Jedidiah Pradhan

Development of a fast scintillator based beam phase measurement system for compact superconducting cyclotrons.

In an isochronous cyclotron, measurements of central phase of the ion beam with respect to rf and the phase width provide a way to tune the cyclotron for maximum energy gain per turn and efficient extraction. We report here the development of a phase measurement system and the measurements carried out at the Variable Energy Cyclotron Centres (VECCs) K = 500 superconducting cyclotron. The technique comprises detecting prompt γ-rays resulting from the interaction of cyclotron ion beam with an aluminium target mounted on a radial probe in coincidence with cyclotron rf. An assembly comprising a fast scintillator and a liquid light-guide inserted inside the cyclotron was used to detect the γ-rays and to transfer the light signal outside the cyclotron where a matching photo-multiplier tube was used for light to electrical signal conversion. The typical beam intensity for this measurement was a few times 10(11) pps.

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.

Fabrication of racetrack-type double pancake HTS coil for K500 extraction beam line steering magnet

A High Temperature Superconductor (HTS) based cryorefrigerator assisted steering magnet sunder development at VECC for the extraction beam line of K500 cyclotron. The magnet designed is specified for ± 3 degree horizontal correction and ± 1.5 degree of vertical correction of the beam of maximum rigidity of 3.3 T-m. The magnet is composed of two sets of double pancake racetrack coil-one set for vertical field (By) and other for horizontal field inside the return iron yoke. Double pancake coils are fabricated in-house using BSCCO-2223 HTS tapes by wet winding technique using cryogenic grade epoxy. The critical characteristics of the coils are tested at liquid nitrogen temperature in terms of critical current and index parameters. The paper describes the winding details of double pancake coils and test results at liquid nitrogen temperature.

Transient stability of NbTi Rutherford cables for energy storage magnet applications

Stability and quench behavior against transient perturbation expected during operation of a fast cycling energy storage magnet is an important issue for its design and safe operation. Understanding of thermal stability in terms of minimum quench energy (MQE) of a superconducting cable under specific operating scenario is of primary importance for its magnet application. Process of current redistribution from quench strand to adjacent strands depends on inductive coupling and has influence on quench development in the cable. The electrodynamic and thermal behavior of a ten-strand Rutherford-type cable for SMES program in the centre is studied numerically in the framework of discrete network modeling. Influence of several parameters such as uncertainties of inter-strand transverse and adjacent resistance, cooling conditions with liquid helium, etc. on MQE and quench behavior of Rutherford cable is discussed in this paper.

Design study of 4.5 MJ sector-toroidal SMES coil

In continuation of SMES technology development in our centre, design study of a 4. 5 MJ (1.25 kW h) sector-toroidal SMES coil using custom make Rutherford type NbTi cable is reported. The sector- toroid is optimized with six modular type solenoid coils connected in series. The basic module is considered to be solenoid type because of its easier winding technique though it is not the best choice from stress considerations. The coil operating current as well as maximum magnetic field at the inner layer has been determined in order to limit voltage across the coil during discharging mode of its operation and also to minimize the overall dynamic and static load in the cryostat. Due to asymmetric field distribution around the coil, each coil experiences a huge centered force that needs to be arrested with proper support structures. Therefore, extensive magneto-structural stress analysis has been carried out using commercial finite element code ANSYS. The paper describes the magnetic design, three dimensional stress analyses in coil and its support structure during cool-down and energisation, design scheme of sector- toroidal SMES cryostat, etc.

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.