Correlations Among Neutron Yield and Dynamical Discharge Characteristics Obtained from Electrical Signals in a 400 J Plasma Focus (original) (raw)
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Neutron emission from a fast plasma focus of 400 Joules
Applied Physics Letters, 2003
The neutron emission from a small and fast plasma focus operating in deuterium is presented. The system operates at low energy in the hundred of joules range (880 nF capacitor bank, 38 nH, 20-35 kV, 176-539 J, ~300 ns current rise time). The neutrons were measured by means of a silver activation counter, and the total neutron yield versus deuterium gas filling pressure was obtained. For discharges operating at 30 kV charging voltage, the maximum neutron yield was (1.06+/-0.13)×106 neutrons per shot at 9 mbar.
Plasma Physics and Controlled Fusion, 2020
The differences in performance of a 1.9 kJ plasma-focus device PACO assembled with three different cathode configurations are experimentally qualified. In particular, the current sheath kinetics and the neutron yield operating with deuterium gas are systematically studied for the whole range of neutron-producing pressures, and the measurements are analyzed searching for relations between relevant physical magnitudes. The pinching time was found correlated with the dimensionless driver parameter, and this feature was found statistically independent of the cathode. The variation of the inductance jump associated with the radial collapse stage is used to estimate the effective pinch length, () 7.3 1.6 mm, and radius, () 3.6 2.1 mm. The maximum production in a single shot was registered for the smallest cathode radius, 41 mm, whereas the intermediate cathode radius, 45 mm, scored better in average. In all configurations, the neutrons per deuteron pair correlates fairly well with an estimation of the effective equilibrium temperature of the pinch, which suggests a prevalence of thermonuclear neutrons measured perpendicularly to the focus axis.
Neutron Correlations with Electrical Measurements in a Plasma Focus Device
Brazilian Journal of Physics, 2008
The measurement of the voltage between electrodes and the discharge current time derivative in Plasma Focus devices can be used to obtain important information on the neutron-producing pinch stage of the mentioned devices. The analysis of a 60-shots experimental run in a 5.7 kJ Mather-type device results in correlations suggesting that the neutron yield depends mostly on the average energy per particle delivered to the plasma during the pinch stage.
Journal of Physics D-applied Physics, 2008
Neutron emission from a deuterium plasma pinch generated in a very small plasma focus (6 mm anode diameter) operating at only tens of joules is presented. A maximum current of 50 kA is achieved 140 ns after the beginning of the discharge, when the device is charged at 50 J (160 nF capacitor bank, 38 nH, 20-30 kV, 32-72 J). Although the stored energy is very low, the estimated energy density in the plasma and the energy per particle in the plasma are of the same order as in higher energy devices. The dependence of the neutron yield on the filling pressure of deuterium was obtained for discharges with 50 and 67 J stored in the capacitor bank. Neutrons were measured by means of a system based on a 3 He proportional counter in current mode. The average neutron yield for 50 J discharges at 6 mbar was (1.2 ± 0.5) × 10 4 neutrons per shot, and (3.6 ± 1.6) × 10 4 for 67 J discharges at 9 mbar. The maximum energy of the neutrons was (2.7 ± 1.8) MeV. Possible applications related to substance detection and others are discussed.
Plasma Physics and Controlled Fusion, 2009
Published literature shows that the neutron yield of the plasma focus has been modeled in two papers using a thermonuclear mechanism. However, it is more widely held that plasma focus neutrons are produced mainly by nonthermalized mechanisms such as beam-target. Moreover these papers use several parameters which are adjusted for each machine until the computed neutron yield Y n data agree with measured Y n data. For this paper numerical experiments are carried out, using the Lee model code, incorporating a beam-target mechanism to compute the Y n versus pressure data of plasma focus devices PF-400 J and FN-II. The Lee model code is first configured for each of these two machines by fitting the computed current waveform against a measured current waveform. Thereafter all results are computed without adjusting any parameters. Computed results of Y n versus pressure for each device are compared with the measured Y n versus pressure data. The comparison shows degrees of agreement between the laboratory measurements and the computed results.
