Nisith K. Das

Nonlinear response of radon and its progeny in spring emission.

Temporal fluctuations of Rn-222 and Po-218 emanated from a thermal spring have been investigated. Nonlinear statistical approach has been employed to the time sequences as to bring out the ingrained structure of the experimental data and the underlying mechanism therein. It is observed that the irregular time series are nonrandom and consistent with the nonlinear process. In addition, our findings reveal that the experimental time dependent data bears the signature of chaotic traits.

Multi-component Adsorption Studies on LiLSX and CMS for Helium Separation

An experimental study is reported on the purification of helium gas from a ternary mixture of helium (30 mol%), nitrogen (60 mol%) and oxygen (10 mol%) employing a single-column Pressure Swing Adsorption (PSA) process. Appropriate adsorbents were selected for effecting this separation by exploiting adsorption equilibrium isotherm and breakthrough measurements in order to choose the optimum operating conditions for the PSA process. The adsorption and breakthrough characteristics for the pure gas as well as for the mixed gases were also examined. The pure gas adsorption isotherms were obtained employing a static method, while mixed gas adsorption studies were undertaken using a volumetric chromatography technique. Computer simulations, along with breakthrough experiments, were performed to study the adsorption dynamics and thereby identify suitable operating parameters as well as vessel dimensions. Based on these data, a single-column PSA system has been developed for the separation of helium gas. The selection of adsorbent, effect of feed pressure, flow rate and cycle time related to the process performance has been established. It was noted that employing an adsorbent such as LiLSX at a flow rate of 2 ℓ/min, a working pressure of 500 kPa and a feed time of 180 s appears to be appropriate for obtaining 98.3% pure He with 65% recovery for the column dimensions chosen.

Cryocooler based test setup for high current applications

A cryo-cooler based cryogenic test setup has been designed, fabricated, and tested. The setup incorporates two numbers of cryo-coolers, one for sample cooling and the other one for cooling the large magnet coil. The performance and versatility of the setup has been tested using large samples of high-temperature superconductor magnet coil as well as short samples with high current. Several un-calibrated temperature sensors have been calibrated using this system. This paper presents the details of the system along with results of different performance tests.

Three stage vacuum system for ultralow temperature installation

We use a three stage vacuum system for developing a dilution fridge at VECC, Kolkata. We aim at achieving a cooling power of 20μW at 100mK for various experiments especially in the field of condensed matter and nuclear physics. The system is essentially composed of four segments-bath cryostat, vacuum system, dilution insert and 3He circulation circuit. Requirement of vacuum system at different stages are different. The vacuum system for cryostat and for internal vacuum chamber located within the helium bath is a common turbo molecular pump backed by scroll pump as to maintain a vacuum ~10−6mbar. For bringing down the temperature of the helium evaporator, we use a high throughput Roots pump backed by a dry pump. The pumping system for 3He distillation chamber (still) requires a high pumping speed, so a turbo drag pump backed by a scroll pump has been installed. As the fridge use precious 3He gas for operation, the entire system has been made to be absolutely leak proof with respect to the 3He gas.