Lee, Paul Choon Keat

The total current I_total waveform in a plasma focus discharge is the most commonly measured quantity, contrasting with the difficult measurement of I_pinch. However, yield laws should be scaled to focus pinch current I_pinch rather than the peak I_total. This paper describes how I_pinch may be computed from the I_total trace by fitting a computed current trace to the measured current trace using the Lee model. The method is applied to an experiment in which both the I_total trace and the plasma sheath current trace were measured. The result shows good agreement between the values of computed and measured I_pinch.

High energy neutrons, more than 2.45 MeV from deuteron-deuteron fusion reaction, have been measured in backward direction of plasma focus devices in many laboratories. However the experimental evidence for high energy deuterons responsible for such neutrons has not been reported so far. In this brief communication, backward high energy deuteron beam from NX2 plasma focus [M. V. Roshan et al., Phys. Lett. A 373, 851 (2009)] is reported, which was measured with a direct and unambiguous technique of nuclear activation. The relevant nuclear reaction for the target activation is ¹²C (d, n)¹³N , which has a deuteron threshold energy of 328 keV.

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) x 10⁴ n/shot for pure D₂ filling at 3 mbars was enhanced to (3.14 ± 0.4) x 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.

The emerging paradigm of oxide-based devices are reshaping the frontiers of sustainable electronics and enabling new functionalities like ferroelectric-photovoltaics, photo-catalytic activity, ferroelectric logics, and terahertz-scale actuation. The intriguing advantages of BiFeO₃ (BFO) based oxide electronics offers the possibility of combining electric and magnetic degrees of freedom and is of interest in applications ranging from non-volatile random-access memories, multiple state storage media, tunnelling barriers, actuation, and sensors. Here, we investigate structural evolution and device performance of a cost-effective and unexplored BFO doped derivative i.e. (Gd, Zn) co-doped BFO thin films synthesized using commercially viable spin-casting technique. Owing to the competing change in dopant cation sizes w.r.t. Host lattice, ABO3 rhombohedral perovskite structure of the BFO did not transform while the optical band gap sequentially reduced from 2.65 to 2.53 eV with increasing Gd–Zn co-dopant concentration. Further, the effects of co-doping and asymmetric electrodes on the IV-characteristics of capacitors and the underlying conduction mechanism of these devices are investigated. Photoconductivity studies show three orders larger photocurrent arising from grain-boundary contributions in 2% (Gd, Zn) – BFO film exhibiting rapid, stable and repeatable photo-response which makes them useful for photosensitive capacitor applications.

This work aims to test the concept of an activation detector for pulsed DD fusion neutron sources, based on the production of metastable ^79m within a LaBr₃(Ce) scintillator crystal via (n, n') inelastic scattering. The pulsed neutron source employed is the NX3 Plasma Focus (PF) device operated in deuterium gas, which yields about 10⁹ neutrons per shot. A range of D₂ gas pressures, from 1 to 13 mbar are used to vary the test conditions. For the sake of comparison, a beryllium fast-neutron activation detector is used simultaneously with the LaBr₃(Ce), and for each NX3 PF shot we derive neutron yield values from both Be and LaBr₃(Ce) detectors, denoted Y_n^Be and Y_n^LaBr. The two detectors are positioned in the equatorial plane (θ=90˚) of the NX3 to expose them to bursts of neutrons with energies close to 2.5 MeV, to simulate a thermonuclear DD fusion source. Overall, the shot-to-shot values of Y_n^Be and Y_n^LaBr obtained compare reasonably well. At each D₂ gas pressures the 10-shot averaged values〈Y_n^Be〉 and 〈Y_n^LaBr〉are mostly within 10% of one another; for the worst case (10 mbar)〈Y_n^LaBr〉is 25% higher than〈Y_n^Be〉. Overall, it is concluded that LaBr₃(Ce) scintillation detectors can function as a capable and readily obtainable fast-neutron activation detector for measuring neutron yields from pulsed DD fusion sources.