rakesh tanna - Academia.edu (original) (raw)

Papers by rakesh tanna

IEEE Transactions on Plasma Science, Nov 1, 2022

APS Division of Plasma Physics Meeting Abstracts, 2020

2017 International Conference on Circuit ,Power and Computing Technologies (ICCPCT), 2017

Aditya Tokamak is a fusion reactor for obtaining nuclear fusion energy from high temperature, ion... more Aditya Tokamak is a fusion reactor for obtaining nuclear fusion energy from high temperature, ionized gas called plasma. The magnetic field is used to confine plasma in the shape of torus. A disruption is a violent event that terminates magnetically confined plasma. In a disruption, the temperature drops drastically and heat particles are released from confinement on a short timescale and dumped on the vessel wall, causing damage in proportion to the stored energy. The loss of confinement is associated with the production of runaway electrons, which may also produce damage. In order to mitigate disruption, it is necessary for early prediction of disruption. The signals like Halpha, Hard X ray, Plasma current, Mirnov coil signal, Vloop, Soft X-ray should be analyse for the detection of plasma disruption. From the signal if there is any peak in the Halpha, Hard X ray and the non negative value appears in Vloop signals before the decayed of the plasma current indicates the disruption. There are hard and soft disruptions. Since the hard disruption is dangerous, methods like Artificial Neural Network (ANN) using mmultilayer perception and the Fast Fourier Transform (FFT) where already used to find the disruption in terms of frequency component signals. Since Aditya Tokamak signals are non stationary, the above mentioned methods for stationary signal, so those methods are not providing correct and satisfactory results. In this work, different wavelet transforms like Daubechies, Discrete Meyer, Symlets and Biorthogonal were applied on the signal and the corresponding approximation and detailed coefficients were obtained from all the signals in order to obtain the disruption. On an average, of thirty signals are used from different shots for the analysis. Out of the above mentioned wavelet transforms, Discrete meyer and Biorthogonal wavelet are providing the better results than others in terms of the statistical parameters such as mean, skewness and kurtosis. Mean is minimum and the skewness and kurtosis are maximum in the disruption signal, which is confirmed with its time domain analysis. Discrete meyer and the Biorthogonal wavelet transforms provide the spectral information in contrast to frequency domain approaches like FFT. It provides early information about the hard disruption. Wavelet transform is better than FFT and ANN. Since the range of parameters responsible for disruption is not fixed by this method the analysis can be strengthened with Framelet transform.

Bulletin of the American Physical Society, Nov 11, 2021

Bulletin of the American Physical Society, Nov 11, 2020

to study the cold-pulse propagation and effect of these puffs on plasma confinement. The results ... more to study the cold-pulse propagation and effect of these puffs on plasma confinement. The results indicate the simultaneous occurrence of plasma detachment along with propagation of a cold pulse, i.e., a decrease in the edge temperature (ρ 0.9-1.0) and an increase in the core temperature on a timescale less than the energy confinement time, after each gas puff. Initial increase in the radiated power, H α and CIII signals and subsequent improvement in confinement indicate plasma detachment from the limiter. The increase in energy confinement time by a factor of 2-3 is due to the density peaking along with the suppression of edge density fluctuations due to flattening of density profile in the edge due to gas puff. Both the cold-pulse and the detachment phenomena have a density threshold, i.e., above n ẽ 2.7 x 10 19 m −3 , no detachment and propagation have been observed.

IEEE Transactions on Plasma Science, 2022

Fusion Engineering and Design, 2022

Nuclear Fusion, 2022

We present numerical simulation studies on impurity seeding using nitrogen, neon, and argon gases... more We present numerical simulation studies on impurity seeding using nitrogen, neon, and argon gases. These impurity gases are ionized by the electron impact ionization. These ions can be at multiply ionized states, recombine again with the plasma electrons, and radiate energy. The radiation losses are estimated using a non-coronal equilibrium model. A set of 2D model equations to describe their self-consistent evolution are derived using interchange plasma turbulence in the edge and SOL regions and solved using BOUT++. It is found that impurity ions (with single or double-positive charges) move in the inward direction with a velocity ∼0.02c s so that these fluxes are negative. These fluxes are analyzed for different strengths of an effective gravity that help to understand the impurity ion dynamics. Increased gravity shows an accumulation of certain charged species in the edge region. The radiation loss is seen to have a fluctuation in time with frequency 5–20 kHz that closely follows...

Review of Scientific Instruments, 2021

A high-resolution spectroscopic diagnostic for the measurement of spatial profiles of impurity io... more A high-resolution spectroscopic diagnostic for the measurement of spatial profiles of impurity ion toroidal rotation velocities on the ADITYA-U tokamak has been upgraded to cover the complete plasma minor radius. Earlier, the coverage of diagnostics toward the plasma edge was restricted due to the placement of collection optics on the tangential port outside the vacuum vessel. The coverage of the full plasma minor radius, from 0 to 24 cm, has been achieved using the newly designed and developed collection optics that have seven lines of sight to view the tokamak plasma mounted inside a customized re-entrant view port which is installed in the shadow of the limiter inside the vacuum vessel. The upgraded diagnostic also includes a faster charged coupled device detector with a smaller pixel size for the detection of a small wavelength shift. The complete spatial profile has been measured using the Doppler shifted passive change exchange spectral line at 529.0 nm from the C5+ ion. In this article, we present the collection optics' design, installation, calibration, and results obtained using the upgraded diagnostic.

