DR SAW SOR HEOH

Pro Vice-Chancellor, Office of Education, Quality and Innovation (EQI)

Director, Centre for Plasma Research (CPR)

INTI International University

List of journal articles published

2014

1. Lee, S., Saw, S.H., Hegazy, H., Ali, Jalil, Damide, V., Fatis, N., Kariri, H., Khabrani, A., Mahasi, A. “Some generalized Characteristics of the Electro-dynamics of the Plasma Focus in Its Axial Phase: Illustrated by an Application to Independently Determine the Drive Current Fraction and the Mass Swept-Up Fraction.” Journal of Fusion Energy, Vol. 33, Issue 3 (June 2014): 235-241.

2. Akel, M., Salo, S.A., Saw, S.H., Lee,S. “Properties of ion beams generated by nitrogen plasma focus.” Journal of Fusion Energy, Vol.33, Issue 2 (April 2014): 189-197

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3. Saw,S.H., Chong, P.L., Rawat, R.S., Ching, C.T.L., Lee, P., Talebitaher, A., Lee, S. “The effect of specific heat ratio on neutron yield.” IEEE Transactions on Plasma Science, Vol.42, Issue 1 (January 2014): 99-104.

2013

1. Saw, S.H., Rawat, R.S., Lee, P., Talebitaher, A., Abdou, A.E., Chong, P.L., Roy, F., Ali, J., Lee, S. “SXR measurements in INTI PF operated in neon to identify typical (normal n) profile for shots with good yield.” IEEE Transactions on Plasma Science, Vol.41, Issue 11 (2013): 3166-3172. Article number 6612699.

2. Lee, S., Saw, S.H. “Plasma focus ion beam fluence and flux – For various gases.” Physics of Plasmas, Vol.20, Issue 6 (June 2013). Article number 062702.

3. Lee, S. , Saw, S.H., Ali, J. “Numerical experiments on radiative cooling and collapse in plasma focus operated in Krypton.” Journal of Fusion Energy, Vol.32, Issue 1 (2013): 42-49.

4. Lee, S., Saw, S.H., Lee, P., Rawat, R.S., Devi, K. “Magnetic Reynolds number and neon current sheet structure in the axial phase of a plasma focus.” Journal of Fusion Energy, Vol.32, Issue 1 (2013): 50-55.

2012

1. Lee, S., Saw, S.H. “Current-step technique to enhance plasma focus compression and neutron yield.” Journal of Fusion Energy, Vol.31, Issue 6 (December 2012): 603-610.

2. Lee, S., Saw, S.H. “The plasma focus-trending into the future.” International Journal of Energy Research, Vol.36, Issue 15 (December 2012): 1366-1374.

3. Lee, S., Saw, S.H. “Plasma focus ion beam fluence and flux-Scaling with stored energy.” Physics of Plasmas, Vol.19, Issue 11 (November 2012). Article number 112703.

4. Saw, S.H., Akel, M., Lee, P.C.K., Ong, S.T., Mohamad, S.N., Ismail, F.D., Nawi, N.D., Devi, K., Sabri, R.M., Baijan, A.H., Ali, J., Lee, S. “Magnetic probe measurements in INTI plasma focus to determine dependence of axial speed with pressure in neon.” Journal of Fusion Energy, Vol.31, Issue 5 (October 2012): 411-417.

5. Abdou, A.E., Ismail, M.I., Mohamed, A.E., Lee, S., Saw, S.H., Verma, R. “Preliminary results of Kansas State University dense plasma focus.” IEEE Transactions on Plasma Science, Vol.40, Issue 10 PART 2 (2012): 2741-2744. Article number 6280679.

6. Mohamed, A.E., Abdou, A.E., Ismail, M.I., Lee, S., Saw, S.H. “Current sheet axial dynamics of 2.5-kJ KSU-DPF under high-pressure regime.” IEEE Transactions on Plasma Science, Vol.40, Issue 10 PART 2 (2012): 2736-2740. Article number 6269936.

7. Javadi, S., Habibi, M., Ghoranneviss, M., Lee, S., Saw, S.H., Behbahani, R.A. “Investigation of structural properties of chromium thin films prepared by a plasma focus device.” Physica Scripta, Vol.86, Issue 2 (August 2012). Article number 025801.

8. Lee, S., Saw, S.H., Rawat, R.S., Lee, P., Verma, R., Talebitaher, A., Hassan, S.M., Abdou, A.E., Ismail, M., Mohamed, A., Torreblanca, H., Al Hawat, Sh., Akel, M., Chong, P.L., Roy, F., Singh, A., Wong, D., Devi, K. “Measurement and processing of fast pulsed discharge current in plasma focus machines.” Journal of Fusion Energy, Vol.31, Issue 2 (April 2012): 198-204.

9. Al-Hawat, Sh., Akel, M., Lee, S., Saw, S.H. “Model parameters versus gas pressure in two different plasma focus devices operated in Argon and Neon.” Journal of Fusion Energy, Vol.31, Issue 1 (February 2012): 13-20.

2011

1. Lee, S., Saw, S.H., Rawat, R.S., Lee, P., Talebithaer, A., Abdou, A.E., Chong, P.L., Roy, F.A., Singh, A., Wong, D., Devi, K. “Correlation of measured soft X-ray pulses with modeled dynamics of the plasma focus.” IEEE Transactions on Plasma Science, Vol.39, Issue 11 PART 3 (November 2011): 3196-3202. Article number 6029306.

2. Lee, S., Saw, S.H. “Nuclear fusion energy-mankind’s giant step forward.” Journal of Fusion Energy, Vol.30, Issue 5 (October 2011): 398-403.

3. Lee, S., Saw, S.H., Abdou, A.E., Torreblanca, H. “Characterizing plasma focus devices – Role of the static inductance – Instability phase fitted by anomalous resistances.” Journal of Fusion Energy, Vol.30, Issue 4 (August 2011): 277-282.

