Search

Your search keyword '"Lepson, J. K."' showing total 94 results
Start Over Author "Lepson, J. K."
94 results on '"Lepson, J. K."'

5. Magnetic-Field Sensitive Line Ratios in EUV and Soft X-ray Spectra

Author

Beiersdorfer, P, Scofield, J, Brown, G. V, Chen, H, Trabert, E, and Lepson, J. K

Subjects
Astrophysics
Abstract

We discovered a class of lines that are sensitive to the strength of the ambient magnetic field, and present a measurement of such a line in Ar IX near 49 A. Calculations show that the magnitude of field strengths that can be measured ranges from a few hundred gauss to several tens of kilogauss depending on the particular ion emitting the line.

Published
2006

6. Laboratory Measurements of the Line Emission from Mid-Z L-Shell Ions in the EUV

Author

Lepson, J. K, Beiersdorfer, P, Chen, H, Gu, M. F, and Kahn, S. M

Subjects
Astrophysics
Abstract

We are continuing EBIT measurements of line lists in the EUV region for use as astrophysical diagnostics and have recently measured the same transitions in much denser plasma of the NSTX tokamak. This allows us to calibrate density-sensitive line ratios at their upper limits. We compare our observations at low and high density with calculations from the Flexible Atomic Code.

Published
2006

7. Emission Line Spectra in the Soft X-ray Region 20 - 75 Angstroms

Author

Lepson, J. K, Beiersdorfer, P, Chen, H, Behar, E, and Kahn, S. M

Subjects
Astronomy
Abstract

As part of a project to complete a comprehensive catalogue of astrophysically relevant emission lines in support of new-generation X-ray observatories using the Lawrence Livermore electron beam ion traps EBIT-I and EDIT-II, emission lines of argon and sulfur in the soft X-ray and extreme ultraviolet region were studied. Observations of Ar IX through Ar XVI and S VII through S XIV between 20 and 75 Angstrom are presented to illustrate our work.

Published
2002

8. Laboratory Data for X-Ray Astronomy

Author

Beiersdorfer, P, Brown, G. V, Chen, H, Gu, M.-F, Kahn, S. M, Lepson, J. K, Savin, D. W, and Utter, S. B

Subjects
Astronomy
Abstract

Laboratory facilities have made great strides in producing large sets of reliable data for X-ray astronomy, which include ionization and recombination cross sections needed for charge balance calculations as well as the atomic data needed for interpreting X-ray line formation. We discuss data from the new generation sources and pay special attention to the LLNL electron beam ion trap experiment, which is unique in its ability to provide direct laboratory access to spectral data under precisely controlled conditions that simulate those found in many astrophysical plasmas. Examples of spectral data obtained in the 1-160 A wavelength range are given illustrating the type of laboratory X-ray data produced in support of such missions as Chandra, X-Ray Multi-Mirror telescope (XMM), Advanced Satellite for Cosmology and Astrophysics (ASCA) and Extreme Ultraviolet Explorer Satellite (EUVE).

Published
2000

9. Emission Line Spectra from Low-Density Laboratory Plasmas

Author

Beiersdorfer, P, Brown, G. V, Drake, J. J, Gu, M.-F, Kahn, S. M, Lepson, J. K, Liedahl, D. A, Mauche, C. W, Savin, D. W, Utter, S. B, and Wargelin, B. J

Subjects
Astrophysics
Abstract

Using spectroscopic equipment optimized for laboratory astrophysics, we are performing systematic measurements of the line emission from astrophysically relevant ions in the wavelength band between 1 and 400 Angstroms important to X-ray missions such as Chandra, XMM, Astro-E, and EUVE. Obtained in a controlled laboratory setting at electron densities similar to those found in stellar coronae, the data are used to test spectral modeling codes for accuracy and completeness. Our effort includes the compilation of the iron L-shell emission lines from 6-18 Angstroms and the iron M-shell emission lines from 50-200 Angstroms. Many lines have been identified for the first time, and the fluxes from lines missing in the spectral modeling codes are assessed. Our measurements also assess the accuracy of line excitation calculations, including direct electron-impact excitation, dielectronic recombination, and resonance excitation. These measurements yield a calibration of specific diagnostic line ratios. Examples of our current measurements are given.

Published
2000

10. Cataloguing Emission Line Spectra from Fe VII-Fe XXIV in the Extreme Ultraviolet

Author

Lepson, J. K, Beiersdorfer, P, Brown, G. V, Kahn, D. A, Liedahl, D. A, Mauche, C. W, and Utter, S. B

Subjects
Space Radiation
Abstract

Detailed laboratory astrophysics measurements are, in progress to produce spectral tables for the Fe VII Fe XXIV line emission in the EUV wavelength band. Results for Fe XIII are presented that update line lists used in the Chandra Emission Line Project.

