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Articles 1 - 15 of 15
Full-Text Articles in Plasma and Beam Physics
Structured Waves Near The Plasma Frequency Observed In Three Auroral Rocket Flights, M Samara, J Labelle
Structured Waves Near The Plasma Frequency Observed In Three Auroral Rocket Flights, M Samara, J Labelle
Dartmouth Scholarship
Abstract. We present observations of waves at and just above the plasma frequency (fpe) from three high frequency electric field experiments on three recent rockets launched to altitudes of 300–900 km in active aurora. The predominant observed HF waves just above fpe are narrowband, short- lived emissions with amplitudes ranging from <1mV/m to 20 mV/m, often associated with structured electron den- sity. The nature of these HF waves, as determined from frequency-time spectrograms, is highly variable: in some cases, the frequency decreases monotonically with time as in the “HF-chirps” previously reported (McAdams and La- Belle, 1999), but in other cases rising frequencies are ob- served, or features which alternately rise and fall in fre- quency. They exhibit two timescales of amplitude variation: a short timescale, typically 50–100 ms, associated with in- dividual discrete features, and a longer timescale associated with the general decrease in the amplitudes of the emissions as the rocket moves away from where the condition f ∼fpe holds. The latter timescale ranges from 0.6 to 6.0 s, corre- sponding to distances of 2–7 km, assuming the phenomenon to be stationary and using the rocket velocity to convert time to distance.
An Experimental Study Of A Pulsed Dc Plasma Flow Control Actuator, Jennifer D. Wall
An Experimental Study Of A Pulsed Dc Plasma Flow Control Actuator, Jennifer D. Wall
Theses and Dissertations
An experiment on the effects of a pulsed DC plasma actuator on a separated flow in a low speed wind tunnel was conducted. The actuator consisted of two asymmetric copper electrodes oriented normal to the flow separated by a dielectric barrier and mounted on a flat plate in the center of the tunnel. A contoured insert was constructed and used to create an adverse pressure gradient in the test section comparable to a Pak-B low pressure turbine blade distribution. Suction was applied from the upper wall to induce separation along the flat plate over the electrodes. The DC power supply …
Backward Amplification And Beam Cleanup Of A Raman Fiber Laser Oscillator Using A Multi-Mode Graded Index Fiber Amplifier, Jesse D. S. Morgan Iii
Backward Amplification And Beam Cleanup Of A Raman Fiber Laser Oscillator Using A Multi-Mode Graded Index Fiber Amplifier, Jesse D. S. Morgan Iii
Theses and Dissertations
This thesis tested a CW fiber-based Raman amplifier implemented in a backward pumped geometry. To create a seed for the amplifier, a CW Nd:YAG laser operating at 1.064µm was used to pump a 50µm multimode graded index fiber using fiber Bragg gratings to create a Raman Fiber Laser (RFL) Oscillator with a Stokes beam at 1.116µm. The Stokes beam was then used to seed two lengths, 5.3km and 2.5km, of 50µm multimode graded index fiber. The fiber amplifier was pumped by a second CW Nd:YAG laser in the backward geometry. Spectral data taken for both fibers indicated that the backward …
A Study Of Collapse Events In Ultraviolet Light Filaments Due To Transient Edge Effects, Paul L. Muller
A Study Of Collapse Events In Ultraviolet Light Filaments Due To Transient Edge Effects, Paul L. Muller
Theses and Dissertations
Intense, short light pulses can form filaments capable of propagating kilometers through the atmosphere. This is due to the nonlinear index of refraction of the atmosphere in response to the pulse's high intensity, which creates a self-focusing effect that further intensifies the pulse. This focusing is balanced by the formation of defocusing plasma by the pulse. A split-step propagation model was used to simulate the propagation of these pulses through the atmosphere and investigate the collapse of long ultraviolet pulses of 10-100 picoseconds in duration due to transient edge effects. The structures of individual collapse events in the pulse were …
Passive Multiple Beam Combination In Optical Fibers Via Stimulated Brillouin Scattering, Kirk C. Brown
Passive Multiple Beam Combination In Optical Fibers Via Stimulated Brillouin Scattering, Kirk C. Brown
Theses and Dissertations
