• D K Chakraborty

      Articles written in Pramana – Journal of Physics

    • Charged particle orbits in Kerr geometry with electromagnetic fields as viewed from locally non-rotating frames

      A R Prasanna D K Chakraborty

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      The charged particle orbits in electromagnetic fields on Kerr background as viewed from a locally non-rotating frame do not exhibit non-gyrating bound orbits, which was an essential feature in the earlier study of Prasanna and Vishveshwara, thus showing the non gyration to be due to the effect of dragging of inertial frames produced by the rotating black hole.

    • Motion of the charged particles off the equatorial plane of a Kerr black hole in an electromagnetic field

      D K Chakraborty A R Prasanna

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      Charged particle orbits off the equatorial plane of a Kerr black hole in an external electromagnetic field is studied, both for dipole as well as uniform magnetic field. Particles are found to get trapped by the magnetic field if the initial value of the parallel velocity is small. Bending of the field lines in the vicinity of the hole and the consequent trapping of the particles in an otherwise uniform magnetic field indicates the significance of general relativistic effects in such cases.

    • Circular orbits of an electron around a proton in Schwarzschild geometry

      D K Chakraborty

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      The energy of an electron in circular orbits around a proton in Schwarzschild geometry has been investigated and is found to be red shifted. The electrical dipole moment of such a system is also estimated.

    • 6.4 GHz ECR ion source at VECC

      G S Taki D K Chakraborty R K Bhandari

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      The 6.4 GHz ECR ion source that was indigenously developed a few years ago has been operating continuously for injecting oxygen and neon beams to the cyclotron since 1997. VEC-ECR is a single stage high magnetic field ion source provided with a negatively biased electron repeller placed on the axis, near the injection mirror point. The supply of cold electrons and use of low mass mixing gas improve the stability of ECR plasma. Very recently, the effect of aluminum oxide coating on the copper plasma chamber wall has been studied. The plasma chamber wall was coated with aluminum by vacuum evaporation method and then exposed to oxygen gas to form aluminum oxide. It was noticed that the process substantially shifts the charge state distribution to the higher charge state with an enhancement of ion current by an order of magnitude. With the aluminized plasma chamber, the VEC-ECR can now produce 12 µA of O7+, 6.5 µA of Ar12+, 1.5 µA of Kr20+ and 1.0 µA of Xe31+.

    • Experimental study of the dependence of beam current on injection magnetic field in 6.4 GHz ECR ion source

      G S Taki P R Sarma D K Chakraborty R K Bhandari P K Ray

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      The ion current from an electron cyclotron resonance (ECR) heavy ion source depends on the confining axial and radial magnetic fields. Some efforts were made by earlier workers to investigate magnetic field scaling on the performance of the ECR source. In order to study the dependence of the ion current on the injection magnetic field in the 6.4 GHz ECR source, we have measured the current by varying the peak injection field and have inferred that the variation of the current is exponential up to our maximum design injection field of 7.5 kG. An attempt has been made to understand this exponential nature on the basis of ion confinement time.

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