We have investigated the propagation of a magnetic dipole assuming a simple model of forward and return flow of fast electrons under a condition of plasma-density inhomogeneity by a particle-in-cell simulation. An exact propagating depiction of the dipolar structure is given under the framework of a simplified ‘electron magnetohydrodynamic’ fluid model (Yadav et al 2008 Phys. Plasmas 15 062308; Yadav et al 2009 Phys. Plasmas 16 040701; Yadav and Das 2010 Phys. Plasmas 17 052306) in a dense plasma. We reproduce this structure in our kinetic calculations. The results indicate that, with a steep plasma density gradient, the structure evolves rapidly toward plasma in a process involving shock formation and rapid dissipation of beam energy, which is consistent with the fluid simulations. In addition, new features are also reported, such as the pinching of the two dipole lobes to form a very strong shear layer, which develops into a Kelvin–Helmholtz instability. The magnetic energy is rapidly converted to kinetic energy of electrons leading to additional plasma heating in inhomogeneous regions, such as the core region in an imploded plasma.

The modification of interchange plasma turbulence in the scrape-off layer (SOL) region by the presence of hot and cold neutral gas molecules has been studied. The nonlinear equations have been solved numerically using two different simulations (“uniform-Te” and “varying-Te”), and the results obtained from both of the models have been compared. The hot neutrals, responsible for the increase in the electron density in the SOL, also account for more ionization of the cold molecules. The effect of hot and cold neutrals on the interchange turbulence is almost similar in the “uniform-Te” model, but in the “varying-Te” model, the influence of the hot neutrals is very small, specifically in the far SOL region. The neutral gas in the “varying Te” model decreases the heat load on the material walls by about 7%. A reduction in the radial velocity by about 25% and effective diffusion coefficient of the plasma particles has been found by the influence of the neutral gas.

Dust clouds are often formed in many dusty plasma experiments, when micron size dust particles introduced in the plasma are confined by spatial non-uniformities of the potential. These formations show self-organized patterns like vortex or circulation flows. Steady-state equilibrium dynamics of such dust clouds is analyzed by 2D hydrodynamics for varying Reynolds number, Re, when the cloud is confined in an azimuthally symmetric cylindrical setup by an effective potential and is in a dynamic equilibrium with an unbounded sheared plasma flow. The nonconservative forcing due to ion flow shear generates finite vorticity in the confined dust clouds. In the linear limit (Re << 1), the collective flow is characterized by a single symmetric and elongated vortex with scales correlating with the driving field and those generated by friction with the boundaries. However in the high Re limit, (Re >= 1), the nonlinear inertial transport (u . del u) is effective and the vortex structure is characterized by an asymmetric equilibrium and emergence of a circular core region with uniform vorticity, over which the viscous stress is negligible. The core domain is surrounded by a virtual boundary of highly convective flow followed by thin shear layers filled with low-velocity co- and counter-rotating vortices, enabling the smooth matching with external boundary conditions. In linear regime, the effective boundary layer thickness is recovered to scale with the dust kinematic viscosity as Delta r approximate to mu(1/3) and is modified as Delta r approximate to (mu L-parallel to/u)(1/2) in the nonlinear regime through a critical kinematic viscosity mu* that signifies a structural bifurcation of the flow field solutions. The flow characteristics recovered are relevant to many microscopic biological processes at lower Re, as well as gigantic vortex flows such as Jovian great red spot and white ovals at higher Re.

In Large Volume Plasma Device(LVPD), an unambigous observation on ETG induced turbulence is made by removal of unutilized primary ionizing and non-thermal electrons from uniform density plasma. Imposition and control of gradient in electron temperature are all achieved by placing a large( 2m diameter) magnetic Electron Energy Filter (EEF) in the middle of the device. In the dressed plasma, the observed ETG turbulence exhibits broadband spectra with frequency residing in lower hybrid range and have wave number, satisfifying the condition . The ETG turbulence induced convective and conductive heat fluxes are measured. Interstingly, it is noticed that particle pinch like sceanrio develops in LVPD. The convective flux, which has both elctrostatic and eletromagnetic components is directed radially inward whereas the energy flux is radially outward. The paper provides a compresenhive discussion on the excitattion of ETG turbulence and its role in plasma transport in core plasma of LVPD.

