Comprehensive Study on Soft X-Ray Emission from Admixtures of Nitrogen and Neon Gases in the APF Plasma Focus Device

The present work is an investigation on the effect of working gas composition as well as applied voltage and operating pressure on the behavior of SXR emitted from the APF device. Three volumetric ratios(90:10), (75:25), and (50:50) of nitrogen:neon (N₂:Ne) admixture were used with operating conditions at applied voltages of 11, 12, and 13 kV and operating pressures of 1.5, 2, 2.5, 3, 3.5, 4, 4.5, and 5 torr. Using (N₂:Ne) gas mixture ratios of (90:10) and (75:25) and at applied voltage of 11 kV, the optimum pressure for maximum intensity of SXR was 3.5 torr. However, for the percentage of (50:50), it shifts to higher pressure of 4 torr. At higher applied voltages of 12 and 13 kV, the optimum pressures shift to higher values, 4 torr for both volumetric ratios (90:10) and (75:25), and 4.5 torr for the ratio of (50:50). It was found that the intensity of SXR increases with the increase of neon (Ne) percentage in the admixture of (N₂:Ne) and applied voltage. The highest intensity was for the volumetric ratio of (50:50) operating at the voltage of 13 kV. Our results illustrated that mixing neon (Ne) with nitrogen (N₂) as the working gas in the PF is a power source of SXR emission.     

The Effect of Applied Voltage and Operating Pressure on Emitted X-Ray from Nitrogen (N<Subscript>2</Subscript>) Gas in APF Plasma Focus Device

In the present work, the effect of applied voltage and operating pressure on behaviour of X-rays emitted from nitrogen gas (N₂) used in APF plasma focus facility is investigated. It was found that the optimum conditions for high emissions of SXR and HXR from the plasma focus (PF) are different. At four applied voltages of 10, 11, 12, and 13 kV, the optimum pressures for SXR and HXR emissions of nitrogen gas (N₂) were obtained. At lower voltages, 10, and 11 kV optimum pressure for SXR emission was 3.5 torr while for HXR emission was 2.5 torr. At higher voltages, 12, and 13 kV, the optimum pressures shift to higher values at 4 and 3 torr for SXR and HXR emissions, respectively. Among the applied voltages, the least intensity of both SXR and HXR was at voltage 10 kV and the most intensity was for 13 kV which confirm with increasing voltage, the intensity of X-ray emission increases. Also the results obtained by images of pin-hole camera were in compatible with the results of detected signals by different filtered Pin-diodes and Scintillation detector. Our results illustrate that the voltage and the pressure are effective parameters in X-ray emission from the PF.     

The Effect of Working Gas Admixture,Applied Voltage and Pressure on Focusing Time Parameter in the APF Plasma Focus Device

In the present research the effects of key parameters, applied voltage, working gas composition and pressure, on the focusing time in the APF plasma focus device are investigated. Pure nitrogen (N₂) and three volumetric ratios (90:10), (75:25), and (50:50) of (N₂:Ne) admixture gases were used as the filling gas in a range of four applied voltage between 10 and 13 kV and seven operating pressure of 1.5–4.5 torr. It was found that with addition of 1 kV in the charging voltage, a decrease of around 50–75 ns happens in the focusing time while with increase of 0.5 torr in operating pressure, an increment of around 100–150 ns occurs in the focusing time. Also it was observed that the focusing time decreases around 50–75 ns with addition of 10% neon (Ne) in volumetric ratio of admixture working gas at all applied voltage and operating pressure.     

Comprehensive Study of Neon HXR and SXR Emitted from APF Plasma Focus Device

Experimental results related to HXR and SXR properties of Neon plasma on the APF plasma focus device is presented. The experiments were carried on over a wide range of neon pressure and at voltages 11, 12 and 13 kV using plastic scintillator (NE102A) coupled with high gain PMT and six filtered photo PIN diodes. For the charging voltages of 11–13 kV with 2.17–3.04 kJ stored energy, the optimum operating pressure in neon is found to be in the range of 3.5–5 torr and the highest HXR emission was observed in the pressure of 5 torr at the voltage 13 kV and the maximum average HXR production is (9.84 ± 0.59) ×10^–7 volt sec. The behavior of SXR intensities were registered by different filters and it was found out that Al-Mylar 6 μm and Cu 10 μm has the highest and lowest amount of X-ray transmission.     

