Shock Wave Heating Research Articles

Applications of the ion beam technique for investigations of hypervelocity impacts

In the presentation we report on experiments at the Karlsruhe Light Ion Facility KALIF employing high-resolution laser-Doppler velocimetry. The schemes of possible EOS experiments using interferometry and the dynamics and the limiting factors of the ablative hypervelocity launching are discussed as well as advantages of the ion beam technique for investigations in the field of hypervelocity impacts and equations of state. So far, we have accelerated aluminum foils of 10 to 30 μm thickness to velocities beyond 12 km/s. Besides the beam power, the limiting factors for the launching are melting of the accelerated flyer plate as a result of shock-wave heating and the heat transfer from the energy deposition zone. The experiments considered include the Hugoniot measurements and measurements at unloading of shock-compressed state down to the vaporization region. Parameters of shock waves that cause melting of aluminum, copper, molybdenum and titanium in release have been measured with a pulse proton beam on KALIF. A way of measurements in the vaporization region has been tested with explosive facilities.

Computer experiments on the measurement of reentry plasma with radio waves

The present paper deals with computer experiments on the measurement of reentry plasma with radio waves. Around the nose of a reentry vehicle, a dense plasma layer is created due to the ionization of neutral particles by shock wave heating. The density of the plasma layer becomes as dense as 10 18−10 19 m −3 and it causes so-called radio backout. Since probing the hot and dense plasma layer is difficult, we propose a remote measurement of the reentry plasma with the reflectometry method, which uses radio wave emission from the vehicle. To study this method quantitatively, we perform computer experiments with an electromagnetic particle code. In the experiments, we emit a pulse wave form with no DC component from a vehicle antenna toward a Gaussian-shaped reentry plasma put in front of the vehicle surface. The obtained phase difference between the emitted and reflected waves is used in the reflectometry method to estimate the spatial density profile. The spectrum of the reflected waves, which has a cut-off frequency at the maximum plasma frequency, is used to estimate the maximum density in the plasma layer. The results of the computer experiments revealed that the plasma parameters estimated with the reflectometry method agree very well with the ones actually used in the experiments.

Numerical models of pressure pulse generation by imploding metal liners

The authors describe numerical calculations of pressure pulse generation using imploding liners. Liners are metal cylinders that are magnetically compressed by an intense axial current flow from a high-power pulse generator. The simulations cover the acceleration of the liner, collision with an internal diagnostic target, followed by compression and shock wave heating of the target. With the projected current waveform of the Atlas capacitor bank (in development at Los Alamos National Laboratory), initial results suggest that it may be possible to achieve pressures exceeding 3000 Gpa (30 Mbar) in a 4 mm diameter sample over an interval of 100-200 ns. The simulations were carried out with Crunch, a new one-dimensional hydrodynamics package for advanced personal computers. The program uses finite-element techniques to solve the coupled problems of hydrodynamics and magnetic diffusion. Crunch fully supports loading and interpolating Sesame equation-of-state tables. The program exhibits excellent stability, even for collisions between material shells and shock convergence on axis.

A cw laser absorption diagnostic for methyl radicals

Absorption of narrow-line laser radiation by methyl radicals produced at high temperatures was studied in the Herzberg β 1 band near 216nm. cw radiation for these measurements was generated in a ring dye laser system using intracavity BBO frequency doubling. Methyl radicals were produced by the shock wave heating of five selected source compounds: azomethane, methyl iodide, tetramethyl tin, tetramethyl silane and ethane. The variation with wavelength of the CH 3 absorption coefficient between 210 and 225 nm was measured at 1625 K and 1.25 atm using ethane/Ar and methyl iodide/Ar gas mixtures. The variation of the absorption coefficient with temperature from 1350 to 2450 K was measured at 216.615 nm using four source compounds. Using this wavelength for CH 3 measurements resulted in a typical detectivity limit of 2ppm at 1650 K, 1 atm, L = 10 cm, with a SNR of unity and a detection bandwidth of 500 kHz.

Experimental shock-wave interference heating on a cylinder at Mach 6and 8

This paper presents the details of an experimental study of shock-wave interference heating on a cylindrical leading edge representative of the cowl of a rectangular hypersonic engine inlet. The study, which was conducted at Mach numbers of 6.3, 6.5, and 8.0, has provided 1) detailed pressure and heat-transfer-rate distributions for a two-dimensional shock-wave interference on a cylinder and 2) insight into the effects of temperature-d ependent specific heats on the phenomena. The peak pressure and heat-transfer rates were 2-25 times the undisturbed flow stagnation-point levels. The peak levels and their gradients increased with Mach number. Variation in specific heats and, hence, in the ratio of specific heats with temperature is manifested in slightly lower loads and amplification factors than for corresponding perfect-gas conditions.

The outer R Aquarii nebula - Comparison of 6 centimeter radio continuum and Balmer line emission

The 6 cm radio continuum structure of the R Aquarii outer nebula is compared with CCD imagery of H-alpha and H-beta line emission. It is shown that the 6 cm VLA imagery is morphologically similar and quantitatively related spatially to Balmer line imagery. There is negligible interstellar or circumstellar absorption along the line of sight to the outer nebula. The 6 cm structure of the outer nebula is consistent with thermal bremsstrahlung emission by a hot, optically thin gas. Spectra of the outer R Aquarii nebula are suggestive of shock-wave heating. The approximate equality of mass loss and radiative cooling suggests that the system's wind is probably enough to power the outer nebula and may account for its long-term persistence.

