Khalid Alamgir

Scope of plasma focus with argon as a soft X-ray source

The X-radiation emission from a low energy plasma focus with argon as a filling gas is investigated. Specifically, the attention is paid to determine the system efficiency for argon K-lines and Cu-K/sub /spl alpha// line emission at different filling pressures, and identify the radiation emission region. The highest argon line emission found at 1.5 mbar is about 30 mJ and the corresponding efficiency is 0.0015%. The same pressure is suitable for high Cu-K/sub /spl alpha// emission, which is about 70 mJ in 4/spl pi/ geometry and the system efficiency is 0.003%. The bulk of X-radiation is emitted from the region close to the anode tip, whereas some radiation emission takes place from the formed hot spots along the focus axis. These radiations are found suitable for backlighting in Al (1-1.56 keV) and Ti (2.9-4.96 keV) energy transmission bands.

Low-energy plasma focus as a tailored X-ray source

A low-energy (2.3 kJ) plasma focus energized by a single 32-μF capacitor charged at 12 kV with filling gases hydrogen, neon, and argon is investigated as an X-ray source. Experiments are conducted with a copper and an aluminum anode. Specifically, attention is given to tailoring the radiation in different windows, e.g., 1.2–1.3 keV, 1.3–1.5 keV, 2.5–5 keV, and Cu-Kα line radiation. The highest X-ray emission is observed with neon filling and the copper anode in the 1.2–1.3 keV window, which we speculate to be generated due to recombination of hydrogenlike neon ions with a few eV to a few 10s of eV electrons. The wall-plug efficiency of the device is found to be 4%. The other significant emission occurs with hydrogen filling, which exhibits wall-plug efficiency of 1.7% for overall X-ray emission and 0.35% for Cu-Kα line radiation. The emission is dominated by the interaction of electrons in the current sheath with the anode tip. The emission with the aluminum anode and hydrogen filling is up to 10 J, which corresponds to wall-plug efficiency of 0.4%. The X-ray emission with argon filling is less significant.

Comparative study of ion, x-ray and neutron emission in a low energy plasma focus

In a low energy (2.3 kJ) Mather-type deuterium plasma focus, neutron and x-ray emission is investigated by time integrated and time resolved detectors. CR-39 nuclear track ion detectors are employed for measuring charged particle angular distribution. Correlation of charged particles with neutron and x-ray emission is also investigated. The neutron emission profile is found to be composed of two pulses, the intensity and anisotropy of which vary with the filling pressure. The charged particle flux is maximum with high fluence anisotropy for the pressure range 2.5-3.0 mbar which is also the optimum pressure for high neutron emission with low fluence anisotropy . The high neutron emission with low fluence anisotropy is attributed to the presence of trapped deuterons in an anomalous magnetic field. The relevant pressure range generates favourable conditions for plasma density and pinch filament diameter. X-ray emission is generally high at low pressure. For the pressure range of 2.5-4.0 mbar, the axial neutron detector registers a hard x-ray pulse, which may escape through a half inch thick Cu flange. These results suggest that at low pressures, the collapsing current sheath interacts with the anode end and causes intense low energy x-ray emission, but the neutron emission remains low. X-rays are dominantly Cu . In the narrow pressure regime 2.5-3.0 mbar, the current sheath forms a pinch filament leading to high neutron yield with low fluence anisotropy.

Characteristics of x-rays from a plasma focus operated with neon gas

The x-ray emission from a low-energy (2.3 kJ) plasma focus is investigated with neon as the filling gas. Two anode configurations are used in the experiment: the conventional cylindrical anode, and tapered anode slightly toward the open end. The latter geometry enhances soft x-ray emission by an order of magnitude. The emission is pressure dependent and, in both cases, the highest emission is observed at 3–3.5 mbar. For the cylindrical anode, the soft x-ray emission is up to 7 J per shot, which is from a pinched plasma column, 5–6 mm long. For the tapered anode, up to 80 J per shot soft x-ray yield in 4π geometry is recorded, which corresponds to 4% wall plug efficiency. The diameter of the x-ray emission filament is much larger compared with the cylindrical anode. The bulk of emitted radiation is of energy 1.2–1.3 keV, which is thought to arise from recombination of hydrogen-like (Ne X) ions with the low-energy electrons.

