scholarly journals First radiative shock experiments on the SG-II laser

2021 ◽  
Vol 9 ◽  
Author(s):  
Francisco Suzuki-Vidal ◽  
Thomas Clayson ◽  
Chantal Stehlé ◽  
Uddhab Chaulagain ◽  
Jack W. D. Halliday ◽  
...  
Keyword(s):  
Initial Pressure ◽  
Large Field ◽  
Radiation Hydrodynamics ◽  
Gas Cell ◽  
Plasma Parameters ◽  
Time Resolved ◽  
Radiative Shock ◽  
First Results ◽  
Point Projection ◽  
Fine Mechanics

Abstract We report on the design and first results from experiments looking at the formation of radiative shocks on the Shenguang-II (SG-II) laser at the Shanghai Institute of Optics and Fine Mechanics in China. Laser-heating of a two-layer CH/CH–Br foil drives a $\sim 40$  km/s shock inside a gas cell filled with argon at an initial pressure of 1 bar. The use of gas-cell targets with large (several millimetres) lateral and axial extent allows the shock to propagate freely without any wall interactions, and permits a large field of view to image single and colliding counter-propagating shocks with time-resolved, point-projection X-ray backlighting ( $\sim 20$  μm source size, 4.3 keV photon energy). Single shocks were imaged up to 100 ns after the onset of the laser drive, allowing to probe the growth of spatial nonuniformities in the shock apex. These results are compared with experiments looking at counter-propagating shocks, showing a symmetric drive that leads to a collision and stagnation from $\sim 40$  ns onward. We present a preliminary comparison with numerical simulations with the radiation hydrodynamics code ARWEN, which provides expected plasma parameters for the design of future experiments in this facility.

Experimental and theoretical studies of the time and space development of plasma parameters in a laser induced spark in helium

1969 ◽  
Vol 310 (1501) ◽  
pp. 231-252 ◽  
Keyword(s):  
Blast Wave ◽  
Initial Pressure ◽  
Front Propagation ◽  
Wave Theory ◽  
Theoretical Models ◽  
Second Phase ◽  
Plasma Parameters ◽  
Secondary Importance ◽  
Time Resolved ◽  
Thermally Driven

An experimental study has been made of laser induced breakdown of a gas. 0⋅2 J of optical frequency radiation was absorbed in helium at 4 atm initial pressure from the focused beam of a Q switched ruby laser. Space and time resolved quantitative data on the plasma development has been compared with theoretical models and some new results obtained. Two main experimental techniques were used. Image converter streak photography gave information on the axial and radial growth of the plasma and the time variation of the emission spectrum. Quantitative spectroscopy techniques were used to study the plasma parameters, leading to electron density, temperature and spatial dimensions. Two phases in the plasma evolution are discussed. The first, during which absorption of the incident laser pulse occurs, is characterized by the formation of a radiation driven breakdown wave. The front propagation and the axial dynamic processes behind the front are discussed. New results concerning the structure behind the front and the shape of the front itself are presented and the axial front propagation is consistent with an existing theoretical model. The second phase is a purely thermally driven expansion. A model for the radial development of the plasma in this phase is outlined, based on blast wave theory but including a treatment of ionization. From the experimental evidence, ionization is only of secondary importance in the basic radial expansion. The data suggest a self similar expansion occurring at a rate consistent with the old blast wave theory but involving radial distributions of parameters departing at the centre from those of the old theory. Good agreement was found between experimental data and predictions of this modified blast wave theory concerning the plasma dimensions and electron number density.

scholarly journals FRATs: Searching for fast radio transient in real-time with LOFAR

2012 ◽  
Vol 8 (S291) ◽  
pp. 233-233
Author(s):  
Heino Falcke ◽  
Keyword(s):  
Time Scales ◽  
Search Space ◽  
Large Field ◽  
New Radio ◽  
Wide Range ◽  
Imaging Observation ◽  
Previous Decade ◽  
First Results ◽  
Single Radio ◽  
Radio Transients

