Dynamics of ion cloud in a linear Paul trap

A linear ion trap setup has been developed for studying the dynamics of trapped ion cloud and thereby realizing possible systematics of a high precision measurement on a single ion within it. The dynamics of molecular nitrogen ion cloud has been investigated to extract the characteristics of the trap setup. The stability of trap operation has been studied with observation of narrow nonlinear resonances pointing out the region of instabilities within the broad stability region. The secular frequency has been measured and the motional spectra of trapped ion oscillation have been obtained by using electric dipole excitation. It is applied to study the space charge effect and the axial coupling in the radial plane.Comment: Colloquium paper, 9 pages, 6 figure

Vortex dynamics and second magnetization peak in PrFeAsO0.60_{0.60}F0.12_{0.12} superconductor

We have studied the vortex dynamics in the PrFeAsO$_{0.60}$F$_{0.12}$ superconducting sample by dc magnetization and dynamic magnetization-relaxation rate $(Q)$ measurements. The field dependence of the superconducting irreversible magnetization $M_s$ reveals a second magnetization peak or fishtail effect. The large value of $Q$ is an indication of moderate vortex motion and relatively weak pinning energy. Data analysis based on the generalized inversion scheme suggests that the vortex dynamics can be described by the collective pinning model. The temperature dependence of the critical current is consistent with the pinning due to the spatial variation in the mean free path near a lattice defect ($\delta l$ pinning). The temperature and field dependence of $Q$ indicates a crossover from elastic to plastic vortex creep with increasing temperature and magnetic field. Finally, we have constructed the vortex phase diagram based on the present data.Comment: 11 pages, 8 Figures, Accepted for publication in Journal of Applied Physic