A non-invasive method of determining the collision frequency νm by measuring the net plasma impendence in a magnetized, capacitive-coupled, radio-frequency (rf) discharge circuit is developed. The collision frequency has been analytically expressed in terms of bulk plasma reactance, wherein standard sheath models have been used to estimate the reactance offered due to the capacitive rf sheaths at the discharge plates. The experimental observations suggest that in the un-magnetized case, νm remains constant over a range of rf current but steadily increases as the background pressure reduces. In the magnetized case, the collision frequency has been observed to decay with the increase in rf current while it remains unaffected by the background pressure. A qualitative discussion has been presented to explain these characteristics.

Whistler turbulence observed in earth’s magnetosphe re as free energy source lies in energetic electrons, electron beams, anisotropies i n temperature and electron distribution function, density gradients, loss cone etc. and is responsible for the precipitation of energetic electrons into the ionosphere. This has been observ ed that when pole bound electrons get trapped in the earth’s magnetic field and suffers l oss cone instability, which results in the excitation of Quasi-Longitudinal (QL) whistlers at l rge oblique angles. We report experimental observation of loss cone dri ven Quasi-Longitudinal (QL) whistlers in a laboratory plasma excited by the ref lected electrons from a magnetic mirror. The QL whistler propagate highly obliquely ( 0 || 1 87 ) / ( tan ≈ = ⊥ − k k θ ) in a broad band of kHz f kHz 80 40 ≤ < with 1 4 . 1 ~ − ⊥ cm k and 1 || 06 . 0 ~ − cm k respectively. It exhibits strong correlation between density and magnetic field fluc tuations ( , = −0.9), and interestingly it shows a continuous variation of wave polarizatio n with frequency. We have compared experimental observations with numerical results ob tained from the theoretical models of Sharma et al. [1], Olga et al. [2] and Quasi Longit udinal (QL) whistlers by Henry G. Booker et al., [3] and found a good agreement between them . This is probably first laboratory demonstration of QL whistlers and detailed results on it will be presented in the conference [4]. References [1] R. R. Sharma and Loukas Vlahos, The Astrophysic al Journal 280, 405(1984). [2] O. P. Verkhoglyadova et. al., J. Geophys. Res. 115, A00F19 (2010). [3] Henry G. Booker and Rolf B. Dyce, Radio Science Journal of Research NBS/ USNC-URSI, Vol. 69D, No. 4, April 1965. [4] A. K. Sanyasi, L. M. Awasthi, P. K. Srivastava, S. K. Mattoo, D. Sharma, R. Singh, R. Paikaray and P. K. Kaw, Phys. Plasmas 24, 102188 (2017). 45 EPS Conference on Plasma Physics P2.4008

Capacitive coupled plasmas (CCP) are widely popular in semiconductor industries. These plasmas are created by radio-frequency (rf) potential applied between two similar/dissimilar parallel plate electrodes inside a vacuum chamber. At low pressures, the electrons adjacent to the plates are stochastically heated by the rapidly oscillating rf electric fields adjacent to the sheaths and resistively heated in the bulk plasma. Measurement of plasma parameters using single Langmuir probe has been limited due to large oscillation in plasma potential.

Soon after lasers were invented, there was tremendous curiosity on the nonlinear phenomena which would result in their interaction with a fully ionized plasma. Apart from the basic interest, it was realized that it could be used for the achievement of nuclear fusion in the laboratory. This led us to a paper on the propagation of a laser beam into an inhomogeneous fusion plasma, where it was first demonstrated that light would go up to the critical layer (where the frequency matches the plasma frequency) and get reflected from there with a reflection coefficient of order unity. The reflection coefficient was determined by collisional effects. Since the wave was expected to slow down to near zero group speed at the reflection point, the dominant collision frequency determining the reflection coefficient was the collision frequency at the reflection point. It turned out that the absorption of light was rather small for fusion temperatures. This placed a premium on investigation of nonlinear phenomena which might contribute to the absorption and penetration of the light into high-density plasma. An early investigation showed that electron jitter with respect to ions would be responsible for the excitation of decay instabilities which convert light waves into electrostatic plasma waves and ion waves near the critical frequency. These electrostatic waves would then get absorbed into the plasma even in the collisionless case and lead to plasma heating which is nonlinear. Detailed estimates of this heating were made. Similar nonlinear processes which could lead to stimulated scattering of light in the underdense region \((\omega >\omega _p)\) were investigated together with a number of other workers. All these nonlinear processes need a critical threshold power for excitation. Another important process which was discovered around the same time had to do with filamentation and trapping of light when certain thresholds were exceeded. All of this work has been extensively verified in laser plasma experiments and have become the backbone of our present understanding of how lasers nonlinearly interact with fully ionized fusion plasmas. A review of this early work will be presented. We shall also present a review of our involvement in the recent work on nonlinearpenetration of light into overdense plasmas with gradual and sharp interfaces.