Many active methods of scaling laser brightness have been demonstrated in recent years. The goal of this research was to demonstrate the feasibility of passively combining multiple laser beams using Stimulated Brillouin Scattering (SBS) in a long multimode optical fiber. This method of combination employed a “Gatling gun” fiber array that allowed several collimated beams to be focused by a lens into an optical fiber. The retroreflected Stokes beam is passed through the center of the beam combiner for analysis. In addition to experimental methodology and equipment used, the theoretical and historical background of SBS in optical fibers is provided. …
Development Of A Multiple Beam Combiner Using Stimulated Raman Scattering In Multimode Fiber, Brian M. Flusche
Development Of A Multiple Beam Combiner Using Stimulated Raman Scattering In Multimode Fiber, Brian M. Flusche
Theses and Dissertations
Beam combination was demonstrated by splitting the beam from a diode pumped Q-switched Nd:YAG laser and pumping a multiple input, single output fiber squid. Beam cleanup of the resulting output beam using stimulated Raman scattering was then demonstrated in both 100 μm fiber (Stokes M2 = 1.86) and 200 μm fiber (Stokes M2 = 1.40). The performance of the 200 μm fiber was compared to that of the 100 μm fiber. Energy conversion efficiency into the Stokes beam was measured as a function of input energy and found to be limited by the attenuation characteristics of the fiber. …
Shockwave Interactions With Argon Glow Discharges, Nicholas S. Siefert
Shockwave Interactions With Argon Glow Discharges, Nicholas S. Siefert
Theses and Dissertations
The purpose of this research was study shock wave interactions with argon glow discharges. Specifically, this thesis sought to answer whether it is possible to compress nonequilibrium electrons at the shock wave. The results in the thesis found that both equilibrium and nonequilibrium electrons could be compressed at the shock front. The double layer at the shock front, normalized by electron temperature, matched the calculated values for the double layer within a factor or two in all cases. The results also demonstrate that excited metastable states can be compressed at the shock front, as well. The culmination of this effort …
The Simulation Of Off-Axis Laser Propagation Using Heleeos, Scott L. Belton
The Simulation Of Off-Axis Laser Propagation Using Heleeos, Scott L. Belton
Theses and Dissertations
Emerging technology high energy laser (HEL) weapon systems create a myriad of new threats to safety as well as security. One of the primary causes of these concerns is off-axis laser propagation caused by ever-present particulate and molecular scattering medium in the atmosphere. The scatter from these aerosols and molecules can redirect some of the HEL's concentrated energy towards unintended targets such as the eyes of pilots, friendly fighters on the surface, or innocent bystanders. Of particular interest to the laser intelligence (LASINT) community is the possibility that off-axis irradiance from HEL weapon systems could be covertly measured with enough …
Spatially-Resolved Temperature Diagnostic For Supersonic Flow Using Cross-Beam Doppler-Limited Laser Saturation Spectroscopy, Grady T. Phillips
Spatially-Resolved Temperature Diagnostic For Supersonic Flow Using Cross-Beam Doppler-Limited Laser Saturation Spectroscopy, Grady T. Phillips
Theses and Dissertations
Optical techniques for measuring the temperature in three-dimensional supersonic reactive flows have typically depended on lineshape measurements using single-beam laser absorption spectroscopy. However, absorption over extended path lengths in flows with symmetric, turbulent eddies can lead to systematically high extracted temperatures due to Doppler shifts resulting from flow along the absorption path. To eliminate these problems, Cross-Beam Saturation Absorption Spectroscopy (CBSAS) and Cross-Beam Inter-Modulated Fluorescence (CBIMF) have been developed which utilize two crossed and nearly copropogating laser beams.to record the spectral signal of an I2 ro-vibrational line in a small three-dimensional volume using a tunable CW dye laser. Temperature …
Macroscopic Computational Model Of Dielectric Barrier Discharge Plasma Actuators, Timothy R. Klein
Macroscopic Computational Model Of Dielectric Barrier Discharge Plasma Actuators, Timothy R. Klein
Theses and Dissertations
Recent progress in the generation and sustainment of gas discharges at atmospheric pressure has energized research in the field of plasma-aerodynamics. Plasma actuators are promising devices that achieve flow control with no moving parts, do not alter the airfoil shape and place no parts in the flow. The operation of a plasma actuator is examined using a macroscopic (force and power addition) computational fluid dynamic model of a dielectric barrier discharge, DBD, in Fluent. A parametric approach is adopted to survey the range of requisite magnitudes of momentum and energy delivered to the flow field and to identify the effects …
