M. Shafiq

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.

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.

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.

Enhanced and reproducible neutron emission from a plasma focus with pre-ionization induced by depleted uranium (U238)

The effect of pre-ionization induced by depleted uranium (92U238) around the insulator sleeve on the neutron emission of (1.8?3.3?kJ) plasma focus device is investigated by employing time resolved and time integrated neutron detectors. The maximum average neutron yield of 2.5 ? 108 is recorded at 3.5?mbar without pre-ionization, which increases up to 3.85 ? 108 with pre-ionization. It is found that the pre-ionization enhances neutron yield, about (50 ? 5)%, broadens the neutron emission pressure range and improves shot-to-shot reproducibility of plasma focus operation for neutron emission. The pinhole images of charged particles emitting zones indicate that the pre-ionization increases the high temperature plasma volume.

X-ray emission from a plasma focus with high-Z inserts at the anode tip

X-ray emission in different energy windows, from a low energy Mather-type plasma focus by employing high Z inserts at the anode tip is investigated. Quantrad Si pin diodes with differential filtering are employed as time-resolved x-ray detectors, whereas a pinhole camera is used for time-integrated analysis. The x-ray flux from the focus region is found to be measurable within the pressure range 0.25–3.5 mbar of hydrogen. The maximum emission in 4π-geometry is found to be 29.4±0.2 J, 3.43±0.05 J and 4.00±0.02 J with Pb, W and Mo inserted anodes, respectively, and corresponding wall plug efficiencies for x-ray generation are 1.28%, 0.15% and 0.2%. The x-ray emission is found predominantly as a result of electron beam activity on the anode tip, which is confirmed by the images recorded by the pinhole camera.

SOFT X-RAY EMISSION IN THE (1.0–1.5 KEV) WINDOW WITH NITROGEN FILLING IN A LOW ENERGY PLASMA FOCUS

A study of soft X-ray emission in the 1.0–1.5 keV energy range from a low energy (1.15 kJ) plasma focus has been conducted. X-rays are detected with the combination of Quantrad Si PIN-diodes masked with Al (50 μm), Mg (100 μm) and Ni (17.5 μm) filters and with a pinhole camera. The X-ray flux is found to be measurable within the pressure range of 0.1–1.0 mbar nitrogen. In the 1.0–1.3 keV and 1.0–1.5 keV windows, the X-ray yield in 4π-geometry is 1.03 J and 14.0-J, respectively, at a filling pressure of 0.25 mbar and the corresponding efficiencies are 0.04% and 1.22%. The total X-ray emission in 4π-geometry is 21.8 J, which corresponds to the system efficiency of about 1.9%. The X-ray emission is found dominantly as a result of the interaction of energetic electrons in the current sheath with the anode tip. Images recorded by the pinhole camera confirm the emission of X-rays from the tip of the anode.

The effect of pre-ionization by a shunt resistor on the reproducibility of plasma focus x-ray emission

The effect of pre-ionization by means of a shunt resistor on the x-ray emission of a low energy (1.8?kJ) plasma focus device powered by a 9??F capacitor bank, charged at 20?kV and giving a peak discharge current of about 175?kA is investigated. Quantrad Si pin-diodes along with a suitable filter are employed as time-resolved x-ray detectors, whereas a multipinhole camera with absorption filters is used for time-integrated analysis. X-ray flux in 4?-geometry is measured as a function of argon filling pressure with and without pre-ionization. It is found that appropriate selection of the shunt resistor increases shot-to-shot reproducibility of the x-ray emission as well as the stability of the pinch filament and broadens the x-ray pulse width. The x-ray emission is also enhanced by (45 ? 5)% at the optimum pressure.

Soft X-Ray Emission Optimization Study with Nitrogen Gas in a 1.2 kJ Plasma Focus

Measurement of soft x-ray emission from a low-energy plasma focus operated with nitrogen within the pressure range of 0.1–1.0 mbar is presented. The x-rays are detected by using an assembly of Quantrad Si PIN-diodes with differential filtering and with a multipinhole camera. In the 1.0–1.3 keV and 1.0–1.5 keV windows, the x-ray yield in 4π geometry is 1.03 J and 14.0 J, respectively, at a filling pressure of 0.25 mbar and the corresponding efficiencies are 0.04% and 1.22%. The total x-ray emission in 4π geometry is estimated at 21.8 J, which corresponds to the system efficiency of about 1.9%. The soft x-ray emission is found dominantly as a result of electron beam activity on the anode tip, which is confirmed by the images recorded by a pinhole camera.

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.