Finite-Element analysis of dump resistor for prototype superconducting magnet carrying 3.60 MA-t
Sunil Kedia, Swati Roy, Subrata Pradhan
Applied Superconductivity, IEEE Transactions,Volume: 20, Issue: 6, pages 2354-2359
Stability margin, transient ac responses, and protection of the magnet system in the case of abnormal quench are some of the important design drivers of superconducting magnets for fusion reactors. A prototype magnet has been designed using a cable-in-conduit conductor with a nominal operation current of 30 kA at 12 T and 5 K at the Institute for Plasma Research, Gandhinagar, India. Protection of the magnet system during off-normal scenarios leading to quench makes the operation of the magnet system more challenging. An external dump resistor is required to extract the stored magnetic energy of the magnet in case of quench. Such a dump resistor has been designed for this 3.60 MA-turns current-carrying prototype superconducting magnet. Finite-element thermal, structural, and electromagnetic analyses have been done for validating the dump resistor parameters using commercially available Ansys software. The maximum temperature rise of the dump resistor system is found to be 540 K, considering cool down by natural convection only. In addition, the maximum stress between the parallel plates of the is found to be less than 1.0 GPa, which is in the acceptable range.
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Reaction order in curing kinetics of cyanate ester an bisphenol-f blend insulation systems in fusion relevant magnets winding packs
Priyanka Brahmbhatt, Jisha Unnikrishnan, J. D. Sudha and Subrata Pradhan
Internal Research report,IPR/RR-459/2010,January, 2010
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Vacuum Pressure Facility at IPR
Subrata Pradhan and Priyanka Brahmbhatt
Internal Technical report IPR/TR-164/2010
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Impact of bending strain on critical current of second generation 344 YBCO high Tc coated conductor
Ananya Kundu, Piyush Raj, Subrata Pradhan
AIP Conference Proceedings,Volume 1349, pages 895-896,
Second generation YBCO coated conductor has been characterized under various bending stresses. The down slope of the critical current with increasing strain has been supported by the SEM analysis of the tape. The tensile as well as flexural strength of the tape also have been determined experimentally at room temperature. The stress profile of the critically bend strip has been analyzed in ANSYS and the maximum stress on the YBCO strip in the operating condition has been quantified.
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Experimental study of critical current characteristics of 2G YBCO tape under twisting moment
Ziauddin Khan, Ananya Kundu and Subrata Pradhan
IPR Internal Research Report, DECEMBER-2011
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Strap joint resistance analysis for second generation YBCO coated conductor
Ananya Kundu, Piyush Raj and Subrata Pradhan
IPR Internal Technical Report, OCTOBER-2011
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Influence of manganese acetyl acetonate on the cure-kinetic parameters of cyanate ester–epoxy blend systems in fusion relevant magnets winding packs
Subrata Pradhan , Priyanka Brahmbhatt, Janardhanan Devaki Sudha , Jisha Unnikrishnan
Journal of Thermal Analysis and Calorimetry,Volume 105, Number 1,pages 301-311
Blending cyanate ester (CE) with epoxy resins offers the possibility to manufacture radiation resistant insulations at a low price compared to pure CE materials. Therefore, it is of special interest to study the influence of the CE content and also the effect of catalyst on the curing behavior of these insulation systems. Here, we present the curing behavior of the CE–epoxy blend system studied by non-isothermal differential scanning calorimetry in combination with Fourier infra red (FTIR) spectroscopy. Effect of amount of catalyst, compositional change, heating rate on the conversion, and enthalpy change were studied. The activation energy (E a) and pre-exponential factor (A), rate constant of different blend systems with and without catalyst, were computed from the modified Ozawa and Kissinger model equations using isoconversional methods. Studies suggested that cure-kinetic parameters calculated from both the models are found to be matching. It was observed that the activation energy is less in the case of catalyzed system than the uncatalyzed system. Predicting the cure profile of this resin system is important under a given set of conditions for achieving the desired, controlled polymerization. This is the first report on the studies of the cure-kinetic parameters of the CE–epoxy blend system, and these observations will definitely pave the way for tuning the process parameters and temperature profile for achieving the desired properties of these insulation systems in fusion relevant magnetic winding packs.
