575 research outputs found
Study of a colliding laser-produced plasma by analysis of time and space-resolved image spectra
The interaction of two counter-propagating laser-produced plasmas was studied using simultaneous
imaging and spectroscopic techniques. Spectrally-filtered time-gated ICCD imaging was used
to obtain information about the spatial dynamics and temporal evolution of the collision process.
While, time-resolved imaging spectroscopy was used to determine the spatial and temporal distributions
of electron temperature and density within the interaction region. We examine specifically
the interaction of plasmas whose parameters match those typically used in pulsed laser deposition
of thin films. These low temperature plasmas are highly collisional leading to the creation of a
pronounced stagnation layer in the interaction region
Experimental and theoretical investigation of plasma radiation Semiannual status report, Sep. 1969 - Feb. 1970
Stark broadening of argon and neon resonance line
More on the Narrowing of Impact Broadened Radio Recombination Lines at High Principal Quantum Number
Recently Alexander and Gulyaev have suggested that the apparent decrease in
impact broadening of radio recombination lines seen at high principal quantum
number n may be a product of the data reduction process, possibly resulting
from the presence of noise on the telescope spectra that is not present on the
calculated comparison spectra. This is an interesting proposal. However, there
are serious problems with their analysis that need to be pointed out. Perhaps
the most important of these is the fact that for principal quantum numbers
below n = 200, where the widths are not in question, their processed generated
profile widths do not fit the widths of the processed lines obtained at the
telescope. After processing, the halfwidths of the generated and telescope
profiles must agree below n = 200 if we are to believe that the processed
generated linewidths above n = 200 are meaningful. Theirs do not. Furthermore,
we find that after applying the linewidth reduction factors found by Alexander
and Gulyaev for their noise added profiles to our generated profiles to
simulate their noise adding effect, the processed widths we obtain still do not
come close to explaining the narrowing seen in the telescope lines for n values
in the range 200 < n < 250. It is concluded that what is needed to solve this
mystery is a completely new approach using a different observing technique
instead of simply a further manipulation of the frequency-switched data.Comment: Six pages with 4 figures. Accepted for publication in Astrophysics
and Space Scienc
Sensitive Observations of Radio Recombination Lines in Orion and W51: The Data and Detection of Systematic Recombination Line Blueshifts Proportional to Impact Broadening
Sensitive spectral observations made in two frequency bands near 6.0 and 17.6
GHz are described for Orion and W51. Using frequency switching we were able to
achieve a dynamic range in excess of 10,000 without fitting sinusoidal or
polynomial baselines. This enabled us to detect lines as weak as T\Delta n$ as
high as 25 have been detected in Orion. In the Orion data, where the lines are
stronger, we have also detected a systematic shift in the line center
frequencies proportional to linewidth that cannot be explained by normal
optical depth effects.Comment: 22 pages, 13 figures. Accepted for publication in Astrophysics and
Space Scienc
Quantum-mechanical calculation of Stark widths of Ne VII n=3, transitions
The Stark widths of the Ne VII 2s3s-2s3p singlet and triplet lines are
calculated in the impact approximation using quantum-mechanical Convergent
Close-Coupling and Coulomb-Born-Exchange approximations. It is shown that the
contribution from inelastic collisions to the line widths exceeds the elastic
width contribution by about an order of magnitude. Comparison with the line
widths measured in a hot dense plasma of a gas-liner pinch indicates a
significant difference which may be naturally explained by non-thermal Doppler
effects from persistent implosion velocities or turbulence developed during the
pinch implosion. Contributions to the line width from different partial waves
and types of interactions are discussed as well.Comment: 8 pages, 3 figures; accepted by Phys. Rev.
The line parameters and ratios as the physical probe of the line emitting regions in AGN
Here we discuss the physical conditions in the emission line regions (ELR) of
active galactic nuclei (AGN), with the special emphasize on the unresolved
problems, e.g. the stratification of the Broad Line Region (BLR) or the failure
of the photoionization to explain the strong observed optical Fe II emission.
We use here different line fluxes in order to probe the properties of the ELR,
such as the hydrogen Balmer lines (Ha to He), the helium lines from two
subsequent ionization levels (He II 4686 and He I 5876) and the strongest Fe II
lines in the wavelength interval 4400-5400 \AA. We found that the hydrogen
Balmer and helium lines can be used for the estimates of the physical
parameters of the BLR, and we show that the Fe II emission is mostly emitted
from an intermediate line region (ILR), that is located further away from the
central continuum source than the BLR.Comment: 8 pages, 9 figures, 2 tables, New Astronomy Reviews (Proceeding of
7th SCSLSA), in pres
Dynamic and Stagnating Plasma Flow Leading to Magnetic Flux Tube Collimation
Highly collimated, plasma-filled magnetic flux tubes are frequently observed
on galactic, stellar and laboratory scales. We propose that a single, universal
magnetohydrodynamic pumping process explains why such collimated, plasma-filled
magnetic flux tubes are ubiquitous. Experimental evidence from carefully
diagnosed laboratory simulations of astrophysical jets confirms this assertion
and is reported here. The magnetohydrodynamic process pumps plasma into a
magnetic flux tube and the stagnation of the resulting flow causes this flux
tube to become collimated.Comment: to be published in PRL; color figures on electronic versio
Using Absorption Imaging to Study Ion Dynamics in an Ultracold Neutral Plasma
We report optical absorption imaging of ultracold neutral plasmas.Images are
used to measure the ion absorption spectrum, which is Doppler-broadened.
Through the spectral width, we monitor ion equilibration in the first 250ns
after plasma formation. The equilibration leaves ions on the border between the
weakly coupled gaseous and strongly coupled liquid states. On a longer
timescale of microseconds, we observe radial acceleration of ions resulting
from pressure exerted by the trapped electron gas.Comment: 4 pages, 4 figure
Stark Broadening of the B III 2s-2p Lines
We present a quantum-mechanical calculation of Stark line widths from
electron-ion collisions for the , lambda = 2066 and 2067
A, resonance transitions in B III. The results confirm the previous
quantum-mechanical R-matrix calculations but contradict recent measurements and
semi-classical and some semi-empirical calculations. The differences between
the calculations can be attributed to the dominance of small L partial waves in
the electron-atom scattering, while the large Stark widths inferred from the
measurements would be substantially reduced if allowance is made for
hydrodynamic turbulence from high Reynolds number flows and the associated
Doppler broadening.Comment: 21 pages, 4 figures; to be published in Phys. Rev.
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