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N. Bisai - One of the best experts on this subject based on the ideXlab platform.
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Modification of plasma flows in edge and SOL regions by influence of Neutral Gas
Physics of Plasmas, 2018Co-Authors: N. Bisai, Santanu Banerjee, Deepak SangwanAbstract:Plasma flows and their profiles in edge and scrape-off layer (SOL) regions of a tokamak plasma are important as these can modify the interchange plasma turbulence. These flows have been investigated in the presence of Neutral Gas numerically using the two-dimensional model equations. A reduction of poloidal flows, radial particle, and energy fluxes has been observed in the edge and SOL regions by the presence of the Neutral Gas. The reduction of radial flux is due to the reduction in the radial velocity of the plasma blob. We have investigated Reynolds stress in the presence of the Gas. It is found that in the presence of ion-Neutral collisions, the magnitude of the stress decreases. The Gas also reduces the diamagnetic drift frequency in the edge and SOL regions.Plasma flows and their profiles in edge and scrape-off layer (SOL) regions of a tokamak plasma are important as these can modify the interchange plasma turbulence. These flows have been investigated in the presence of Neutral Gas numerically using the two-dimensional model equations. A reduction of poloidal flows, radial particle, and energy fluxes has been observed in the edge and SOL regions by the presence of the Neutral Gas. The reduction of radial flux is due to the reduction in the radial velocity of the plasma blob. We have investigated Reynolds stress in the presence of the Gas. It is found that in the presence of ion-Neutral collisions, the magnitude of the stress decreases. The Gas also reduces the diamagnetic drift frequency in the edge and SOL regions.
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Role of Neutral Gas in scrape-off layer of tokamak plasma in the presence of finite electron temperature and its gradient
Physics of Plasmas, 2016Co-Authors: N. Bisai, P. K. KawAbstract: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....
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Role of Neutral Gas in scrape-off layer tokamak plasma
Physics of Plasmas, 2015Co-Authors: N. Bisai, R. K. Jha, P. K. KawAbstract:Neutral Gas in scrape-off layer of tokamak plasma plays an important role as it can modify the plasma turbulence. In order to investigate this, we have derived a simple two-dimensional (2D) model that consists of electron continuity, quasi-Neutrality, and Neutral Gas continuity equations using Neutral Gas ionization and charge exchange processes. Simple 1D profile analysis predicts Neutral penetration depth into the plasma. Growth rate obtained from the linear theory has been presented. The 2D model equations have been solved numerically. It is found that the Neutral Gas reduces plasma fluctuations and shifts spectrum of the turbulence towards lower frequency side. The Neutral Gas fluctuation levels have been presented. The numerical results have been compared with Aditya tokamak experiments.
P. K. Kaw - One of the best experts on this subject based on the ideXlab platform.
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Role of Neutral Gas in scrape-off layer of tokamak plasma in the presence of finite electron temperature and its gradient
Physics of Plasmas, 2016Co-Authors: N. Bisai, P. K. KawAbstract: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....
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Role of Neutral Gas in scrape-off layer tokamak plasma
Physics of Plasmas, 2015Co-Authors: N. Bisai, R. K. Jha, P. K. KawAbstract:Neutral Gas in scrape-off layer of tokamak plasma plays an important role as it can modify the plasma turbulence. In order to investigate this, we have derived a simple two-dimensional (2D) model that consists of electron continuity, quasi-Neutrality, and Neutral Gas continuity equations using Neutral Gas ionization and charge exchange processes. Simple 1D profile analysis predicts Neutral penetration depth into the plasma. Growth rate obtained from the linear theory has been presented. The 2D model equations have been solved numerically. It is found that the Neutral Gas reduces plasma fluctuations and shifts spectrum of the turbulence towards lower frequency side. The Neutral Gas fluctuation levels have been presented. The numerical results have been compared with Aditya tokamak experiments.
Amnon Fruchtman - One of the best experts on this subject based on the ideXlab platform.
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Nonmonotonic plasma density profile due to Neutral-Gas depletion
Physics of Plasmas, 2010Co-Authors: Amnon FruchtmanAbstract:The dependencies in a Gas discharge of the plasma density and of the Neutral-Gas depletion on the magnetic-field intensity and on the plasma particle flux are studied. It is shown that if plasma particle flux density outward of the discharge is fixed, varying the magnetic field intensity does not affect Neutral-Gas depletion. When there are plasma end losses along magnetic-field lines while Neutral-Gas is depleted, an increase in the magnetic field intensity results in a nonmonotonic plasma density profile across field lines. The plasma density then has a local minimum at the center of the discharge.
