High-sensitivity plasma density retrieval in a common-path second-harmonic interferometer through simultaneous group and phase velocity measurement

Precise measurements of the plasma density in ionized gas cells and discharged capillaries are critical to the design and operation of plasma-based accelerators, active plasma lenses, and plasma-based radiation sources. In this manuscript, a spectral-domain common-path second-harmonic interferometer is upgraded with the simultaneous measurement of the group and phase velocity, allowing for high-sensitivity density characterization (from the phase velocity advance) without the need for phase tracking from zero-density (enabled by the group velocity delay). The technique is applied to 1.5-cm-long plasma structures, without density ambiguity in parameter scans with >2π phase jumps. The single-shot sensitivity in phase retrieval is demonstrated at 63 mrad, equivalent to a density-length product of 1.8·1015 cm -2 . This is an improvement of ×45 compared to group velocity analysis alone

Contaminants in Unionid Mussels from the Confluence of the Mississippi and Illinois Rivers

Unionid mussels were collected from three mussel beds near the confluence of the Mississippi and Illinois rivers in 2003 to evaluate concentrations of selected elements and organic compounds in three abundant species and to preliminarily investigate the relative contribution of these waterways to observed contaminant burdens. Copper (Cu), selenium (Se), and zinc (Zn) concentrations were higher and lead (Pb) concentrations were lower in Amblema plicata collected downstream of the confluence than in those collected upstream. Mean concentrations of nickel (Ni), total mercury (Hg), methylmercury (MeHg), Pb, and Zn varied by species. Concentrations of cadmium (Cd) decreased with age in A. plicata from two of three sites. Tissue concentrations of some elements, e.g., arsenic (As), Cd, Cu, Pb, Se, and Zn, were similar to or higher than those previously reported for unionid mussels from areas of contaminated sediment. Concentrations of Cd, Cu, and Zn in A. plicata were comparable to those collected from the Mississippi River approximately 450 and 900 km upstream from our study sites (Naimo et al. 1992). Although total Hg concentrations we observed were an order of magnitude lower than in that study, MeHg concentrations were above those associated with reductions in soft tissue mass in a study of Elliptio complanata (Salazar et al. 1995). A number of polychlorinated biphenyl (PCB) congeners were detected in A. plicata tissues, with 85% of detections occurring in mussels from downstream of the confluence. Concentrations of individual PCB congeners were ???33 ng/g ww and the maximum summed PCB congener concentration was 100.2 ng/g ww. Although few persistent pesticides were detected, -hexachlorocyclohexane (HCH) was detected in each of the species collected from below the confluence of the two rivers, and in A. plicata collected above it on both the Mississippi and Illinois rivers, at a maximum concentration of 103.5 ng/g ww. Aldrin, ??-HCH and dichlorodiphenyltrichloroethane (DDT) were detected in few of the specimens collected. The findings of this preliminary investigation suggest that unionid mussels from near the confluence of the Mississippi and Illinois rivers may be at risk of negative health effects of elevated exposure to certain environmental contaminants. Studies examining the health and productivity of unionid mussels from this area appear warranted.published or submitted for publicationis peer reviewe

Resonant laser‐plasma electron acceleration

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87302/2/65_1.pd

Experimental observation of nonlinear Thomson scattering

A century ago, J. J. Thomson showed that the scattering of low-intensity light by electrons was a linear process (i.e., the scattered light frequency was identical to that of the incident light) and that light's magnetic field played no role. Today, with the recent invention of ultra-high-peak-power lasers it is now possible to create a sufficient photon density to study Thomson scattering in the relativistic regime. With increasing light intensity, electrons quiver during the scattering process with increasing velocity, approaching the speed of light when the laser intensity approaches 10^18 W/cm^2. In this limit, the effect of light's magnetic field on electron motion should become comparable to that of its electric field, and the electron mass should increase because of the relativistic correction. Consequently, electrons in such high fields are predicted to quiver nonlinearly, moving in figure-eight patterns, rather than in straight lines, and thus to radiate photons at harmonics of the frequency of the incident laser light, with each harmonic having its own unique angular distribution. In this letter, we report the first ever direct experimental confirmation of these predictions, a topic that has previously been referred to as nonlinear Thomson scattering. Extension of these results to coherent relativistic harmonic generation may eventually lead to novel table-top x-ray sources.Comment: including 4 figure

Quasi-monoenergetic femtosecond photon sources from Thomson Scattering using laser plasma accelerators and plasma channels