A Comprehensive Time-Resolved Study of X-Ray Signals in a 4?kJ Dense Plasma Focus Facility

In the present research, time-resolved of X-ray signals are investigated in a 4?kJ PF device using five filtered PIN-diodes and a Scintillation detector. At applied voltage 12?kV using nitrogen (N₂) gas, the optimum pressures for maximum yield of HXR and SXR emission were 3?torr and 4?torr respectively. At each operating pressure, multiple pulses in SXR signals with respect to amplitude and duration of emission were studied in a time span of 700–800?ns. According to energy response of filters used, the origin of X-ray pulses and also the approximate energy of X-ray photons were analyzed. It was found that at higher pressure 4?torr, the yield of SXR photons in different pulses increases 20–30% in comparison with the results obtained at pressure 3?torr while the yield of HXR decreases. The results confirm that the operating pressure is an effective parameter on the yield of SXR and HXR emitted from this device.     

Experimental Observation of Hot Spots in a Filippov-Type Plasma Focus Device

In this paper we have presented the experimental results of hot spots observation in different working conditions in Filippov-type Plasma Focus Device “Dena” (90 kJ, 25 kV), analyzing of these results have shown that the working conditions have great influence on hot spots formation. In using the pure gases like D₂, Ar, Kr and Ne the formation of hot spots has been seen rarely, and it can be related to impurities like vapoured metal from the anode surface, also in using the light impurities hot spots were not formed, and only for the heavy impurities like Kr the formation of hot spots have been observed. The discharge voltage also plays an important role in hot spots formation, for voltages less than 16 kV, hot spots have not been observed. Also, using the conic insert anode leads to more and distinct hot spots than the case of flat one. The best results of hot spot observation in these experiments have been achieved by using a conic insert anode and D₂ + 1% Kr as working gas.     

Anisotropic Investigation of Hard X-ray Emission with Flat Anode Tips in APF Plasma Focus Device

In this paper behavior of hard X-ray (HXR) anisotropy and its intensity along the anode bar from APF plasma focus facility (16 kV, 36 μf, and 115 nH) with different anode tip materials investigated experimentally. Magnetic probe signals registered to choose only discharges with high degree of current sheath symmetry. The signals obtained by scintillation detectors by a special arrangement at each angular position show that the employment of higher Z anode insert materials not only increase the intensity of HXR signal, but also result to high degree isotropic emission of HXR. The side on emitted intensity along the anode bar has been studied by moving the detector in the direction of central electrode axis. The results confirm the importance of anode tip material on HXR signal intensity.     

Experimental Study of Hard X-ray Emission with Different Anode Tips in APF Plasma Focus Device

To investigate the effect of different anode tips on the hard X-ray (HXR) emission from APF plasma focus device (16 kV, 36 μf, and 115 nH) we considered two shapes of anode tips, i.e., flat or conic, with Cu, Al and W anode tip materials. The highest HXR intensity was observed with conic W anode insert and the lowest with flat Al anode insert. In comparison with the hollow anode tube the HXR signals obtained from flat and especially conic W inserts nearly tending to have the same intensity along the axis of the device. Therefore the shape and the material of the anode tip has significant effect on the production of HXR emissions. This study show that the employment of a convenient shape of anode tip results to more isotropic emission of HXR.     

Investigation of the Neutron Angular Distribution and Neutron Yield on the APF Plasma Focus Device

This paper presents an experimental study of neutron yield as well as neutron angular distribution on the APF plasma focus device. The system operates with pure deuterium gas in varying the filling pressure and working voltages of 11.5 and 13.5 kV. The maximum average of neutron yield is (2.88 ± 0.29 × 10⁸) neutrons per shot at the pressure of 7 torr. The neutron angular distribution is measured with housing an array of seven silver activation Geiger-Muller counters at the angles of 0°, ±30°, ±60°, and ±90° in a distance of 90 cm from the anode tip. The results of neutron angular distribution suggest that the neutron production mechanism may be predominantly beam target model.     

Effect of Quartz and Pyrex Insulators Length on Hard-X ray Signals in APF Plasma Focus Device

This paper, presents the variation of hard X-ray (HXR) intensity in the APF plasma focus device for different insulator sleeves. For Pyrex and Quartz insulators, the lengths of 40 and 50 mm seems optimal to yield maximum HXR intensity, respectively. Also using the Pyrex insulator leads to production of higher HXR intensity than the Quartz insulator. The results illustrate that the length and the material of the insulator has a considerable effect on the HXR intensity.     

Characterization of the Soft X-Ray Emission from the APF Plasma Focus Device Operated in Neon

Experimental results related to soft X-ray (SXR) properties of Neon plasma on the APF plasma focus device is presented. The experiments were carried on over wide range of neon pressure and at voltages 11, 12 and 13 kV six filtered photo PIN diodes and pin-hole camera. For the charging voltages of 11–13 kV with 2.17–3.04 kJ stored energy, the optimum operating pressure in neon is found to be in the range of 3.5–5 torr. The behavior of SXR intensities was registered by different filters and found out that Al-Mylar 6 μm and Cu 10 μm has the highest and lowest amount of X-ray transmission, respectively.     

