Rakesh K. Bhandari

Low energy micron size beam from inductively coupled plasma ion source

A high brightness inductively coupled plasma ion source based focused ion beam system is being developed. This system is intended to produce a low energy high current micron size beam of the heavier gaseous elements for high speed, micro milling applications. The basic aim of this development is to cater the needs of those applications which cannot be addressed by the conventional liquid metal ion source based FIB. A novel idea has been implemented in the design of the ion source where, a double plasma chamber is designed to initiate the plasma at low RF power. The plasma is first initiated by the capacitive coupling at low RF power in one chamber. This in turn triggers a strong, high density inductive discharge in another chamber, which is Faraday shielded by a thin slotted copper foil. The ion beam is extracted through 1 mm diameter aperture in the plasma electrode using a simple two electrode extraction system. The ion source has produced argon ion beam of 57 mA/cm2 with an angular current density of ∼...

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.

Vacuum system of the cyclotrons in VECC, Kolkata

The vacuum system of the K=130 Room Temperature Cyclotron (RTC) (operational since 1978) has been recently modernized and the same of the Kbend=520 Superconducting Cyclotron (SCC), currently under commissioning, is being deployed for remote monitoring and control. The vacuum system of RTC is designed to achieve and maintain vacuum level of 2×10−6 mbar inside 23 m3 volume of Resonator tank and DEE tank. This has been upgraded by replacing several valves, Freon units, gauges and pumps. The relay based manual control system has been replaced by PLC based automated system. The SCC vacuum system also has an elaborate arrangement comprising of turbo molecular pumping modules with associated isolation valves and characteristic gauges. This paper describes essential elements, typically used to obtain high (1×10−7 mbar) vacuum using rotary pumps, diffusion pumps and cold traps/turbo-molecular pumps and other system components such as valves, gauges and baffles. The supervisory control methodology/scheme of both the vacuum systems, developed in-house using EPICS (Experimental Physics and Industrial Control System), a standard open-source software tool for designing distributed control system, is also elaborated here.

Commissioning of the Main Magnet of Kolkata K-500 Superconducting Cyclotron

Commission of the Kolkata K-500 superconducting cyclotron magnet has been underway at the Variable Energy Cyclotron Centre. The cooldown and energisation experience is described in this paper.

Vacuum Control Systems of the Cyclotrons in VECC, Kolkata

VECC has undertaken the modernization of the K-130 Room Temperature Cyclotron (RTC) (operational since 1978) and commissioning of K-500 Superconducting Cyclotron (SCC) at present. The control system of RTC vacuum system has been upgraded to Programmable Logic Controller (PLC) based automated system from relay based manual system. A distributed PLC based system is under installation for SCC vacuum system. The requirement of high vacuum in both the cyclotrons (1×10−6 mbar for RTC and 5 × 10−8 mbar SCC) imposes the reliable local and remote operation of all vacuum components and instrumentation. The design and development of the vacuum control system of two cyclotrons using the Experimental Physics and Industrial Control System (EPICS) distributed real-time software tools are presented.

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.

Status of Design and Development of Delhi Light Source at IUAC, Delhi

In the first phase of Delhi Light Source (DLS) project, a photocathode based normal conducting RF gun will be used to produce electron beam of energy ~ 8 MeV. The short pulses from a high power laser system will be split in to many pulses (‘Comb beam’) and will be used to produce electron beam bunches which will be injected in to a compact, variable gap undulator magnet to produce THz radiation. Different components of the facility e.g. the copper cavity, photocathode deposition setup, high power RF system, laser device, Undulator magnet etc. are being designed, developed or procured. It is expected that the production of electron beam and THz radiation will be demostrated by end of 2017 and 2018 respectively.

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.

Design, Installation and Commissioning of new Vacuum chamber for Analysing Magnet of K-130 Cyclotron

In view of up-gradation of K-130 Cyclotron at VECC, Kolkata, we have designed a new Vacuum chamber to modify the existing vacuum chamber system. This new chamber is meant for C-shaped 1T dipole type 159.5° Analysing Magnet of 4710 OD × 2750 ID × 1075 mm tall in the RIB feeder beam-line. The welded type vacuum chamber is made of SS-304. The chamber with trapezoidal cross-section is of 4447 OD × 4057 ID × 61.5 mm average height. Pumping ports and modules are selected accordingly to ensure the required high vacuum for beam transport. The chamber improves the base vacuum and reduces the complicated O-ring replacement mandatory for existing chamber made of aluminium alloy. The new chamber is installed at site along with all the pumping module and beam line components. This paper presents the detailed design, installation and commissioning results.

Micro fabrication by low energy ion beam from plasma based ion sources

An inductively coupled plasma ion source based micro machining system is being developed. The system parameters, in which mainly the source parameters like brightness, ion energy spread and source size, are optimized for increasing the efficiency of the system. Preliminary tests show 6 KeV Argon ion beam focused to 1.4 micron size with current density 600 mA/cm2. Possibilities of micro fabrication on silicon and copper target are explored. The paper describes inductively coupled plasma ion source based micro machining system, the preliminary results and challenges and benefits of using plasma generated ions for micro fabrication techniques.