Abstract. Neutron bursts with magnitude up to 10 9 were observed to be associated with atmospheric lightning discharge. where D is deuterium (1H 2) and He 3 is helium 3. To observe, if neutron emission <2 x 10 •ø is associated with lightning, a sensitive detector is required (the neutron emission is so low that it will make no statistically significant change in the atomic isotopes; therefore neutrons cannot be detected by anomalies in isotopes). We report here our effort to detect neutron bursts, associated with lightning, using a highsensitivity, large area neutron detecting system. The techniques used to record neutron emission data had an important difference. The laboratory at Gulmarg triggered their detection system by lightning-produced electromagnetic radiation and then recorded the neutron bursts. However, this technique has one pitfall. A large burst of cosmic ray may trigger lightning and also produce neutrons (by muons or spallation), which may be mistakenly assumed to be produced by lightning. Therefore our group at Mumbai recorded the bursts in untriggered mode and observed the burst neutron emission under different weather conditions. Since cosmic rays emission remains, on the average, the same for different weather conditions, therefore observing higher burst counts during lightning suggests neutron emission (either produced or associated with lightning). The two techniques are complimentary; therefore positive results by both the techniques confirm neutron emission is associated with lightning. Experimental SetupThe neutron detection system at Mumbai consisted of 16 BF 3 detectors of 0.05 m diameter, embedded in polyethylene neutron slowing-down material. The detector setup was housed in a professionally made, and tested, radio-frequency shielded enclosure. It could shield radio-frequency disturbances, radiated as well as conducted (through wire/cables) until 10 GHz by 110 dB. This provided the detection setup, immunity from radio-frequency interferences, which were even two orders of magnitude higher than interference produced during lightning. The burst counts, emitted in 100-/,rs time intervals, were continuously detected and stored.The number of neutrons (N) produced in a burst, associated with lightning, is given by Cn = K [exp(-qr)/d2]Nwhere Cn are counts recorded by detecting system during lightning and d is the distance between the detector and burst neutron source, which in this case is lightning. Exp(-qr) represents the attenuation of neutrons in moist atmosphere and 6867
For long-life operation, easy to mount and compact in size penning type ion sources are widely used in different fields of research such as neutron generators, material research, and surface etching. One penning type ion source has been developed in our laboratory. Applying high voltage of 2 kV between two oppositely biased electrodes and using permanent magnet of 500 gauss magnetic field along the axis, we had produced the glow discharge in the plasma region. The performance of this source was investigated using nitrogen gas. Deuterium ions were produced and extracted on the basis of chosen electrodes and the angle of extraction. Using a single aperture plasma electrode, the beam was extracted along the axial direction. The geometry of plasma electrode is an important factor for the efficient extraction of the ions from the plasma ion source. The extracted ion current depends upon the shape of the plasma meniscus. A concave shaped plasma meniscus produces converged ion beam. The convergence of extracted ions is related to the extraction electrode angle. The greater the angle, the more the beam converges. We had studied experimentally this effect with a compact size penning ion source. The detailed comparison among the different extraction geometry and different electrode angle are discussed in this paper.
Plasma foci of compact sizes and operating with low energies (from tens of joules to few hundred joules) have found application in recent years and have attracted plasma-physics scientists and engineers for research in this direction. We are presenting a low energy and miniature plasma focus which operates from a capacitor bank of 8.4 μF capacity, charged at 4.2–4.3 kV and delivering approximately 52 kA peak current at approximately 60 nH calculated circuit inductance. The total circuit inductance includes the plasma focus inductance. The reported plasma focus operates at the lowest voltage among all reported plasma foci so far. Moreover the cost of capacitor bank used for plasma focus is nearly 20 U.S. dollars making it very cheap. At low voltage operation of plasma focus, the initial breakdown mechanism becomes important for operation of plasma focus. The quartz glass tube is used as insulator and breakdown initiation is done on its surface. The total energy of the plasma focus is approximately 75 J. The plasma focus system is made compact and the switching of capacitor bank energy is done by manual operating switch. The focus is operated with hydrogen and deuterium filled at 1–2 mbar.
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