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1.
Wang, Ge, active 2013.
Rapid frequency chirps of an Alfvén wave in a toroidal plasma.
Degree: PhD, Physics, 2013, University of Texas – Austin
URL: http://hdl.handle.net/2152/21380 
► Results from models that describe frequency chirps of toroidal Alfvén eigenmode excited by energetic particles are presented here. This structure forms in TAE gap and…
(more)
▼ Results from models that describe frequency chirps of toroidal Alfvén eigenmode excited by energetic particles are presented here. This structure forms in TAE gap and may or may not chirp into the continuum. Initial work described the particle wave interaction in terms of a generic Hamiltonian for the particle wave interaction, whose spatial dependence was xed in time. In addition, we have developed an improved adiabatic TAE model that takes into account the spatial prole variation of the mode and the nite orbit excursion from the resonant ux surfaces, for a wide range of toroidal mode numbers. We have shown for the generic xed prole model that the results from the adiabatic model agree very well with simulation result except when the adiabatic condition breaks down due to the rapid variations of the wave amplitude and chirping frequency. We have been able to solve the adiabatic problem in the case when the spatial prole is allowed to vary in time, in accord with the structure of the response functions, as a function of frequency. All the models predict that up-chirping holes do not penetrate into the continuum. On the other hand clump structures, which down chirp in frequency may, depending on detailed parameters, penetrate the continuum. The systematic theory is more restrictive than the generic theory, for the conditions that enable clump to penetrate into the continuum. In addition, the systematic theory predicts an important nite drift orbit width eect, which eventually limits and suppresses a down-chirping response in the lower continuum. This interruption of the chirping occurs when the trapped particles make a transition from intersecting both resonant points of the continuum to just one resonant point.
Advisors/Committee Members: Berk, H. L. (advisor).
Subjects/Keywords: Frequency chirps; Toroidal Alfvén eigenmode; Energetic particle; Adiabatic theory; Variational principle
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APA (6th Edition):
Wang, Ge, a. 2. (2013). Rapid frequency chirps of an Alfvén wave in a toroidal plasma. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/21380
Chicago Manual of Style (16th Edition):
Wang, Ge, active 2013. “Rapid frequency chirps of an Alfvén wave in a toroidal plasma.” 2013. Doctoral Dissertation, University of Texas – Austin. Accessed April 11, 2021.
http://hdl.handle.net/2152/21380.
MLA Handbook (7th Edition):
Wang, Ge, active 2013. “Rapid frequency chirps of an Alfvén wave in a toroidal plasma.” 2013. Web. 11 Apr 2021.
Vancouver:
Wang, Ge a2. Rapid frequency chirps of an Alfvén wave in a toroidal plasma. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2013. [cited 2021 Apr 11].
Available from: http://hdl.handle.net/2152/21380.
Council of Science Editors:
Wang, Ge a2. Rapid frequency chirps of an Alfvén wave in a toroidal plasma. [Doctoral Dissertation]. University of Texas – Austin; 2013. Available from: http://hdl.handle.net/2152/21380
University of Texas – Austin
2.
Correa, Cynthia Elizabeth.
Studies of transient behavior and of the unbounded magnetized plasma jet configuration in the magnetohydrodynamic regime.
Degree: PhD, Physics, 2015, University of Texas – Austin
URL: http://hdl.handle.net/2152/31644
► Two studies with analytical and computational components of dynamics of plasmas and electromagnetic fields in the magnetohydrodynamic (MHD) regime are carried out to explain important…
(more)
▼ Two studies with analytical and computational components of dynamics of plasmas and electromagnetic fields in the magnetohydrodynamic (MHD) regime are carried out to explain important and novel results from two laboratory plasma experiments. The first study provides a possible mechanism to explain transient magnetic fluctuations observed in the Large Plasma Device at the
University of California - Los Angeles [Gekelman, 1991] and shows good qualitative agreement with the experimental results. The calculations are based on the nonmodal approach, which recovers transient dynamics missed by the conventional spectral treatment of configurations with sheared flow. The second study demonstrates several effects of the presence of boundaries on the evolution of a bounded magnetized plasma jet for the parameters and the configuration of the Helimak experiment at the
University of
Texas at
Austin [Gentle, 2008]. The bounded magnetized plasma jet is simulated with a Chebyshev-τ code. Both of these studies focus on time and length scales where the plasma is most adequately described by a resistive-viscous MHD model.
Advisors/Committee Members: Berk, H. L. (advisor), Horton, Wendell (committee member), Reichl, Linda (committee member), Bengtson, Roger (committee member), Milosavljevic, Milos (committee member).
