Plasma Focus Experiments Research Articles

Preliminary observations on possible implications of new Bohr orbits (resulting from electromagnetic spin-spin and spin-orbit coupling) in “cold” quantum mechanical fusion processes appearing in strong “plasma focus” and “capillary fusion” experiments

The theoretical interpretation of recently observed “excess heat” (i.e. break-even) in low intensity electrolytic and discharge experiments (with both deuterium and hydrogen) as resulting from a new type of non-nuclear quantum phenomena (i.e. spin-spin and spin-orbit couplings added to the usual Coulomb potential in specially structured dense media) leads to the prediction that “fusion ashes” of deuterium (or deuterium compounds now in vanishingly small quantities) will grow with the current intensity input, thus increasing the excess energy output. To test this prediction one can study the dynamic of fusion reactions in simple capacitor bank discharges into deuterated media, both in plasma focus (PF) and capillary fusion (CF) type experiments.

80 kV, 8.9 kJ plasma focus experiments

High‐voltage, low‐energy, Mather‐geometry plasma focus experiments were performed to study large sheath formation input power, fast rundown, and current optimization and stabilization during collapse and pinch. For the parameters of these experiments, large bank impedance and short implosion time lead to small pinch current depression. Double‐peaked x‐ray emission data correlates with I‐dot compression spikes; Cu Kα radiation is believed to dominate. I‐dot data indicate that on‐axis sheath bouncing occurs. Center electrode damage, reduced compression dynamics, and sheath bouncing suggest the use of larger electrode radius for these operating parameters. B‐dot probe data indicate a rundown current sheath full‐width‐half‐maximum thickness of 7.4 mm.

Comparative analysis of large plasma focus experiments performed at IPF, Stuttgart, and IPJ, Świerk

The paper presents a comparison of the main characteristics and experimental results obtained in plasma focus (PF) experiments in the POSEIDON 500 kJ facility in Stuttgart and the PF-360 kJ device in Świerk. Parameters of various electrodes and insulators are given, and studies on the evolution of the discharges are summarized. Selected data on X-ray, ion and neutron emission are given. Also presented are recent experimental results — a maximum neutron yield of up to 2.5 × 1011 for 500 kJ/80 kV runs with a new ceramic insulator in POSEIDON and an average neutron yield of 1.2 × 1011 for operation at 171 kJ/36 kV in PF-360. Particular attention is paid to the neutron scaling and the saturation effects observed at higher energy and current levels. Proposals are made for new experimental studies which can facilitate further progress in PF research.

Multislit streak photography for plasma dynamics studies

A microscope slide with several transparent slits installed in a streak camera is used to record time-resolved two-dimensional information when a curved luminous plasma sheath traverses these slits. Applying this method to the plasma focus experiment, the axial run-down trajectory and the shapes of the plasma sheath at various moments can be obtained from a single streak photograph.

Manifestation of an ion acceleration mechanism in computer simulations and plasma-focus experiments

A feature of dynamical pinches is their tendency to generate nonthermal (fast) particles. The development of ion runaway and manifestations of a recently proposed ion gyro-reflection-acceleration in computer simulations and Schlieren pictures taken at plasma focus experiments are studied. Consequences concerning pinch equilibrium and stability are outlined.

Angular distribution of x-ray radiation from optically thick z-pinch plasmas

A z-pinch plasma is an x-ray radiation source of small size concerning the z-direction radiation. However, the plasma is optically thick with respect to the resonance lines, which contain a large fraction of the total radiation. The influence of the opacity on efficiency and spatial radiation distribution has been examined. A computer simulation solving the radiation transport equation demonstrates that the efficiency of the x-ray output decreases due to absorption, but only slightly because photon trapping is mostly followed by reemission. Using this result another computer code could determine the following features concerning the angular radiation distribution: (1) The average r-direction intensity is larger than the z-direction intensity. (2) The ratio of z-direction intensity to r-direction intensity varies from shot to shot. (3) The standard deviation of z-direction intensity is larger than that of the r-direction intensity. Several plasma focus experiments were carried out, the results of which provide good qualitative proof of the above predictions.

On the Boil-Off Time of Probe Surfaces in Plasmas

The time required for the melting of the surface of a glass-insulated probe inserted in a plasma is computed including the influence of plasma mass motion. This effect is relevant for probe measurements in moving current sheaths of electrical gas discharges. For dense plasma focus experiments, it is shown that the time of formation of a transition layer of evaporated material is shorter than the ion relaxation time in the plasma and the transit time of the current sheath by the probe position.

Reduction of a time of flight experiment to tomography

Abstract We propose a novel generalization of time of flight analysis which yields unambiguous information about the velocity spectrum as a function of time of a point pulsed particle source. The records of several particle counters placed at various prescribed distances from the source are combined in a way derived from tomography theory to give a well defined set of moments of the source emission function. A variety of reconstructions can then be made, which we illustrate by computer examples. The resolution of the method is investigated. There are possible applications to plasma focus and laser fusion experiments.