The Capacitively Coupled Plasma discharge featuring operation in current driven triple frequency configuration has analytically been investigated, and the outcome is verified by utilising the 1D3V particle-in-cell (PIC) simulation code. In this analysis, the role of middle frequency component of the applied signal has precisely been explored. The discharge parameters are seen to be sensitive to the ratio of the chosen middle frequency to lower and higher frequencies for fixed amplitudes of the three frequency components. On the basis of analysis and PIC simulation results, the middle frequency component is demonstrated to act as additional control over sheath potential, electron sheath heating, and ion energy distribution function (iedf) of the plasma discharge. For the electron sheath heating, effect of the middle frequency is seen to be pronounced as it approaches to the lower frequency component. On the other hand, for the iedf, the control is more sensitive as the middle frequency approaches towards the higher frequency. The PIC estimate for the electron sheath heating is found to be in reasonably good agreement with the analytical prediction based on the Kaganovich formulation.

Major disruptions in Aditya tokamak are initiated by the growth and subsequent locking of m/n = 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.

Preliminary design of the central solenoid (CS) for SST-2 and Indian DEMO reactor has been initiated. The expected maximum magnetic field calculated by magnet design code MAC at the conductor location is ∼13 T. The key role of the CS magnet is for initiating efficient plasma current and maintaining it for longer duration. In order to maximize the CS capability, the higher magnetic field with a greater magnetic flux linkage is required, and this could be possible with a large area of the solenoid. CS consists of a number of modules acting independently, each following an individual current profile leads to a better initial null formation, plasma current build up, longer pulse duration, and good shaping. Hence, the function of CS is to provide the required volt-sec for plasma initiations, sustaining plasma current, and to provide good equilibrium for few hundreds of seconds. For this purpose, it is advantageous to split CS into many modules. The dimensional parameters of various modules, tentative model, volt-sec capability, and allowable ramp rates are the prime requisites for CS design. The total volt-sec requirements for long pulsed plasma, which include plasma initiation, ramp up, flat top, and ramp down, are estimated using plasma properties. In this estimation, inductive flux and resistive flux requirements are estimated using appropriate analytical or empirical formula. In the flat top, only resistive flux is considered. The duration of the flat top is about few hundreds of seconds, and for steady-state operation of the reactor, during the flat top, the noninductive current drive mechanism will fully sustain the plasma current. This methodology is applied to typical ITER-like discharges and compared with ITER CS available volt-sec. The same methodology is used to estimate for SST-2 and Indian DEMO reactor. The radial buildup of inboard side of Tokomaks is obtained through a system code which uses physics and engineering constraints. This provides the available space for the CS coil. It is observed that the negative convertor operation is needed to enhance the available volt-sec. In order to fulfill the plasma physics requirements with the available inner bore area and height, a multimodule CS coil is proposed with Nb 3 Sn conductor. This work has been carried out for ITER CS to validate the procedure and applied to SST2 and DEMO. The tentative model of CS coil, calculation methodology of magnetic field, expected electromagnetic forces, stored volt-sec, and current ramp-up and ramp-down requirements will be presented in this paper.

The role of neutral gas molecules in the Scrape-off Layer (SOL) region of tokamak plasma is important as it is expected to modify the plasma turbulence. Two-dimensional model has been used that consists of electron continuity, molecular ion continuity, quasi-neutrality, electron energy, and neutral molecular gas continuity equations in the presence of electron impact molecular ionizations and other non-ionizing collisions. The growth rate obtained from these equations has been presented using linear theory. It is observed that the growth rate increases with the neutral gas ionization coefficients. The nonlinear equations are solved numerically in the presence and absence of the neutral gas molecules. Radial profiles of plasma density, electron temperature, and electric field have been obtained. It is found that the neutral gas reduces electric fields. More significant reduction of the poloidal electric field has been found by the neutral gas. Time series obtained from the numerical data has been analyzed. A strong decrease in fluctuation of the plasma density, electron temperature, and potential has been found at the outer region the SOL plasma in the presence of the gas molecules.