Subjects/Keywords: Plasma
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APA (6th Edition):
Correa, C. E. (2015). Studies of transient behavior and of the unbounded magnetized plasma jet configuration in the magnetohydrodynamic regime. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/31644
Chicago Manual of Style (16th Edition):
Correa, Cynthia Elizabeth. “Studies of transient behavior and of the unbounded magnetized plasma jet configuration in the magnetohydrodynamic regime.” 2015. Doctoral Dissertation, University of Texas – Austin. Accessed April 11, 2021.
http://hdl.handle.net/2152/31644.
MLA Handbook (7th Edition):
Correa, Cynthia Elizabeth. “Studies of transient behavior and of the unbounded magnetized plasma jet configuration in the magnetohydrodynamic regime.” 2015. Web. 11 Apr 2021.
Vancouver:
Correa CE. Studies of transient behavior and of the unbounded magnetized plasma jet configuration in the magnetohydrodynamic regime. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2015. [cited 2021 Apr 11].
Available from: http://hdl.handle.net/2152/31644.
Council of Science Editors:
Correa CE. Studies of transient behavior and of the unbounded magnetized plasma jet configuration in the magnetohydrodynamic regime. [Doctoral Dissertation]. University of Texas – Austin; 2015. Available from: http://hdl.handle.net/2152/31644
3.
Siemon, Carl Joseph.
Interaction of charged particle beams with plasmas.
Degree: PhD, Physics, 2014, University of Texas – Austin
URL: http://hdl.handle.net/2152/28480
► This thesis focuses on the propagation of charged particle beams in plasmas, and is divided into two main parts. In the second chapter, a novel…
(more)
▼ This thesis focuses on the propagation of charged particle beams in plasmas, and is divided into two main parts. In the second chapter, a novel theoretical model for underdense electron beam propagation during the nonlinear stage of the resistive Weibel instability (WI) is presented and is used to calculate the stopping time of the beam. The model and supporting simulation results lead to the conclusion that the WI initially enhances beam deceleration but then reduces it when compared to a filamentation-suppressed beam (without WI), so that the overall stopping time of the beam is essentially unaffected by the instability. Using the theoretical model, a criterion is derived that determines when deceleration is no longer enhanced by the instability. We also demonstrate that exotic plasma return current distributions can be obtained within and outside of beam filaments that sharply contrast those observed in collisionless systems. For example, the plasma return current is reversed in selected areas. In the next chapter, a new method for initiating the modulation instability (MI) of a proton beam in a proton driver plasma wakefield accelerator using a short laser pulse preceding the beam is presented. A diffracting laser pulse is used to produce a plasma wave that provides a seeding modulation of the proton bunch with the period equal to that of the plasma wave. Using the envelope description of the proton beam, this method of seeding the MI is analytically compared with the earlier suggested seeding technique that involves an abrupt truncation of the proton bunch. The full kinetic simulation of a realistic proton bunch is used to validate the analytic results. It is further used to demonstrate that a plasma density ramp placed in the early stages of the laser-seeded MI leads to its stabilization, resulting in sustained accelerating electric fields (of order several hundred MV/m) over long propagation distances (100-1000 m). The final chapter describes a harmonic expansion formalism that attempts to explain the post-linear stage of the MI. The formalism is developed first, and then several crippling problems with it are identified.
Advisors/Committee Members: Berk, H. L. (advisor), Mahajan, Swadesh M. (advisor).
Subjects/Keywords: Weibel instability; Modulation instability; PDPWA; Inertial confinement fusion; Proton-driven plasma wakefield acceleration
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APA (6th Edition):
Siemon, C. J. (2014). Interaction of charged particle beams with plasmas. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/28480
Chicago Manual of Style (16th Edition):
Siemon, Carl Joseph. “Interaction of charged particle beams with plasmas.” 2014. Doctoral Dissertation, University of Texas – Austin. Accessed April 11, 2021.
http://hdl.handle.net/2152/28480.
MLA Handbook (7th Edition):
Siemon, Carl Joseph. “Interaction of charged particle beams with plasmas.” 2014. Web. 11 Apr 2021.
Vancouver:
Siemon CJ. Interaction of charged particle beams with plasmas. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2014. [cited 2021 Apr 11].
Available from: http://hdl.handle.net/2152/28480.
Council of Science Editors:
Siemon CJ. Interaction of charged particle beams with plasmas. [Doctoral Dissertation]. University of Texas – Austin; 2014. Available from: http://hdl.handle.net/2152/28480
University of Texas – Austin
4.
Zhou, Tianchun.
MHD GAMs and kinetic GAMs driven by energetic particles.
