• BHASKAR BISWAS

      Articles written in Pramana – Journal of Physics

    • Commissioning and validation of the injector and electron beam transport systems for the IR-FEL at RRCAT

      SONA CHANDRAN BHASKAR BISWAS SHANKAR LAL ARVIND KUMAR R S SAINI M KHURSHEED SAKET KUMAR GUPTA PRAVIN NERPAGAR R K PANDIT K K PANT

      More Details Abstract Fulltext PDF

      The first observation of lasing in an infra-red free electron laser (IR-FEL) at the Raja Ramanna Centre for Advanced Technology has been reported recently with a measured power output, i.e. $\sim10^{5}$ times higher than the expected spontaneous radiation power for the electron beam parameters used in the experiment. IR-FEL design simulations, however, estimate a power gain of $10^{7}$ which is three orders of magnitude higher than the experimentally achieved value. To understand this difference between the measured and the expected power output from the IR-FEL, the electron beam used in the experiments has been characterised and FEL simulations have been repeated after considering the measured electron beam parameters. A reasonably good agreement is obtained between the measured results and those predicted by FEL simulations. Experiments have also been performed to study the expected variation in electron beam properties over a macropulse, which should be minimum for an oscillator FEL like the IR-FEL. This paper reports the results from the experiments for characterisation of the electron beam in the IR-FEL set-up and the results from FEL simulations, considering these measured electron beam parameters.

    • Compact and strong window core steering magnets with homogeneous dipole field

      BHASKAR BISWAS

      More Details Abstract Fulltext PDF

      A typical axially compact, square window core steering magnet has a very small 2D good field region (GFR) of 18% of the iron core aperture. It is weak with 85% of its dipole in the fringes. Increasing the currentfed area (coil) to increase the dipole strength lowers the good field zone. Some novel and simple coil shapes can expand their 2D/3D GFR to 94/40% of the iron aperture. They are axially compact, i.e., stronger with 60–65% of the dipole in fringes. The reduction in error sextupole field is more profound. A novel 2D coil shape with vanished 2D sextupole proves the concept. For axially short cores, a gap between the coil and the iron aperture can increase the 3D sextupole, missing in 2D simulations. A new asymmetric one-axis steering magnet core and coil shape with high dipole field and homogeneity is also given. The new, practical coil shapes significantly improve the dipole field homogeneity and strength of these magnets.

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