ACCURATE WAVELENGTH MEASUREMENTS AND MODELING OF Fe xv TO Fe xix SPECTRA RECORDED IN HIGH-DENSITY PLASMAS BETWEEN 13.5 AND 17 A (original) (raw)

X-ray spectrum of a laser-produced iron plasma

Physical Review A, 1976

We present the analysis of the x-ray spectrum between 9.5 and 17.0 A of a laser-produced iron plasma. Wavelengths and relative intensities for 96 lines are measured. For the strongest part of the spectrum, above 13 A, almost all of the observed lines are identified as radiation from Fe" ", Fe" "', and Fe"'" ions. Measurements were made with a curved-crystal spectrograph. Calculations were full intermediate coupling, Hartree-Fock with relativistic corrections. Coulomb-approximation oscillator strengths were used to help in the line identification.

Modelling spectral emission from fusion plasmas

AIP Conference Proceedings, 2012

The paper adopts initially an historical perspective, commencing from ∼ 1970 and has a focus on interests and developments at Culham Laboratory from the time when Nicol Peacock led the UKAEA spectroscopy team. In spite of earlier setbacks, Nicol kept faith in the diagnostic value of quantitative prediction of spectral emissivities in the magnetic confinement fusion domain. So he facilitated and supported continued advance in population modelling in medium density, high temperature, non-LTE, non-stationary plasma on from the original pioneering work of Bates, Kingston and McWhirter (1962) [1]. Calculation of populations of excited states of ions and the distribution between ionisation stages of an element in such plasma requires knowledge of many individual reactions. So precision in spectral prediction is dependent on the availability of such reaction data and carries the additional burden of the generation of such data or its compilation and assessment. The paper charts a little of the evolution of these models and their data through the seventies and eighties on into this century at Culham, heavily influenced by Nicol. With JET/EP2 and ITER, population structure and ionisation state studies move on, with attention now much focussed on very heavy species, especially tungsten. Modern methods seek to make the atomic physics of such systems manageable for fusion plasma analysis, through techniques such as bundling, superstaging and extended spectral simulation. Most modern tokamaks have neutral beam heating, so electron collisions are not the end of the population story. Charge transfer between plasma impurity ions and fast neutral hydrogen is the driving reaction for CXS (charge exchange spectroscopy) and impurity ion impact with the fast hydrogen, the driving reaction for BES (beam emission spectroscopy), spectroscopy usually carried out at visible wavelengths. Nicol was interested in all these aspects, although he preferred the VUV. Developments here again recognise ITER and the strengthing of data and models for heavier systems and are included for completeness. But Nicol's heart was really in spectral line diagnostics, so the paper concludes with the state of efforts to enable easy, universal access to spectral analysis across the scope of Culham activity, of which it is hoped he would approve.

Observation of Quasi-Continuum Line Emission from Fe VII to Fe X in the Extreme-Ultraviolet Region below 140 Å

The line emission of Fe VII-Fe X ions in the extreme-ultraviolet region below 140 Å was measured in controlled laboratory experiments under conditions representative of stellar coronae. The observations are compared with predictions from standard spectral models using the CHIANTI and MEKAL atomic databases. We find that the atomic databases miss most of the line flux in this region. While some of the missing lines form isolated features, most add up to form a quasi continuum in the 60-120 Å region. This incompleteness can explain the poor fit when applying global-fitting techniques to spectra from cool stars measured by the Extreme-Ultraviolet Explorer satellite, the origin of which has been a source of controversy since the original observations were made.

X-ray spectral measurements and collisional-radiative modeling of hot, gold plasmas at the omega laser

High Energy Density Physics, 2008

M-Band and L-Band Gold spectra between 3 to 5 keV and 8 to 13 keV, respectively, have been recorded by a photometrically calibrated crystal spectrometer. The spectra were emitted from the the plasma in the laser deposition region of a 'hot hohlraum'. This is a reduced-scale hohlraum heated with ≈ 9 kJ of 351 nm light in a 1 ns square pulse at the Omega laser. The space-and time-integrated spectra included L-Band line emission from Co-like to Ne-like gold. The three L-Band line features were identified to be the 3s→2p, 3d 5/2 →2p 3/2 and 3d 3/2 →2p 1/2 transitions at ≈9 keV, ≈10 keV and ≈13 keV, respectively. M-Band 5f→3d, 4d→3p, and 4p→3s transition features from Fe-like to P-like gold were also recorded between 3 to 5 keV. Modeling from the radiation-hydrodynamics code LASNEX, the collisional-radiative codes FLYCHK and SCRAM, and the atomic structure code FAC were used to model the plasma and generate simulated spectra for comparison with the recorded spectra. Through these comparisons, we have determined the average electron temperature of the emitting plasma to be ∼ 6.5 keV. The electron temperatures predicted by LASNEX appear to be too large by a factor of about 1.5.

Emission lines of Fe xv in spectra obtained with the Solar Extreme-Ultraviolet Research Telescope and Spectrograph

Monthly Notices of the Royal Astronomical Society, 2005

Recent R-matrix calculations of electron impact excitation rates in Mg-like Fe XV are used to derive theoretical emission-line ratios involving transitions in the 243-418 Å wavelength range. A comparison of these with a data set of solar active region, subflare and off-limb spectra, obtained during rocket flights by the Solar Extreme-Ultraviolet Research Telescope and Spectrograph (SERTS), reveals generally very good agreement between theory and observation, indicating that most of the Fe XV emission lines may be employed with confidence as electron density diagnostics. In particular, the 312.55-Å line of Fe XV is not significantly blended with a Co XVII transition in active region spectra, as suggested previously, although the latter does make a major contribution in the subflare observations. Most of the Fe XV transitions which are blended have had the species responsible clearly identified, although there remain a few instances where this has not been possible. We briefly address the long-standing discrepancy between theory and experiment for the intensity ratio of the 3s 2 1 S-3s3p 3 P 1 intercombination line at 417.25 Å to the 3s 2 1 S-3s3p 1 P resonance transition at 284.16 Å.

Numerical Simulations of Fe ii Emission Spectra

The Astrophysical Journal Supplement Series, 1999

This paper describes the techniques that we have used to incorporate a large-scale model of the Feì on and resulting Fe II emission into CLOUDY, a spectral synthesis code designed to simulate conditions within a plasma and model the resulting spectrum. We describe the numerical methods we use to determine the level populations, mutual line overlap Ñuorescence, collisional e †ects, and the heatingcooling e †ects of the atom on its environment. As currently implemented, the atom includes the lowest 371 levels (up to 11.6 eV) and predicts intensities of 68,635 lines. We describe our data sources, which include the most recent transition probabilities and collision strengths. Although we use detailed Ðts to temperature-dependent collision strengths where possible, in many cases the uncertain approximation g6 is the only source for collision data. The atom is designed to be readily expanded to include more levels and to incorporate more accurate sets of collision and radiative data as computers grow faster and the atomic databases expand. We present several test cases showing that the atom goes to LTE in the limits of high particle and radiation densities. We give an overview of general features of the Fe II spectra as their dependencies on the basic parameters of our models (density, Ñux, microturbulent velocity, the Fe abundance, and Lya pumping). Finally, we discuss several applications to active galactic nuclei to illustrate the diagnostic power of the Fe II spectrum and make some predictions for UV observations.