Molecule density in Scrape-off Layer (SOL) of tokamak plasma is normally high. These molecules take part in many important reactions with the plasma and can modify plasma turbulence. A two-dimensional model has been derived for this purpose to study the plasma turbulence in the presence of the neutral gas. The growth rate obtained from these equations has been presented using linear theory. It is observed that the growth rate decreases with the increase of the molecular density and increases with the neutral gas ionization coefficient. The nonlinear equations have been solved numerically using two different simulations that are simulations using uniform and nonuniform electron temperature. The simulation results have been analyzed to identify role of neutral gas and electron temperature of the plasma. It is found that the neutral gas modifies plasma profiles, electric fields and also reduces the plasma fluctuation levels.

Several experiments, related to controlled thermonuclear fusion research and highly relevant for large size tokamaks including ITER, have been carried out in ADITYA, an ohmically heated circular limiter tokamak. Repeatable plasma discharges of maximum plasma current of ~ 160 kA and discharge duration beyond ~ 250 ms with plasma current flattop duration of ~ 140 ms has been obtained for the first time in ADITYA. The discharge reproducibility has been improved considerably with Lithium wall conditioning and improved plasma discharges are obtained by precisely controlling the plasma position. In these discharges, chord-averaged electron density ~ 3.0 – 4.0 x 10^19 m^-3 using multiple hydrogen gas puffs, electron temperature of the order of ~ 500 700 eV have been achieved. Novel experiments related to disruption control are carried out and disruptions, induced by hydrogen gas puffing are successfully mitigated using biased electrode and ICR pulse techniques. Runaway electrons are successfully mitigated by applying a short local vertical field (LVF) pulse. A thorough disruption database has been generated by identifying the different categories of disruption. Detailed analysis of several hundred disrupted discharges showed that the current quench time is inversely proportional to q_edge. Apart from this, for volt-sec recovery during the plasma formation phase, low loop voltage start-up and current ramp-up experiments have been carried out using ECRH. Successful recovery of volt-sec leads to achievement of longer plasma discharge durations. In addition to that Neon gas puff assisted radiative improved confinement mode has also been achieved in ADITYA. In this paper, all the above mentioned experiments will be discussed.

In order to investigate physics of nonlinear interaction of high-power microwave (HPM) with an over-dense (f plasma > f wave ) plasma, an experimental system SYMPLE (System for Microwave and Plasma Experiments), is being developed. The work is taken up in two phases: Phase-1 addressing interaction of plasma with moderate power HPM, ((1/2;εE μ 2 ) /(nkT e ) ~ 1), and Phase-2 involving extremely intense (eE μ /mω ~ c) HPM. Here `E μ ' is the wave field, `n' the plasma density, T e ' the electron temperature, and `m' the electron mass. The interaction of these intense waves with plasma at the critical density layer (f plasma =f wave ) is predicted to involve various phenomena, ranging from generation of parametric instabilities to hot electron generation, leading to wave absorption in plasma. Understanding of the underlying physics has implications in inertial fusion. The parametric generation of SYMPLE as well as various aspects of the development of the Phase1 system, with a 3 MW, 3 GHz Magnetron source, a washer gun plasma, and a TE 10 -TM 01 HPM mode converter is discussed here.

This paper presents the equilibrium properties of a magnetized plasma column sustained by direct-current (dc) operated hollow cathode discharge in conjunction with a conducting end-plate, acting as the anode. The survey of radial plasma characteristics, performed in argon plasma, shows hotter plasma in the periphery as compared to the central plasma region; whereas the plasma density peaks at the center. The off-centered peak in radial temperature is attributed due to inhomogeneous power deposition in the discharge volume in conjunction with short-circuiting effect by the conducting end plate. A theoretical model based on particle flux and energy balance is given to explain the observed characteristics of the plasma column.