4. Saw, S.H., Lee, S. “Scaling the plasma focus for fusion energy considerations.” International Journal of Energy Research, Vol.35, Issue 2 (February 2011): 81-88.

2010

1. Akel, M., Al-Hawat, Sh., Saw, S.H., Lee, S. “Numerical experiments on oxygen soft X-ray emissions from low energy plasma focus using Lee model.” Journal of Fusion Energy, Vol.29, Issue 3 (June 2010): 223-231.

2. Saw, S.H., Lee, S., Roy, F., Chong, P.L., Vengadeswaran, V., Sidik, A.S.M., Leong, Y.W., Singh, A. “In situ determination of the static inductance and resistance of a plasma focus capacitor bank.” Review of Scientific Instruments, Vol.81, Issue 5 (May 2010). Article number 053505.

3. Lee, S., Saw, S.H. “Numerical experiments providing new insights into plasma focus fusion devices.” Energies, Vol.3, Issue 4 (April 2010): 711-737. (Full text open access)

2009

1. Lee, S., Saw, S.H., Lee, P., Rawat, R.S. “Numerical experiments on plasma focus neon soft x-ray scaling.” Plasma Physics and Controlled Fusion, Vol.51, Issue 10 (2009). Article number 105013. (Full text open access)

2. Lee, S., Rawat, R.S., Lee, P., Saw, S.H. “Soft x-ray yield from NX2 plasma focus.” Journal of Applied Physics, Vol.106, Issue 2 (2009). Article number 023309.

3. Lee, S., Saw, S.H., Soto,L., Springham, S.V., Moo, S.P. “Numerical experiments on plasma focus neutron yield versus pressure compared with laboratory experiments.” Plasma Physics and Controlled Fusion, Vol.51, Issue 7 (2009). Article number 075006. (Full text open access)

4. Saw,S.H., Lee, P.C.K., Rawat, R.S., Lee, S. “Optimizing UNU/IC TP PFF plasma focus for neon soft X-ray operation. IEEE Transactions on Plasma Science, Vol.37, Issue 7 PART 2 (2009): 1276-1282.

5. Lee, S., Saw, S.H. “Response to “Comment on ‘Pinch current limitation effect in plasma focus’” [Appl. Phys. Lett. 94, 076101 (2009)] - Review.” Applied Physics Letters, Vol.94, Issue 7 (2009). Article number 076102.

2008

1. Lee, S., Saw, S.H. “Neutron scaling laws from numerical experiments.” Journal of Fusion Energy, Vol.27, Issue 4 (December 2008): 292-295.

2. Lee, S., Lee, P., Saw, S.H., Rawat, R.S. “Numerical experiments on plasma focus pinch current limitation.” Plasma Physics and Controlled Fusion, Vol.50, Issue 6, (June 2008). Article number 065012. (Full text open access)

3. Lee, S., Saw, S.H., Lee, P.C.K., Rawat, R.S., Schmidt, H. “Computing plasma focus pinch current from total current measurement.” Applied Physics Letters, Vol.92, Issue 11 (2008). Article number 111501.

4. Lee, S., Saw, S.H. “Pinch current limitation effect in plasma focus.” Applied Physics Letters, Vol.92, Issue 2 (2008). Article number 021503.

Abstract

Properties of ion beams generated by nitrogen plasma focus

Akel, M., Salo, S.A., Saw, S.H., Lee,S. (2014)

Numerical experiments have been systematically carried out using the modified Lee model code on various plasma focus devices operated with nitrogen gas. The ion beam properties (ion beam energy, ion beam flux, ion beam fluence, beam ion number, ion beam current, power flow density, and damage factor) of the plasma focus have been studied versus gas pressure for each plasma focus device. The results show that, for these studied plasma focus devices, the mean ion energies decrease with increasing gas pressure, while the beam ion number increases with higher pressure. The fluence, flux, ion current, power flow density and damage factor have maximum values at the optimum pressure. It is shown that, the maximum power flow densities range from 10¹² to 10¹⁴ W m^-2 and the damage factor values reach almost 10⁹-10¹¹ W m^-2s^0.5. The obtained results provide much needed benchmark reference values and scaling trends for ion beams of a plasma focus operated in nitrogen gas. These results could be used as an indicator for ion properties emitted from nitrogen plasma focus for various applications including material processing. © 2013 Springer Science+Business Media New York.

Source : Journal of Fusion Energy

Document type : Article

Source type : Journal

Keywords: Ion beam properties; Lee model; Nitrogen gas; Plasma focus

The effect of specific heat ratio on neutron yield

Saw,S.H., Chong, P.L., Rawat, R.S., Ching, C.T.L., Lee, P., Talebitaher, A., Lee, S. (2014)

It is known that the radius ratio of a plasma pinch depends on the specific heat ratio γ of the pinch plasma, where radius pinch ratio is defined as: radius of plasma pinch column/radius of anode. The lower the specific heat ratio the lower would be the pinch radius ratio with corresponding increased compression and pinch density. The deuterium plasma focus pinch is invariably fully ionized and has a specific heat ratio of practically the highest possible value of 5/3. If the deuterium plasma focus could have its specific heat ratio reduced below 5/3 we might expect its radius ratio to be correspondingly reduced, increasing the pinch density, thus improving the D-D fusion neutron yield. To demonstrate this effect we run the Lee model code in deuterium but hypothetically fix the specific heat ratio, reducing it at each run. The results show that indeed the radius ratio is reduced, increasing the compression, and the neutron yield is substantially increased. The effect is used to explain the observed neutron yield enhancement when a deuterium plasma focus doped with a small amount of krypton. © 1973-2012 IEEE.

