M. Zakaullah

A simple facility for the teaching of plasma dynamics and plasma nuclear fusion

A small plasma focus (3.3 kJ) is designed from the viewpoint of simplicity, reliability, and cost effectiveness to act as a source of pulsed high‐density plasmas. The simplicity of the device and associated diagnostics coupled with its rich variety of plasma phenomena makes this device ideal for the teaching of plasma nuclear fusion particularly for developing countries where such facilities are at present rarely available. Six sets of the device have been constructed and tested in various gases with better than 95% reliability and reproducibility in various plasma phenomena including neutron production of 0.5–1.0×108 per discharge when operated in 3‐Torr deuterium. The design principles, procedures, and parameters are discussed and test results shown.

X-ray backlighting of wire array Z-pinch implosions using X pinch

The dynamics of wire arrays have been studied using a point-projection X-pinch x-ray backlighter installed in one of the return posts of the MAGPIE generator. Variations of diameter (15–50 μm aluminum) and number of wires (two or four) in the X-pinch enabled backlit images in the range of 140–200 ns after the current start. A temporal and spatial resolution of <1 ns and 5 μm is achieved. The radiographic images of aluminum wire array show that the wire cores are present at the original position until 80% of the implosion time and the size of the wire cores is 0.25 mm for aluminum and 0.1 mm for tungsten. A very fine structure of the order of 10 μm has been observed in titanium wire arrays.

Plasma focus as a possible x-ray source for radiography

A study of x-ray emission from a low energy (1.8?kJ) plasma focus (PF) device powered by a 9??F capacitor bank, charged at 20?kV and giving peak discharge current of about 175?kA by using three different anode shapes with a lead insert at the tip is reported. Quantrad Si PIN-diodes with differential filtering are employed as time-resolved x-ray detectors, whereas a multipinhole camera with suitable absorption filters is used for time-integrated analysis. The x-ray flux in different energy windows is measured as a function of the hydrogen filling pressure for each anode. The maximum values of the energy-integrated x-ray flux are found to be 1.36?0.06?J?sr?1, 2.70?0.11?J?sr?1 and 2.17?0.09?J?sr?1 for a cylindrical anode with a 75? cut at the tip, a tapered anode with a 75? cut at the tip and a tapered anode without any cut, respectively. The maximum x-ray emission in 4?-geometry is estimated to be 17.09?0.75?J, 27.91?1.28?J and 27.25?1.13?J with a cylindrical anode with a 75? cut at the tip, a tapered anode with a 75? cut at the tip and a tapered anode without any cut, respectively, and the corresponding wall plug efficiencies for x-ray generation are 0.95%, 1.55% and 1.51%. X-ray emission, presumably due to the electrons bombardment activity at the anode tip, was dominant, which is confirmed by the pinhole images. To demonstrate the feasibility of the present PF device as a possible x-ray source for good contrast radiography, a set of experimental images is presented.

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.

Spectral study of the electron beam emitted from a 3 kJ plasma focus

In a 3?kJ Mather-type plasma focus device operated in neon, the electron beam emission is investigated using both a magnetic electron energy analyser (in the 30?660?keV range) and a Rogowski coil (coupled with an appropriate RC passive integrator). Several electron emission features are identified and correlated with the x-ray emission in different energy ranges. The electron beam output shows very strong correlation with the general plasma dynamics (breakdown, axial and radial acceleration, pinch and post-pinch phases). The electrons energy spectra showed most of the electron emission concentrating below 200?keV and negligible emission with energy above 350?keV. At 4?mbar neon, the electron emission, as well as the beam energy, is the highest and has a good shot-to-shot reproducibility.

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.

Imaging of fusion reaction zone in plasma focus

In a low energy (2.3 kJ) Mather-type deuterium plasma focus,neutron and charged particle emission is investigated by using time-resolved neutrondetectors and time-integrated charged particle pinhole imaging camera. The time-integrated charged particle pinhole images demonstrate the varying influence of magnetohydrodynamic(MHD)instabilities vis-a-vis filling pressure. The neutron production mechanism at play strongly depends upon the pressure. At lower pressure, the plasma column is highly unstable due to MHDinstabilities and the neutron emission is found to be low with fluence anisotropy exceeding 3.5. At optimum pressure (2.5 mbar for this system), an almost stable dense plasma of about 17 mm3 volume is formed about 5 mm away from the anode, with neutron emission at its highest and the fluence anisotropy lowest. At higher pressure, the plasma column is stable, although it moves away from the anode like a jet and may then be called a moving boiler. In this case, the neutron emission is lowered compared to its optimum value and fluence anisotropy is increased. The data suggest beam-target mechanism at low pressure, trapped gyrating particles at optimum pressure and a jetlike moving boiler at higher pressure.

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 Cuu200aKα line emission mode. The emission is dominated by the interaction of electrons in the current sheath with the anode tip. The Cuu200aKα 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 Cuu200aKα lines in 4π geometry. The radiation yield represents a system efficiency of 1.7% for overall x-ray emission, and 0.35% for the Cuu200aKα line.