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Akel M.,Syrian Atomic Energy Commission | Lee S.,Australian Institute for Plasma Focus Studies | Lee S.,Nanyang Technological University | Lee S.,INTI International University
Journal of Fusion Energy | Year: 2012

Numerical experiments are carried out systematically to determine the argon soft X-Ray yield Y sxr for optimized argon plasma focus with storage energy E0 from 1 kJ to 1 MJ. The ratio c = b/a, of outer to inner radii; and the operating voltage V0 are kept constant. E0 is varied by changing the capacitance C0. These numerical experiments were investigated on argon plasma focus at different operational gas pressures (0.41, 0.75, 1, 1.5, 2.5 and 3 Torr) for two different values of static inductance L0 (270 and 10 nH). Scaling laws on argon soft X-Ray yield, in terms of storage energies E 0, peak discharge current I peak and focus pinch current I pinch were found. It was found that the argon X-ray yields scale well with Y sxr = 8 × 10 -11I pinch 4.12 for the high inductance (270 nH) and Y sxr = 7 × 10 -13I pinch 4.94 for the low inductance (10 nH), (where yields are in joules and current in kilo amperes). While the soft X-ray yield scaling laws in terms of storage energies were found to be as Y sxr = 0.05 × E 0 0.94 at energies in the 1-100 kJ region. The scaling 'drops' as E 0 is increased, and Y sxr scales as Y sxr = 1.01 × E 0 0.33 at high energies towards 1 MJ for 10 nH at argon gas pressure of 1 Torr. The optimum efficiencies for SXR yield were found to be 0.00077% with a capacitor bank energy of 112.5 kJ for high inductance (270 nH) and 0.005% with a capacitor bank energy of 4.5 kJ for low inductance (10 nH). Therefore for larger devices, it may be necessary to operate at a higher voltage and use higher driver impedance to ensure increasing X-ray yield efficiency beyond the optimum values. As storage energy is changed the required electrode geometry for optimum yield is obtained and the resultant plasma pinch parameters are found. Required values of axial speed for argon soft X-ray emission were found to be in the range 11-14 cm/μs. © Springer Science+Business Media, LLC 2011. Source


Akel M.,Syrian Atomic Energy Commission | Lee S.,Australian Institute for Plasma Focus Studies | Lee S.,Nanyang Technological University | Lee S.,INTI International University
Journal of Fusion Energy | Year: 2012

For operation of the plasma focus in argon, a focus pinch compression temperature range of 1.4-5 keV (16.3 × 10 6-58.14 × 10 6 K) is found to be suitable for good yield of argon soft X-rays (SXR) Ysxr. This is based on reported temperature measurements of argon plasmas working at regime for X-ray output. Using this temperature window, numerical experiments have been investigated on AECS PF-2 plasma focus device with argon filling gas. The model was applied to characterize the 2.8 kJ plasma focus AECS PF-2. The optimum Ysxr was found to be 0.0035 J. Thus, we expect to increase the argon Ysxr of AECS PF-2, without changing the capacitor bank, merely by changing the electrode configuration and operating pressure. The Lee model code was also used to run numerical experiments on AECS PF-2 with argon gas for optimizing soft X-ray yield with reducing L 0, varying z0 and 'a'. From these numerical experiments we expect to increase the argon Ysxr of AECS PF-2 with reducing L 0, from the present computed 0.0035 J at L 0 = 270 nH to maximum value of near 0.082 J, with the corresponding efficiency is about 0.03%, at an achievable L 0 = 10 nH. © Springer Science+Business Media, LLC 2011. Source


Lee S.,INTI International University | Lee S.,Australian Institute for Plasma Focus Studies | Saw S.H.,INTI International University
Journal of Fusion Energy | Year: 2012

A current-step technique is applied to the plasma focus by modifying the Lee Model code, incorporating a current-step bank to add current to the focus pinch at the time of the current dip. For a 50 kV, 1 MJ, 6 μs risetime bank, the current-step from a 200 kV, 0.4 MJ, 0.8 μs rise-time bank maintains the pinch current at 2.2 MA, enhances compression by 1.9 and increases the neutron yield from 2.5 × 10 12 to 1.03 × 10 13. The increase is attributed mainly to the step nature of the current which favorably shifts the end-point of compression; rather than to the scaling in terms of energy or current. © Springer Science+Business Media, LLC 2012. Source


Lee S.,Australian Institute for Plasma Focus Studies | Lee S.,INTI International University | Lee S.,University of Malaya
Journal of Fusion Energy | Year: 2014

The code couples the electrical circuit with plasma focus (PF) dynamics, thermodynamics and radiation. It is energy-, charge- and mass-consistent and accounts for the effects of transit times of small disturbances and plasma self-absorption. It has been used in design and interpretation of Mather-type PF experiments and as a complementary facility to provide diagnostic reference numbers in all gases. Information computed includes axial and radial dynamics, SXR emission characteristics and yield for various applications including microelectronics lithography and optimization of machines. Plasma focus neutron yield calculations, current and neutron yield limitations, deterioration of neutron scaling (neutron saturation), radiative collapse, speed-enhanced PF, current-stepped PF and extraction of diagnostic and anomalous resistance data from current signals have been studied using the code; which also produces reference numbers for fluence, flux and energy of deuteron beams and ion beams for all gases. There has been no pause in its continuous evolution in three decades so much so that the model code has no formal source reference except www.plasmafocus.net. This review presents, for the first time a comprehensive up-to-date version of the 5-phase model code. The equations of each phase are derived. Those of the first two phases are normalized to reveal important scaling parameters. The focus pinch phase is discussed with radiation-coupled dynamics necessitating the computation of radiation terms moderated by plasma self-absorption. Neutron and ion beam yields are computed. The 5-phase model code appears to be adequate for all Mather-type PF, lacking only in one aspect that for high inductance PF (termed Type 2) the measured current waveform contains an extended dip which cannot be fitted by the 5-phase code; necessitating an extended 6-phase code. This sixth phase (termed phase 4a) is dominated by anomalous resistance, providing a way to extract valuable data on anomalous resistivity from the current trace. © 2014 Springer Science+Business Media New York. Source


Akel M.,Syrian Atomic Energy Commission | Lee S.,Australian Institute for Plasma Focus Studies | Lee S.,INTI International University
Journal of Fusion Energy | Year: 2013

Numerical experiments were carried out using 5-phase Lee model on different plasma focus devices with different filling gases. The relation of radiation power gain/loss terms as a function of temperature has been demonstrated. Variation of radial trajectories versus pressure with 0.1 Torr step has been investigated. Radiative collapse phenomena in plasma focus devices have been observed for heavy noble gases (Ar, Kr, Xe). Obtained results showed that the line radiation emission and tube voltage have huge values near the radiative collapse regime. © 2012 Springer Science+Business Media, LLC. Source

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