Published
2000

18. Current Research with Highly Charged Ions in EBIT and SuperEBIT

Author

Beiersdorfer, P., Britten, J. A., Brown, G. V., Chen, H., Clothiaux, E. J., Cottam, J., F?rster, E., Gu, M.-F., Harris, C. L., Kahn, S. M., Lepson, J. K., Neill, P. A., Savin, Daniel Wolf, Schulte-Schrepping, H., Schweikhard, L., Smith, A. J., Träbert, E., Tschischgale, J., Utter, S. B., and Wong, K. L.

Published
2001
Full Text
View/download PDF

29. EUV spectroscopy on NSTX

Author

Lepson, J K, primary, Beiersdorfer, P, additional, Clementson, J, additional, Gu, M F, additional, Bitter, M, additional, Roquemore, L, additional, Kaita, R, additional, Cox, P G, additional, and Safronova, A S, additional

Published
2010
Full Text
View/download PDF

37. New Results in Laboratory X-ray Astrophysics

Author

Beiersdorfer, P., primary, Chen, H., additional, Boyce, K. R., additional, Brown, G. V., additional, Kelley, R. L., additional, Porter, F. S., additional, Stahle, C. K., additional, Lepson, J. K., additional, Jernigan, J. G., additional, Wargelin, B. J., additional, and Kahn, S. M., additional

Published
2005
Full Text
View/download PDF

44. X-Ray Emission from Highly Charged Ions Colliding with a Relativistic Electron Beam in the SuperEBIT Electron Beam Ion Trap.

Author

Beiersdorfer, P., Beck, B., Becker, J. A., Lepson, J. K., and Reed, K. J.

Subjects
ION traps, ELECTRON beams, X-rays, COLLISIONS (Nuclear physics)
Abstract

The high-energy electron beam ion trap SuperEBIT at the Lawrence Livermore National Laboratory allows the study of the x-ray emission from highly charged ions interacting with electrons with energy in excess of 200 keV. Radiation from ions as highly charged as Cf[sup 96+] has been produced this way. The facility is being used to investigate the contributions from quantum electrodynamics in heavy ions. Here the focus is lithium-like ions, especially U[sup 89+], which provide the opportunity for the most accurate test of QED in highly charged ions. We have also used the facility to measure the degree of x-ray line polarization as a function of the energy of the electron collision energy. For example, we have studied the linear polarization of the K-shell emission lines of Fe[sup 24+] for electron-impact energies high as 120 keV. A new area of research is the investigation of nuclear excitation by electronic transitions. This is the inverse process of internal conversion, where an atomic x ray is absorbed by the nucleus resulting in an excited nuclear state. We are planning to study this process in [sup 189]Os using 217 keV atomic x rays generated in the interaction with a 196 keV electron beam. [ABSTRACT FROM AUTHOR]

Published
2003

45. New Insights into the X-ray Spectra of Heliumlike and Neonlike Ions.

Author

Beiersdorfer, P., Chen, H., Hey, D., May, M. J., Osterheld, A. L., Reed, K. J., Scofield, J. H., Thorn, D. B., Bitter, M., Boyce, K. R., Brown, G. V., Gendreau, K. C., Kelley, R. L., Porter, F. S., Stahle, C. K., Szymkowiak, A. E., Olson, R. E., Lepson, J. K., Gu, M.-F., and Behar, E.

Subjects
X-ray spectra, IONS, ELECTRON beams, TOKAMAKS
Abstract

Recent measurements of the K-shell and L-shell x-ray spectra of highly charged heliumlike and neonlike ions are presented that were performed on the Livermore electron beam ion traps and the Princeton tokamaks. These measurements provide new insights into collisional and indirect line formation processes, identifications of forbidden lines, and a new plasma line diagnostic of magnetic field strength. [ABSTRACT FROM AUTHOR]

Published
2002

46. Current Research with Highly Charged Ions in EBIT-II and SuperEBIT

Author

Beiersdorfer, P., primary, Britten, J. A., additional, Brown, G. V., additional, Chen, H., additional, Clothiaux, E. J., additional, Cottam, J., additional, F?rster, E., additional, Gu, M.-F., additional, Harris, C. L., additional, Kahn, S. M., additional, Lepson, J. K., additional, Neill, P. A., additional, Savin, D. W., additional, Schulte-Schrepping, H., additional, Schweikhard, L., additional, Smith, A. J., additional, Tr?bert, E., additional, Tschischgale, J., additional, Utter, S. B., additional, and Wong, K. L., additional

Published
2001
Full Text
View/download PDF

48. Measuring plasma impurities in Alcator C-Mod as a function of time in the extreme ultraviolet.

Author

Beiersdorfer, P., Brown, G. V., Kamp, J. B., Magee, E. W., Lepson, J. K., Podpaly, Y., and Reinke, M. L.

Subjects
ULTRAVIOLET spectrometry, FIELD theory (Physics), ELECTRON beams, ION traps, PLASMA astrophysics, WAVELENGTHS, IONS, TUNGSTEN
Abstract

Copyright of Canadian Journal of Physics is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Published
2011
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results