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Purification of Niobium Oxide by dissolution and solvent extraction
Priyanka Brahmbhatt, Subrata Pradhan,K.C.Nathsharma, B.B. Nayaj
Minerals and Metallurgical Processing,November 2011, Vol.28, NO. 4
An attempt was made to extract niobium oxide from ~98.5% Nb2O5 using solvent extraction processes. Nb2O5 is used as the feed material in carbothermic reduction processes aimed at producing high-homogeneity, superconductor-grade niobium on a laboratory scale. The Nb metal used for superconductor applications requires a residual resistivity ratio (RRR) > 300, which in turn needs a stringent purity of Nb and allows impurities (substitutional and interstitial) in ppm levels only. In this paper, solvent extraction of niobium was studied under various experimental conditions, such as effect of different extractants, concentration of methyl isobutyl ketone (MIBK) in the organic phase and concentration of various acids. The concentrate was digested with hydrofluoric acid, with ammonium fluoride (NH4F) as a stripping agent. The extraction of niobium from low hydrofluoric- (HF-) bearing solution was found to be low. Thus, various concentrations of hydrofluoric acid and sulfuric acid, as well as hydrofluoric acid and hydrochloric acid, were investigated towards obtaining a maximum amount of niobium in the filtrate and a minimum amount of niobium in the residue. A McCabe - Thiele plot for extraction of niobium from the aqueous phase, HF-bearing solution using HCl with 85% MIBK in kerosene has been constructed to determine the O:A ratio and the number of stages of the process.
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Cure kinetics studies of cyanate ester and bisphenol-F epoxy blend
Priyanka Brahmbhatt, Jisha Unnikrishnan, J. D. Sudha, Subrata Pradhan
Journal of Applied Polymer Science,Volume 125, Issue 2, pages 1068–1076, 15 July 2012
Cyanate ester and Bisphenol-F blends with manganese acetylacetonate in nonylphenol as catalyst and cocatalysts respectively is an attractive candidate as the insulation impregnation materials for fusion grade magnets winding packs that is required to be operating in moderate irradiated environments in fusion devices like Tokamaks. The curing kinetics of this blend system as a thermosetting polymer has been investigated in this paper in detail for 60 : 40 (epoxy:ester) composition strongly driven from application interests. The order of reactions in both chemical kinetics controlled region as well as diffusion controlled regimes have been experimentally found out using Differential Scanning Calorimetric (DSC) studies. Corresponding rate constants and associated cure kinetics have been consequently determined. The second order kinetic model, as it is found, does not fit in to the epoxy-cyanate ester reaction mechanism. The results, therefore, have been discussed in the context of widely used autocatalytic models and variable “n” kinetics models appropriate for chemical controlled region. The reaction conversion rate dα/dt of the cyanate ester-epoxy blend is more rapid in chemical controlled regime compared to that in the diffusion controlled regime. The order of reaction is not constant throughout the reaction and is higher in chemical controlled regime. The variable “n” kinetic model has been employed to determine the hypothetical temperature (350.81 K) below which no more curing reaction would occur. The activation energy and the pre-exponential factors have been determined in the chemical controlled regime using Arrhenius reaction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
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Kinetics of Nb3Sn, Cu6Sn5 and Cu3Sn layer growth
Yogendra Singh and Subrata Pradhan
IPR Internal Technical Report,April-2012
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Temperature distribution in fibre-glass composite impregnated with epoxy-cyanate ester blend
Priyanka Brahmbhatt, Moni Banaudha and Subrata Pradhan
Internal Technical report, IPR/RR-568/2012, September, 2012
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I-V characteristics, minimum quench energy and normal zone propagation studies of forced flow gas cooled YBCO tape
Ananya Kundu, Piyush Raj, Sunil Kedia, Kalpesh Doshi, Yohan Khristi and Subrata Pradhan
Indian Journal of Cryogenics. Volume 38,2013
Fundamental investigations on self-field I-V characteristics as well initial quench induced normal zone propagation characteristics of second generation YBCO coated conductor has been carried out in forced flow nitrogen gas cooling (77 K) condition that simulates practical applications. A special forced flow facility laboratory set-up was developed in order to characterize the coated conductor in laboratory. Normal zone in conductor is initiated by a heater element glued to the conductor surface. The minimum quench energy (MOE) and normal zone propagation velocity (NZPV) have been estimated by monitoring voltage and temperature evolution along the length of the conductor. The minimum quench energy (MOE) value has been evaluated for a particular transport current by varying the heater energy. The minimum quench energy and the normal zone propagation velocity in the YBCO conductor under the forced flow nitrogen gas cooled condition is experimentally estimated to be 0.393 kJ/cc and 0.33 cm/s respectively under self-field criterion.
