• Sushil Kumar

      Articles written in Pramana – Journal of Physics

    • Effect of upflowing field-aligned electron beams on the electron cyclotron waves in the auroral magnetosphere

      Sushil Kumar S K Singh A K Gwal

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      The role of low density upflowing field-aligned electron beams (FEBs) on the growth rate of the electron cyclotron waves at the frequencies $\omega_{r}$ < $\Omega_{­e}$, propagating downward in the direction of the Earth's magnetic field, has been analysed in the auroral region at $\omega_{e}/\Omega_{e}$ < 1 where $\omega_{e}$ is the plasma frequency and $\Omega_{­e}$ is the gyrofrequency. The FEBs with low to high energy ($E_{b}$) but with low temperature ($T_{|b}$) have no effect on these waves. The FEBs with $E_{b}$ < 1 keV and $T_{|b}$ (> 1.5 keV) have been found to have significant effect on the growth rate. Analysis has revealed that it is mainly the $T_{|b}$ which inhibits the growth rate (magnitude) and the range of frequency (bandwidth) of the instability mainly in the higher frequency spectrum. The inhibition in the growth rate and bandwidth increases with increase in $T_{|b}$. The FEBs with less $E_{b}$ (giving drift velocity) reduce growth rate more than the beams with larger $E_{b}$. The inhibition of growth rate increases with the increase in the ratio $\omega_{e}/\Omega_{e}$ indicating that the beams are more effective at higher altitudes.

    • Systematic of signature inversion in $(h_{11/2})_{\text{p}}\otimes (i_{13/2})_{\text{n}}$ for odd–odd nuclei in rare-earth nuclei

      Kawalpreet Kalra Alpana Goel Sukhjeet Singh Sushil Kumar A K Jain

      More Details Abstract Fulltext PDF

      Systematic features of the signature inversion phenomenon in $(h_{11/2})_{\text{p}}\otimes (i_{13/2})_{\text{n}}$ in doubly-odd rare-earth nuclei are presented. These features are generally observed in high-$j$ orbitals, mainly, in $(h_{9/2})$, $(h_{11/2})$ and $(i_{13/2})$. Calculations are carried out within the framework of the two quasiparticle plus rotor model (TQPRM) to explain strong odd–even staggering and signature inversion observed in these high-$j$ orbitals. The shifting of point of inversion to lower/higher spin with the increase in neutron/proton numbers is well explained by the calculations. It is found that 1/2[541] proton orbital of $h_{9/2}$ is necessary in the lower mass region to obtain the point of inversion.

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