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Neutral-Gas depletion and repletion in plasmas
Physics of Plasmas, 2010Co-Authors: Amnon Fruchtman, J.-m. RaxAbstract:Repletion of Neutrals, an unexpected increase in the Neutral-Gas density when ionization is intense, has been recently predicted to occur in a Gas discharge when a thermalized Neutral Gas is collisionless enough, so that its inertia dominates over the drag by collisions with ions. A parameter is identified here that determines which process should occur, Neutral-Gas repletion or the more expected Neutral-Gas depletion. The particle and momentum balance equations of the plasma and Neutrals are solved, and it is demonstrated how when this parameter is varied, the Neutral-Gas density exhibits a transition between depletion and repletion.
Pascal Chabert - One of the best experts on this subject based on the ideXlab platform.
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Dynamics of Neutral Gas depletion investigated by time- and space-resolved measurement of xenon atom ground state density
Journal of Physics D: Applied Physics, 2012Co-Authors: L. Liard, Ane Aanesland, Pascal ChabertAbstract:The dynamics of Neutral Gas depletion in high-density plasmas is investigated by time- and space-resolved measurements of the xenon ground state density. Two-photon absorbed laser induced fluorescence experiments were carried out in a helicon reactor operating at 10 mTorr in xenon Gas. When the plasma is magnetized, a plasma column is formed from the bottom of the chamber up to the pumping region. In this situation it is found that two phenomena, with different time scales, are responsible for the Neutral Gas depletion. The magnetized plasma column is ignited in a short (millisecond) time scale leading to a Neutral Gas depletion at the discharge centre and to an increase of Neutral Gas density at the reactor walls. This is explained both by Neutral Gas heating and by the rise of the plasma pressure at the discharge centre. Then, on a much longer (second) time scale, the overall Neutral Gas density in the reactor decreases due to higher pumping efficiency when the magnetized plasma column is ignited. The pumping enhancement is not observed when the plasma is not magnetized, probably because in this case the dense plasma column vanishes and the plasma is more localized near the antenna.
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Plasma transport under Neutral Gas depletion conditions
Journal of Physics D: Applied Physics, 2007Co-Authors: L. Liard, J.-m. Rax, J.-l. Raimbault, Pascal ChabertAbstract:It was previously shown that plasma transport is enhanced by Neutral Gas depletion when the plasma pressure is not negligible compared with the Neutral Gas pressure. Consequently, the plasma flux leaving the discharge is not a linear function of the central plasma density. The latest theoretical treatments of this problem have assumed isothermal fluids in pressure balance, discarding Neutral Gas heating. We present a model that incorporates the effects of Neutral Gas heating on the plasma transport enhancement. This model shows that (i) Neutral Gas depletion is more pronounced than previously calculated due to Gas heating and (ii) as a consequence the plasma transport is further enhanced and the non-linearity of the plasma flux leaving the discharge is more pronounced.
J.-m. Rax - One of the best experts on this subject based on the ideXlab platform.
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Neutral-Gas depletion and repletion in plasmas
Physics of Plasmas, 2010Co-Authors: Amnon Fruchtman, J.-m. RaxAbstract:Repletion of Neutrals, an unexpected increase in the Neutral-Gas density when ionization is intense, has been recently predicted to occur in a Gas discharge when a thermalized Neutral Gas is collisionless enough, so that its inertia dominates over the drag by collisions with ions. A parameter is identified here that determines which process should occur, Neutral-Gas repletion or the more expected Neutral-Gas depletion. The particle and momentum balance equations of the plasma and Neutrals are solved, and it is demonstrated how when this parameter is varied, the Neutral-Gas density exhibits a transition between depletion and repletion.
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Plasma transport under Neutral Gas depletion conditions
Journal of Physics D: Applied Physics, 2007Co-Authors: L. Liard, J.-m. Rax, J.-l. Raimbault, Pascal ChabertAbstract:It was previously shown that plasma transport is enhanced by Neutral Gas depletion when the plasma pressure is not negligible compared with the Neutral Gas pressure. Consequently, the plasma flux leaving the discharge is not a linear function of the central plasma density. The latest theoretical treatments of this problem have assumed isothermal fluids in pressure balance, discarding Neutral Gas heating. We present a model that incorporates the effects of Neutral Gas heating on the plasma transport enhancement. This model shows that (i) Neutral Gas depletion is more pronounced than previously calculated due to Gas heating and (ii) as a consequence the plasma transport is further enhanced and the non-linearity of the plasma flux leaving the discharge is more pronounced.