Source : IEEE Transactions on Plasma Science

Document type : Article

Source type : Journal

Keywords: Deuterium: Lee model code; neutron yield; plasma pinching effect; specific heat ratio

SXR measurements in INTI PF operated in neon to identify typical (normal n) profile for shots with good yield

Saw, S.H., Rawat, R.S., Lee, P., Talebitaher, A., Abdou, A.E., Chong, P.L., Roy, F., Ali, J., Lee, S. (2013)

The six-phase Lee model code was developed to compute the anomalous resistance phase (RAN) following the pinch phase in a plasma focus (PF) discharge. One important method to check such modeling is to look at the soft X-ray (SXR) emission time profile and to correlate this to the PF dynamics. A two-channel filtered SXR spectrometer coupled with an Excel-based analytical template was recently developed to speed up the correlation process. Using this system, we have determined that the neon PF typically operates in a normal (N) mode in which it emits characteristic He-like H-like neon line SXR (in a photon energy window of 900-1550 eV) reproducibly and efficiently. The characteristic neon line SXR pulse straddles the pinch duration starting strongly 10 ns before the start of the pinch, then diminishes through the 10-ns pinch and tails off into the subsequent RAN1 phase. We present the correlated time profiles of shots operating in the efficient N mode as well as, for comparison, poor shots, which are distinctly different in SXR time profiles. The profiles indicate the difference in dynamics of normal and poor shots. Statistics are presented as well as comparison of the yields from the numerical experiments and measurements. In the series that were studied the proportion of N-mode operation ranges from 70% in one series to 80% in another series over pressure range 1-4 torr. At 2 torr, it was found that 90% recorded the normal N profile. The results reinforce the view that while the Lee Model code incorporates the correct physics in its sequence of phases, refinement is needed to extend the radiative phase to the period before the pinch. © 2013 IEEE.

Source : IEEE Transactions on Plasma Science

Document type : Article

Source type : Journal

Keywords: Neon soft X-rays (SXRs); plasma focus (PF); plasma focus (PF) modeling; soft X-ray (SXR) measurements

Plasma focus ion beam fluence and flux – For various gases

Lee, S., Saw, S.H. (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.

Source : Physics of Plasmas

Document type : Article

Source type : Journal

Keywords: Beam properties; Deuteron beams; Energy fluences; Flux equations; Radiative cooling

Numerical experiments on radiative cooling and collapse in plasma focus operated in Krypton

Lee, S. , Saw, S.H., Ali, J. (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.

Source : Journal of Fusion Energy

Document type : Article

Source type : Journal

Keywords: Plasma focus; Plasma focus modeling; Plasma focus radiation; Radiative collapse; Radiative cooling

Magnetic Reynolds number and neon current sheet structure in the axial phase of a plasma focus

Lee, S., Saw, S.H., Lee, P., Rawat, R.S., Devi, K (2013)

The Magnetic Reynolds Number (MRN) in neon is computed as a function of Neon shock speed. The magnetic field profiles at various positions in the axial run down phase of the INTI Plasma Focus device are measured over a range of pressures from 2 to 20 Torr. These profiles are assessed for good electromagnetic coupling including measuring the current per unit current sheet thickness as a comparative measure of current sheet diffusion. It was found that at an axial current sheet speed of over 3.5 cm/μs (corresponding to MRN > 15), the current sheet has a compact profile with current density of 55 kA/cm of sheet thickness whereas at speeds below 2.8 cm/μs (corresponding to MRN < 10) the profile is more diffuse with current density less than 30 kA/cm of sheet thickness. Based on these studies it is proposed to take a speed of 3 cm/μs corresponding to an MRN of 10 as the minimum speed of neon current sheet below which the electromagnetic coupling begins to weaken. © 2012 Springer Science+Business Media, LLC.

Source : Journal of Fusion Energy

Document type : Article

Source type : Journal

Keywords: Current sheet diffusion; Magnetic Reynold Number; Plasma focus device; Shock speed

Current-step technique to enhance plasma focus compression and neutron yield.

