall. A high-sensitivity, fast-response commercial radiographic film was used as a X-ray detector. Experimentally obtained images are presented showing a very high penetration power of the X-ray beam, demonstrating that the presented compact-chamber Plasma Focus is suited for introspective visualisation of pieces manufactured on metal.

20

The role of anomalous resistivities in Plasma Focus discharges

Bruzzone H.

Nukleonika

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2001

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Vol. 46, suppl. 1

3--7

EN

The existence of plasma microturbulence in Plasma Focus (PF) devices is a widely accepted fact within the PF community. This microturbulence must be generated as a final stage of microscopic instabilities, which could develop during certain phases of the plasma evolution. Among the candidate instabilities to occur in these devices, the lower hybrid drift instability is the one with better possibilities, because its triggering condition (electron drift velocity approaching ion thermal velocity) has reasonable chances to be fulfilled. The main effect of the development of this instability is the modification of the collision frequencies in the plasma, which adds an anomalous term to the plasma resistivity. The theory for evaluating this extra term exists, and has been already used in PF 1D numerical simulations and in Z-pinch calculations. The role of this anomalous resistivity in PF behaviour has been the subject of considerable speculations. In this work, a 1D MHD (magnetohydrodynamics) calculation of the pinch stage in a PF device will be presented, including anomalous resistivity effects and their influence on electric fields and the discharge current are discussed.