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You searched for subject:( Braginskii). Showing records 1 – 2 of 2 total matches.

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EPFL

1. Wersal, Christoph. Neutral atom dynamics and plasma turbulence in the tokamak periphery.

Degree: 2017, EPFL

Understanding the physical mechanisms at play in the interaction between turbulent plasma and neutral particles is a crucial issue that we approach in this Thesis by using a first-principles self-consistent model of the tokamak periphery implemented in the GBS code. While the plasma is modeled by the drift-reduced two-fluid Braginskii equations, a kinetic model for the neutrals is developed, valid in short and in long mean free path scenarios. The model includes ionization, charge-exchange, recombination, and elastic collisional processes. The neutral kinetic equation is solved by using the method of characteristics. We identify the key elements determining the interaction between neutrals and the turbulent plasma focusing on a tokamak with a toroidal rail limiter on the high-field side equatorial midplane. For this purpose, we simulate the dynamics of the plasma and the neutrals in a domain that includes both the confined edge region and the scrape-off layer (SOL). It turns out that, in the considered plasma conditions, neither the fluctuations of the neutral moments, nor the friction between neutrals and the plasma impact the time-averaged plasma profiles significantly. Thanks to this study, we derive a simple model for the neutral-plasma interaction, which is helpful to identify and understand the principal physical processes at play in the tokamak periphery. By studying the dynamics of the neutral-plasma interplay along the magnetic field lines in the SOL, we derive a refined two-point model from the drift-reduced Braginskii equations that balances the parallel and perpendicular transport of plasma and heat, and takes into account the plasma-neutral interaction. The model estimates the electron temperature drop along a field line, from a region far from the limiter to the limiter plates. The refined two-point model is shown to be in very good agreement with the simulation results. Finally, we self-consistently simulate a diagnostic neutral gas puff, which is often used experimentally as a tool to learn about the turbulence properties in the tokamak periphery. In particular, we investigate the impact of neutral density fluctuations on the D-α light emission, finding that at a radial distance from the gas puff smaller than the neutral mean free path, neutral density fluctuations are anti-correlated with plasma density, electron temperature, and D-α fluctuations, while at distances from the gas puff larger than the neutral mean free path, a non-local shadowing effect influences the neutrals, and the D-α fluctuations are correlated with the neutral density fluctuations. Advisors/Committee Members: Ricci, Paolo.

Subjects/Keywords: plasma physics; controlled fusion; scrape-off layer; turbulence; kinetic neutral atomdynamics; fluid simulations; kinetic simulations; drift-reduced Braginskii model; limiter configuration; two-point model

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Wersal, C. (2017). Neutral atom dynamics and plasma turbulence in the tokamak periphery. (Thesis). EPFL. Retrieved from http://infoscience.epfl.ch/record/228975

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Wersal, Christoph. “Neutral atom dynamics and plasma turbulence in the tokamak periphery.” 2017. Thesis, EPFL. Accessed November 12, 2019. http://infoscience.epfl.ch/record/228975.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Wersal, Christoph. “Neutral atom dynamics and plasma turbulence in the tokamak periphery.” 2017. Web. 12 Nov 2019.

Vancouver:

Wersal C. Neutral atom dynamics and plasma turbulence in the tokamak periphery. [Internet] [Thesis]. EPFL; 2017. [cited 2019 Nov 12]. Available from: http://infoscience.epfl.ch/record/228975.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Wersal C. Neutral atom dynamics and plasma turbulence in the tokamak periphery. [Thesis]. EPFL; 2017. Available from: http://infoscience.epfl.ch/record/228975

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation


Australian National University

2. Caneses Marin, Juan Francisco. Helicon wave propagation and plasma equilibrium in high-density hydrogen plasma in converging magnetic fields .

Degree: 2015, Australian National University

In this thesis, we investigate wave propagation and plasma equilibrium in MAGPIE, a helicon based linear plasma device constructed at the Australian National University, to study plasma-material interactions under divertor-relevant plasma conditions. We show that MAGPIE is capable of producing low temperature (1–8 eV) high density hydrogen plasma (2–3×1019 m-3) with 20 kW of RF power when the confining magnetic field is converging. The original research herein described comprises: (1) Characterization of hydrogen plasma in MAGPIE, (2) Analysis of the RF compensation of double Langmuir probes, (3) Excitation, propagation and damping of helicon waves in uniform and non-uniform magnetic fields and (4) Steady-state force balance and equilibrium profiles in MAGPIE. We develop an analytical model of the physics of floating probes to describe and quantify the RF compensation of the DLP technique. Experimental validation for the model is provided. We show that (1) whenever finite sheath effects are important, overestimation of the ion density is proportional to the level of RF rectification and suggest that (2) electron temperature measurements are weakly affected. We develop a uniform plasma full wave code to describe wave propagation in MAGPIE. We show that under typical MAGPIE operating conditions, the helical antenna is not optimized to couple waves in the plasma; instead, the antenna’s azimuthal current rings excites helicon waves which propagate approximately along the whistler wave ray direction, constructively interfere on-axis and lead to the formation of an axial interference pattern. We show that helicon wave attenuation can be explained entirely through electron-ion and electron-neutral collisions. Results from a two-dimensional full wave code reveal that RF power deposition is axially non-uniform with both edge and on-axis components associated with the TG and helicon wave respectively. Finally, force balance analysis in MAGPIE using a two-fluid “Braginskii” type formalism shows that the electron fluid exists in a state of dynamic (flowing) equilibrium between the electric, pressure and thermal forces. The pressure gradient, driven by the non-uniform RF heating, accelerates the plasma into the target region to velocities close to the ion sound speed. From the measured axial plasma flux we find that the plasma column in MAGPIE can be divided into an ionizing and a recombining region. For the conditions investigated, a large fraction of the plasma created in the ionizing region is lost in the recombining region and only a small fraction reaches the end of the device. The equilibrium plasma density along the length of MAGPIE can be quantitatively explained using a 1D transport calculation which includes volumetric particle sources and magnetic compression. We show that the…

Subjects/Keywords: Helicon plasma; linear plasma device; hydrogen plasma; plasma discharge; RF plasma source; magnetized plasma; Double Langmuir probes; Whistler waves; Collisional damping of plasma waves; Low temperature plasma; plasma flow; Mach probes; magnetic probes; thermal ionization; plasma recombination; light-ion plasma; plasma fluid model; Braginskii

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Caneses Marin, J. F. (2015). Helicon wave propagation and plasma equilibrium in high-density hydrogen plasma in converging magnetic fields . (Thesis). Australian National University. Retrieved from http://hdl.handle.net/1885/105038

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Caneses Marin, Juan Francisco. “Helicon wave propagation and plasma equilibrium in high-density hydrogen plasma in converging magnetic fields .” 2015. Thesis, Australian National University. Accessed November 12, 2019. http://hdl.handle.net/1885/105038.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Caneses Marin, Juan Francisco. “Helicon wave propagation and plasma equilibrium in high-density hydrogen plasma in converging magnetic fields .” 2015. Web. 12 Nov 2019.

Vancouver:

Caneses Marin JF. Helicon wave propagation and plasma equilibrium in high-density hydrogen plasma in converging magnetic fields . [Internet] [Thesis]. Australian National University; 2015. [cited 2019 Nov 12]. Available from: http://hdl.handle.net/1885/105038.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Caneses Marin JF. Helicon wave propagation and plasma equilibrium in high-density hydrogen plasma in converging magnetic fields . [Thesis]. Australian National University; 2015. Available from: http://hdl.handle.net/1885/105038

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

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