Structure of a plane and stationary ionizing current sheath

A simple model that describes the structure of a plane and stationary current sheath moving against a neutral gas pushed by a magnetic field (like the one found in Plasma Focus experiments) is given. The numerical solutions of the equations are presented, and approximate analytical relationships between some features of the structure and the presence of the neutral gas and the magnitude of the pushing magnetic field are derived.

Ion beam formation in an m = 0 unstable Z pinch

It is well known both in early Z-pinch experiments and more recently in plasma focus experiments that highly accelerated ion beams are formed, this being inferred from the axial centre-of-mass motion of the neutrons produced by nuclear reactions. Two acceleration mechanisms are discussed here. The first, proposed in ref. 1, concerns the acceleration of ions across an electrostatic sheath adjacent to the anode, this sheath having a thickness less than an ion Larmor radius but greater than an electron Larmor radius. The electrons in the sheath, being magnetised, have a c E × B/B 2 drift through which the J r B θ force is provided to satisfy momentum conservation. The second is a new mechanism arising from the occurrence of a violent m = 0 instability, and relies on large ion Larmor radius effects. It is shown that the inclusion of the Hall terms and finite ion Larmor radius (FLR) terms in the MHD equations removes the mirror symmetry each side of an m = 0 neck. A detailed consideration of particle orbits during the formation of the highly compressed neck shows that on the cathode side of the neck an energetic ion beam is formed close to the axis, whilst on the anode side an equal and opposite momentum is distributed among a larger number of ions throughout the cross-section.

Comparison of plasma focus calculations

A simple model for the current history of plasma focus experiments is presented. The presence of a leak current which does not pass through the plasma sheath is allowed. Results are found to compare quite well with those of much more sophisticated two-dimensional magnetohydrodynamic calculations. For the Frascati experiment, which has detailed current measurements, computed results do not agree with experimentally derived values. A reasonable match for the total current in the Frascati experiment can be found by lowering the leak current. Both total and leak current can be matched if a mass loss from the run-down region is allowed.

Comparison of four calibration techniques of a silver activated Geiger counter for the determination of the neutron yield on the Frascati plasma focus experiment

The theoretical background of four independent calibration methods and their application to the silver activated Geiger counter used to determine the neutron yield of the Frascati 1 MJ plasma focus machine are described. The first method is based on the exposure of an indium foil to a number of plasma focus shots sufficient to induce a measurable activity in the foil. This method requires knowledge of the plasma focus neutron spectrum and of the indium energy-dependent activation cross section. The following methods resort to a reference radioactive neutron source, used respectively in the saturation and in the removal mode. The fourth method is based on the exposure of a nuclear emulsion plate to a single shot of the plasma focus machine. The experimental results are reported and discussed. Possible improvements, including the use of a rhodium activated counter, are suggested.

A system for a multiframing interferometry and its application to a plasma focus experiment

A four-framing Mach-Zehnder interferometer system which has variable intervals from frame to frame is developed. TEA N(2) lasers that are operated with atmospheric-pressure N(2) gas are employed as light sources. Applicability of the system is demonstrated for a rapidly changing plasma in the plasma focus discharge.

Two-dimensional magnetohydrodynamic calculations of the plasma focus

Two-dimensional magnetohydrodynamic calculations on plasma focus experiments in the Mather geometry are described. The properties of the two-dimensional numerical solutions are discussed. Detailed results are given for a specific problem which compares favorably with experiment. The numerical solution for the plasma focus previously given by Potter has been rerun with substantial disagreement. Arguments are given to show that the Potter code is incorrect.

Nonlinear evolution of the sausage instability

Sausage instabilities of an incompressible, uniform, perfectly conducting Z pinch are studied in the nonlinear regime. In the long wavelength limit (analogous to the ’’shallow water theory’’ of hydrodynamics), a simplified set of universal fluid equations is derived, with no radial dependence, and with all parameters scaled out. Analytic and numerical solutions of these one-dimensional equations show that an initially sinusoidal perturbation grows into a ’’spindle’’ or cylindrical ’’spike and bubble’’ shape, with sharp radial maxima. In the short wavelength limit, the problem is shown to be mathematically equivalent to the planar semi-infinite Rayleigh–Taylor instability, which also grows into a spike-and-bubble shape. Since the spindle shape is common to both limits, it is concluded that it probably obtains in all cases. The results are in agreement with dense plasma focus experiments.

Contraction of Z pinches actuated by radiation losses

An equilibrium model of the radial motion of Z pinches is developed, based on the Bennett relation, radiation losses, and Ohmic heating. The highly localized x-ray sources observed in some plasma focus experiments can be explained by the model.