Rishi Verma

Order of magnitude enhancement in neutron emission with deuterium-krypton admixture operation in miniature plasma focus device

The effect of varied concentrations of deuterium-krypton (D2–Kr) admixture on the neutron emission of a fast miniature plasma focus device was investigated. It was found that a judicious concentration of Kr in D2 can significantly enhance the neutron yield. The maximum average neutron yield of (1±0.27)×104 n/shot for pure D2 filling at 3 mbars was enhanced to (3.14±0.4)×105 n/shot with D2+2% Kr admixture operation, which represents a >30-fold increase. More than an order of magnitude enhancement in the average neutron yield was observed over the broader operating range of 1–4 mbars for D2+2% Kr and D2+5% Kr admixtures.

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.

Experimental study of neutron emission characteristics in a compact sub-kilojoule range miniature plasma focus device

In order to gain insight into the possible neutron production mechanism in sub-kilojoule miniature plasma foci, the anisotropy in neutron and hard x-ray emissions from a newly developed fast miniature plasma focus device (2.4??F, 27?nH, T/4 ~ 400?ns, 12?15?kV, 170?270?J, total mass ~25?kg) is investigated. The system produces an average neutron yield of (1.2?0.2) ? 106?neutrons/shot into 4? sr at ~80?kA peak discharge current and 5.5?mbar deuterium operation, as measured by a 3He proportional counter. Relative measurements of radiation yields, to gauge the emission anisotropy, have been performed using a pair of fast scintillator?photomultiplier detectors placed along the axial (0?) and radial (90?) directions. The average forward to radial neutron yield anisotropy is found to be 1.3?0.2. The average peak neutron energy for the axial and radial directions is estimated to be (2.9?0.3)?MeV and (2.6?0.1)?MeV, respectively. The observed higher fluence along the anode axis and the coincidence between occurrence of maximum neutron yield and anisotropy at 5.5?mbar deuterium filling gas pressure, suggest that the neutron production mechanism in the sub-kilojoule range miniature plasma focus device FMPF-1 may be predominantly beam?target in nature.

Realization of enhancement in time averaged neutron yield by using repetitive miniature plasma focus device as pulsed neutron source

In this paper, we report the experimental demonstration of enhancement in time averaged neutron yield by an order of magnitude, using the fast miniature plasma focus FMPF-2 in repetitive mode. The newly developed FMPF-2 device (2.4 µF, 56 nH, 13.8 kV, T/4 ~ 575 ns) operates up to 10 Hz in the quasi-continuous mode. Using pure deuterium as the fuelling gas, the time averaged neutron output of (6.2 ± 4) × 105 neutrons s−1 at 1 Hz operation was enhanced to (6.5 ± 0.6) × 106 neutrons s−1 at 10 Hz operation for the burst length of 30 consecutive shots. The stability in neutron emission in repetitive mode of operation from 1 to 10 Hz has also been investigated and the evidenced consequential issues of critical concern that are responsible for degradation in neutron yield during the repetitive mode of operation have been highlighted.

Order of magnitude enhancement in x-ray yield at low pressure deuterium-krypton admixture operation in miniature plasma focus device

In a 200J fast miniature plasma focus device about 17- and 10-fold increase in x-ray yield in spectral ranges of 0.9–1.6keV and 3.2–7.7keV, respectively, have been obtained with deuterium-krypton (D2–Kr) admixture at operating pressures of ⩽0.4mbar. In the pressure range of >0.4–1.4mbar, about twofold magnification in average x-ray yield along with broadening of optimum pressure range in both spectral ranges were obtained for D2–Kr admixtures. An order of magnitude enhancement in x-ray yields at low pressures for admixture operation will help in achieving high performance device efficiency for lithography and micromachining applications.

Neon soft x-ray emission studies from the UNU-ICTP plasma focus operated with longer than optimal anode length

The UNU-ICTP plasma focus with a significantly longer than conventional anode can still be a reasonably good neon soft x-ray (SXR) source. The highest average neon SXR yield of 3.3 J was achieved at 3 mbar. The time difference between the two first peaks of the voltage probe signal at the radial collapse phase was found to be inversely related to the SXR yield, i.e. the smaller the time difference, the higher the yield and vice versa. The estimation of average current sheath speeds using the shadowgraphic method coupled with laser and focus peak timing signals showed that the average axial rundown speed is similar to the one obtained for the optimal anode length but the average radial compression speed is decreased significantly. The range of pressure for a good neon SXR yield, however, has become much narrower, making efficient plasma focus operation a very sensitive function of the filling gas pressure for longer than the optimal anode length.