Experimental Study of Current Discharge Behavior and Hard X-ray Anisotropy by APF Plasma Focus Device

Amirkabir (APF) is a new Mather-type plasma focus device (16 kV, 36 μf, and 115 nH). In this work we present some experimental results as variation of discharge current signal respect to applied voltage at the optimum pressure, focusing time of plasma versus gas pressure, and variations of current discharge with different insulator sleeve dimensions. As we prospected optimum pressure tending to increase as we tried to higher voltage levels. The time taken by the current sheath to lift-off the insulator surface and therefore quality of pinched plasma depends on the length of the insulator sleeve. The results show that the insulator diameter can influence on pinch quality. Behavior of hard X-ray (HXR) signals with the pressure and also anisotropy of HXR investigated by the use of two scintillation detectors. The distribution of HXR intensity shows a large anisotropy with a maximum intensity between 22.5° and 45° and also between −22.5° and −67.5°.     

Influence of Pyrex Insulator Thickness and it’s Length on Hard X-Ray Intensity in APF Plasma Focus Device

In order to improve the HXR emission from APF plasma focus device we have investigated the effect of insulator sleeve outer diameter (O.D.) and its length. Fourteen different insulator sleeve geometries at three different filling gas pressures of 6, 7 and 8 Torr of neon are used in the present investigation. The average HXR yield, measured using scintillation detector, has been found to increase with the increase in insulator sleeve O.D. from 31 to 34 mm. Further increase in insulator sleeve diameter to 37 mm, however, decreased the HXR yield. The highest magnitude of 234.5 kA was achieved for 34 mm O.D. of sleeve at filling gas pressure of 7 Torr and voltage of 12 kV.     

Influence of Different CH4/N2 Ratios on Structural and Mechanical Properties of a-CNx:H Film Synthesized Using Plasma Focus

Carbon nitride films were synthesized by operating the dense plasma focus device with different CH₄/N₂ admixture gas ratios and fixed 20 focus shots. The pressure and axial distance from anode tip were kept constant at 3 mbar and 8 cm respectively. Raman and X-ray photoelectron spectroscopy (XPS) techniques were used to observe the effect of CH₄/N₂ ratio on carbon nitride bonding. The XPS analysis showed that the terminating group C≡N is more dominant for the films synthesized using higher concentration of nitrogen which gives softer films. Field emission scanning electron microscopy results showed that the deposited films consist of nanoparticles and their agglomerates. The size of agglomerates increases with decreasing concentration of nitrogen in CH₄/N₂ admixture gas. Nanoindentation results showed the increase in hardness and elastic modulus values of films with decreasing concentration of nitrogen in CH₄/N₂ admixture gas. The hardness and elastic modulus values were found to be dependent on sp³ content in the film as well as the C≡N. The hardness and elastic modulus values of 10.7 and 229.8 GPa respectively were achieved for the films deposited with fixed 20 focus deposition shots and using CH₄/N₂ admixture gas ratio of 7:3.     

Theoretical critical angels of ion channeling in carbon nanotubes

We have developed a mass- and charge-dependent equation to predict theoretical critical angles for ion channeling in carbon nanotubes. We focus M (ion mass) effects how to reduce Ze (ion nucleus charge) effects on Ψ_C (critical angles). As an instance, we give theoretical critical angels of He, Ne, Ar, Kr, Xe and Rn ion channeling in carbon nanotubes. We find that for (10, 10) single-wall carbon nanotubes, Ψ_C(He) ≈ Ψ_C(Ne) ≈ Ψ_C(Ar) ≈ Ψ_C(Kr) ≈ Ψ_C(Xe) ≈ Ψ_C(Rn) ≈ 23.3 (keV/E)^1/2 deg. This is because (Z/M)^1/2 ≈ 0.66 [amu]^?1/2.     

Designing of a Quadrupole Paul Ion Trap

The ion motion equation in a Paul ion trap known as Mathieu differential equation has been solved for the first time by using Runge–Kutta methods with 4th, 6th, and 8th orders. The first stability regions in a_z − q_z plane and the corresponding q_max values were determined and compared. Also, the first stability regions of ²⁰\textNe ⁺ {}^{20}{\text{Ne}}^{ + } , ⁴⁰\textAr ⁺ {}^{40}{\text{Ar}}^{ + } , ⁸⁰\textKr ⁺ {}^{80}{\text{Kr}}^{ + } , ¹³¹\textXe ⁺ {}^{131}{\text{Xe}}^{ + } ions in the V_dc − V_ac plane were drown, and the threshold voltages for the ion separation was investigated.     