Lee, S., Saw, S.H. (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 : Journal of Fusion Energy Document type : Article Source type : Journal Keywords: Current-step plasma focus; Focus pinch compression enhancement; Neutron enhancement technique; Plasma focus modeling; Plasma focus new technology The plasma focus-trending into the future Lee, S., Saw, S.H. (2012) The plasma focus is a promising small-scale alternative to the huge Tokamak project in the development of nuclear fusion energy. Its strength lies in the characteristic that the plasma condition is the same whether the plasma focus is a small sub-kilojoule machine or a large one with thousands of kilojoules of stored energy and the related constancy of the dynamic resistance. Yet, this strength turns out to result in a weakness. The observed neutron 'saturation' is more correctly stated as a 'scaling deterioration' effect. This critical weakness is due to the same constancy of the plasma condition intimately related to a constancy of the dynamic resistance. The understanding of this situation points to a new class of plasma focus devices to overcome the 'saturation' of the electric current. Plasma focus technology has to move to ultra high voltage technology and take advantage of circuit manipulation techniques in order to move into a new era of high performance. This paper examines fundamental scaling properties of the plasma focus including speeds, temperatures, dimensions and times. It links up these basic scaling characteristics with the crucial ideas of the inherent yield scaling deterioration, thus providing a clear understanding of its overall performance characteristics, paving the way for future exploitation. © 2011 John Wiley & Sons, Ltd. Source : International Journal of Energy Research Document type : Article Source type : Journal Keywords: Neutron saturation; New plasma focus devices; Nuclear fusion; Plasma focus; Plasma focus properties; Plasma focus scaling Plasma focus ion beam fluence and flux-Scaling with stored energy Lee, S., Saw, S.H. (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 × 10^20 and 2.2-33 × 10^6, respectively, are found to be independent of E0 from 0.4 to 486 kJ. Typical inductance machines (33-55 nH) produce 1.2-2 × 10^15 ions per kJ carrying 1.3%-4% E0 at mean ion energy 50-205 keV, dropping to 0.6 × 10^15 ions per kJ carrying 0.7% E0 for the high inductance INTI PF. © 2012 American Institute of Physics. Source : Physics of Plasmas Document type : Article Source type : Journal Keywords: Deuteron beams; Energy fluences; Experimental measurements; Fluences; Ion energies; Lee model; Plasma focus Magnetic probe measurements in INTI plasma focus to determine dependence of axial speed with pressure in neon Saw, S.H., Akel, M., Lee, P.C.K., Ong, S.T., Mohamad, S.N., Ismail, F.D., Nawi, N.D., Devi, K., Sabri, R.M., Baijan, A.H., Ali, J., Lee, S. (2012) Current sheath dynamics generated in INTI plasma focus device operated with neon gas has been studied. A 3-Turn Rogowski coil design has been used to measure derivative current. A new magnetic probe was designed and used to study of current sheath arrival time, current profile and velocity variation in the axial phase at different experimental conditions. The current sheath's average velocity was found to vary with pressure-0.51 with a R2 value of 0.9 which agrees well with the theoretically expected variation of pressure ^-0.5. © Springer Science+Business Media, LLC 2011. Source : Journal of Fusion Energy Document type : Article Source type : Journal Keywords: Current sheath; INTI plasma focus device; Magnetic probe; Neon gas Preliminary results of Kansas State University dense plasma focus Abdou, A.E., Ismail, M.I., Mohamed, A.E., Lee, S., Saw, S.H., Verma, R. (2012) Kansas State University (KSU) dense plasma focus (DPF) is a 2.5-kJ DPF machine newly commissioned at the Plasma Radiation Physics Laboratory at KSU. The machine was designed to be used as a multiradiation source for applications in nuclear science and engineering. Neutrons are emitted from deuterium-deuterium (D-D) fusion reactions during high-power electric discharges at 17 kV, 140 kA, and 5 mbar. The machine circuit parameters were calculated using the short-circuit test. The emitted neutrons were measured using several radiation detection techniques. The 2.45-MeV characteristic D-D neutron energy was confirmed using the time-of-flight technique using a BC-418 plastic scintillator. The maximum neutron yield was roughly measured to be 2.8 x10 ^8 neutrons per shot using a set of BTI BD-PND bubble detectors. Moreover, the neutron yield variation with pressure was measured and compared with the computed neutron yield using Lee model. Finally, the measured current showed good agreement with Lee six-phase model. © 2012 IEEE. Source : IEEE Transactions on Plasma Science Document type : Article Source type : Journal Keywords: Dense plasma focus (DPF); Lee model; Multiradiation source; Neutron yield Current sheet axial dynamics of 2.5-kJ KSU-DPF under high-pressure regime Mohamed, A.E., Abdou, A.E., Ismail, M.I., Lee, S., Saw, S.H. (2012) In dense plasma focus (DPF) machines, the high-pressure (HP) regime of operation can be used as alternative technique to short-circuit (SC) test as the current sheet motion is minimal. The SC test was performed to get the right values for the static parameters of the machine. HP shots of more than 30 mbar were performed on the 2.5-kJ Kansas State University DPF machine to determine the deviation of HP values from SC values in computed static inductance and resistance. The test was performed using various gases over a wide range of molecular/atomic mass, starting from hydrogen as the lightest gas up to argon. It was found that the deviation in static inductance and resistance computed from HP method is inversely proportional to gas molecular mass at a certain pressure. The heavy gases like neon and argon were found to give the most accurate results. At 60 mbar of argon, the inductance deviation was 6.5%, and the resistance deviation was 14%. It was found also that increasing gas pressure over 30 mbar using heavy gases like Ar or Ne gives no effective improvement on the computed static impedance. Snowplow model was used to predict the axial position and the axial speed of the current sheet during the HP regime. The model showed that the average axial speed in heavy gases like argon was 0.8 cm/μ whereas in hydrogen, it was 1.6 cmμ. © 2012 IEEE. Source : IEEE Transactions on Plasma Science Document type : Article Source type : Journal Keywords: Axial speed; High-pressure (HP) discharge; Plasma focus; Plasma resistance; Snowplow model; Static inductance Investigation of structural properties of chromium thin films prepared by a plasma focus device Javadi, S., Habibi, M., Ghoranneviss, M., Lee, S., Saw, S.H., Behbahani, R.A. (2012) We report the synthesis of chromium thin films on Si(400) substrates by utilizing a low-energy (1.6kJ) plasma focus device. The films of chromium are deposited with different numbers of