Existence of a return direction for plasma escaping from a pinched column in a plasma focus discharge (original) (raw)
Related papers
Physics of Plasmas
This paper concerns the evolution of internal structures and the neutron production in plasma-focus discharges performed in the presence of a permanent magnet (placed inside the anode front) and within a residual magnetic field (after the removal of this magnet). The initial magnetic field generated by this magnet prevented: (i) the effective compression of a dense pinch column, (ii) the formation of plasma organized structures, and (iii) the evolution of plasma instabilities. The experimental results have shown an increase in the initial magnetic field due to a magnetic dynamo effect in the presence of the permanent magnet, as well as in a series of shots performed after its removal. It was observed that the appearance of plasmoidal structures is necessary for the emission of fusion neutrons. A characteristic quasicylindrical plasma layer of the radius corresponding to the plasma lobule tops, which might be identified with a ring region of the acceleration of fast deuterons, was also observed.
IEEE Transactions on Plasma Science
Plasma in a pinch column, as produced by a plasma-focus discharge at the deuterium filling and the current intensity reaching 1 MA, was investigated at the total neutron yield reaching about 10 10 per discharge. The use was made of neutron diagnostics, laser interferometry, soft X-ray measurements, optical emission spectroscopy, magnetic probes, as well as electron and ion measurements with the temporal, spatial, and energetic resolutions. The detailed studies showed the ordered toroidal, helical, and plasmoidal structures which could contain currents with poloidal and toroidal components and their associated magnetic fields. Their spontaneous transformations were explained by changes in a topology of magnetic field lines due to magnetic reconnections. A nonthermal acceleration of fast electrons and ions (producing hard X-rays and fusion neutrons, respectively) corresponded to: 1) the formation of plasmoids in the pinch column and 2) a decay of pinch constrictions and secondary plasmoids during the evolution of instabilities. A filamentary structure of the current flow could explain the high energy density and fast transformations of the magnetic energy into kinetic energy of electron and ion beams (reaching energy of hundreds of kiloelectronvolt). This paper summarizes the results obtained with the PF-1000 facility in 2009-2017, and describes the internal transformations in a dense plasma column during the evolution of MHD instabilities.
Keywords Langmuirprobe, electron temperature, density,longitudinal magnetic field. PACS 52.25.Xz, 52.80.Hc, 52.70.Ds Thev ariations of plasma parameters of ad cd ischarge in an on-uniform magnetized plasma were measured usingf ast floatingd oubleL angmuirp robes. As olenoidi su sed to produce au niform magnetic field parallel to thed ischarge axis. Thea xial changes of thep lasma parameters are presented in ther ange of longitudinal magnetic fields 200 to 600 Gauss at thepressure range 0 . 3 to 2 . 1 Torr and discharge currents 5 and 15 mA in argon gas. Theexperimental results indicatethat,asaconsequence of theaxial magnetic field and thevariations in thedischarge tube radii, theplasma parameters at smallradius exhibitobvious changes in theirdistributions along theaxiscompared to thesituationofunmagnetized plasma.
The main issues of research on dense magnetized plasmas in PF discharges
Plasma Sources Science and Technology, 2008
This invited lecture presents the main physical problems met during studies of dense (>10 16 cm −3) plasma influenced by strong magnetic fields, i.e. when ion cyclotron motions are weakly disturbed by electron-ion collisions. Examples of high-current pulsed discharges of the Z-pinch and plasma-focus (PF) type, which can produce dense magnetized plasma (DMP) are presented. The paper concerns mainly PF-type discharges. Particular attention is paid to different phases of such discharges. The breakdown and formation of a dense plasma layer (current sheath), its axial acceleration and the final radial collapse phase are analyzed. The most important physical phenomena are identified, and some theoretical models are described. The main issues of experimental and theoretical studies of DMP in PF-type facilities are shown.
