Correlation of measured neon soft X-ray pulses of the INTI plasma focus with the reflected shock phase at 12KV

The six-phase Lee Model Code is used to fit the computed current waveform to the measured waveform of the INTI Plasma Focus (PF;2.2 kJ at 12 kV), a T2 PF device, operated as a source of Neon soft X-ray (SXR) with optimum yield around 2.5 - 3 Torr of neon. The characteristic He-like and H-like neon line SXR pulse is measured using a pair of SXR detectors with selected filters that, by subtraction, have a photon energy window of 900 to 1550 eV covering the region of the characteristic neon SXR lines. The aim of this paper is to investigate the correlation between the time histories of the measured Neon soft X-ray pulse and the reflected shock phase of the computed current waveform which has been fitted to the measured current waveform. Results shows that the characteristic neon SXR measured at 3.17 J with a pulse duration of 249 ns starts typically after the radial inward shock phase and increases in magnitude few ns before the pinch phase. It tails unto the first anomalous resistance, and decays at the second anomalous resistance

Numerical Experiments Providing New Insights into Plasma Focus Fusion Devices

Recent extensive and systematic numerical experiments have uncovered new insights into plasma focus fusion devices including the following: (1) a plasma current limitation effect, as device static inductance is reduced towards very small values; (2) scaling laws of neutron yield and soft x-ray yield as functions of storage energies and currents; (3) a global scaling law for neutron yield as a function of storage energy combining experimental and numerical data showing that scaling deterioration has probably been interpreted as neutron ‘saturation’; and (4) a fundamental cause of neutron ‘saturation’. The ground-breaking insights thus gained may completely change the directions of plasma focus fusion research

Numerical Experiments Providing New Insights into Plasma Focus Fusion Devices

energie

Estimating Ratio of Peak to Uniform Values of Various profiles of relevance of Plasma Focus Pinch

In the Lee Model code for radiative plasma focus computation, both the density profile and the temperature profile (versus anode radius) of the pinch column are approximated by step functions with uniform values across the column radius. This means that the computed density and temperatures will be lower than the physical situation where the density and temperature profiles will certainly have peak values higher than the uniform (with radius) values of the step function. It has been shown that the density profile is side-peaked (somewhat shell-shaped or like the shape of a volcanic crater) with the assumption of no reflected shock wave; whereas the temperature profile is centre-peaked somewhat like a Gaussian shape. The aim of this paper is to investigate the use of higher degree mathematical function, where the crater-shaped profile can be well represented, to pproximate the plasma focus density profile. Two different approximated functions will be discussed: namely Gaussian distribution function and Bézier function. From these profiles we obtain the likely ratio of the profiled peak temperature to the step function uniform temperature and the peak density to the step function uniform density. In this manner we are able to suggest correction factors to the temperature and density computed by the Lee Model code

ESTIMATING RATIO OF PEAK TO UNIFORM VALUES OF VARIOUS PROFILES OF RELEVANCE TO PLASMA FOCUS PINCH COLUMNS

In the Lee Model code for radiative plasma focus computation, both the density profile and the temperature profile (versus anode radius) of the pinch column are approximated by step functions with uniform values across the column radius. This means that the computed density and temperatures will be lower than the physical situation where the density and temperature profiles will certainly have peak values higher than the uniform (with radius) values of the step function. It has been shown that the density profile is side-peaked (somewhat shell-shaped or like the shape of a volcanic crater) with the assumption of no reflected shock wave; whereas the temperature profile is centre-peaked somewhat like a Gaussian shape. The aim of this paper is to investigate the use of higher degree mathematical function, where the crater-shaped profile can be well represented, to pproximate the plasma focus density profile. Two different approximated functions will be discussed: namely Gaussian distribution function and Bézier function. From these profiles we obtain the likely ratio of the profiled peak temperature to the step function uniform temperature and the peak density to the step function uniform density. In this manner we are able to suggest correction factors to the temperature and density computed by the Lee Model code

Characterization of electron beams emitted from dense plasma focus machines using argon, neon and nitrogen

The measured current traces of two low energy machines namely the AECS PF-2 and INTI PF are used for studying of the produced electron beam features using the modified Lee code (RADPFV5.15REB) at different conditions. The fitting procedures between measured and computed current traces are made for each point of pressure. In the case of AECS PF-2 working with neon, the electron fluence reaches the maximum value 2.35 × 1022 electrons m-2 for 1.6 Torr and the flux achieves 2.42 × 1030 electrons m-2s-1 near 1.5 Torr. The electron number has a peak of 5.74 × 1014 at 0.9 Torr. The computed results demonstarte also the maximum value of the power flow density of 2.44 × 1016 Wm-2, and the superior damage factor of around 1.95 × 1012 Wm-2s0.5 at a pressure of 0.4 Torr. Argon presents the action of radiative cooling topping at highly magnified 6.13 × 1031 m-2s-1 at 0.9 Torr. The damage factor reaches almost 175 × 1012 Wm-2s0.5 for Ar but it is only 1.29 × 1012 Wm-2s0.5 for N2. The huge values for argon are a result of enhanced compression due to radiative cooling. In the case of INTI PF device, the electron energy extends from 58 keV (for N2) to 256 keV (for Ar). The results indicate that the electron fluence ranges from 2 × 1022 electrons m-2 for N2 to 88 × 1022 electrons m-2 for Ar

Effects of approximation and close-fitting technique of corona model on neon soft x-ray emission in 3-kJ plasma focus

In plasma focus (PF), the thermodynamic parameters such as ion fraction α, effective ionic charge number Zeff, and effective specific heat ratio γ at different temperatures may be calculated by corona model (CM). In the Lee model code, the neon Zeff and γ are stored in subroutines using convenient tables and polynomials derived from the CM (we call this approach approximated CM). In this paper, the thermodynamic parameters of the CM are close fitted to the data, thus replacing the approximate CM data with a more accurate close-fitting CM (CFCM). The comparisons of the Lee model code using the approximated CM and CFCM subroutines are conducted, with the main emphasis on optimum neon soft X-ray (SXR) emission and their properties. The suitable focus pinch temperature window of 200-500 eV is applied to generate the optimum neon SXR yield (Ysxr). The optimum neon Ysxr is found to be 3.19 and 3.49 J at the optimum pressure P0 = 3.1 torr with approximated CM and CFCM subroutines, respectively. A high optimum value of SXR yield is obtained using CFCM subroutines in the Lee model, which is nearer to the experimental value compared with the approximated CM subroutines. The use of CFCM in the Lee model contributes to better estimation for further numerical experiment studies and gives confidence that the model is sufficiently realistic in describing the PF dynamics and SXR emission