focus shots (15, 25 and 35) at a distance of 8cm and at 0° angular position with respect to the anode axis. The films are investigated structurally by x-ray diffraction analysis and morphologically by atomic force microscopy and scanning electron microscopy. The elemental composition is characterized by energy dispersive x-ray analysis. Furthermore, Vicker's micro hardness is used to study the mechanical properties of the deposited films. The degree of crystallinity of chromium films, the size of the particles and the hardness values of the films increase when the number of focus shots is raised from 15 to 25 and then decrease when the substrate is treated with 35 shots. We discuss the dynamic processes involved in the formation of the chromium films. © 2012 The Royal Swedish Academy of Sciences. Source : Physica Scripta Document type : Article Source type : Journal Keywords: Angular positions; Chromium film; Chromium thin films; Degree of crystallinity; Deposited films; Dynamic process; Elemental compositions; Energy dispersive x-ray; Hardness values; Low energies; Plasma focus devices Measurement and processing of fast pulsed discharge current in plasma focus machines Lee, S., Saw, S.H., Rawat, R.S., Lee, P., Verma, R., Talebitaher, A., Hassan, S.M., Abdou, A.E., Ismail, M., Mohamed, A., Torreblanca, H., Al Hawat, Sh., Akel, M., Chong, P.L., Roy, F., Singh, A., Wong, D., Devi, K. (2012) The fast pulsed electric discharge current drives all physical processes in the plasma focus device; in turn all physical processes in the focus affect the current waveform. Thus the discharge current waveform is the most important indicator of plasma focus performance. This underlies the importance of properly measuring, processing and interpreting the discharge current waveform. This paper reports the measurement of fast pulsed discharge current by the Rogowski coil, in two different modes: the current transformer, "I" mode, and current derivative, "Idot" mode. The processing and interpretation of recorded current waveform to obtain useful information about the physical processes in the plasma focus device are discussed. The current transformer with a large number of turns and a sub-1 Ohm terminator has good high frequency response, necessary for the sharp current dip region when dI/dt exceeds 2 × 10 ^11 A/s. However the signal is "noisy" in the current dip region. Several methods to extract the current dip from the noise are discussed and examples of how low pass filters affect the signals are shown. The dI/dt coil, the Rogowski coil in "Idot" mode, with a few turns terminated by 50-Ohm is also described. Integrating the 1 GSa/s digital waveform does remove the high frequency noise components, yet the extracted waveform shows sharp angular features indicative of the retention of short-time features. This makes the dI/dt coil superior to the current transformer. A 7-turn coil is tested against the Lee Model code and found to be suitable to measure the plasma focus discharge current. © Springer Science+Business Media, LLC 2011. Source : Journal of Fusion Energy Document type : Article Source type : Journal Keywords: Lee Model code; Plasma focus; Pulsed current measurements; Rogowski coil Model parameters versus gas pressure in two different plasma focus devices operated in Argon and Neon Al-Hawat, Sh., Akel, M., Lee, S., Saw, S.H. (2012) For the plasma focus device AECS PF-2 operated in Ar and INTI PF in Ne, model parameters of mass and current in the axial phase of plasma focus were found by matching the measured and calculated current waveforms over a range of pressures. The results show a value of f m = 0.05 ± 0.01 over 0.2-1.2 Torr in Ar; and fm = 0.04 ± 0.01 over 0.7-4.1 Torr in Neon. The value of f c = 0.7 was fitted for all cases. Combining these results with those published for several other small machines it would appear that, where measured current waveforms are not available for example in designing new machines, a good compromise would be to take a guideline value of f m = 0.05 and f c = 0.7 for both Argon and Neon. © Springer Science+Business Media, LLC 2011. Source : Journal of Fusion Energy Document type : Article Source type : Journal Keywords: Argon; Lee model; Model parameters; Neon; Plasma focus device Correlation of measured soft X-ray pulses with modeled dynamics of the plasma focus Lee, S., Saw, S.H., Rawat, R.S., Lee, P., Talebithaer, A., Abdou, A.E., Chong, P.L., Roy, F.A., Singh, A., Wong, D., Devi, K. (2011) The six-phase Lee model code is used to fit the computed current waveform to the measured current waveform of 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 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, has a photon energy window of 900 to 1550 eV covering the region of the characteristic neon SXR lines. From the analysis of the fitted current and the measured SXR pulses, the characteristic neon SXR pulses are correlated to the pinch dynamics, and the subsequent slightly harder SXR pulses are correlated to the anomalous resistance phase. The characteristic neon SXR yield is measured; the pulse has a duration of 25 ns. The characteristic neon SXR typically starts 10 ns before the pinch phase and continues through the end of the 10-ns pinch phase, tailing into the anomalous resistance phase. Harder SXR pulses, probably Bremsstrahlung, are correlated to the anomalous resistance phase, with the main pulse occurring nearly 200 ns after the characteristic neon SXR pulse. © 2006 IEEE. Source : IEEE Transactions on Plasma Science Document type : Article Source type : Journal Keywords: Neon soft X-rays (SXR); PF modeling; plasma focus (PF) dynamics; SXR measurements Nuclear fusion energy-mankind’s giant step forward Lee, S., Saw, S.H. (2011) Estimates of energy supply versus consumption indicate the middle of this century as the critical point when world energy supply will no longer keep pace with the demand. The demand grows inexorably because of both the world population growth as well as the growth of average per capita energy consumption. Technological and economic progress are closely correlated with per capita energy consumption. Hence the inadequacy of energy supplies will limit the progress of human civilization, stifling its soaring spirit. Conservationism, making incremental improvements in this situation, is completely inadequate. What is needed is a giant step-the development of a new, limitless, clean source of energy-nuclear fusion energy. Nuclear fusion technology, when perfected to fusion-burn only deuterium, will have a fuel supply lasting millions of year, even with continuing energy consumption growth as in the past. Intensive efforts in five decades of Tokamak research has advanced the fusion product up by 10 ^7 times, to the point when breakeven is only a step away. The next step necessarily involves international collaboration on an unprecedented scale in ITER-the International Thermonuclear Experimental Reactor, on which work has started in Cadarache France. ITER and later Demo are envisioned to bring