AbstractLOFAR is an innovative new radio interferometer operating at low radio frequencies from 10 to 270 MHz. It combines a large field-of-view, high fractional bandwidth, rapid response, and a wide range of baselines from tens of meters to thousand kilometers. Its use of phased-array technology and its digital nature make LOFAR an extremely versatile instrument to search for transient radio phenomena on all time scales. Here we discuss in particular the search for fast radio transients (FRATs) at sub-second time scales. In fact, at these time scales the radio sky is rather dynamic due to coherent emission processes. Objects like pulsars, flaring stars, or planets like Jupiter are able to produce bright short flares. For pulsars, most previous detection strategies made use of the rotation of pulsars to detect them, using Fourier techniques, but it is also possible to detect pulsars and other objects through their single pulses. Such surveys have, e.g., led in the previous decade to the detection of Rapid Radio Transients (RRATS), but the unprobed search space is still rather large. LOFAR is now conducting a rather unique survey over the entire northern sky, searching for bright dispersed single radio pulses. This FRATs survey makes use of the LOFAR transient buffer boards (TBBs), which had initially been used to detect nanosecond radio pulses from cosmic rays. The TBBs store the radio data from each single receiver element of LOFAR and allow one to look back in time. A trigger system that runs parallel to normal imaging observation allows one to detect single pulses in an incoherent beam of all LOFAR stations, covering several tens to hundred square degrees at once. Once triggered, the data can be used to localize the pulse and to discriminate cosmic sources from terrestrial interference through 3D localization. The system has been successfully tested with known pulsars and first results of the ongoing survey will be presented.

scholarly journals Investigations of Laser Produced Plasmas Generated by Laser Ablation on Geomaterials. Experimental and Theoretical Aspects

Symmetry ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1391 ◽  
Author(s):  
Enescu ◽  
Irimiciuc ◽  
Cimpoesu ◽  
Bedelean ◽  
Bulai ◽  
...  
Keyword(s):  
Morphological Structure ◽  
Optical Emission ◽  
Ionic Species ◽  
Plasma Parameters ◽  
Mineral Contents ◽  
Plasma Dynamics ◽  
Time Resolved ◽  
Type Group ◽  
Group Invariance ◽  
Ablation Plasma

Several surface investigation techniques, such as X-ray diffraction (XRD), EDX, and optical microscopy, were employed in order to describe the mineral contents in several geomaterials. Space and time resolved optical emission spectroscopy was implemented to analyze the plasma generated by the laser–geomaterial interaction. The values of the plasma parameters (velocity and temperature) were discussed with respect to the nature of the minerals composing the geomaterials and the morphological structure of the samples. Correlations were found between the excitation temperatures of the atomic and ionic species of the plasmas and the presence of calcite in the samples. A mathematical model was built to describe the dynamics in ablation plasma using various mathematical operational procedures: multi structuring of the ablation plasma by means of the fractal analysis and synchronizations of the ablation plasma entities through SL (2R) type group invariance and in a particular case, through self-modulation in the form of Stoler type transformations. Since Stoler type transformations are implied in general, in the charge creation and annihilation processes, then the SL (2R) type group invariance become fundamental in the description of ablation plasma dynamics.

scholarly journals Photometric Monitoring Of The Lensed QSO 0957+561

1996 ◽  
Vol 173 ◽  
pp. 53-54
Author(s):  
D. Sinachopoulos ◽  
M. Burger ◽  
E. van Dessel ◽  
M. Geffert ◽  
M. Thibor ◽  
...  
Keyword(s):  
Time Delay ◽  
Gravitational Lens ◽  
Large Field ◽  
Photometric Study ◽  
First Results ◽  
Photometric Monitoring

We present our first results of a photometric monitoring project of the twin quasar 0957+561. This project aims mainly at the improvement of the determination of the time delay ΔT(A,B) for this gravitational lens, since the “time delay controversy on QSO 0957+561 (is) not yet decided” (Pelt et al. 1994). In addition, the quite large field of the CCD used allows also a long-term astrometric and photometric study of stars and galaxies in the field within a radius of about 10 arcminutes around the lens.

