• B S Rao

      Articles written in Pramana – Journal of Physics

    • A comparative study of the ionic keV X-ray line emission from plasma produced by the femtosecond, picosecond and nanosecond duration laser pulses

      V Arora P A Naik B S Rao P D Gupta

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      We report here an experimental study of the ionic keV X-ray line emission from magnesium plasma produced by laser pulses of three widely different pulse durations (FWHM) of 45 fs, 25 ps and 3 ns, at a constant laser fluence of $\sim 1.5 \times 10^4$ J cm-2. It is observed that the X-ray yield of the resonance lines from the higher ionization states such as H- and He-like ions decreases on decreasing the laser pulse duration, even though the peak laser intensities of $3.5 \times 10^{17}$ W cm-2 for the 45 fs pulses and $6.2 \times 10^{14}$ W cm-2 for the 25 ps pulses are much higher than $5 \times 10^{12}$ W cm-2 for the 3 ns laser pulse. The results were explained in terms of the ionization equilibrium time for different ionization states in the heated plasma. The study can be useful to make optimum choice of the laser pulse duration to produce short pulse intense X-ray line emission from the plasma and to get the knowledge of the degree of ionization in the plasma.

    • Three-dimensional simulation of laser–plasma-based electron acceleration

      A Upadhyay K Patel B S Rao P A Naik P D Gupta

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      A sequential three-dimensional (3D) particle-in-cell simulation code PICPSI-3D with a user friendly graphical user interface (GUI) has been developed and used to study the interaction of plasma with ultrahigh intensity laser radiation. A case study of laser–plasma-based electron acceleration has been carried out to assess the performance of this code. Simulations have been performed for a Gaussian laser beam of peak intensity $5 \times 10^{19}$ W/cm2 propagating through an underdense plasma of uniform density $1 \times 10^{19}$ cm-3, and for a Gaussian laser beam of peak intensity $1.5 \times 10^{19}$ W/cm2 propagating through an underdense plasma of uniform density $3.5 \times 10^{19}$ cm-3. The electron energy spectrum has been evaluated at different time-steps during the propagation of the laser beam. When the plasma density is $1 \times 10^{19}$ cm-3, simulations show that the electron energy spectrum forms a monoenergetic peak at $\sim 14$ MeV, with an energy spread of $\pm 7$ MeV. On the other hand, when the plasma density is $3.5 \times 10^{19}$ cm-3, simulations show that the electron energy spectrum forms a monoenergetic peak at $\sim 23$ MeV, with an energy spread of $\pm 7.5$ MeV.

    • Solar diurnal anisotropy measured using muons in GRAPES-3 experiment in 2006

      P K Mohanty D Atri S R Dugad S K Gupta B Hariharan Y Hayashi A Jain S Kawakami S D Morris P K Nayak A Oshima B S Rao

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      The GRAPES-3 experiment at Ooty contains a large-area (560 m$^{2}$) tracking muon detector. This detector consists of 16 modules, each 35 m$^{2}$ in area, that are grouped into four supermodules of 140 m$^{2}$ each. The threshold energy of muons is $\sec(\theta)$ GeV along a direction with zenith angle $\theta$ and the angular resolution of the muon detector is $6^{\circ}$. Typically, it records $\sim 4 \times 10^{9}$ muons every day. The muon detector has been operating uninterruptedly since 2001, thus providing a high statistics record of the cosmic ray flux as a function of time over one decade. However, prior to using these data, the muon rate has to be corrected for two important atmospheric effects, namely, variations in atmospheric pressure and temperature. Because of the near equatorial location of Ooty ($11.4^{\circ}$N), the seasonal variations in the atmospheric temperature are relatively small and shall be ignored here. Due to proximity to the equator, the pressure changes at Ooty display a dominant 12 h periodic behaviour in addition to other seasonal changes. Here, we discuss various aspects of a novel method for accurate pressure measurement and subsequent corrections applied to the GRAPES-3 muon data to correct these pressure-induced variations. The pressure-corrected muon data are used to measure the profile of the solar diurnal anisotropy during 2006. The data, when divided into four segments, display significant variation both in the amplitude ($\sim 45\%$) and phase ($\sim42$ m) of the solar diurnal anisotropy during 2006, which was a period of relatively low solar activity.

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