Gautam Pal

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.

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.

Design of large vacuum chamber for VEC superconducting cyclotron beam line switching magnet

VEC K500 superconducting cyclotron will be used to accelerate heavy ion. The accelerated beam will be transported to different beam halls by using large switching magnets. The vacuum chamber for the switching magnet is around 1000 mm long. It has a height of 85 mm and width varying from 100 mm to 360 mm. The material for the chamber has been chosen as SS304.The material for the vacuum chamber for the switching magnet has been chosen as SS304. Design of the vessel was done as per ASME Boiler and Pressure Vessel Code, Section VIII, Division 1. It was observed that primary stress values exceed the allowable limit. Since, the magnet was already designed with a fixed pole gap; increase of the vacuum chamber plate thickness restricts the space for beam transport. Design was optimized using stress analysis software ANSYS. Analysis was started using plate thickness of 4 mm. The stress was found higher than the allowable level. The analysis was repeated by increasing plate thickness to 6 mm, resulting in the reduction of stress level below the allowable level. In order to reduce the stress concentration due to sharp bend, chamfering was done at the corner, where the stress level was higher. The thickness of the plate at the corner was increased from 6 mm to 10 mm. These measures resulted in reduction of localized stress.

Design of cryo-refrigerator assisted HTS steering magnet for K500 cyclotron beam line

The steering magnet is required for the external beam line of K-500 cyclotron to provide corrective steering capabilities. A conventional copper based steering magnet for high rigidity beam (maximum up to 3.3 T-m) becomes very bulky and difficult to integrate in beam line if large steering (±3 degree horizontal (X) and ±1.5 degree vertical (Y)) is required. Recently, commercial availability of long length (more than 100 m) high temperature superconductor (HTS) tape along with availability of high power cryo-refrigerator has given opportunity to develop compact conduction-cooled HTS magnet operating at temperature of 20 K or even higher. Although many prototype magnets using HTS tape have been fabricated and evaluated, there are only few applications in the particle accelerator fields. The paper describes the physics design aspect of the X-Y steering magnet along with details of cryostat.

Quench analysis of a novel compact superconducting cyclotron

Design and analysis of a compact superconducting cyclotron dedicated for medical applications in the fields of nuclear medicine and therapy is presently being pursued in our organization. The novelty of this cyclotron lies in the fact that it does not consist of any iron-pole. The cyclotron magnet will be made of a set of NbTi coils comprising of solenoid and sector coils which are housed in two halves on either sides of the median plane. The average magnetic field is 1.74 T and the maximum extraction energy is 25 MeV, which is sufficient for production of 99mTc from Mo. In this paper, quench analyses of the coils have been discussed in details considering adiabatic condition. The entire cryostat magnet along with coils, formers and support links were modelled for the quench simulation. Self and mutual inductances of all the coils were obtained from a separate magnetic analysis and used in the simulation. Parametric analyses were carried out with different quench initiation energy at various critical locations on the coil surface. The corresponding quench behaviour, i.e. maximum temperature rise, maximum voltage and current decay in each of the coils have been studied.

Development of a Ne gas target for 22Na production by proton irradiation

The article presents the design and development of a neon gas target for the production of (22)Na using a proton beam from the room temperature cyclotron in Variable Energy Cyclotron Centre, Kolkata. The target design is made to handle a beam power of 85 W (17 MeV, 5 μA). The design is based on simulation using the computer code FLUKA for the beam dump and CFD-CFX for target cooling. The target has been successfully used for the production of (22)Na in a 6 day long 17 MeV, 5 μA proton irradiation run.

Quench simulation of a 9T supercoducting solenoid magnet for VECC RIB facility beam line

It is important to evaluate the peak temperature and voltage of superconducting magnet to ensure its safe operation. If the peak temperature and voltage exceed certain limit, it will impair the electrical integrity of the insulation material or even cause a meltdown of the cable. In this paper, temperature rise, voltage drop of high field superconducting magnet for VECC RIB facility have been discussed. The results obtained from simple and approximate theoretical formulation have been compared from results obtained from simulation using a quench solver computer code OPERA. The quench protection techniques and its effects on temperature rise and voltage drop has also been discussed in this paper for the optimum design of superconducting solenoid from quench point of view.

Performance of Variable Energy Cyclotron Centre superconducting cyclotron liquid nitrogen distribution system

The liquid nitrogen distribution at Variable Energy Cyclotron Centre, Kolkata, India K500 superconducting cyclotron uses parallel branches to cool the thermal shield of helium vessel housing the superconducting coil and the cryopanels. Liquid nitrogen is supplied to the thermal shields from a pressurised liquid nitrogen dewar. Direct measurement of flow is quite difficult and seldom used in an operational cryogenic system. The total flow and heat load of the liquid nitrogen system was estimated indirectly by continuous measurement of level in the liquid nitrogen tanks. A mathematical model was developed to evaluate liquid nitrogen flow in the parallel branches. The model was used to generate flow distribution for different settings and the total flow was compared with measured data.

Performance of the beam chamber vacuum system of K = 500 cyclotron at Variable Energy Cyclotron Centre Kolkata

The beam chamber of Variable Energy Cyclotron Centre, Kolkatas K = 500 superconducting cyclotron is pumped by liquid helium cooled cryopanel with liquid nitrogen cooled radiation shield. Performance of the vacuum system was evaluated by cooling the cryopanel assembly with liquid nitrogen and liquid helium. Direct measurement of beam chamber pressure is quite difficult because of space restrictions and the presence of high magnetic field. Pressure gauges were placed away from the beam chamber. The beam chamber pressure was evaluated using a Monte Carlo simulation software for vacuum system and compared with measurements. The details of the vacuum system, measurements, and estimation of pressure of the beam chamber are described 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.