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Featured researches published by S. K. Singh.


Journal of Applied Physics | 2010

High power microwave generation from coaxial virtual cathode oscillator using graphite and velvet cathodes

Rakhee Menon; Amitava Roy; S. K. Singh; S. Mitra; Vishnu Sharma; Senthil Kumar; Archana Sharma; K. V. Nagesh; K. C. Mittal; D. P. Chakravarthy

High power microwave (HPM) generation studies were carried out in KALI-5000 pulse power system. The intense relativistic electron beam was utilized to generate HPMs using a coaxial virtual cathode oscillator. The typical electron beam parameters were 350 kV, 25 kA, and 100 ns, with a few hundreds of ampere per centimeter square current density. Microwaves were generated with graphite and polymer velvet cathode at various diode voltage, current, and accelerating gaps. A horn antenna setup with diode detector and attenuators was used to measure the microwave power. It was observed that the microwave power increases with the diode voltage and current and reduces with the accelerating gap. It was found that both the peak power and width of the microwave pulse is larger for the velvet cathode compared to the graphite cathode. In a coaxial vircator, velvet cathode is superior to the graphite cathode due to its shorter turn on time and better electron beam uniformity.


Review of Scientific Instruments | 2007

Characterization and analysis of a pulse power system based on Marx generator and Blumlein.

D. D. P. Kumar; S. Mitra; K. Senthil; Archana Sharma; K. V. Nagesh; S. K. Singh; Jayanta Mondal; Amitava Roy; D. P. Chakravarthy

A pulse power system (1 MV, 50 kA, and 100 ns) based on Marx generator and Blumlein pulse forming line has been studied for characterization of a general system. Total erected Marx inductance and series resistance are calculated from modular testing of Marx generator and testing of Marx generator with Blumlein. The complete pulse power system has been tested with the termination of a liquid resistor load for finding the Blumlein characteristic impedance. Equivalent electrical circuits during the charging and discharging of the Blumlein are constructed from the characterized parameters of the system. These equivalent circuits can be used in the analysis of prepulse voltage and droop in the flat top of the main pulse in the pulse power systems based on Marx generator and Blumlein.


Scientific Reports | 2015

Expression profiling of lymph nodes in tuberculosis patients reveal inflammatory milieu at site of infection.

Abhijit Maji; Richa Misra; Anupam Kumar Mondal; Dhirendra Kumar; Divya Bajaj; Anshika Singhal; Gunjan Arora; Asani Bhaduri; Andaleeb Sajid; Sugandha Bhatia; S. K. Singh; Harshvardhan Singh; Vivek Rao; Debasis Dash; E. Baby Shalini; Joy Sarojini Michael; Anil Chaudhary; Rajesh S. Gokhale; Yogendra Singh

Extrapulmonary manifestations constitute 15 to 20% of tuberculosis cases, with lymph node tuberculosis (LNTB) as the most common form of infection. However, diagnosis and treatment advances are hindered by lack of understanding of LNTB biology. To identify host response, Mycobacterium tuberculosis infected lymph nodes from LNTB patients were studied by means of transcriptomics and quantitative proteomics analyses. The selected targets obtained by comparative analyses were validated by quantitative PCR and immunohistochemistry. This approach provided expression data for 8,728 transcripts and 102 proteins, differentially regulated in the infected human lymph node. Enhanced inflammation with upregulation of T-helper1-related genes, combined with marked dysregulation of matrix metalloproteinases, indicates tissue damage due to high immunoactivity at infected niche. This expression signature was accompanied by significant upregulation of an immunoregulatory gene, leukotriene A4 hydrolase, at both transcript and protein levels. Comparative transcriptional analyses revealed LNTB-specific perturbations. In contrast to pulmonary TB-associated increase in lipid metabolism, genes involved in fatty-acid metabolism were found to be downregulated in LNTB suggesting differential lipid metabolic signature. This study investigates the tissue molecular signature of LNTB patients for the first time and presents findings that indicate the possible mechanism of disease pathology through dysregulation of inflammatory and tissue-repair processes.


Physics of Plasmas | 2009

Shot to shot variation in perveance of the explosive emission electron beam diode

Amitava Roy; R. Menon; S. K. Singh; M. R. Kulkarni; P. C. Saroj; K. V. Nagesh; K. C. Mittal; D. P. Chakravarthy

The shot to shot variation in perveance of a planar diode with explosive emission graphite cathode in a range of accelerating gaps 3–12 mm is investigated experimentally. The typical electron beam parameters were 200 kV, 12 kA, 100 ns, with a few hundreds of A/cm2 current density. The diode perveance remains less than the Child–Langmuir value, indicating that only a fraction of the cathode take part in the emission process. A simple statistical analysis of the diode perveance shows that the shot to shot variation is more pronounced for the later part of the accelerating pulse. The cathode plasma expansion velocity and the effective initial emission area have been calculated from the perveance data. It was found that the plasma expansion velocity varies from 3 to 6.5u2002cm/μs. The mean expansion velocity and the standard deviation increase with the increase in the accelerating gap. The initial emission areas also varies randomly on a shot to shot basis and at the beginning of the accelerating pulse only 4%–35...