PreviousNext No Access14th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 3-6 August 2015Interplanetary Alfvén Waves, HILDCAAs, Acceleration of Magnetospheric Relativistic “Killer” Electrons and Auroral Zone HeatingAuthors: B.T. TsurutaniG.S. LakhinaA. SenP.K. KawE. EcherM.V. AlvesE. da CostaR. HajraW.D. GonzalezJ.H.A. SobralM.A. AbduL.E. VieiraC.G.M. BrumB.T. TsurutaniBTT, Stancrest, Glendale, CA, USASearch for more papers by this author, G.S. LakhinaIndian Inst.for Geomagnetism (IIG), Navi Mumbai, IndiaSearch for more papers by this author, A. SenInst. for Plasma Research (IPR), Bhat, IndiaSearch for more papers by this author, P.K. KawInst. for Plasma Research (IPR), Bhat, IndiaSearch for more papers by this author, E. Echer4INPE, Sao Jose dos Campos, SP, BrazilSearch for more papers by this author, M.V. Alves4INPE, Sao Jose dos Campos, SP, BrazilSearch for more papers by this author, E. da CostaIFMG, Ouro Preto, MG, BrazilSearch for more papers by this author, R. HajraINPE, Sao Jose dos Campos, SP, BrazilSearch for more papers by this author, W.D. GonzalezINPE, Sao Jose dos Campos, SP, BrazilSearch for more papers by this author, J.H.A. SobralINPE, Sao Jose dos Campos, SP, BrazilSearch for more papers by this author, M.A. AbduINPE, Sao Jose dos Campos, SP, BrazilSearch for more papers by this author, L.E. VieiraINPE, Sao Jose dos Campos, SP, BrazilSearch for more papers by this author, and C.G.M. BrumNatl. Astro. Iono. Cen.(NAIC) Arecibo Observatory, PRSearch for more papers by this authorhttps://doi.org/10.1190/sbgf2015-301 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract We review one aspect of space weather, high-speed solar wind streams (HSSs) emanating from solar coronal holes. We will trace the important plasma features from the Sun to the Earth’s magnetosphere and ionosphere. In particular we will discuss the formation of Alfvén waves in interplanetary space, the effects of magnetic reconnection between the southward component of the Alfvénic wave magnetic fields with the Earth’s magnetopause fields, the eventual acceleration of ~ MeV electrons and loss of these particles to the ionosphere and atmosphere. Keywords: space, weather, coronal mass ejections, geomagneticsPermalink: https://doi.org/10.1190/sbgf2015-301FiguresReferencesRelatedDetails 14th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 3-6 August 2015ISSN (online):2159-6832Copyright: 2015 Pages: 1553 publication data© 2015 Published in electronic format with permission by the Brazilian Geophysical SocietyPublisher:Society of Exploration Geophysicists HistoryPublished Online: 06 Aug 2015 CITATION INFORMATION B.T. Tsurutani, G.S. Lakhina, A. Sen, P.K. Kaw, E. Echer, M.V. Alves, E. da Costa Jr., R. Hajra, W.D. Gonzalez, J.H.A. Sobral, M.A. Abdu, L.E. Vieira, and C.G.M. Brum, (2015), "Interplanetary Alfvén Waves, HILDCAAs, Acceleration of Magnetospheric Relativistic “Killer” Electrons and Auroral Zone Heating," SEG Global Meeting Abstracts : 1503-1508. https://doi.org/10.1190/sbgf2015-301 Plain-Language Summary Keywordsspaceweathercoronal mass ejectionsgeomagneticsPDF DownloadLoading ...

Collisionless heating of the electrons in the vicinity of the sheath region corresponding to higher order sinusoidal signals in a current-driven radio-frequency capacitively coupled plasma discharge has been investigated analytically and further verified by particle-in-cell simulation. The simulation results for collisionless sheath heating are found to be in good agreement with analytical predictions. In contrast to the voltage driven case, it is demonstrated that a pure sinusoidal waveform gives maximum electron sheath heating with a current-driven configuration and the ion energy can be controlled by varying the pulse width.

Interactions of two Li plasma plumes and shock waves are investigated at various pressures (∼10−5 to 3 mbar) in the argon gas ambient. Fast imaging and optical emission spectroscopy are used to study the plume dynamics and characteristic emission of plasmas. The plasma plumes are created in laser-blow-off geometry. The expansion of plasma plumes in the ambient gas leads to the formation of an interaction zone. The formation of interaction zone is dependent on the ambient pressure and below a certain pressure, no significant change is observed in the shape and size of the interaction plasma. In the higher pressure, formation of interaction zone and its shape are dependent on ambient pressure. Dynamics of seed plasmas and interaction zone are also affected by the shock-shock interactions. The shock-shock interaction depends on the angle of incidence (α) between two shock waves at the initial time of interaction but as the plumes expand, the shock-shock interaction does not follow α dependence.