Spectroscopic Diagnosis Of A Dense Hydrogen Plasma Source

This report gives the details of experiments performed to measure the levels and the angular distribution of oscillating electric fields in an aluminum plasma produced by the Phoenix advanced pulsed radiation source. The electric field values were obtained by measuring the L (beta), L (gamma), L (sigma), and L (epsilon) line profiles of Al XIII and fitting the profiles to a model for the Phoenix plasma source. The model attempts to take into account all of the mechanisms which lead to broadening of the observed profiles for the conditions present in the Phoenix plasma. The main broadening mechanisms used in the model include Doppler broadening from the bulk motion of the plasma, stark broadening by electrons, ions and oscillating electric fields, and self absorption. In addition to the flat crystal and two curved crystal spectrometers used to measure the lines profiles, a pinhole camera and a four frame camera were used to try and obtain the size of the most dense retions in the plasma. The size of these "hot spots" were found to be less than 500 microns. From fits of the experimental profiles to the data, the level of anomalous electric fields in the Phoenix plasma source were found to be Eo = 1 - 9 Gv/cm, indicative of a strong Langmuir turbulence. The fields were also found to develop anisotropically, primarily along the direction of the discharge.

A spectroscopic diagnostic tool has been developed to determine the electron temperature and the neutral density in helium, hydrogen and argon plasmas from absolutely calibrated spectroscopic measurements. For each gas, a method of analysis which uses models specific to each species present in the plasma (neutral atom or singly ionized atom) has been defined. The experimental electron density is used as an input parameter to the models, and the absolutely calibrated spectroscopic data are processed beforehand to obtain the populations of the upper excited levels corresponding to the observed spectral lines. For helium plasmas, the electron temperature is inferred from the experimental helium ion excited level p = 4 population using a corona model, and then the neutral density is determined from the experimental helium neutral excited level populations using a collisional-radiative model for helium neutrals. For hydrogen plasmas, combinations of the electron temperature and the neutral density are determined from the experimental hydrogen neutral excited level populations using a collisional-radiative model specific to hydrogen atoms. For argon plasmas, the electron temperature is inferred from the experimental argon ion excited level populations using a collisional-radiative model for argon ions, and then the neutral density is determined from the experimental argon neutral excited level populations using a collisional-radiative model for argon neutrals. This diagnostic tool was applied to three experiments with different geometries and plasma conditions to test the validity of each data analysis method. The helium and hydrogen data analysis methods were tested and validated on helium and hydrogen plasmas produced in the VASIMR experiment, a plasma propulsion system concept. They gave electron temperatures and neutral densities that were consistent with other diagnostics and theory. The argon diagnostic tool was tested on argon plasmas produced in the VASIMR experiment, the Helimak experiment and the Helicon experiment. The electron temperature and neutral density obtained on both the Helimak and the Helicon experiments were consistent with other diagnostics and with theory, and validated the method of analysis. An impurity problem on the VASIMR experiment made it difficult for the data analysis to be validated.

This book focuses on the characteristics of optical radiation, or a spectrum, emitted by various plasmas. In plasma, the same atomic species can produce quite different spectra, or colours, depending on the nature of the plasma. This book gives a theoretical framework by which a particular spectrum can be interpreted correctly and coherently. The uniqueness of the book lies in its comprehensive treatment of the intensity distribution of spectral lines and the population density distribution among the atomic levels in plasmas. It is intended to provide beginners with a good perspective of the field, laying out the physics in an extremely clear manner and starting from an elementary level. A useful feature of the book is the asterisked sections and chapters which can be skipped by readers who only wish to gain a quick and basic introduction to plasma spectroscopy. It will also be useful to researchers working actively in the field, acting as a guide for carrying out experiments and interpreting experimental observations.

Although based on lectures given for graduate students and postgraduates starting in plasma physics, this concise introduction to the fundamental processes and tools is as well directed at established researchers who are newcomers to spectroscopy and seek quick access to the diagnostics of plasmas ranging from low- to high-density technical systems at low temperatures, as well as from low- to high-density hot plasmas. Basic ideas and fundamental concepts are introduced as well as typical instrumentation from the X-ray to the infrared spectral regions. Examples, techniques and methods illustrate the possibilities. This book directly addresses the experimentalist who actually has to carry out the experiments and their interpretation. For that reason about half of the book is devoted to experimental problems, the instrumentation, components, detectors and calibration.

Market: Plasma physicists and students. Upon publication in 1968, Plasma Diagnostics represented the most up- to-date survey of the experimental methods used in plasma analysis, including the necessary theoretical background. This work emphasizes spectroscopic techniques along with in-depth sections on laser techniques and electric and magnetic probe methods. The evaluation of collision and transport cross sections, heat and electrical conductivity, and viscosity are some of the many applications of plasma diagnostics reviewed as well. This long-awaited reprint volume is of interest to both physicists and students of theoretical physics as it deals with plasma theory from a fundamental point of view, stressing a careful derivation and discussion of the equations.

A system to determine the density and temperature of ground state hydrogen atoms in a plasma by vacuum ultraviolet laser absorption spectroscopy is described. The continuous tunability of the spectrometer allows for analysis at any of the Lyman transitions. The narrow bandwidth of the laser system allows for the accurate determination of the absorption lineshape and hence the translational temperature. The utility of the system is exemplified by data obtained on an ion-source plasma. The measurements demonstrate the quality of the data as well as illustrating the behavior of this ion source under varying discharge conditions. 9 refs., 5 figs., 1 tab.

The results of the present work show an opportunity of pure spectroscopic detection of the degree of dissociation of hydrogen in low temperature plasmas and indicate an insufficient knowledge about elementary processes for plasma diagnostic.

Spectral Line Broadening by Plasmas deals with spectral line broadening by plasmas and covers topics ranging from quasi-static approximation and impact approximation to intermediate approximations and correlation effects. Experimental results for hydrogen lines, lines with forbidden components, and ionized helium lines are presented. Applications such as density and temperature measurements are also considered. Comprised of four chapters, this volume begins with an overview of the effects of electric fields from electrons and ions (both acting as point charges) on spectral line shapes. The next chapter surveys theoretical work, paying particular attention to quasi-static, impact, and intermediate approximations as well as correlation effects. Stark broadening experiments are then discussed, with special emphasis on experiments capable of checking the accuracy or validity limits of the various approximations. The final chapter is devoted to applications in laboratory plasma physics and astronomy, focusing on density and temperature measurements and opacity calculations as well as the analysis of stellar atmospheres, amplitudes and spectra of plasma waves, and radio frequency lines. This book should appeal to students, practitioners, and researchers in pure and applied physics.