• S N Sen

      Articles written in Pramana – Journal of Physics

    • Validity of diffusion theory in radio frequency breakdown in molecular gases in longitudinal magnetic field

      S N Sen D C Jana

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      The breakdown of a gas excited by a radio frequency voltage of frequency 5.6 MHz has been studied in a cylindrical discharge tube 7.2 cm long and 2.9 cm in dia and fitted with two internal electrodes at a distance of 2.5 cm in hydrogen, oxygen and air within the pressure range of a few microns to 2 torr in the presence of a longitudinal magnetic field varying from zero to 800 G. Experimental results indicate that the breakdown is diffusion controlled and the values of (a/P) at differentE/P values calculations obtained by Brown as well as by Kihara’s theory have been compared with (a/P) values obtained in the literature. It is concluded that the diffusion theory is also valid when the frequency of the exciting voltage is scaled down to radio frequency provided the collision frequency is much higher than the exciting frequency. The change of diffusion length in the presence of longitudinal magnetic field has been obtained from measuredE/P values and comparison with theoretical values indicates that there is quantitative agreement for small (H/P) values whereH is the magnetic field. The calculated values of pressure at which the breakdown voltage shows a minimum in the presence of magnetic field is in very good agreement with experimental values. It is concluded that in the presence of magnetic field also the loss of electrons takes place predominantly by the process of diffusion.

    • Enhancement of spectral intensities of mercury triplet lines in longitudinal magnetic field

      S N Sen S K Sadhya

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      The variation of intensity of the spectral lines of the triplet series of mercury namely (73S1 → 63P012) (λ5461 Å,λ 4358 Å,λ 4047 Å) in the presence of a longitudinal magnetic field between zero and 2000 gauss has been investigated. The effect of magnetic field is found to be different as regards the variation of intensity and the occurrence of maxima in the three lines. These variations can be explained by considering the reabsorption of the spectral lines. A mathematical theory has been presented and an expression for (Iul)B/Iul has been deduced where (Iul)B and (Iul) are the intensities of the lines with and without the magnetic field. The experimental results agree fairly well with the theoretical model.

    • Voltage current and power relation in an arc plasma in a variable axial magnetic field

      S N Sen M Gantait

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      The variation of voltage, current and output power in a mercury arc plasma has been investigated in an axial magnetic field (0–1350 G) for three values of discharge current namely 3, 4 and 5 A. The voltage increases and current decreases almost linearly and the output power also increases with increase of the magnetic field. The conductivity value in magnetic field has been calculated and an analytical expression presented to represent the variation of conductivity in the magnetic field. Utilizing this expression the variation of output power with magnetic field can be explained.

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