Peaked density profiles in neon and lithium doped discharges on FTU

Peaked density profiles are observed in FTU discharges when the recycling condition of the chamber is influenced by the action of the liquid lithium limiter (LLL) [1]. Turbulence analysis of lithium doped FTU plasmas [2], [3] has shown that the presence of the light impurity modifies the phase between fluctuating fields responsible for transport and consequently leads to an inward deuterium pinch and outward impurity flux.Analogous peaked discharges were produced by Ne-gas puffing in different L mode plasma scenarios that have been recently obtained on FTU with following plasma parameters: I = 360 kA, B = 5–6.5 T, n_e0 = 0.2–1 × 10²⁰ m⁻³, T_e0 = 1–4 keV, as well as in similar experiments on other machines [4]. In fact the Ne seeded plasmas show an increase of the peaking factor around 30% [5]. UV spectroscopy measurements confirm that the electron-density peaking arises from a convective flow and cannot be attributed to the contribution of the injected Ne alone.The Ne doped discharges analysis together with lithium conditioned ones is useful to extend the interpretative framework of the particle transport. In this work a comparison of the diffusion coefficient and of the pinch velocity of the two cases is conducted. By using a two-colors scanning interferometer providing very high spatial and time resolution, it is indeed possible to estimate the D and U coefficients of a simple model for the particle flux [6].     

Swelling behaviors of GMZ bentonite–sand mixtures inundated in NaCl–Na2SO4 solutions

In this study, the swelling behaviors of compacted GMZ bentonite–sand mixtures inundated in NaCl–Na₂SO₄ solutions are investigated and the influence of chemical solutions on the swelling behaviors of GMZ bentonite–sand mixtures as backfill/buffer material in China for high level radioactive waste (HLW) is investigated. The sand addition ratios of the bentonite–sand mixtures are 0%, 20%, 30% and 50%, and the total dissolved solids (TDS) of the NaCl–Na₂SO₄ (NaCl:Na₂SO₄ = 2:1 by mass) solution are 0.5, 1.0, 3.0, 6.0 and 12.0 g/L (pH 7.1). The specimens of bentonite–sand mixtures for swelling tests are prepared by static-compaction to various dry densities, ranging from 1.50 to 1.90 g/cm³.Test results indicate that liquid limit (LL) and plasticity limit (PL), swell time, maximum swelling pressure and maximum swelling strain decrease with the increase of TDS for GMZ bentonite–sand mixtures. All of the LL, PI and maximum swelling strain are decreased exponentially with TDS increase: very quickly as TDS < 3.0 g/L, slowly as TDS = 3.0–6.0 g/L and almost stabilized as TDS > 6.0 g/L. The maximum swelling pressure shows a linear reduction with the TDS increasing, but the pure bentonite indicates a high sensitivity than the bentonite–sand mixtures with 30% sand addition ratio. As NaCl–Na₂SO₄ (TDS = 0.5 g/L) solution was used according to the ground water, with initial dry density of 1.70 g/cm³, the maximum swelling pressure of specimens decrease exponentially while the maximum strain decrease linearly with the increase of sand addition. With 30% sand addition in 0.5 g/L NaCl–Na₂SO₄ solution, the maximum swelling pressure increase exponentially while the maximum strain increase linearly with the increase of initial dry density.Compared with the pure bentonite, bentonite–sand mixtures show a better tolerance withstanding the chemical attack to ground water chemistry because of the replacement of some quantity of expansive clay by quartz sand in the mixtures.     

Numerical Experiments on Soft X-ray Emission Optimization of Nitrogen Plasma in 3 kJ Plasma Focus SY-1 Using Modified Lee Model

The X-ray emission properties of nitrogen plasmas are numerically investigated using corona plasma equilibrium model. The X-ray emission intensities of nitrogen Ly _α , Ly _β and He _α , He _β lines are calculated. The optimum plasma temperature for nitrogen X-ray output is concluded to be around 160 eV. The Lee model is modified to include nitrogen in addition to other gasses (H₂, D₂, He, Ne, Ar, Xe). It is then applied to characterize the 2.8 kJ plasma focus PF-SY1, finding a nitrogen soft X-ray yield (Ysxr) of 8.7 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 = 0.09 Torr, anode length = 7.2 cm and anode radius = 2.58 cm. The optimum Ysxr was 64 mJ. Thus we expect to increase the nitrogen Ysxr of PF-SY1 sevenfold from its present typical operation; without changing the capacitor bank, merely by changing the electrode configuration and operating pressure.