Dynamics and Density Measurements in a Small Plasma Focus of Tens-of-Joules-Emitting Neutrons
IEEE Transactions on Plasma Science, 2011
Dynamics in the radial phase and plasma conditions in the pinch phase have been studied using interferometry in a plasma focus device that operates in the range of tens of joules of stored energy in the capacitor bank and tens of kiloamperes, PF-50J. The results of these experiments using deuterium as filling gas, together with the simultaneous measurements of neutron production, are reported in this paper. The results show that the typical dynamics, pinch conditions, and electron density observed in larger machines are also present in this experiment operated at only tens of joules. Index Terms-Neutron emission, pinch plasma density, plasma focus (PF). I. INTRODUCTION T HE PF-50J is a small fast plasma focus (PF) device conceived to operate in the range of tens of joules and tens of kiloamperes. It has been constructed at the Chilean Nuclear Energy Commission, being an improved version of a previous design [1], [2]. The main electric characteristics of the device are as follows: 160-nF equivalent capacitance, ∼40-nH total inductance in a short circuit, 150-ns first quarter of a period, 25-30-kV charge voltage, energy E ∼ 50-72 J, and 50-70-kA peak current in a short circuit. In a PF, after that a plasma sheet is formed over the insulator surface, the plasma sheet first moves toward the anode end (axial phase) and then implodes on the anode axis (radial phase) [3]. The last is being accompanied by the pinch evidence given by the characteristic dip and peak in the current derivative and voltage
Optimized Design of Sub-kilo Joule Dense Plasma Focus and Measurement of Neutron Yield
Journal of Fusion Energy, 2020
This paper specifically talks about optimized design strategy of sub-kilo Joule Dense plasma focus (PF) fusion device in a full-fledged systematic manner. Recently, there are many pulsed power groups working in design and development of various PF devices in the range of sub-kilo joule energy. Few of them are publishing with the optimized operating parameters for the maximum neutron yield. Most of them, talks about the estimation of PF parameters based on traditional high voltage break down mechanisms in vacuum, plasma pinch behavior and neutron generation, which are optimized for higher energy level (few kJ to MJ) PF devices. It has been very tricky and iterative way to achieve maximum neutron yield for a sub kJ PF device. A conceptual design strategy is presented for estimation of four critical PF tube parameters. These four parameters are: Anode radius, cathode radius, effective anode length and insulator length. This is very important to know these parameters, in advance of actual fabrication and plasma pinch experiments. A 400 J PF device is designed and operated at 20 kV with the help of above design strategy in single go. Maximum neutron yield is measured 50% higher with wide range of deuterium gas pressure (6-12 mbar) among sub kJ PF devices. A detailed design strategy, experimental pulsed power system development, neutron measurement and results are discussed.
2005
The average total neutron yield is measured, using an indium foil activation detector, at various combinations of filling gas pressures (including the higher pressure operation regime) of deuterium, capacitor bank charging voltages, anode lengths and insulator sleeve lengths to optimize the neutron yield from the NX2 Plasma Focus device. A remarkable six-fold increase in the average maximum total neutron yield, to a record value of (7 ± 1) × 10 8 neutrons per shot, compared to the similar energy UNU-ICTP Plasma Focus device is achieved for deuterium at a relatively much higher filling gas pressure of 20 mbar. The average peak neutron energy for the axial direction (0˚), radial direction (90˚) and backward direction (180˚) is estimated to be 2.89 ± 0.25 MeV, 2.49 ± 0.20 MeV and 2.11 ± 0.12 MeV, respectively. The average forward to radial neutron yield anisotropy is found to be 1.46 ± 0.28. The neutron energy and anisotropy measurements suggest that the neutron production mechanism may be predominantly beam target.