Nuclear Fusion, 2020

The generation and subsequent loss of runaway electrons (REs) during the operation sequence in a ... more The generation and subsequent loss of runaway electrons (REs) during the operation sequence in a tokamak is a potent threat to the plasma-facing components and the interface of actively cooled parts. Control and mitigation of REs are of prime importance to the safe operation and machine health of a fusion device. A supersonic molecular beam injection (SMBI) system has been installed in the ADITYA-U tokamak to explore the effects of the high Mach number molecular beam on the REs and ways to mitigate the REs. In the majority of discharges in which SMBI has been injected, a burst in hard x-rays has been observed accompanying the SMBI pulse, indicating significant RE loss. This is followed by a long RE-mitigated phase in the discharge. The most plausible explanation of the mitigation of REs is minor disruption caused by SMBI. This in turn triggers field line stochastization and subsequent rapid RE loss. Finally, this leads to reorganization of the flux surfaces, resulting in bigger isla...

Physics of Plasmas, 2017

Major disruptions in Aditya tokamak are initiated by the growth and subsequent locking of m/n ¼ 2... more Major disruptions in Aditya tokamak are initiated by the growth and subsequent locking of m/n ¼ 2/1 and 3/1 tearing modes, which leads to the thermal quench of the plasma. Thick filaments are seen to evolve at the low field side (LFS) of the plasma column following the thermal quench, and during the current quench. The number of filaments and inter filament spacing are observed to be related with the plasma stored energy just prior to the disruption. Rapid enhancement of the outward particle flux is seen during the thermal quench phase and the plasma conductivity reduces considerably. Interchange modes, with low poloidal wavenumber, are inferred to grow due to the reduced plasma conductivity and enhanced effective diffusivity. This may be a plausible explanation for the visualization of the thick filaments at the LFS.

2018 9th International Conference on Computing, Communication and Networking Technologies (ICCCNT), 2018

A disruption is a violent event that terminates magnetically confined plasma. Most commonly occur... more A disruption is a violent event that terminates magnetically confined plasma. Most commonly occurring disruptions in Aditya Tokamak are due to Magneto Hydro Dynamic instability, Density limitations, Equilibrium failures, safety factor (q) limit disruptions and Discharge failures due to hardware faults. The major functionality problem in Aditya Tokamak is due to disruption of plasma. Hence the functionality problems can be controlled by choosing the suitable parameter which can identify the plasma disruption by its property and analysis of signal. The signal which undergo plasma disruption can be for various causes and the reason for the disruption needed to be known to avoid the disruption. various transforms like wavelet, framelet etc., can be used for processing the signal and for finding the parameter which can be suitable for diagnosing plasma disruption. the real time data which are obtained from Aditya Tokamak is used for analysis. A detailed study is done and the various causes for disruptions are discussed. The signals are processed and analyzed using various transform and GUI (Graphical User Interface) is created for displaying live demo of analysis and for analyzing the future acquiring signal.

Nuclear Fusion, 2021

Short bursts (∼1 ms) of gas, injecting ∼1017–1018 molecules of hydrogen and/or deuterium, lead to... more Short bursts (∼1 ms) of gas, injecting ∼1017–1018 molecules of hydrogen and/or deuterium, lead to the observation of cold pulse propagation phenomenon in hydrogen plasmas of the ADITYA-U tokamak. After every injection, a sharp increase in the chord-averaged density is observed followed by an increase in the core electron temperature. Simultaneously, the electron density and temperature decrease at the edge. All these observations are characteristics of cold pulse propagation due to the pulsed gas application. The increase in the core temperature is observed to depend on the values of both the chord-averaged plasma density at the instant of gas-injection and the amount of gas injected below a threshold value. Increasing the amount of gas-puff leads to higher increments in the core-density and the core-temperature. Interestingly, the rates of rise of density and temperature remain the same. The gas-puff also leads to a fast decrease in the radially outward electric field together with a rapid increase in the loop-voltage suggesting a reduction in the ion-orbit loss and an increase in Ware-pinch. This may explain the sharp density rise, which remains mostly independent of the toroidal magnetic field and plasma current in the experiment. Application of a subsequent gas-puff before the effect of the previous gas-pulse dies down, leads to an increase in the overall electron density and consequently the energy confinement time.

Fusion Engineering and Design, 2021

Abstract The stabilization of plasma column confined inside the vacuum vessel is supported by sup... more Abstract The stabilization of plasma column confined inside the vacuum vessel is supported by superposition of different vertical and horizontal magnetic field. These time varying magnetic field induces current in the vacuum vessel along with other neighbouring conducting structures. Magnetic probe results are greatly affected by induced vessel current in any nuclear-fusion experimental device. A central conductor is installed inside the ADITYA-U sectionalized segment of vacuum vessel for the calibration of Mirnov probes. The poloidal field distribution around the inner periphery of the vacuum vessel surface is investigated experimentally by using Mirnov probe garland. An analysis is described for the magnetic field at different sinusoidal frequencies and conductors at different radial and vertical locations. Mismatching in the measured magnetic field and applied current in the central conductor, measured at different frequencies hints at the presence of induced vessel current. Dissimilarity in the simulated and measured magnetic signal is computed to characterise the induced vessel current for different Mirnov probes. This technique may be useful to characterise the induced vessel current during ADITYA-U plasma discharges.