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Investigation of multistage cable twisting pattern with a cable twisting model for 30kA CICC
Piyush Raj, Subrata Pradhan
Indian Journal of Cryogenics. Volume 38 (2012- 13)
Superconducting cable with multistage twisted strands is an imporlant component of the TF (toroidal field) magnets. A computational model describes the strands twisting pattern at each stage of the cabling. Modeling the pattern of a superconductor cable made of multistage twisted strands is necessary for indigenously developed 30kA NbTi strands CICC. The spatial structure of such superconducting cable is essential for appreciating the load and the performance of CICC at cryogenic temperature. This paper proposes cabling patterns of the strands and gives an approximate position of each stand during the twisting in various stages. These are proposed to be validated with currently developed 30kA CICC at IPR-BARC.
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Mechanical and Dielectric Evaluation of Glass Fibre Reinforced Epoxy-Cyanate Composites
Priyanka Brahmbhatt and Subrata Pradhan
Indian Journal of Cryogenics, volume 38 (2013)
The insulation system for the magnet winding pack is a fibre reinforced plastic (FRP) laminate, which consists of a S-glass fibre reinforcement tape, vaccum impregnated with epoxy-cyanate blend system. In order to evaluate the mechanical behavior of composites, different proportion of epoxy-cyanate blends were prepared to impregnate glass fibres. The insulation laminates were irradiated at room temperature using Am-Be source up to fast neutron fluence of 2.38 x 1012 n/m2 (E> 0.1MeV) to investigate the radiation induced degration in mechanical strength of the insulation system. The short beam shear tests and ultimate tensile tests (as per ASTM standards) were performed at room temperature on the composites prior to and after irradiation to evaluate the inter-laminar shear strength and ultimate tensile strength of the composites. The objective of this paper is to evaluate the mechanical and dielectric properties of the glass fiber reinforced epoxy-cyanates composites without using kapton.
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Characterization of a laboratory scale high-Tc 'D-shaped' magnet
Ziauddin Khan, Ananya Kundu and Subrata Pradhan
Physica Scripta, Volume 87, Number 3, doi:10.1088/0031-8949/87/03/035704
A 'D-shaped' laboratory scale magnet resembling the toroidal field magnet of a tokamak has been fabricated using technical grade BSCCO high-Tc superconductor tape. The I–V characteristic as a function of the current ramp rate, as well as the critical current behavior under low external transverse magnetic fields, has been experimentally investigated at liquid nitrogen temperature. Degradation up to 46% in the critical current of the magnet with respect to its virgin tape has been observed. Hysteresis behavior has also been observed during ramp-up and ramp-down. The normal zone propagation velocity for quenching the magnet has been obtained experimentally to be 2.5 cm s−1 for a transport current of 60 A at 80 K for the critical current of about 150 A.