Physics of Plasmas | 2010

Electron beam current in high power cylindrical diode

Amitava Roy; R. Menon; S. Mitra; Vishnu Sharma; S. K. Singh; K. V. Nagesh; D. P. Chakravarthy

Intense electron beam generation studies were carried out in high power cylindrical diode to investigate the effect of the accelerating gap and diode voltage on the electron beam current. The diode voltage has been varied from 130 to 356 kV, whereas the current density has been varied from 87 to 391u2002A/cm2 with 100 ns pulse duration. The experimentally obtained electron beam current in the cylindrical diode has been compared with the Langmuir–Blodgett law. It was found that the diode current can be explained by a model of anode and cathode plasma expanding toward each other. However, the diode voltage and current do not follow the bipolar space-charge limited flow model. It was also found that initially only a part of the cathode take part in the emission process. The plasma expands at 4.2u2002cm/μs for 1.7 cm anode-cathode gap and the plasma velocity decreases for smaller gaps. The electrode plasma expansion velocity of the cylindrical diode is much smaller as compared with the planar diode for the same accel...


Review of Scientific Instruments | 2009

Prepulse minimization in KALI-5000

D. D. P. Kumar; S. Mitra; K. Senthil; Vishnu Sharma; S. K. Singh; Amitava Roy; Archana Sharma; K. V. Nagesh; D. P. Chakravarthy

A pulse power system (1 MV, 50 kA, and 100 ns) based on Marx generator and Blumlein pulse forming line has been built for generating high power microwaves. The Blumlein configuration poses a prepulse problem and hence the diode gap had to be increased to match the diode impedance to the Blumlein impedance during the main pulse. A simple method to eliminate prepulse voltage using a vacuum sparkgap and a resistor is given. Another fundamental approach of increasing the inductance of Marx generator to minimize the prepulse voltage is also presented. Experimental results for both of these configurations are given.


international conference on recent advances in microwave theory and applications | 2008

Generation of short duration high power microwave using KALI - 5000

D. D. P. Kumar; Vishnu Sharma; S. K. Singh; Amitava Roy; S. Mitra; K. Senthil; Rakhee Menon; Archana Sharma; K. V. Nagesh; D. P. Chakravarthy

A pulse power system (1 MV, 5 0kA, and 100 ns) based on dual polarity charged Marx generator and Blumlein pulse forming line (PFL) was built to generate high power microwaves. This paper describes the inherent prepulse present with the Blumlein configuration and the mitigation strategies adopted. Further, a qualitative attempt to verify the generation of high power microwave output on the system is presented.


international vacuum electronics conference | 2011

High power microwave generation from a reflex triode virtual cathode oscillator

Amitava Roy; Archana Sharma; Rakhee Menon; S. Mitra; K. V. Nagesh; D. P. Chakravarthy; D. Senthil Kumar; Saket Khandekar; Vijay Bhaskar Somu; Srinivas Nekkanti; Ajay Kumar Saini; Shiva Rai; Dheeraj Kumar Singh; Vishnu Sharma; S. K. Singh

Experiments were carried out to generate intense relativistic electron beams and High Power Microwaves (HPM) with reflex triode geometry from 1 kJ pulse power system. The typical electron beam parameters were 300 kV, 12 kA, and 300 ns, with a current density of a few hundreds of amperes per square centimeter. We present a power optimization study of the HPM generated from the reflex-triode vircator for various anode-cathode (AK) gaps. A horn antenna setup with diode detector and attenuators was used to measure the microwave power. The HPM frequency was measured with a D-dot probe along with a high band width oscilloscope. It was found that the microwave power and E-field peaks at 15 mm AK Gap and the frequency at this gap is 2.2 GHz. The highest microwave power is emitted when all the power is delivered into a single frequency with minimal mode hopping.


Review of Scientific Instruments | 2011

High voltage pulse shaping of e-beam diode using perveance variation.

S. Mitra; Vishnu Sharma; K. Senthil; Amitava Roy; D. D. P. Kumar; Rakhee Menon; S. K. Singh; Archana Sharma; K. V. Nagesh; D. P. Chakravarthy

This paper presents a new high voltage pulse shaping methodology for pulsed power applications. The aim is to generate high voltage square pulse across anode cathode gap of e-beam diodes. The non-linear time varying perveance characteristics of e-beam diodes are used for shaping of output voltage pulse across it, generated directly from Marx generator. Analytically, it has been shown in the paper that under certain conditions, if achieved, Marx generator feeding an e-beam diode can produce a square-like pulse at the output, without any extra pulse shaping arrangements. Experimental results to support the analysis are also presented in the paper.


Tropical Agriculture | 2016

Effect of irrigation N and biofertilizers on yield and nutrient uptake by wheat 87

Sabyasachi Mitra; S. K. Singh; Siddhartha Bandyopadhyay; C.S. Singh

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Amitava Roy

Bhabha Atomic Research Centre

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D. P. Chakravarthy

Bhabha Atomic Research Centre

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K. V. Nagesh

Bhabha Atomic Research Centre

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S. Mitra

Bhabha Atomic Research Centre

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Archana Sharma

Bhabha Atomic Research Centre

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Vishnu Sharma

Bhabha Atomic Research Centre

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D. D. P. Kumar

Bhabha Atomic Research Centre

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K. Senthil

Bhabha Atomic Research Centre

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Rakhee Menon

Bhabha Atomic Research Centre

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Abhijit Maji

Institute of Genomics and Integrative Biology

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