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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.


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.


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.


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 are carried out systematically to determine the nitrogen soft X-ray yield for optimized nitrogen plasma focus with storage energy E0 from 1 to 200 kJ. Scaling laws on nitrogen soft X-ray yield, in terms of storage energies E0, peak discharge current I peak and focus pinch current Ipinch were found. It was found that the nitrogen X-ray yields scales on average withysxr,N = 1.93 × E01.21J (E0 in kJ) with the scaling showing gradual deterioration as E0 rises over the range. A more robust scaling is Ysxr = 8 ×10-8I pinch3.38. The optimum nitrogen soft X-ray yield emitted from plasma focus is found to be about 1 kJ for storage energy of 200 kJ. This indicates that nitrogen plasma focus is a good water-window soft X-ray source when properly designed. © 2012 Springer Science+Business Media, LLC.


Akel M.,Syrian Atomic Energy Commission | Lee S.,Australian Institute for Plasma Focus Studies | Lee S.,INTI International University | Saw S.H.,Australian Institute for Plasma Focus Studies | Saw S.H.,INTI International University
IEEE Transactions on Plasma Science | Year: 2012

We adapted the Lee Model code as a branch version RADPF5.15K to gases of special interest to us, namely, nitrogen and oxygen and applied numerical experiments specifically to our AECS PF-1 and AECS PF-2. We also generalized the numerical experiments to other machines and other gases to look at scaling laws and to explore recently uncovered insights and concepts. The required thermodynamic data of nitrogen, oxygen, neon, and argon gases (ion fraction, the effective ionic charge number, the effective specific heat ratio) were calculated, the X-ray emission properties of plasmas were studied, and suitable temperature range (window) for generating H-and He-like ions (therefore soft X-ray emissions) of different species of plasmas were found. The code is applied to characterize the AECS-PF-1 and AECS-PF-2, and for optimizing the nitrogen, oxygen, neon, and argon SXR yields. In numerical experiments we show that it is useful to reduce static inductance L0 to a range of 15-25 nH; but not any smaller. These yields at diverse wavelength ranges are large enough to be of interest for applications. Scaling laws for argon and nitrogen SXR were found. Model parameters are determined by fitting computed with measured current waveforms in neon for INTI PF and in argon for the AECS PF-2. Radiative cooling effects are studied indicating that radiative collapse may be observed for heavy noble gases (Ar, Kr, Xe) for pinch currents even below 100 kA. The creation of the consequential extreme conditions of density and pulsed power is of interest for research and applications. © 2012 IEEE.


Lee S.,INTI International University | Lee S.,Australian Institute for Plasma Focus Studies | Saw S.H.,INTI International University | Saw S.H.,Australian Institute for Plasma Focus Studies | Ali J.,University of Technology Malaysia
Journal of Fusion Energy | Year: 2013

The Plasma Focus has wide-ranging applications due to its intense radiation of SXR, XR, electron and ion beams and fusion neutrons when operated in deuterium. The 5-phase Lee Model code has been developed for the focus operated in various gases including D, D-T, He, Ne, N, O, Ar, Kr and Xe. Radiation-coupled motion is included in the modelling. In this paper we look at the effect of radiation cooling and radiation collapse in krypton. The Pease-Braginskii current is that current flowing in a hydrogen pinch which is just large enough for the Bremsstrahlung to balance Joule heating. This radiation-cooled threshold current for a hydrogen pinch is 1.6 MA. It is known that in gases undergoing line radiation strongly the radiation-cooled threshold current is considerably lowered. We show that the equations of the Lee Model code may be used to compute this lowering. The code also shows the effect of radiation cooling leading to radiative collapse. Numerical experiments based on experimentally fitted model parameters are run to demonstrate a regime in which radiation collapse is observed in Kr at a pinch current of 50-100 kA. © 2012 Springer Science+Business Media, LLC.


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.


Lee S.,INTI International University | Lee S.,Australian Institute for Plasma Focus Studies | Lee S.,University of Malaya | Saw S.H.,INTI International University | Saw S.H.,Australian Institute for Plasma Focus Studies
Physics of Plasmas | Year: 2012

Measurements on plasma focus ion beams include various advanced techniques producing a variety of data which has yet to produce benchmark numbers [A Bernard, J. Mosc. Phys. Soc. 8, 93-170 (1998)]. This present paper uses the Lee Model code [S Lee, http://www.plasmafocus.net (2012)], integrated with experimental measurements to provide the basis for reference numbers and the scaling of deuteron beams versus stored energy E0. The ion number fluence (ions m-2) and energy fluence (J m-2) computed as 2.4-7.8 × 1020 and 2.2-33 × 106, respectively, are found to be independent of E0 from 0.4 to 486 kJ. Typical inductance machines (33-55 nH) produce 1.2-2 × 1015 ions per kJ carrying 1.3%-4% E0 at mean ion energy 50-205 keV, dropping to 0.6 × 1015 ions per kJ carrying 0.7% E0 for the high inductance INTI PF. © 2012 American Institute of Physics.


Lee S.,INTI International University | Lee S.,Australian Institute for Plasma Focus Studies | Lee S.,University of Malaya | Saw S.H.,INTI International University | Saw S.H.,Australian Institute for Plasma Focus Studies
Physics of Plasmas | Year: 2013

A recent paper derived benchmarks for deuteron beam fluence and flux in a plasma focus (PF) [S. Lee and S. H. Saw, Phys. Plasmas 19, 112703 (2012)]. In the present work we start from first principles, derive the flux equation of the ion beam of any gas; link to the Lee Model code and hence compute the ion beam properties of the PF. The results show that, for a given PF, the fluence, flux, ion number and ion current decrease from the lightest to the heaviest gas except for trend-breaking higher values for Ar fluence and flux. The energy fluence, energy flux, power flow, and damage factors are relatively constant from H 2 to N2 but increase for Ne, Ar, Kr and Xe due to radiative cooling and collapse effects. This paper provides much needed benchmark reference values and scaling trends for ion beams of a PF operated in any gas. © 2013 AIP Publishing LLC.


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.

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