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YBCO Superconductor Characterization under shear strain
Ziauddin Khan, Ananya Kundu, Yuvakiran Paravastu and Subrata Pradhan
International Journal of Advanced Materials Manufacturing and Characterization, Vol:3, Issue:1, March 2013
YBCO based high temperature superconductors in practical applications are subjected to shear strain. `Critical current characteristics’ of such high temperature superconductors are known to get degraded in strain state. In this work, shear stresses resulting from the finite twisting of HTS tape having varying widths have been modeled using FEA analysis for different twisting angles. Supporting the findings of this model, an American Superconductor Corporation (AMSC) 2G YBCO tape of a given width has been twisted and experimentally investigated in self field for a given current ramp-rate. Under uniform twist of the YBCO tape at 77 K, the degradation in the current carrying ability up to 30% was observed. The irreversibility in the current carrying ability of HTS tape was also observed beyond the twisting angle per unit length of 25 degree/cm. The superconductor to resistive transition index, `n’ is found to behave in an identical manner to the critical current as a function of twisting angle. Such degradation is largely attributed to the torsional shear strain resulting from the twisting.
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Effect of Fabrication Processes on SS316lN Jacket Material for Fusion Relevant Superconducting Magnet
Mahesh Ghate, A. Kumar, P. Charkhawala, N. Chauhan, S. Pradhan
Fusion Science and Technology 03/2014; Volume 65(Number 2):255-261. DOI: 10.13182/FST13-652
The effects of various fabrication processes, such as compaction and swaging, during the fabrication of a cable-in-conduit conductor on the mechanical and metallurgical properties of jacket material (SS316LN) are discussed in this paper. Microstructure analysis of various samples is carried out, and the change in microstructures has been studied using scanning electron microscopy image analysis. The variation in hardness for the jacket material is also tested after swaging and compaction operations. The jacket samples are tested for their tensile strength, reduction in area, elongation, and impact strength as per applicable American Society for Testing and Materials standards. The ultimate tensile strength (UTS) is observed to be decreased for a sample compacted to 733 MPa when compared to virgin samples. On the contrary, the UTS increased significantly up to 1027 MPa in swaged samples. There is no linear relationship between tensile strength of SS316LN after cold working operations. The effect of thermal shock on the mechanical and metallurgical properties of the jacket material is also investigated.
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Design, Development and Fabrication of Indigenous 30 kA NbTi CICC for Fusion Relevant Superconducting Magnet
Mahesh Ghate, Piyush Raj, Arun Singh, Subrata Pradhan, M. M. Hussain, K. K. Abdulla,
Cryogenics; 06/2014; DOI:10.1016/j.cryogenics.2014.06.008
The fusion relevant superconducting magnet is under development in India using a cable-in-conduit-conductor (CICC) with operating current of 30 kA at 5.5 T and 4.5 K. The 30 kA NbTi based CICC is designed on the basis of desired critical design parameters as well as mechanical fabrication considerations. The 30 kA CICC has been designed having square cross-section (30 mm × 30 mm) consisting NbTi as superconducting cable, SS316LN as jacket material and SS304 foil as wrapping around the cabled strands. The design configuration of 30 kA NbTi CICC has been discussed in this paper. The NbTi base high current carrying strands have been fabricated indigenously using direct extrusion and cold drawing process. The 100 m long NbTi–Cu strands twisting, insertion of cabled strands into a circular conduit has been developed with pull through technology. The welding process qualification and effects of cold work on jacket material at room temperature have been elaborated in this paper. The manufacturing parameters and quality procedures for development of CICC have been successfully established and demonstrated with fabrication of 100 m NbTi based CICC without any technical difficulties.
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Kinetics of Nb3Sn, Cu6Sn5 and Cu3Sn layer growth
Yogendra Singh and Subrata Pradhan
Journal of Materials Science and Surface Engineering Vol. 1 (2), 2014, pp 52-57
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Temperature Distribution in Fibre-glass Composite Impregnated with Epoxy-Cyanate Ester Blend
Priyanka Brahmbhatt, Moni Banaudha, Subrata Pradhan
International Journal of Composite Materials 2014, 4(1): 38-44 , DOI: 10.5923/j.cmaterials.20140401.06
Cyanate ester and epoxy blend have been identified as an attractive insulating material for fusion grade magnet winding packs. An insulation system comprising of fibre glass composites and cyanate ester blend has been analyzed during its vacuum pressure impregnation and curing. The transient one dimensional distribution of temperature and extent of cure has been evaluated both analytically and experimentally in this paper. The one dimensional transient (1-D) heat transfer characteristics evaluation has been carried out on 60:40 (epoxy: cyanate) which has been optimally prescribed blend for fusion grade winding process. The analytical formulation solves the heat transfer differential equations incorporating internal heat generation resulting from the exothermic chemical reaction in both chemical and diffusional kinetic regimes. In support to the analytical formulation, carefully designed experiments have been carried out on such samples. On comparing the results obtained from analytical formulism and those measured during experiments have been found to be matching well. These results have the potential to design the vacuum pressure impregnation of large size fusion relevant winding packs.
