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Title: Identifying New Saturation Mechanisms Hindering the Development of Plasma-Based Laser Amplifiers Utilizing Stimulated Raman Backscattering
Authors: Turnbull, David
Advisors: Suckewer, Szymon
Contributors: Mechanical and Aerospace Engineering Department
Keywords: backscattered raman amplification
langmuir decay instability
particle trapping
stimulated brillouin scattering
stimulated raman backscattering
Subjects: Plasma physics
Mechanical engineering
Environmental economics
Issue Date: 2013
Publisher: Princeton, NJ : Princeton University
Abstract: Stimulated Raman Backscattering (SRBS) has the potential to supplement existing laser amplification technology in order to exceed the maximum intensity that is attainable with modern systems. It utilizes a three wave interaction in plasma in order to transfer the energy from a long, low intensity pumping pulse to a short, counterpropagating seed pulse that undergoes temporal compression as it is amplified and should ultimately be able to reach unfocused intensities up to a relativistic limit about five orders of magnitude larger than conventional systems. If proven viable, it could democratize research conducted with ultraintense laser systems as well as open up new realms of physics. Following theoretical suggestions and previous experimental conclusions, longer and more uniform preformed plasma channels were successfully created by focusing one of the plasma-forming beams to a line using an axicon lens. The beams amplified in those plasma channels were in fact more energetic than those previously reported in the published literature. However, results remained far afield of the theoretical predictions, which prompted an effort to reconcile the analytical work suggesting this scheme can be highly efficient with the experimental results demonstrating saturation. A Frequency-Resolved Optical Gating diagnostic was built in order to obtain greater insight into the amplified pulse shape and frequency distribution, data from which indicated that there was very often a frequency shift that seems to detune the interaction. Several mechanisms appear to be potentially viable sources of this shift. One possibility is that an ion acoustic wave induces wave collapse of the primary Langmuir wave mediating SRBS; this would also increase the damping rate and might even facilitate particle trapping. Additional evidence of this scenario later appeared in the time-integrated spectrometer data. Another possibility is that the amplified seed pulse triggers additional ionization of the plasma. Since both of these effects would require a very low initial electron temperature, a method for determining that value using only the gas density and electron density was developed, the results of which were consistent with the requisite conditions. The development of advanced laser technology is relevant to the pursuit of inertial fusion energy. The importance of fusion as a future option for electricity generation was investigated using integrated assessment modeling. The results suggest that fusion energy could be very valuable under imposed limits on carbon dioxide emissions, in particular if other carbon-neutral baseload technologies prove uncompetitive or are otherwise constrained by nonmarket impediments.
Alternate format: The Mudd Manuscript Library retains one bound copy of each dissertation. Search for these copies in the library's main catalog
Type of Material: Academic dissertations (Ph.D.)
Language: en
Appears in Collections:Mechanical and Aerospace Engineering

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