Dynamics Of An Atmospheric Pressure Plasma Plume Generated By Submicrosecond Voltage Pulses, Xinpei Lu, Mounir Laroussi
Dynamics Of An Atmospheric Pressure Plasma Plume Generated By Submicrosecond Voltage Pulses, Xinpei Lu, Mounir Laroussi
Electrical & Computer Engineering Faculty Publications
Nonequilibrium plasmas driven by submicrosecond high voltage pulses have been proven to produce high-energy electrons, which in turn lead to enhanced ionization and excitations. Here, we describe a device capable of launching a cold plasma plume in the surrounding air. This device, "the plasma pencil," is driven by few hundred nanosecond wide pulses at repetition rates of a few kilohertz. Correlation between current-voltage characteristics and fast photography shows that the plasma plume is in fact a small bulletlike volume of plasma traveling at unusually high velocities. A model based on photoionization is used to explain the propagation kinetics of the …
Plasma Emission Redistribution In A Single Cylce Of A Pulsed Dc Magnetron, W. Zhu, G. Buyle, J. Lopez, S. Shanmugmurthy, A. Belkind, K. Becker, R. De Gryse
Plasma Emission Redistribution In A Single Cylce Of A Pulsed Dc Magnetron, W. Zhu, G. Buyle, J. Lopez, S. Shanmugmurthy, A. Belkind, K. Becker, R. De Gryse
Physics Faculty Publications
Time-resolved images of the optical emissions from a pulsed dc titanium target planar rectangular sputtering magnetron plasma were taken using Argon spectral filters and a Roper Scientific ICCD camera with a time resolution of 0.05-0.2 μs. At the beginning of the 'on-time', when the power is turned on, the discharge initially starts preferentially in two opposite curved sections ('cross corners') of the magnetron race track, where it exhibits the most intense plasma emissions. During the rest of the 'on-time', the emissions from the straight sections of the race track of the magnetron are always slightly more intense than the emissions …
Measured Stark Widths And Shifts Of The Neutral Argon Spectral Lines In 4s–4p And 4s–4p′ Transitions, Vladimir Milosavljevic, Albert R. Ellingboe, Stevan Djenize
Measured Stark Widths And Shifts Of The Neutral Argon Spectral Lines In 4s–4p And 4s–4p′ Transitions, Vladimir Milosavljevic, Albert R. Ellingboe, Stevan Djenize
Articles
We investigate the Stark widths (W) and the shift (d), of the seven neutral argon (Ar I) spectral lines from the 4s–4p and 4s–4p′ transitions. The line shapes are measured in a linear, low-pressure, optically thin pulsed arc discharge at about 16 000 K electron temperature (T) and about 7.0 × 1022 m− 3 electron density (N). The new data separates the electron width (We) and ion width Wi from the total Stark width (Wt), as well the separation of electron total Stark …
Electron Bernstein Wave Simulations And Comparison To Preliminary Nstx Emission Data, Josef Preinhaelter, Jakub Urban, Pavol Pavlo, Gary Taylor, Steffi Diem, Linda L. Vahala, George Vahala
Electron Bernstein Wave Simulations And Comparison To Preliminary Nstx Emission Data, Josef Preinhaelter, Jakub Urban, Pavol Pavlo, Gary Taylor, Steffi Diem, Linda L. Vahala, George Vahala
Electrical & Computer Engineering Faculty Publications
Simulations indicate that during flattop current discharges the optimal angles for the aiming of the National Spherical Torus Experiment (NSTX) antennae are quite rugged and basically independent of time. The time development of electron Bernstein wave emission (EBWE) at particular frequencies as well as the frequency spectrum of EBWE as would be seen by the recently installed NSTX antennae are computed. The simulation of EBWE at low frequencies (e.g., 16 GHz) agrees well with the recent preliminary EBWE measurements on NSTX. At high frequencies, the sensitivity of EBWE to magnetic field variations is understood by considering the Doppler broadened electron …
Plasma Treatment Of Bulk Niobium Surfaces For Srf Cavities, M. Rašković, L. Vuškovic, S. Popović, L. Phillips, A. -M. Valente-Feliciano, S. B. Radovanov, L. Godet
Plasma Treatment Of Bulk Niobium Surfaces For Srf Cavities, M. Rašković, L. Vuškovic, S. Popović, L. Phillips, A. -M. Valente-Feliciano, S. B. Radovanov, L. Godet
Physics Faculty Publications
Two types of electric discharges were used to demonstrate the validity of plasma surface treatment for superconducting radio-frequency (SRF) cavities. The experiments were performed on disc-shaped Nb samples and compared with identical samples treated with buffer chemical polishing (BCP) techniques. Surface analysis indicates comparable or superior properties of plasma-treated samples. These promising results are still preliminary and additional work is in progress.