online the first commercial nuclear fusion energy reactor by 2050. Using this as the starting point and the history of the uptake of nuclear fission reactors as a guide, a scenario is described here which depicts a not unreasonable rapid take up of nuclear fusion energy starting after the middle of this century. Just into the next century fusion energy should be able to take up the slack and allow Mankind to continue its progress and growth. Because the development of fusion energy is such a complex technological task it is probable that there will be several decades when the constraints of energy shortage will be severely felt as shown by the flattening of the energy consumption from around 2040 to 2100. Such a period of stagnation seems unavoidable even with the envisaged development and rapid adoption of fusion energy. On the other hand without nuclear fusion energy the scenario depicts a severe downturn unavoidably in the fortunes of Mankind with world population shrinking below 5 billion and eventually even lower. © 2011 Springer Science+Business Media, LLC. Source : Journal of Fusion Energy Document type : Article Source type : Journal Keywords: Nuclear fusion energy; World energy consumption; World energy supplies; World population Characterizing plasma focus devices – Role of the static inductance – Instability phase fitted by anomalous resistances Lee, S., Saw, S.H., Abdou, A.E., Torreblanca, H. (2011) Plasma focus devices with low static inductance L 0 (type T1) are found to be well modeled by the 5-phase Lee code; whereas those with high L 0 (type T2) are found to have an extended dip ED beyond the regular dip RD modeled by the code. Differentiating factors based on inductance and inductive energy ratios are found and the physics explained. To model type T2's, anomalous resistance terms are proposed extending the model to 6 phases. These anomalous resistance terms represent the plasma instabilities that occur during and after the pinch phase. The fitted terms are experimental results derived from the measured current waveform. An example is tested to validate the method. © Springer Science+Business Media, LLC 2009. Source : Journal of Fusion Energy Document type : Article Source type : Journal Keywords: Lee model code; Plasma focus; Plasma focus classification; Plasma focus energy distributions; Plasma focus inductance; Plasma focus instability phase; Plasma focus modeling Scaling the plasma focus for fusion energy considerations Saw, S.H., Lee, S. (2011) Using the Lee model code for dense plasma focus, series of numerical experiments were systematically carried out to determine the scaling of bank energies with total current and focus pinch current and the scaling of neutron yields with energies and currents. The numerical experiments were carried out over a range of bank energies from 8kJ extending up to 24MJ on the PF1000 and a proposed less damped modern bank. It also includes a study on the effects of increasing bank energies by increasing bank charging voltage and capacitance of the bank for a practical optimum plasma focus machine. The results provide convincing data to show that it is possible to scale up the plasma focus machine at just 3MJ for D-D neutron yield of 10^13 per shot and 10^15 neutrons per shot when it is converted to operate in D-T. © 2010 John Wiley & Sons, Ltd. Source : International Journal of Energy Research Document type : Article Source type : Journal Keywords: Dense plasma focus; Focus pinch current; Fusion energy; Neutron scaling law; Neutrons source Numerical experiments on oxygen soft X-ray emissions from low energy plasma focus using Lee model Akel, M., Al-Hawat, Sh., Saw, S.H., Lee, S. (2010) The X-ray emission properties of oxygen plasmas are numerically investigated using corona plasma equilibrium model. The Lee model is here modified to include oxygen in addition to other gases. It is then applied to characterize the Rico Plasma Focus (1 kJ), finding a oxygen soft X-ray yield (Ysxr) of 0.04 mJ in its typical operation. Keeping the bank parameters and operational voltage unchanged but systematically changing other parameters, numerical experiments were performed finding the optimum combination of pressure = 3 Torr, anode length = 1.5 cm and anode radius = 1.29 cm. The optimum Ysxr was 43 mJ. Thus we expect to increase the oxygen Ysxr of PF-1 kJ thousand-fold from its present typical operation; without changing the capacitor bank, merely by changing the electrode configuration and operating pressure. The modified version of the Lee model code is also used to run numerical experiments with oxygen gas, for optimizing the oxygen soft X-ray yield on the new plasma focus device PF-SY2 (2.8 kJ). The static inductance L 0 of the capacitor bank is progressively reduced to assess the effect on pinch current I pinch. The experiments confirm the I pinch, limitation effect in plasma focus, where there is an optimum L 0 below which although the peak total current, I peak, continues to increase progressively with progressively reduced inductance L 0, the I pinch and consequently the soft X-ray yield, Ysxr, of that plasma focus would not increase, but instead decreases. The obtained results indicate that reducing the present L 0 of the PF-SY2 device will increase the oxygen soft X-ray yield till the maximum value after that the Ysxr will decrease with I pinch decreasing. © Springer Science+Business Media, LLC 2009. Source : Journal of Fusion Energy Document type : Article Source type : Journal Keywords: Lee Model RADPF5.15 K; Low energy plasma focus; Oxygen gas; Soft X-ray In situ determination of the static inductance and resistance of a plasma focus capacitor bank Saw, S.H., Lee, S., Roy, F., Chong, P.L., Vengadeswaran, V., Sidik, A.S.M., Leong, Y.W., Singh, A. (2010) The static (unloaded) electrical parameters of a capacitor bank are of utmost importance for the purpose of modeling the system as a whole when the capacitor bank is discharged into its dynamic electromagnetic load. Using a physical short circuit across the electromagnetic load is usually technically difficult and is unnecessary. The discharge can be operated at the highest pressure permissible in order to minimize current sheet motion, thus simulating zero dynamic load, to enable bank parameters, static inductance L0, and resistance r0 to be obtained using lightly damped sinusoid equations given the bank capacitance C0. However, for a plasma focus, even at the highest permissible pressure it is found that there is significant residual motion, so that the assumption of a zero dynamic load introduces unacceptable errors into the determination of the circuit parameters. To overcome this problem, the Lee model code is used to fit the computed current trace to the measured current waveform. Hence the dynamics is incorporated into the solution and the capacitor bank parameters are computed using the Lee model code, and more accurate static bank parameters are obtained. © 2010 American Institute of Physics. Source : Review of Scientific Instruments Document