Efficiency of plasma focus for argon K-series line radiation emission

X-radiation emission from a low-energy Mather-type plasma focus operated with argon is investigated. Attention is paid to finding the pressure range for the highest argon K-series line emission. The argon line radiation yield is highest at 1.5 mbar and the emitted energy in 4π geometry is estimated to be about 30 mJ, with a system efficiency of 0.0015%. The emission at an energy exceeding 3 keV is found to be highest at a 0.5 mbar filling pressure, giving a total yield of 0.7 J in 4π geometry, which corresponds to a device efficiency of about 0.028%. This emission is mainly due to the interaction of energetic electrons with the anode.

Enhanced copper K-alpha radiation from a low-energy plasma focus

A low-energy (2.3 kJ) plasma focus is operated in an enhanced Cu Kα line emission mode. The emission is dominated by the interaction of electrons in the current sheath with the anode tip. The Cu Kα line radiation of 0.4 J/sr is recorded in the side-on direction, which steadily increases in the end-on direction and attains the value of 0.8 J/sr. It is estimated about 40 J of energy is radiated as x rays, out of which 8 J is in the form of Cu Kα lines in 4π geometry. The radiation yield represents a system efficiency of 1.7% for overall x-ray emission, and 0.35% for the Cu Kα line.

Simple hydrothermal synthesis of very-long and thin silver nanowires and their application in high quality transparent electrodes

Solution-processed silver nanowire (AgNW) random mesh is a strong contender to commercial indium tin oxide (ITO); however, its performance is limited due to large contact resistance between nanowires and post-processing treatments. As an alternative, long nanowires can decrease the number of contact points and contact resistance. Here, a simple modified hydrothermal method for the synthesis of very-long silver nanowires (AgNWs) and their use in a high quality transparent conducting electrode without post-processing has been developed. Well dispersed very-long and thin silver nanowires are synthesized by using glucose as a reducing agent and silver chloride as a silver source. The lengths of the wires are in the range of 200 to 500 μm with an average diameter of 45–65 nm. To the best of our knowledge, this is the first report on long nanowires having a thin diameter with greater than 200 microns length. As compared to other transparent conductors and nanowire networks, this AgNW network shows a higher percolative figure of merit (FoM, Π) with low haze. A flexible touch screen using the AgNW network is also demonstrated which has shown good performance even on a bendable surface.

Correlation of plasma electron temperature with neutron emission in a low-energy plasma focus

Correlation of neutron emission with plasma electron temperature in a low-energy (2.3 kJ) plasma focus is investigated. To determine the plasma temperature by continuum X-ray analysis, cobalt is selected as the filter, which discriminates the line radiation from the background impurities like carbon, nitrogen, and oxygen, or the copper of which plasma focus electrodes are made. For a pressure range of high neutron emission (1-4 mbar), the neutron yield is found to correlate with the plasma temperature. The highest temperature recorded is 5 keV at 2.5 mbar, the filling pressure for the highest neutron emission in this device.

Improved temperature measurement in a plasma focus by means of a cobalt filter

The characteristics of cobalt as a soft x-ray filter are investigated. It is found to be a good choice to diagnose 0.5-5 keV hot plasmas in a device like a plasma focus. The focus plasma temperature is found to be filling pressure dependent. The highest temperature recorded is 5 keV at a filling pressure of 2.5 mbar, which gives the highest neutron yield in the 2.3 kJ low-energy Mather-type device under study. The advantage of the cobalt filter is to prevent contamination of the temperature-sensitive continuum radiation by the dominant Cu Kα line radiation. The energy dependence of the detector sensitivity is incorporated to yield a more accurate temperature measurement. The Ni-Co filter combination helps to estimate the Cu Kα line radiation from the device, which is the highest at 0.5 mbar. The emitted energy is estimated to be 1.2 J in the 4π geometry, which corresponds to system efficiency of about 0.045%. The Cu Kα is 90-95% of the total x-ray emission.

TUNING THE OPTICAL PROPERTIES OF MULTIWALL CARBON NANOTUBE THIN FILMS BY N+ ION BEAMS IRRADIATION

Measurements of optical transmission in the visible spectral range of N+ irradiated thin films of multiwall carbon nanotubes (MWCNTs) at various doses prepared by a vacuum filtration method are reported. An increase in optical transmission was observed corresponding to increase in N+ ion doses. Changes in Raman spectra at different ions doses ranging from 5x10(15) ions/cm(2) to 1 x 10(17) ions/cm(2) indicate that the structure of graphene evolves from a highly ordered layer to a disordered domains. These structural changes result in a dramatic increase in the optical transmission. Additionally, the increase of optical transmission of irradiated MWCNTs thin film as a function of electrical conductivity at various doses is also discussed. The optical transmission increases in irradiated MWCNT thin films is found to be a function of defects density in MWCNTs.