M. Sharif

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.

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.

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.

X-ray emission scaling law from a plasma focus with different anode tip materials "Cu, Mo, and W…

X-ray emission from a 2.3–5.3kJ Mather-type plasma focus [Phys. Fluids 7, 5 (1964)] employing copper, molybdenum, and tungsten anode tip is studied. Argon is used as a working gas. Characteristic CuKα and Mo K-series emission and their ratio to the continuous x-rays are determined. From the variation of the x-ray yield data with filling pressure at different charging voltages, scaling laws are obtained. X-ray pinhole images demonstrate that a significant amount of x-ray emission is from the anode tip. The comparison of the ratio of characteristic to continuum radiation for copper anode with typical x-ray tube data reveals that the contribution of very high energy electron beam from the focus region for x-ray generation through thick target bremsstrahlung mechanism is not significant. Rather, electrons with energy of the order of, or even less than, the charging voltage are responsible for bulk of the x-ray emission.

Study of the x-ray emission scaling law in a low energy plasma focus

The performance of a low energy (0.6–1.8 kJ) Mather-type plasma focus (PF) device as a Cu–Kα x-ray source is examined. The Cu–Kα and total x-ray emissions are measured for argon and hydrogen filling. It is found that Cu–Kα emission varies as YK [J] ~ [E(kJ)]3.5–4.5 ~ [I(100 kA)]3.5–4.5, whereas the total x-ray emission is found to follow Ytot [J] ~ [E( kJ)]4.5–5.5 ~ [I(100 kA)]4.5–5.5. At optimum conditions, the system with discharge energy of 1.8 kJ is found to generate x-rays with 1.44 ± 0.07% efficiency. About 32% of the emission constitutes the Cu–Kα line radiation. With a cut at the anode tip, the x-ray flux in the side-on direction is increased three times. The modified geometry may help in using the PF as a radiation source for x-ray diffraction.

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.

Study of molybdenum K-series line radiation emission from a low energy plasma focus

K-series line radiation emission of Mo and Cu from a low energy Mather-type plasma focus is investigated. Quantrad Si pin diodes are employed as time resolved X-ray detectors, where as a pin hole camera is used for time integrated analysis. The measurable X-ray flux for hydrogen is observed in the pressure range of 0.5–3.5 mbar. Mo and Cu K-line radiation emission in this geometry has the highest values of about 0.05 J/sr and 0.17 J/sr, respectively at a filling pressure of 2.0 mbar. The corresponding efficiencies are 0.03% and 0.09%, respectively. Total X-ray emission and efficiency in 4 π -geometry are also obtained with values 4.12 J and 0.18% at 2.0 mbar. The Mo K-line radiation emission may result due to interaction of energetic electron beam emitted from the focus region with the molybdenum insert.  2002 Elsevier Science B.V. All rights reserved.

GENERATION OF TITANIUM K-RADIATION IN A 1 KJ PLASMA FOCUS

Titanium K-series line radiation emission from a low energy Mather-type plasma focus operated with hydrogen was investigated by employing Quantrad Si pin diodes as time resolved X-ray detectors. It has the highest value of 1.6 ± 0.1 J in 4π-geometry, and the corresponding machine efficiency is about 0.16 ± 0.01%. The total X-ray emission is about 3.2 ± 0.2 J, and the corresponding machine efficiency is about 0.32 ± 0.02%. The Ti K-line radiation emission may result from the interaction of energetic electron beam emitted from the focus region, and the energetic electrons in the current sheath, with the anode tip.

A Simple Technique to Record X-Ray Fluence Anisotropy of a Source

A simple technique to record the fluence anisotropy of x-rays emitted from a source is presented. The simplicity of the technique and response curves of the photographic film, along with corresponding filters, enables one to readily use the same for diagnostic purposes in different sources such as plasma focus, vacuum spark, z-pinch, and laser-produced plasmas. As an application example, the technique is employed to measure fluence anisotropy of x-ray emission in a low-energy plasma focus operated with hydrogen. With increase in filling pressure, the anisotropy is found to increase, although the total x-ray emission is lowered. It is therefore concluded that at a lower filling pressure of 0.75 mbar, the x-ray emission is dominantly due to interaction of energetic electrons in the current sheath, whereas at a higher filling pressure of 2.5 mbar, the contribution of energetic electron beam is much higher.