Simulating cometary and stellar x-ray emission in the laboratory using microcalorimeters and an electron beam ion trap
The mixing of atomic and macroscopic processes taking place in non-terrestrial objects creates complex, dynamic, and intriguing environments. High-resolution x-ray spectra from these sources measured by satellites such as Chandra, XMM-Newton, and the Solar Maximum Mission provide a means for understanding the physics governing these sources. Laboratory measurements of the atomic processes have proved crucial to the interpretation of these spectra. For example using the LLNL electron beam ion traps EBIT-I and EBIT-II a detailed study of the x-ray spectrum of Fe XVII has been conducted addressing the large ratio predicted by theory compared to observations of considerably smaller values of the relative intensity of the 2p-3d {sup 1}P{sub 1} resonant to the {sup 3}D{sub 1} intercombination line. The difference was often attributed to opacity effects. However, laboratory measurements in the optically thin limit agree with observations demonstrating that the prediction is too large and opacity need not be invoked. The laboratory results thus provide a benchmark in the optically thin limit for accurate estimates of opacity effects. To uncover the source of the discrepancy between theory and observation, we have performed a series of experiments that successively uncovered more details about the Fe XVII lines produced in coronal plasmas. Most recently, we used a 32 channel array microcalorimeter from the Astro-E x-ray satellite program to measure the excitation cross section of various Fe XVII lines in the laboratory. These measurements resolve long-standing issues thought to be associated with non-equilibrium processes. We have also used the Astro-E microcalorimeter, and more recently its upgrade from the Astro-E2 project, and the magnetic trapping mode of EBIT-I to accurately measure x-ray emission from charge exchange recombination and to simulate the x-ray line production process in comets. Using only the laboratory measurements, we fit the moderate resolution x-ray spectrum from the comet C/Linear1999 observed by the ACIS-S CCD instrument on the Chandra X-ray Observatory. The good fit to the data shows that we are able to recreate in the laboratory the charge exchange process taking place in comets. With the launch of the Astro-E2 satellite in 2005, whose second generation XRS microcalorimeter array has an energy resolution of 6-7 eV, a factor of 20-30 better than Chandra's ACIS-S CCD, high resolution spectra of comets should become available. These measurements coupled with the laboratory measurements at LLNL using the sister Astro-E2 calorimeter array, will make it possible to accurately diagnose the composition of the solar wind at various locations in the solar system.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15014219
- Report Number(s):
- UCRL-PROC-204049; TRN: US0802094
- Resource Relation:
- Journal Volume: 730; Conference: Presented at: Atomic Processes in Plasmas, Albuquerque, NM, United States, Apr 19 - Apr 22, 2004
- Country of Publication:
- United States
- Language:
- English
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