In situ measurements of coupled wind-wave dynamics using PIV

2020 ◽  
Author(s):  
Marc Buckley ◽  
Jochen Horstmann
Keyword(s):  
Boundary Layers ◽  
In Situ Measurements ◽  
Large Field ◽  
Small Scale ◽  
Wave Dynamics ◽  
Image Velocimetry ◽  
First Results ◽  
Oceanic Wave ◽  
Wave Boundary

<p>Small-scale turbulent dynamics within the coupled atmospheric and oceanic wave boundary layers control air-sea fluxes of momentum and scalars. However measuring and understanding small-scale dynamics very close to the rapidly moving ocean surface remains technically challenging.</p><p>We present novel in situ measurements of small-scale motions in the airflow above, and in the water below the wavy air-water interface. A high resolution, large field of view PIV system (Particle Image Velocimetry) was developed for in situ air-water measurements within the first millimeters to meters above and below the wavy surface. The system was recently deployed on a single pile platform in the Szczecin lagoon (Baltic Sea coast, Germany). We will show first results and we will discuss the influence of waves on the partitioning of momentum flux within the coupled air-water wave boundary layers.</p>

Time-resolved investigation of plasma parameters during deposition of Ti and TiO2 thin films

2003 ◽  
Vol 174-175 ◽  
pp. 909-913 ◽  
Author(s):  
H. Bäcker ◽  
P.S. Henderson ◽  
J.W. Bradley ◽  
P.J. Kelly
Keyword(s):  
Thin Films ◽  
Tio2 Thin Films ◽  
Plasma Parameters ◽  
Time Resolved

Separation of gas and dust in the winds of AGB stars

2018 ◽  
Vol 14 (S343) ◽  
pp. 462-463
Author(s):  
Lars Mattsson ◽  
Christer Sandin ◽  
Paolo Ventura
Keyword(s):  
High Resolution ◽  
Asymptotic Giant Branch ◽  
Radiation Hydrodynamics ◽  
Symmetric Model ◽  
Spherically Symmetric ◽  
Agb Stars ◽  
First Results ◽  
Forced Turbulence ◽  
Spherically Symmetric Model ◽  
Entire Picture

AbstractWe present first results from a project aiming at a better understanding of how gas and dust interact in dust-driven winds from Asymptotic Giant Branch (AGB) stars. We are at the final stage of developing a new parallelised radiation-hydrodynamics (RHD) code for AGB-wind modelling including a new generalised implementation of drift. We also discuss first results from high-resolution box simulations of forced turbulence intended to give quantitative “3D corrections” to dust-driven winds from AGB stars. It is argued that modelling of dust-driven winds of AGB stars is a problem that may need to be treated in a less holistic way, where some parts of the problem are treated separately in detailed simulations and are parameterised back into a less detailed (1D spherically symmetric) model describing the entire picture.

scholarly journals Time-Resolved Spectroscopy of Short Period RS CVn Systems

1993 ◽  
Vol 137 ◽  
pp. 392-394
Author(s):  
C. Lázaro ◽  
M.J. Arévalo
Keyword(s):  
Spectral Type ◽  
Main Sequence ◽  
Eclipsing Binaries ◽  
Time Resolved ◽  
Binary Model ◽  
Short Period ◽  
First Results ◽  
Orbital Phase ◽  
Phase Resolution ◽  
Orbital Periods

AbstractWe have initiated a programme of spectroscopic observations of RS CVn short-period group, with orbital phase resolution. The systems of this group are all eclipsing binaries with both components at the Main Sequence, and most of them have similar spectral type components. The high rotational velocities and their short orbital periods (less than 1 day) hinder the spectroscopic study of these stars. We presents the first results yielded by Hα line observations of the systems XY UMa and WY Cnc. Both systems were observed during 1991 with reasonably wide orbital phase coverage. The analysis of the spectra is made by comparison with a binary model, constructed from the observed spectra of normal stars of the same spectral type as the RS CVn system components. The model accounts for the partial contribution of each component at any orbital phase within eclipses.

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