type : Article Source type : Journal Keywords: Capacitor bank; Circuit parameter; Current sheets; Current traces; Damped sinusoids; Electrical parameter; Electromagnetic loads; In-situ; Lee model; Measured currents; Plasma focus; Residual motion; Short circuit; Zero dynamics Numerical experiments providing new insights into plasma focus fusion devices Lee, S., Saw, S.H. (2010) 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. © 2010 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland. Source : Energies Document type : Article Source type : Journal Keywords: Neutron saturation; Numerical experiments; Plasma focus; Scaling laws Open Access : PDF full text Numerical experiments on plasma focus neon soft x-ray scaling Lee, S., Saw, S.H., Lee, P., Rawat, R.S. (2009) Numerical experiments are carried out systematically to determine the neon soft x-ray yield Ysxr for optimized neon plasma focus with storage energy E0 from 0.2 kJ to 1 MJ. The ratio c = b/a, of outer to inner electrode radii, and the operating voltage V0 are kept constant. E0 is varied by changing the capacitance C0. Parametric variation at each E0 follows the order operating pressure P 0, anode length z0 and anode radius a until all realistic combinations of P0, z0 and a are investigated. At each E0, the optimum combination of P0, z0 and a is found that produces the biggest Ysxr. At low energies the soft x-ray yield scales as Ysxr ∼ E0 ^1.6 whilst towards 1 MJ it becomes Ysxr ∼ E0 ^0.8. The Y sxr scaling laws are found to be Ysxr∼ I peak ^3.2 (0.1-2.4 MA) and Ysxr∼ I peak ^3.6 (0.07-1.3 MA) throughout the range investigated. When numerical experimental points with other c values and mixed parameters are included, there is evidence that the Ysxr versus Ipinch scaling is more robust and universal, remaining unchanged whilst the Y sxr versus Ipinch scaling changes slightly, with more scatter becoming evident. © 2009 IOP Publishing Ltd. Source : Plasma Physics and Controlled Fusion Document type : Article Source type : Journal Keywords: Inner-electrodes; Low energies; Neon plasma; Numerical experimental; Numerical experiments; Operating pressure; Operating voltage; Optimum combination; Parametric variation; Plasma focus; Soft X-ray; Storage energy Open Access : PDF Full text Soft x-ray yield from NX2 plasma focus Lee, S., Rawat, R.S., Lee, P., Saw, S.H. (2009) The Lee model code is used to compute neon soft x-ray yield Ysxr for the NX2 plasma focus as a function of pressure. Comparison with measured Ysxr shows reasonable agreement in the Ysxr versus pressure curve, the absolute maximum yield as well as the optimum pressure. This gives confidence that the code gives a good representation of the neon plasma focus in terms of gross properties including speeds and trajectories and soft x-ray yields, despite its lack of modeling localized regions of higher densities and temperatures. Computed current curves versus pressure are presented and discussed particularly in terms of the dynamic resistance of the axial phase. Computed gross properties of the plasma focus including peak discharge current Ipeak, pinch current Ipinch, minimum pinch radius r min, plasma density at the middle duration of pinch n pinch, and plasma temperature at middle duration of pinch T pinch are presented and the trends in variation of these are discussed to explain the peaking of Ysxr at optimum pressure. © 2009 American Institute of Physics. Source : Journal of Applied Physics Document type : Article Source type : Journal Keywords: Current curve; Dynamic resistance; Function of pressure; Lee model; Neon plasma; Peak discharge; Pinch current; Pinch radius; Plasma focus; Plasma temperature; Pressure curve; Soft X-ray Numerical experiments on plasma focus neutron yield versus pressure compared with laboratory experiments Lee, S., Saw, S.H., Soto,L., Springham, S.V., Moo, S.P. (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 non-thermalized 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 Yn data. For this paper numerical experiments are carried out, using the Lee model code, incorporating a beam-target mechanism to compute the Yn 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 Yn versus pressure for each device are compared with the measured Yn versus pressure data. The comparison shows degrees of agreement between the laboratory measurements and the computed results. © 2009 IOP Publishing Ltd. Source : Plasma Physics and Controlled Fusion Document type : Article Source type : Journal Keywords: Current waveforms; Laboratory experiments; Laboratory measurements; Lee model; Measured currents; Neutron yields; Numerical experiments; Plasma focus; Plasma focus devices; Pressure data; Two machines Open Access : PDF Full text Optimizing UNU/IC TP PFF plasma focus for neon soft X-ray operation Saw,S.H., Lee, P.C.K., Rawat, R.S., Lee, S. (2009) The United Nations University/International Centre for Theoretical Physics Plasma Focus Facility (UNU/ICTP PFF), a 3.3-kJ plasma focus, was designed for operation in deuterium with a speed factor S such that the axial run-down time matches the current rise time at an end axial speed of nearly 10 cm/μs. For operation in neon, we first consider that a focus pinch temperature between 200 and 500 eV may be suitable for a good yield of neon soft X-rays, which corresponds to an end axial speed of 6-7 cm/μs. On this basis, for operation in neon, the standard UNU/ ICTP PFF needs to have its anode length z 0 reduced by some 30%-40% to maintain the time matching. Numerical experiments using the Lee model code are carried out to determine the optimum configuration of the electrodes for the UNU/ICTP PFF capacitor system. The results show that an even more drastic shortening of anode length z 0 is required, from the original 16 to 7 cm, at the same time, increasing the anode radius "a" from 0.95 to 1.2 cm, to obtain an optimum yield of Y sxr = 9.5 J. This represents a two- to threefold increase in the Y sxr from that computed for the standard UNU/ ICTP PFF. © 2009 IEEE. Source : IEEE Transactions on Plasma Science Document type : Article Source type : Journal Keywords: Dense plasma focus; Neon plasma; Numerical experiments; Soft X-ray (SXR) source Response to “Comment on ‘Pinch current limitation effect in plasma focus’” [Appl. Phys. Lett. 94, 076101 (2009)] - Review Lee, S., Saw, S.H. (2009) The main point of the comment [Appl. Phys. Lett. 94, 076101 (2009)] is that Eq. (2) and consequentially Eq. (3) of the commented paper [Appl. Phys. Lett. 92, 021503 (2008)] require correction. The alternative equation suggested in the comment is derived using Kirchhoff's voltage rule. The comment consider only the energy distribution in the inductive components and the resultant equation confirms a progressive lowering of the Ipinch / Ipeak ratio as the static inductance L0 is reduced, lowering from 0.87 to 0.31 as L0 is reduced from 100 to 5 nH according to the revised formula corresponding to Eq. (3), compared to 0.63-0.25 according to Eq. (3). This progressive lowering of the ratio