Degree: PhD, Physics, 2009, University of Texas – Austin
URL: http://hdl.handle.net/2152/27161
► In this dissertation, we investigate the n=0 Geodesic Acoustic Modes (GAM) in the framework of both magneto-hydrodynamics and kinetics. In MHD, the purpose is to…
(more)
▼ In this dissertation, we investigate the n=0 Geodesic Acoustic Modes (GAM) in the framework of both magneto-hydrodynamics and kinetics. In MHD, the purpose is to understand the numerical results out of the CASTOR code (1). Effects of energetic particle are ignored. The leading perturbation is the density perturbation, which leads to a local GAM. The coupling of density perturbation to the magnetic perturbation, which is treated to be smaller, leads to global a GAM. We recover the numerical results from the CASTOR code and obtain and analytical solution to the radial eigen-mode equation though asymptotic matching. To understand recent experimental results on DIII-D (2) a kinetic theory is constructed in which magnetic perturbations are neglected and energetic ions are treated on the same footing as the thermal species based on drift kinetics. Not only do the energetic particles destabilize the local GAM induced by thermal species, but they are also crucial to establish the global GAM due to their large orbit shifts. Polarization of thermal ions is included. A mechanism for fast GAM excitation through NBI is proposed, based on our local kinetic GAM theory when there exists a loss boundary in pitch angle.
Advisors/Committee Members: Berk, H. L. (advisor).
Subjects/Keywords: GAM; MHD; Kinetic; Energetic
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APA ·
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APA (6th Edition):
Zhou, T. (2009). MHD GAMs and kinetic GAMs driven by energetic particles. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/27161
Chicago Manual of Style (16th Edition):
Zhou, Tianchun. “MHD GAMs and kinetic GAMs driven by energetic particles.” 2009. Doctoral Dissertation, University of Texas – Austin. Accessed April 11, 2021.
http://hdl.handle.net/2152/27161.
MLA Handbook (7th Edition):
Zhou, Tianchun. “MHD GAMs and kinetic GAMs driven by energetic particles.” 2009. Web. 11 Apr 2021.
Vancouver:
Zhou T. MHD GAMs and kinetic GAMs driven by energetic particles. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2009. [cited 2021 Apr 11].
Available from: http://hdl.handle.net/2152/27161.
Council of Science Editors:
Zhou T. MHD GAMs and kinetic GAMs driven by energetic particles. [Doctoral Dissertation]. University of Texas – Austin; 2009. Available from: http://hdl.handle.net/2152/27161
University of Texas – Austin
5.
Eremin, Denis.
Self-consistent dynamics of nonlinear phase space structures.
Degree: PhD, Physics, 2004, University of Texas – Austin
URL: http://hdl.handle.net/2152/1959
► This thesis investigates the self-consistent dynamics of nonlinear ”hole” and ”clump” phase space structures and the nonlinear modes supported by the structures in the presence…
(more)
▼ This thesis investigates the self-consistent dynamics of nonlinear ”hole” and
”clump” phase space structures and the nonlinear modes supported by the
structures in the presence of dissipation due to the background plasma. A
system consisting of a single mode driven by a weakly destabilizing distribution
function in a dissipative medium close to the threshold of linear instability
exhibits explosive instability. This instability results in the formation of the
phase space structures and the corresponding modes.
The holes and clumps were expected to persist for an appropriate collisional
time scale. However, for certain initial conditions Fokker-Planck calculations
for the nonlinear system abruptly break down in the course of the
calculation. We find that this is because an adiabatic description of phase
space structures at zero collisionality does not necessarily lead to continual
adiabatic frequency sweeping.
For a class of initial distribution functions criteria are found that detervii
mine whether adiabatic frequency sweeping will continue indefinitely or suddenly
terminate. For certain other initial distribution functions that describe
the predominantly deeply trapped particles, critical points may be encountered
where the adiabatic analysis fails to yield a unique solution. Except
for establishing boundary conditions, the contribution of passing particles is
found to be unimportant in the dynamics of the phase space structures within
the framework of the adiabatic description.
