Mahmud Vahdat Roshan

FePt nanoparticle formation with lower phase transition temperature by single shot plasma focus ion irradiation

Uniform FePt nanoparticles were synthesized through nanostructuring of pulsed laser deposited FePt thin films by single shot H+ ion irradiation using a plasma focus device. The annealing temperature required for phase transition from low Ku face-centred cubic to high Ku face-centred tetragonal, for ion irradiated samples, is simultaneously lowered down to 400 °C. The energetic H+ ion irradiation significantly reduces the activation energy for atomic ordering by increasing the number of vacancies. The advantage of using a plasma focus device is that it can achieve nanostructuring in much shorter time, in single shot ion exposure with pulse duration of typically about a few hundreds of nanoseconds, as compared with much longer duration required by continuous ion sources.

Short-Lived PET Radioisotope Production in a Small Plasma Focus Device

High-energy deuterons from a small plasma focus device (1.7 kJ) have been used for short-lived radioisotope production. For the 12C(d, n)13N reaction, 40 kBq of 13N was obtained by bombarding a graphite target at a 1-Hz shot repetition rate for 30 s. This could be increased to 10 MBq at a 16-Hz repetition rate. Plasma focus devices operating with higher bank energies should produce substantially higher isotope yields.

Nanostructured magnetic CoPt thin films synthesis using dense plasma focus device operating at sub-kilojoule range

A repetitive NX2 dense plasma focus (DPF) device, operating at a low voltage of 8 kV with a stored energy of capacitor bank in the sub-kilojoule range (~880 J), was successfully used to deposit nanostructured magnetic CoPt thin films. The samples were synthesized at different filling hydrogen gas pressures and using different numbers of plasma focus deposition shots. The size of agglomerates/nanoparticles and the thickness of the CoPt thin films depend strongly on the filling gas pressure and the number of plasma focus deposition shots; hence it provides a possibility to control the CoPt agglomerates/nanoparticles size and the deposition rate by simply changing the operating parameters of the DPF system. The typical deposition rate of nanostructured CoPt thin film in the DPF device is much higher as compared with that of conventional PLD. The as-deposited CoPt nanoparticles are in the magnetically soft fcc phase and an annealing temperature of about 600 °C is required for phase transition to the magnetically hard fct phase, which may find possible applications in high density data storage.

Neutron and high energy deuteron anisotropy investigations in plasma focus device

The anisotropies of neutron and high energy deuteron emissions from the NX2 plasma focus device [M. V. Roshan et al., Phys. Lett. A 373, 851 (2009)] are studied. The nuclear activation of graphite targets is used to measure the fluences of high energy deuterons in the axial and radial directions. Two bismuth germanate scintillation detectors connected to multichannel analyzer systems are used for the detection of 511 keV gamma rays resulting from positron annihilation in the two targets. In addition, fast neutron activation detectors are employed to measure the axial and radial fluences of fusion neutrons. These detection systems are calibrated using the simulation code MCNPX [L. S. Waters et al., AIP Conf. Proc. 896, 81 (2007)]. Two distinct regimes of neutron and deuteron anisotropies are observed for the NX2 device. For deuterium gas pressures below 10 mbar, the neutron anisotropy increases with increasing pressure, while the overall neutron yield remains low. For gas pressures of 10–14 mbar, the neutr...

Correlation Analysis of Intense and High-Energy Deuteron Beam, Pinch Images, and Neutron Yield

The time-integrated imaging of pinched plasma column in the NX2 plasma focus device is performed using a general-purpose digital SLR camera with neutral density filters (ND 0.9). Although it is very simple, some useful information is obtained from the pinch phase of plasma focus device, and the images are compared with the neutron yield, electron, and ion beams produced in the compressed plasma column. The correlation between the pinch images, the range of deuteron energies, and the optimum neutron condition shows two regimes of plasma focus performance: high-pressure regime for maximum neutron yield production and low-pressure regime for high-energy ion (and electron) beam production.

Effect of Anode Shapes on Neutron Emission from a Repetitive Plasma Focus Device

The conventional tapered anode of the NX2 repetitive plasma focus device has been changed to two other shapes (straight and spherical) to investigate the effect of anode shape on neutron emission characteristics of the device. The newly designed beryllium counter and 3He proportional counter are used for estimation of neutron yield and time resolved neutron emission characteristics are measured using two PMT based plastic scintillator detectors located at different radial distances from the anode axis. It is found that the straight anode mostly produces multiple neutron peaks, the spherical anode on the other hand essentially has a single neutron peak in its signal while the tapered anode has a mixed behavior. It is found that there is no significant difference in the average neutron yield (typically of the order of 107 neutrons per shot) for different anode shapes. However the pressure at which the maximum neutron yield occurs depends on the anode shape. The anode with spherical tip shows the most stable neutron emission with consistently good neutron yield over a much wider pressure range than the other anode shapes.