C. Mallik

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.

Improved Spindle Cusp Magnetic Field for ECRIS

Magnetic field of minimum‐B configuration is very important for achieving more plasma confinement and closed electron cyclotron resonance (ECR) surface for electron heating and plasma discharge. The spindle cusp magnetic field configuration forms the modified minimum‐B configuration. The absolute magnetic field at the chamber surface on mid‐plane has been optimized and improved sufficiently and symmetrized to the field at the point cusp positions on the central axis. With enhancement of electrostatic and magnetic mirror action at the cusp positions the density of the plasma as well as confinement is boosted. The system becomes simpler, more compact and cost‐effective compared to the conventional one to generate and extract highly charged heavy ions (HCHI). A co‐operative and collaborative effort is essential to develop and test such conceived new ECRIS.

Design and field configuration for a 14.4 GHz ECR ion source in Kolkata

The K500 cyclotron under construction will be capable of accelerating ions like O 6+ , Ne 4+ , Ar 16+ , Kr 27+ etc. We aim to get ~200 euA maximum intensity of the extracted beam of O 6+ from the ion source and decided to have >2BECR magnetic field on the cylindrical surface and the injection ends of the plasma chamber (P Ch) and slightly less than this at the extraction end. The success of the high field operation of ECRs at other places (U-AECR at LBL [1]) suggests generation of proper magnetic field configuration for the 14.4 GHz microwave heating. The absolute composite magnetic field have been evaluated due to the coils (C1,C2) at the two ends and a –ve coil (NC) at the mid-length and a Halbach type sextupole (PM-Hex).