Czechoslovak Journal of Physics, 2004
This invited lecture concerns Plasma-Focus (PF) devices belonging to the family of the dynamic Z-pinches which produce dense, hot and magnetized plasmas. The plasma is formed by an inter-electrode discharge of a capacitor bank, and the dynamics of the current sheet has two different phases: 1—A long-time phase (lasting several microseconds) of a breakdown and the axial acceleration, during which the current sheath is formed and pushed out by the Lorentz force; 2—A short-time phase, lasting a few hundreds nanoseconds, during which the pinch is created and (after the maximum compression) disrupted by instabilities. This lecture presents physics governing the behavior of current-carrying plasma in PF discharges. The lecture describes different phases of the PF phenomena: the breakdown and the early stage of the current sheath formation, dynamics of the axial acceleration (run-down) and the radial implosion, the formation of a transient quasi-equilibrium near the stagnation point, and a post-pinch phase. Some experimental results obtained with a large (mega-joule) PF-1000 facility are presented and discussed.
Modeling and Diagnostic of the Plasma of Magnetic Field Supported Discharges
Contributions to Plasma Physics, 2005
In this paper we present an experimental study of the variations of plasma parameters in both the axial as well as in radial directions in a 30 cm long cylindrical magnetron with outer cylindrically-shaped anode (diameter 58 mm) and coaxially placed cathode with a diameter of 1.8 cm. The measurements were made using three radially movable cylindrical Langmuir probes placed at three different axial positions between the magnetic coils. From the measurements there were evaluated electron density, electron mean energy, plasma potential and floating potential in dependence of the magnetic field (10-40 mT) and the argon pressure (2-7 Pa). In order to measure the axial variations of the discharge current, one half of the cathode length is segmented into 14 isolated segments with length of about 10 mm. The physical processes occurring in electrode regions and the positive column of a cylindrical magnetron discharge in crossed electric and magnetic fields are investigated basing on the solution of the Boltzmann kinetic equation by a multiterm decomposition of the electron phase space distribution function in terms of the spherical tensors. The influence of the distribution function anisotropy on the absolute values and radial profiles of the electron density and rates of various transport and collision processes is analyzed. The spiral lines for the directed particle and energy transport are obtained to illustrate the anisotropy effects in dependence on magnetic field. The electron equipressure surfaces are constructed in the form of ellipsoids of pressure and their transformation in the cathode and anode regions is studied. A strong anisotropy of the energy flux tensor in contrast to a weak anisotropy of the momentum flux density tensor is found. Particular results are obtained for the cylindrical magnetron discharge in argon at pressure 3 Pa, current 200 mA and magnetic fields ranging within 10 − 40 mT.
Scenario of a magnetic dynamo and magnetic reconnection in a plasma focus discharge
Matter and Radiation at Extremes, 2020
Paper published as part of the special topic on Special Issue on the 11th International Conference on Dense Zpinches (DZP2019) DZP2019 ARTICLES YOU MAY BE INTERESTED IN Ion acceleration and neutron production in hybrid gas-puff z-pinches on the GIT-12 and HAWK generators Matter and Radiation at Extremes 5, 026401 (2020);
Plasma motion observations in a very small plasma focus in the limit of low energy
2003
A. Clausse PLADEMA, UNCPBA Tandil and Comisión Nacional de Energía Atómica, Argentina Recibido el 3 de febrero de 2002; aceptado el 2 de abril de 2002 A very small plasma focus device has been designed and constructed. The plasma focus operates in the limit of low energy (160 nF capacitor bank, 65 nH, 20 − 40 kV, ∼ 32 − 100 J). The design of the electrode was assisted by a simple model of a Mather plasma focus. A neutron yield of 10 4 − 10 5 is expected when the discharge is operated with deuterium. Experiments in H2 has been performed at pressures over the range 0.1 to 2 mbar. The diagnostics used in the experiments include current derivative, voltage monitor, and plasma image using a ICCD camera gated at 5 ns. The umbrella-like current sheath running over the end of the coaxial electrodes and the pinch after the radial collapse can be clearly observed in the photographs. The velocity of the radial collapse is of the order of 10 5 m/s. The observations are similar to the results obtained with devices operating at energies several order of magnitude higher.
Temporal distribution of linear densities of the plasma column in a plasma focus discharge
Nukleonika, 2015
Experiments were carried out on the PF-1000 plasma focus device, with a deuterium filling and with deuterium puffing from a gas-puff nozzle placed on the axis of the anode face. The current was reaching 2 MA. 15 interferometric frames from one shot were recorded with a Nd:YLF laser and a Mach–Zehnder interferometer, with 10–20 ns delay between the frames. As a result, the temporal and spatial distribution of the linear densities and the radial and axial velocities of the moving of plasma in the dense plasma column could be estimated.