4,112 research outputs found
Using the X-FEL to understand X-ray Thomson scattering for partially ionized plasmas
For the last decade numerous researchers have been trying to develop
experimental techniques to use X-ray Thomson scattering as a method to measure
the temperature, electron density, and ionization state of high energy density
plasmas such as those used in inertial confinement fusion. With the advent of
the X-ray free electron laser (X-FEL) at the SLAC Linac Coherent Light Source
(LCLS) we now have such a source available in the keV regime. One challenge
with X-ray Thomson scattering experiments is understanding how to model the
scattering for partially ionized plasmas. Most Thomson scattering codes used to
model experimental data greatly simplify or neglect the contributions of the
bound electrons to the scattered intensity. In this work we take the existing
models of Thomson scattering that include elastic ion-ion scattering and the
electron-electron plasmon scattering and add the contribution of the bound
electrons in the partially ionized plasmas. Except for hydrogen plasmas almost
every plasma that is studied today has bound electrons and it is important to
understand their contribution to the Thomson scattering, especially as new
X-ray sources such as the X-FEL will allow us to study much higher Z plasmas.
Currently most experiments have looked at hydrogen or beryllium. We will first
look at the bound electron contributions to beryllium by analysing existing
experimental data. We then consider several higher Z materials such as Cr and
predict the existence of additional peaks in the scattering spectrum that
requires new computational tools to understand. For a Sn plasma we show that
the bound contributions changes the shape of the scattered spectrum in a way
that would change the plasma temperature and density inferred by the
experiment.Comment: 13th International Conference on X-ray Lasers Paris, France June 10,
2012 through June 15, 201
Average-Atom Model for X-ray Scattering from Warm Dense Matter
A scheme for analyzing Thomson scattering of x-rays by warm dense matter,
based on the average-atom model, is developed. Emphasis is given to x-ray
scattering by bound electrons. Contributions to the scattered x-ray spectrum
from elastic scattering by electrons moving with the ions and from inelastic
scattering by free and bound electrons are evaluated using parameters (chemical
potential, average ionic charge, free electron density, bound and continuum
wave functions, and occupation numbers) taken from the average-atom model. The
resulting scheme provides a relatively simple diagnostic for use in connection
with x-ray scattering measurements. Applications are given to dense hydrogen,
beryllium, aluminum, titanium, and tin plasmas. At high momentum transfer,
contributions from inelastic scattering by bound electrons are dominant
features of the scattered x-ray spectrum for aluminum, titanium, and tin.Comment: 22 pages, 10 figures Presentation at Workshop IV: Computational
Challenges in Warm Dense Matter at IPAM (UCLA) May 21 - 25, 201
Shuttle Ku-band and S-band communications implementation study
Various aspects of the shuttle orbiter S-band network communication system, the S-band payload communication system, and the Ku-band communication system are considered. A method is proposed for obtaining more accurate S-band antenna patterns of the actual shuttle orbiter vehicle during flight because the preliminary antenna patterns using mock-ups are not realistic that they do not include the effects of additional appendages such as wings and tail structures. The Ku-band communication system is discussed especially the TDRS antenna pointing accuracy with respect to the orbiter and the modifications required and resulting performance characteristics of the convolutionally encoded high data rate return link to maintain bit synchronizer lock on the ground. The TDRS user constraints on data bit clock jitter and data asymmetry on unbalanced QPSK with noisy phase references are included. The S-band payload communication system study is outlined including the advantages and experimental results of a peak regulator design built and evaluated by Axiomatrix for the bent-pipe link versus the existing RMS-type regulator. The nominal sweep rate for the deep-space transponder of 250 Hz/s, and effects of phase noise on the performance of a communication system are analyzed
X-ray Thomson scattering for partially ionized plasmas including the effect of bound levels
X-ray Thomson scattering is being developed as a method to measure the
temperature, electron density, and ionization state of high energy density
plasmas such as those used in inertial confinement fusion. Most experiments are
currently done at large laser facilities that can create bright X-ray sources,
however the advent of the X-ray free electron laser (X-FEL) provides a new
bright source to use in these experiments. One challenge with X-ray Thomson
scattering experiments is understanding how to model the scattering for
partially ionized plasmas in order to include the contributions of the bound
electrons in the scattered intensity. In this work we take the existing models
of Thomson scattering that include elastic ion-ion scattering and the
electron-electron plasmon scattering and add the contribution of the bound
electrons in the partially ionized plasmas. We validated our model by analyzing
existing beryllium experimental data. We then consider several higher Z
materials such as Cr and predict the existence of additional peaks in the
scattering spectrum that requires new computational tools to understand. We
also show examples of experiments in CH and Al that have bound contributions
that change the shape of the scattered spectra.Comment: SPIE 2013 Optics and Photonics, San Diego, CA, United States August
25, 2013 through August 29, 2013. arXiv admin note: substantial text overlap
with arXiv:1212.5972, arXiv:1207.507
Space Shuttle program communication and tracking systems interface analysis
The Space Shuttle Program Communications and Tracking Systems Interface Analysis began April 18, 1983. During this time, the shuttle communication and tracking systems began flight testing. Two areas of analysis documented were a result of observations made during flight tests. These analyses involved the Ku-band communication system. First, there was a detailed analysis of the interface between the solar max data format and the Ku-band communication system including the TDRSS ground station. The second analysis involving the Ku-band communication system was an analysis of the frequency lock loop of the Gunn oscillator used to generate the transmit frequency. The stability of the frequency lock loop was investigated and changes to the design were reviewed to alleviate the potential loss of data due the loop losing lock and entering the reacquisition mode. Other areas of investigation were the S-band antenna analysis and RF coverage analysis
Engineering evaluations and studies. Volume 2: Exhibit B, part 1
Ku-band communication system analysis, S-band system investigations, payload communication investigations, shuttle/TDRSS and GSTDN compatibility analysis are discussed
Engineering evaluations and studies. Volume 3: Exhibit C
High rate multiplexes asymmetry and jitter, data-dependent amplitude variations, and transition density are discussed
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