Paramita Mukherjee

Optimization of Support System for FAIR Energy Buncher Dipole Magnet

In superconducting magnets, the coils are placed inside a helium chamber and suspended from the outer vacuum chamber using supports. Many superconducting magnets, currently under operation, use support links with intermediate temperature intercepts to reduce the heat leak to the helium system. The support links for large superconducting magnets, required for spectrometry, need to provide excellent alignment of the coils with respect to the yoke after cooldown and magnet energization to achieve high magnetic field qualities. Optimization of such support system requires detailed design analysis of the entire structure using finite-element method software. This paper presents an analytical model for studying the effect of support stiffness over its performance after cooldown and magnet energization. Higher stiffness of the supports ensures that the coil movement is less under magnetic force. On the other hand, higher stiffness results in higher conduction heat load to helium. This study tries to find out the most suitable value of support stiffness that ensures both the conditions-less movement of coil and less conduction heat load to helium. Optimization of the support system for a large spectrometer magnet of FAIR, Germany is presented here using this model. This study shows that this model also finds the instability region of the support system where any small movement of the coil results in uncontrollable deformation. In addition, the results show that the initial alignment of the coil is another important parameter to achieve the desired coil alignment after energization and how this can be achieved at different magnet excitation levels.

Microstructural characterisation of proton irradiated niobium using X-ray diffraction technique

Abstract The microstructural parameters in pure Nb, irradiated with 5 MeV proton beam have been evaluated as a function of dose using X-ray diffraction line profile analysis. In order to assess the microstructural changes in the homogeneous region and in the peak damage region of the damage energy deposition profile, X-ray diffraction patterns have been collected using two different geometries (Bragg-Brentano and parallel beam geometries). Different X-ray line profile analysis like Williamson–Hall (W–H) analysis, modified W–H analysis, double-Voigt analysis, modified Rietveld technique and convolutional multiple whole profile fitting have been employed to extract the microstructural parameters like coherent domain size, microstrain within the domain, dislocation density and arrangement of dislocations. The coherent domain size decreases drastically along with increase in microstrain and dislocation density in the first dose for both the geometries. With increasing dose, a decreasing trend in microstrain associated with decrease in dislocation density is observed for both the geometries. This is attributed to the formation of defect clusters due to irradiation which with increasing dose collapse to dislocation loops to minimise the strain in the matrix. This is corroborated with the observation of black dots and loops in the TEM images. No significant difference is observed in the trend of microstructural parameters between the homogeneous and peak damage region of the damage profile.

Positron Annihilation Study of Zr-2.5 wt.% Nb alloy Irradiated by Ar9+ heavy ions

Zr-2.5 Nballoy is used as a pressure tube material in pressurized heavy water reactor (PHWR). It is one of the most critical component which decides the lifespan of the reactor. The in-reactor degrading phenomenon of prime concern is dimensional changes caused by irradiation induced creep and growth processes. The present study aims to understand the mechanism of irradiation damage by irradiating the alloy with heavy ion. Such type of irradiation study would facilitate larger damage of material in a shorter time. Zr-2.5Nb alloy samples were irradiated using 315 keV Ar9+ ion for different durations. The irradiation doses were varied in the range of 3.1X1015 to 4.17X1016 Ar9+/cm2. SRIM calculation was carried out to evaluate damage profile in the irradiated samples. Beam based Positron Annihilation Spectroscopy (PAS) technique was used for depth profiling to characterize defect distribution in the alloys. The no. of defects generated is seen to increase with the increase in the fluence.

Scaling behaviour of Portevin-Le Chatelier effect

The scaling behavior of the Portevin-Le Chatelier (PLC) effect is studied by deforming a substitutional alloy, Al-2.5%Mg and an interstitial alloy, low carbon steel (0.15%C, 0.33%Mn, 0.04%P, 0.05%S, 0.15%Si and rest Iron) at room temperature for a wide range of strain rates. To reveal the exact scaling nature, the time series data of true stress vs. time, obtained during the tensile deformation (corrected for drift due to strain hardening by polynomial fitting method), are analyzed by two complementary methods: the standard deviation analysis and the diffusion entropy analysis. From these analyses we could establish that in the entire span of strain rates, PLC effect showed Levy walk type of scaling property.