We derived a self-consistent dispersion relation for the perturbed eigenmodes
of the system and benchmarked the result with the dispersion relation
obtained earlier in Ref. [53] and demonstrated their agreement. We analyzed
this dispersion relation and demonstrated that the critical points of the adiabatic
theory occur exactly where linear instability is triggered. Numerical runs
were performed to test both the adiabatic theory and the instability analysis of
a BGK (Bernstein-Greene-Kruskal) mode for a model problem where the distribution
function of passing particles has zero slope with respect to the action
variable. This problem has same essential features as the problem where the
slope of the passing particle distribution function is constant. In particular,
linear instability of the same nature is also predicted to arise whenever adiabatic
analysis predicts termination of frequency sweeping. This procedure has
the virtue of enabling a precise comparison of the theory with the simulations
and indeed it does so until instability sets in. The model problem was also
used to demonstrate the agreement between the numerical growth rate and
the growth rate predicted in the instability analysis. Then a passing particle
distribution function was used that has a constant slope with respect to the
action variable, and it too showed agreement with the theory for the evolution
of the adiabatic phase, for where the onset of the instability was predicted
to occur, and for where the persistence of the phase space…
Advisors/Committee Members: Berk, H. L. (advisor).
Subjects/Keywords: Phase space (Statistical physics); Particles (Nuclear physics); Adiabatic invariants; Plasma (Ionized gases); Dispersion relations; Alpha rays
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APA (6th Edition):
Eremin, D. (2004). Self-consistent dynamics of nonlinear phase space structures. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/1959
Chicago Manual of Style (16th Edition):
Eremin, Denis. “Self-consistent dynamics of nonlinear phase space structures.” 2004. Doctoral Dissertation, University of Texas – Austin. Accessed April 11, 2021.
http://hdl.handle.net/2152/1959.
MLA Handbook (7th Edition):
Eremin, Denis. “Self-consistent dynamics of nonlinear phase space structures.” 2004. Web. 11 Apr 2021.
Vancouver:
Eremin D. Self-consistent dynamics of nonlinear phase space structures. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2004. [cited 2021 Apr 11].
Available from: http://hdl.handle.net/2152/1959.
Council of Science Editors:
Eremin D. Self-consistent dynamics of nonlinear phase space structures. [Doctoral Dissertation]. University of Texas – Austin; 2004. Available from: http://hdl.handle.net/2152/1959
6.
-1430-6073.
Explosive evolution of near-threshold kinetic instabilities.
Degree: PhD, Physics, 2017, University of Texas – Austin
URL: http://hdl.handle.net/2152/62258
► In the past, studies of waves close to marginal stability have revealed a rich variety of behavior in different physical contexts. One of the possible…
(more)
▼ In the past, studies of waves close to marginal stability have revealed a rich variety of behavior in different physical contexts. One of the possible outcomes is an explosive growth of the mode amplitude, which forms the core of this thesis. This outcome has been predicted in both the fluid mechanics and the plasma literature. While we make some comments regarding the fluids context, in this work we focus on the near-threshold waves that are excited in kinetic systems (such as plasmas). With a few exceptions, the explosive behavior is found to asymptote to an attractor that depends on a system parameter that we shall discuss. When the mode amplitude is sufficiently large, the explosive growth loses physical meaning, and here we explore the transition between the weakly-nonlinear regime where the explosive description holds, and the strongly-nonlinear phase where the mode amplitude saturates. By investigating the phase space dynamics associated with the kinetic response, we find a link between a local flattening, or folding, of the particle distribution function and the breakdown of the explosive description. Since the explosive growth sets the stage for long-term frequency chirping modes, it is hoped that the present work can be of relevance for the prediction of the variety of chirping modes that have been observed in many experimental situations. These modes are expected to have a very significant effect on the confinement properties of fusion plasmas.
Advisors/Committee Members: Berk, H. L. (advisor), Breizman, Boris N. (advisor), Morrison, Philip J (committee member), Waelbroeck, Francois L (committee member), Gamba, Irene M (committee member).
Subjects/Keywords: Physics; Plasma physics; Nuclear fusion; Nonlinear physics; Wave instabilities; Nonlinear waves
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APA (6th Edition):
-1430-6073. (2017). Explosive evolution of near-threshold kinetic instabilities. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/62258
Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete
Chicago Manual of Style (16th Edition):
-1430-6073. “Explosive evolution of near-threshold kinetic instabilities.” 2017. Doctoral Dissertation, University of Texas – Austin. Accessed April 11, 2021.
http://hdl.handle.net/2152/62258.
Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete
MLA Handbook (7th Edition):
-1430-6073. “Explosive evolution of near-threshold kinetic instabilities.” 2017. Web. 11 Apr 2021.
Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete
Vancouver:
-1430-6073. Explosive evolution of near-threshold kinetic instabilities. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2017. [cited 2021 Apr 11].
Available from: http://hdl.handle.net/2152/62258.
Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete
Council of Science Editors:
-1430-6073. Explosive evolution of near-threshold kinetic instabilities. [Doctoral Dissertation]. University of Texas – Austin; 2017. Available from: http://hdl.handle.net/2152/62258
Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete
. 
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