Narrow bandwidth, high energy photon sources can be generated by Thomson scattering of laser light from energetic electrons, and detailed control of the interaction is needed to produce high quality sources. We present analytic calculations of the energy-angular spectra and photon yield that parametrize the influences of the electron and laser beam parameters to allow source design. These calculations, combined with numerical simulations, are applied to evaluate sources using conventional scattering in vacuum and methods for improving the source via laser waveguides or plasma channels. We show that the photon flux can be greatly increased by using a plasma channel to guide the laser during the interaction. Conversely, we show that to produce a given number of photons, the required laser energy can be reduced by an order of magnitude through the use of a plasma channel. In addition, we show that a plasma can be used as a compact beam dump, in which the electron beam is decelerated in a short distance, thereby greatly reducing radiation shielding. Realistic experimental errors such as transverse jitter are quantitatively shown to be tolerable. Examples of designs for sources capable of performing nuclear resonance fluorescence and photofission are provided

Silurian and Devonian Formations in Southeastern Indiana

Indiana Geological Survey Guidebook 1This conference was planned to provide an opportunity to observe and discuss outcrops of Silurian and Devonian rocks in southeastern Indiana. The broad aspects of the stratigraphy and fauna were emphasized since most persons attending were not familiar with these formations. It was hoped the discussions would help solve many problems concerning these rocks. Any assistance that can be provided in the subsurface identification and correlation of the counterparts of these formations in the surrounding basin areas will help make the conference a success. Campbell's (1942) recent reclassification of the Devonian will be especially interesting to those familiar with the older classification and terminology. The opportunity to become acquainted and discuss mutual problems was an important part of the program.Department of Geology, Indiana University; Indiana Division of Geology; Indiana Department of Conservatio

On the Theory of Relativistic Strong Plasma Waves

The influence of motion of ions and electron temperature on nonlinear one-dimensional plasma waves with velocity close to the speed of light in vacuum is investigated. It is shown that although the wavebreaking field weakly depends on mass of ions, the nonlinear relativistic wavelength essentially changes. The nonlinearity leads to the increase of the strong plasma wavelength, while the motion of ions leads to the decrease of the wavelength. Both hydrodynamic approach and kinetic one, based on Vlasov-Poisson equations, are used to investigate the relativistic strong plasma waves in a warm plasma. The existence of relativistic solitons in a thermal plasma is predicted.Comment: 13 pages, 8 figure

Electron acceleration by nonlinear plasma waves resonantly driven with optimized high‐intensity laser pulse trains

A method for generating large‐amplitude nonlinear plasma waves, which utilizes an optimized train of independently adjustable, intense laser pulses, is analyzed in one dimension both theoretically and numerically (using both Maxwell‐fluid and particle‐in‐cell codes). Optimal pulse widths and interpulse spacings are computed for pulses with either square or finite‐rise‐time sine shapes. A resonant region of the plasma wave phase space is found where the plasma wave is driven most efficiently by the laser pulses. The width of this region, and thus the optimal finite‐rise‐time laser pulse width, was found to decrease with increasing background plasma density and plasma wave amplitude, while the nonlinear plasma wavelength, and thus the optimal interpulse spacing, increases. Also investigated are damping of the wave by trapped background electrons, and the sensitivities of the resonance to variations in the laser and plasma parameters. Resonant excitation is found to be superior for electron acceleration to either beatwave or single‐pulse excitation because comparable plasma wave amplitudes may be generated at lower plasma densities, reducing electron‐phase detuning, or at lower laser intensities, reducing laser‐plasma instabilities. Practical experimental methods for producing the required pulse trains are discussed. ©1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87311/2/270_1.pd

Resonantly driven laser‐plasma electron accelerators

A method for generating large‐amplitude nonlinear plasma waves, which utilizes an optimized train of independently adjustable, intense laser pulses, is analyzed in 1‐D both theoretically and numerically (using both Maxwell‐fluid and particle‐in‐cell codes). Optimal pulse widths and interpulse spacings are computed for pulses with either square or finite‐risetime sine shapes. A resonant region of the plasma wave phase space is found where the plasma wave is driven by the laser most efficiently. The width of this region, and thus the optimal finite‐risetime laser pulse width, was found to decrease with increasing plasma density and plasma wave amplitude, while the nonlinear plasma wavelength, and thus the optimal interpulse spacing, was found to increase. Also investigated are the resonance sensitivities to variations in the laser and plasma parameters. Non‐linear Landau damping of the wave by trapped background electrons is found to be important. Resonant excitation by this method is shown to more advantageous for electron acceleration than either the single pulse wakefield or the plasma beatwave concepts, because comparable plasma wave amplitudes may be generated at lower plasma densities, thus reducing electron‐phase detuning, or at lower laser intensities, thus reducing laser‐plasma instabilities. Practical experimental methods for producing the required pulse trains are discussed. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87549/2/551_1.pd