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Development of a Prototype Hybrid DC Circuit Breaker for Superconducting Magnets Quench Protection
Swati Roy, Deven Kanabar, Chiragkumar Dodiya, and Subrata Pradhan
IEEE Transactions on Applied Superconductivity, Digital Object Identifier 10.1109/TASC.2014.2331288
A quench protection system for superconducting magnets mainly involves a mechanical dc circuit breaker (CB) and a dump resistor where the entire energy of the inductive magnet is dumped during quench. During the current commutation to the dump resistor, these mechanical CB experiences arcing at their contacts, which causes degradation in the performance as well as life expectancy of the CB, affecting the reliability of the entire quench protection system and appears as threat to the expensive and critical superconductor magnets also. A combination of mechanical and static breakers, which is termed a hybrid dc CB, presents a novel technique for arcless current commutation into the dump resistor. Furthermore, the current commutation time can also be reduced by adopting real-time switching schemes. A series of experiments has been done at the Magnet Technology Development Division Laboratory, Institute for Plasma Research, Gandhinagar, India, for testing the hybrid CB operation and operation at various current levels up to 800 A using a mechanical contactor as the mechanical CB and an insulated gate bipolar transistor as the static switch. A significant improvement in the voltage profile across the dump resistor has been observed using the hybrid CB exhibiting arcless current commutation into the dump resistor. Furthermore, an overall reduction in the current interruption time between a mechanical CB operation and a hybrid CB has been observed. The time for current commutation into the dump resistor with the conventional mechanical breaker is 48 ms, whereas that with the hybrid CB is observed to be 18 ms.
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Installation and Testing of 220V, 1500A DC Power Supply at IPR
Deven Kanabar, Swati Roy and Dr. S. Pradhan
Internal Technical Report, IPR/TR-278/2014
A 220V, 1500A DC Power Supply with several features has been designed, developed, fabricated and installed at Institute for Plasma Research (IPR), Gandhinagar with Indian Vendor for the testing of fabricated ELM coil having inductance and resistance of 6.48mH and 100 mΩ respectively. Critical parameters, designed stages and essential tests and outcomes of 220V, 1500A DC power supply has been discussed in this paper.
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Feasibility testing of Hybrid DC Circuit breaker for Fusion Relevant Superconducting Magnet Quench Protection
Swati Roy, Deven Kanabar, Chiragkumar Dodiya, and Subrata Pradhan
Symposium on Fusion Technology (SOFT), October 2014
Quench protection system of superconducting magnets is mainly dependent on the reliability of DC circuit breaker (CB). The concept of Hybrid DC CB basically comprises of a mechanical breaker in parallel with a static breaker which provides arcless current commutation to the dump resistor for fast ramp down and extraction of inductive energy of the superconducting magnets in case of quench. This scheme has been experimentally validated with series of experiments for currents upto 1.5kA DC using combination of mechanical switch and Insulated gate bipolar transistor (IGBT) based static breaker and the obtained test results are discussed in this paper. In non-quench state, the mechanical breaker carries continuous DC current minimizing the on-state losses. But when quench occurs, the current is diverted from breaker to static breaker and finally static breaker commutes the current into the dump resistor where the load current representing the energy of the superconducting magnet, decays exponentially. A dedicated control system has been developed for the sequential opening and closing of the IGBT and mechanical breaker in this simulated quench protection system set up. These experimental results build confidence in scaling up Hybrid CB concept for implementation in Protection system for Prototype fusion grade superconducting magnets.
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