Ipinch / Ipeak due to the inductive energy distribution is one of two factors responsible for the pinch current limitation. The other factor is the progressive reduction in the L-C interaction time compared to the current dip duration denoted by δcap in Eq. (2). The comment does not deal with δcap at all; hence, its conclusion based on inductive energy distribution only is not useful, since in the low L0 region when pinch current limitation begins to manifest, δcap becomes more and more the dominant factor. In any case, the results of the paper do not depend on Eqs. (2) and (3), which are used in the paper only for illustrative purposes. © 2009 American Institute of Physics. Source : Applied Physics Letters Document type : Review Source type : Journal Keywords: Dominant factors; Energy distributions; Interaction time; Kirchhoff; Pinch currents; Plasma focus Neutron scaling laws from numerical experiments Lee, S., Saw, S.H. (2008) Experimental data of neutron yield Y n against pinch current I pinch is assembled to produce a more global scaling law than available. From the data a mid-range point is obtained to calibrate the neutron production mechanism of the Lee Model code. This code is then used for numerical experiments on a range of focus devices to derive neutron scaling laws. The results are the following: Y n= 2 × 10 ^11 Ipinch ^4.7 and Y n= 9 × 10 ^9 I peak ^3.9. It is felt that the scaling law with respect to I pinch is rigorously obtained by these numerical experiments when compared with that obtained from measured data, which suffers from inadequacies in the measurements of I pinch. © 2008 Springer Science+Business Media, LLC. Source : Journal of Fusion Energy Document type : Article Source type : Journal Keywords: Focus modeling; Lee Model; Neutron scaling; Pinch current; Plasma Focus Numerical experiments on plasma focus pinch current limitation Lee, S., Lee, P., Saw, S.H., Rawat, R.S. (2008) Contrary to the general expectation that performance of a plasma focus would progressively improve with progressive reduction of its static inductance Lo, a recent paper suggests that there is in fact an optimum L o below which although the peak total current increases progressively the pinch current and consequently the neutron yield of that plasma focus would not increase, but instead decreases. This paper describes the numerical experiments and results that led to this conclusion. © 2008 IOP Publishing Ltd. Source : Plasma Physics and Controlled Fusion Document type : Article Source type : Journal Keywords: General (CO); Numerical experiments; pinch current; Plasma focus (PF) Open Access : PDF Full text Computing plasma focus pinch current from total current measurement Lee, S., Saw, S.H., Lee, P.C.K., Rawat, R.S., Schmidt, H. (2008) The total current Itotal waveform in a plasma focus discharge is the most commonly measured quantity, contrasting with the difficult measurement of Ipinch. However, yield laws should be scaled to focus pinch current Ipinch rather than the peak Itotal. This paper describes how Ipinch may be computed from the Itotal trace by fitting a computed current trace to the measured current trace using the Lee model. The method is applied to an experiment in which both the Itotal trace and the plasma sheath current trace were measured. The result shows good agreement between the values of computed and measured Ipinch. © 2008 American Institute of Physics. Source : Applied Physics Letters Document type : Article Source type : Journal Keywords: Lee model; Plasma sheath Pinch current limitation effect in plasma focus Lee, S., Saw, S.H. (2008) The Lee model couples the electrical circuit with plasma focus dynamics, thermodynamics, and radiation. It is used to design and simulate experiments. A beam-target mechanism is incorporated, resulting in realistic neutron yield scaling with pinch current and increasing its versatility for investigating all Mather-type machines. Recent runs indicate a previously unsuspected "pinch current limitation" effect. The pinch current does not increase beyond a certain value however low the static inductance is reduced to. The results indicate that decreasing the present static inductance of the PF1000 machine will neither increase the pinch current nor the neutron yield, contrary to expectations. © 2008 American Institute of Physics. Source : Applied Physics Letters Document type : Article Source type : Journal Keywords: Pinch current limitation effect; Plasma focus dynamics Some generalized Characteristics of the Electro-dynamics of the Plasma Focus in Its Axial Phase: Illustrated by an Application to Independantly Determine the Drive Current Fraction and the Mass Swept-Up Fraction Lee, S., Saw, S.H., Hegazy, H., Ali, Jalil, Damide, V., Fatis, N., Kariri, H., Khabrani, A., Mahasi, A. (2014) We describe the axial phase of the Mather plasma focus by two coupled equations of motion and circuit. We non-dimensionalised these equations resulting in two coupled equations which are characterised by only three scaling parameters α, β and δ which are ratios of electrical to transit times, inductances and impedances respectively. The normalised current waveform, trajectory and speed profile are unique for each combination of α, β, δ which are the ratios of characteristic times (electrical discharge vs. axial transit), inductances (tube inductance vs. static inductance) and impedances (stray resistance vs. electrical surge impedance). This leads to important information and insight into various aspects of the axial phase. In the present work we show that in a time-matched plasma focus shot we deduce the value of axial phase current fraction fc simply by measuring the calibrated voltage waveform and the uncalibrated current waveform. The scaling parameters β and δ are fixed; and by form-fitting the measured current waveform to the normalised current waveform using the value of α of the shot is determined uniquely; from which the peak current and the ratio of peak to average speed [the speed form factor (SFF)] are obtained. The average transit speed is measured by time-of-flight using the voltage upturn as indicator of end of axial phase. Then the SFF yields the peak speed. The measured voltage (back EMF), peak current and peak axial speed (all at the end of axial phase) allows the unambiguous measurement of fc. The value of the mass swept-up fraction fm is deduced from α which is the ratio of the characteristic discharge and the characteristic transit times, both deduced during the non-dimensionalisation of the equations. Analysis of a time-matched shot in the INTI PF at 15 kV, 3 Torr D2 gave fc = 0.68 and fm = 0.05. Source : Journal of Fusion Energy Document type : Article Source type : Journal Keywords: Plasma focus equations; Focus axial phase characteristics; Measurement of model parameters; Plasma focus back EMF Link : http://link.springer.com/article/10.1007/s10894-013-9658-1 Back to Top Any inquiries, please email to masilah.mansor@newinti.edu.my HOME

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