[en] Possibilities of optimizing focus devices of a given energy content in terms of large neutron yield and high reliability of discharges are investigated experimentally using a Mather focus device with an energy content of 12 kJ. The following experimental parameters were varied: the material of the insulator in the ignition region, the structure of the outer electrode, the length of the inner electrode, the filling pressure, and the level and polarity of the battery voltage. Measurements of the aximuthal and axial current distribution in the accelerator, correlated in time with high-speed photographs of the flashline form an important part of plasma diagnostics. A functioning scheme of the focus discharge has been established as an aid to further optimization of plasma focus devices. This scheme makes use of theoretical and experimental findings; it accounts for the multiparameter character of the discharge and illuminates connections between the experimental parameters and the targets neutron yield and reliability. (orig./AK)

[en] Possibilities of optimizing focus machines with a given energy content in the sense of high neutron yield and high reliability of the discharges are investigated experimentally. For this purpose, a focus machine of the Mather type with an energy content of 12 kJ was constructed. The following experimental parameters were varied: the material of the insulator in the ignition zone, the structure of the outside electrode, the length of the inside electrode, the filling pressure and the amount and polarity of the battery voltage. An important part of the diagnostic program consists of measurements of the azimuthal and axial current distribution in the accelerator, correlated with short-term photographs of the luminous front as a function of time. The results are given. A functional schematic has been drafted for focus discharge as an aid in extensive optimization of focus machines, combining findings from theory and experiments. The schematic takes into account the multiparameter character of the discharge and clarifies relationships between the experimental parameters and the target variables neutron yield and reliability

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[en] This chapter describes the focus project at Dusseldorf University which is based on experimental and theoretical studies made at Stuttgart University concerning an increase of the effective discharge current for the plasma focus from a condenser bank of constant energy. The results of a theoretical analysis show that efforts are necessary in designing a condenser bank with respect to bank voltage and initial current rise in order to draw maximum current. Gives the projected characteristics of the extremely fast high voltage bank and discusses the objectives

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[en] Numerical and experimental studies have been made concerning an increase of the effective discharge current for the plasma focus from a bank of constant energy. From the higher discharge current an increased neutron yield is expected. Experimentally an 85 kV/12 kJ device with a current rise time of 600 ns was investigated. The obtained neutron yield was larger by a factor of 3 compared to devices of equal energy but low voltage. The geometrical and pressure variations, necessary for optimization, are discussed. Using MHD-calculations and impedance considerations, various banks, including those with high voltage and low inductance, are compared with respect to plasma data and discharge current. (orig.)

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[en] The plasma focus current is measured using small magnetic probes, which are decoupled from the ground potential. It is found, that only some - pressure dependent - fraction of the total current in the device flows at the focus region. The correlation between this current and the neutron yield can be described as Y approximately I⁴. The occurrence of m = 0 instabilities in the focus plasma appears in the probe signal and is also correlated to the neutron yield. A comparison between MHD-calculations and the observed field structures is presented. (author)

[en] Conventional plasma focus devices of different capacitor bank energy (kilojoules to megajoules) show very similar discharge behavior with respect to breakdown, compression, and pinch data. The use of SPEED 1: a plasma focus driven by a fast high impedance bank (voltage 200 kV, initial current rise >5 x 10₁₂ A/sec, bank impedance 160 mΩ),: allowed the investigation of a 400 nsec discharge in a parameter range not previously accessible. Considerable improvement of current and neutron efficiency (30 A/J; 10₆/J) has been achieved as compared with values (< or =20 A/J; 2 x 10₅/J) of conventional slow devices of equal energy (20 kJ). Exceptional compression dynamics (current derivative spike >10₁₃ A/sec FWHM 10 nsec) is observed from electric signals. This is due to the current stabilizing effect of the high bank impedance and especially to improved current sheath structure (reduced thickness, enhanced conductivity). Current density and conductivity of the sheath depend on ignition parameters at breakdown (voltage, current rise), the low values of which are possibly responsible for the similarity of the discharge behavior of conventional devices. Conclusions on further improvements are drawn