Neutron Emission Characteristics of NX-3 Plasma Focus Device: Speed Factor as the Guiding Rule for Yield Optimization

This paper reports the results of characterization and optimization experiments carried out on a newly developed NX-3 dense plasma focus device (20 kJ at 20 kV, a quarter time period of ~ 3 μs, and 10 kJ/600 kA at 14 kV) at the Plasma Radiation Source Laboratory, NIE, Nanyang Technological University, Singapore. Initial experiments were conducted with an electrode assembly configuration having anode radius and length of 20 and 160 mm, respectively, for detailed neutron emission characterization of NX-3 device followed by further optimization of neutron yield using various other electrode configurations designed using the Lee Code. At ≥10-kJ operation, the average neutron yield on the order of 109 neutrons/pulse in 4πsr was obtained for the deuterium filling gas pressure range of 6-8 mbar. The neutron yield of ~ 4.6 ×109 neutrons/pulse at 10 kJ/6 mbar is the highest ever reported for a device with the same stored energy. The neutron anisotropy measurements point to the beam-target mechanism as the dominant neutron production mechanism for NX-3 plasma focus device. Further optimization of neutron yield in NX-3 was achieved with the peak average neutron yield being enhanced from ~ (2.38 ±0.31) ×109 neutrons/shot for the initial electrode configuration to about ~ (3.40 ±0.43) ×109 neutrons/shot for the electrode configuration with anode radius and length of 26 and 140 mm, respectively. The analysis of neutron yield results for various electrode assembly configurations demonstrates the speed factor as a key optimization tool for maximization of neutron yield.

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.

Preliminary Results of Kansas State University Dense Plasma Focus

Kansas State University (KSU) dense plasma focus (DPF) is a 2.5-kJ DPF machine newly commissioned at the Plasma Radiation Physics Laboratory at KSU. The machine was designed to be used as a multiradiation source for applications in nuclear science and engineering. Neutrons are emitted from deuterium-deuterium (D-D) fusion reactions during high-power electric discharges at 17 kV, 140 kA, and 5 mbar. The machine circuit parameters were calculated using the short-circuit test. The emitted neutrons were measured using several radiation detection techniques. The 2.45-MeV characteristic D-D neutron energy was confirmed using the time-of-flight technique using a BC-418 plastic scintillator. The maximum neutron yield was roughly measured to be 2.8 × 108 neutrons per shot using a set of BTI BD-PND bubble detectors. Moreover, the neutron yield variation with pressure was measured and compared with the computed neutron yield using Lee model. Finally, the measured current showed good agreement with Lee six-phase model.

Design and performance analysis of transmission line-based nanosecond pulse multiplier

Conventionally, Marx generators are used for the production of short duration, high voltage pulses but since many discharge gap switches are utilized for stepping up the voltage, there are many disadvantages. Here, an alternative and much simpler technique for the multiplication of nanosecond high voltage pulses has been presented in which multiplication takes place by switching single spark gap providing voltage gain of ‘nxV’ wheren is the subsequent number of stages. Stepped up high voltage pulse with fixed voltage gain of defined shape with fast rise time and good flat top is produced without using additional pulse-forming network. Its operation has been made repetitive by switching single spark gap. Multipurpose use, low cost, small size, light weight (weighing less than 50 kg) and portability are the additional benefits of the system. The reported nanosecond pulser has been made by cascading three stages of Blumlein. To cross check its performance the parasitic impedance of the system has been evaluated to realize its adverse effect on the voltage gain and pulse shape. Also its operation has been simulated by PSPICE circuit simulator program and good agreement has been obtained between simulated and experimental results. Applications of this pulse generator include X-ray generation, breakdown tests, ion implantation, streamer discharge studies and ultra wideband generation, among others.