Laser photolysis shock tube for combustion kinetics studies

An excimer laser photolysis method has been developed for shock tube kinetics studies of elementary combustion reactions. The excimer laser provides a high intensity source of UV photons well suited to the rapid production of reactive radicals, while shock wave heating provides a convenient means of varying the reaction environment over a wide temperature range. An ArF excimer (193.3 nm) was used to photolyze H 2 O behind reflected shock waves to produce H and OH radicals. The temporal variation of the OH concentration was monitored using a cw, narrow-linewidth laser absorption diagnostic, and the rate coefficient of the dominant reaction after photolysis, H+H 2 O→OH+H 2 , was determined. The measured rate coefficient, k =2.4(±.25)×10 14 exp (−10750 (±500)/T,K) cm 3 mole −1 s −1 , T=1600–2500 K, is in good agreement with other recent studies of this reaction in both the forward and reverse directions.

The ionization mechanism in low level emission galaxy nuclei: Shocks

We analyze the emission component of galaxy nuclei at very low intensity levels (W(Hα)≤2A). This emission level is considerably lower than that of classical LINERS like NGC 1052. We have access to weaker emission lines by averaging spectra with similar line ratios for Hα [NII], and [SII]. From the resulting spectrum for very low level emission nuclei, the [SII] λλ6717, 6731/[SIII] λλ9069, 9532 line ratio criterion (Diazet al., 1985a) unambiguously shows that shock-wave heating is the mechanism responsible for the ionization in such objects.

The structure of the inner R Aquarii nebula in the light of H-alpha and forbidden N II 6584 A emission

The structure of the inner R Aqr nebulosity in the light of H-alpha and forbidden N II 6584 A emission was investigated using data obtained on November 28, 1986, by the Space Telescope Science Institute coronograph on the ESO 2.2-m telescope. The results are presented in the form of photometrically accurate contour maps of the region. In addition to the previously established features of the inner nebulosity, a bright new feature was detected at 8.4 arcsec from the nucleus at 20 deg p.a., emitting a total flux of 1.7 x 10 to the -12th and 2.2 x 10 to the -12th ergs/sq cm per sec in the H-alpha and N II lines, respectively, which appeared to be associated with the extended feature at the end of the jet. The N II/H-alpha ratio 1.3 of the new feature is strongly suggestive of shock-wave heating or photoionization by a power-law continuum as the principal excitation mechanism. In addition to the 20-deg p.a. feature, a weaker feature, visible only in H-alpha was detected at 3.8 arcsec, 306 deg p.a. 25 references.

Studies of Flow Fields in Low-Pressure Spraying Plasmas Using Laser Diagnostics

AbstractIn order to make desirable surface layers by low pressure plasma spraying (LPPS), optimum operating conditions and plasma torch gun designs must be decided upon for understanding LPPS plasma and powder behavior. As the first step of this approach, LPPS plasmas without powders were measured by the Thomson scattering, the Michelson interferometry and a Pitot tube. These diagnostics revealed that LPPS plasma jets may be treated as supersonic neutral gas flows as the first approximation. In addition, the neutral particle temperature Tn and ion temperature Ti were found to be the same as the electron temperature Te, which is 1 eV at an oblique shock wave heating point and 0.2 eV at the sugsequent cooling point. LPPS plasmas and flows were modeled by a computer Simulation of a supersonic nozzle flow, 2nd yielded reasonable understanding of the thermodynamic and fluid-mechanical conditions.

OPTICAL EMISSION-LINE GAS IN THE NUCLEI OF NORMAL GALAXIES : IMPLICATIONS FOR NUCLEAR ACTIVITY.

ABSTRACT The properties of the optical emission-line gas in normal galactic nuclei are reviewed to investigate how common nuclear activity is in normal galaxies. In H II region nuclei, the weakness of the lines from highly ionized species reflects the lack of photons of requisite ionization energy produced by the exciting stars, and the presence of a nuclear spectrum is strongly correlated with a relatively hot stellar population. The gas in Seyferts is modeled as heated and ionized by a central source of high-energy photons, and is shown to be in a highly disturbed state. Evidence for the two models explaining LINER spectra, photoionization by a dilute but energetic continuum source (where nuclear activity is nearly universal), and shock-wave heating (where nuclear activity may not necessarily be manifested), is presented. A Space Telescope spectroscopic and imaging survey of these nuclei will help clarify many of these issues.

OPTICAL SPECTROSCOPY OF THE FILAMENTARY HALO THAT SURROUNDS HD 148397AND NGC 6164-65.

ABSTRACT Optical spectra have been obtained for the recently-discovered faint filamentary halo that surrounds both the extremely young star HD 148937 and the peculiar S-shaped nebula NGC 6164-65. This halo, interpreted to be a wind-generated interstellar bubble, has a spectrum which appears to result from both shock-wave heating and photoionization.

Implications of the Galilean satellites ice envelope explosions II. The origin of the irregular satellites

The problem of the origin of the irregular satellites is solved readily in the context of a hypothesis involving explosion of the massive ice envelopes of the Galilean satellites saturated by electrolysis products. The thrown-off unexploded (primary) ice fragments of the outermost cold layers of the envelopes are also saturated by electrolysis products. In the course of explosive ejection their internal energy increases due to shock wave heating, as a result of which they will be able to detonate in subsequent sufficiently energetic collisions. The secondary fragments from new explosions may acquire additional velocity up to a few km s−1 without breakup into small pieces.

Experimental study of laser acceleration of planar targets at the wavelength 0.26 μm

The main characteristics of accelerated aluminum targets, which are the target velocity, the uniformity of the acceleration and the backside temperature have been studied in laser experiments performed at wavelength 0.26 μm with an absorbed flux of a few 1013 W/cm2, in 400-ps pulse duration by using the double-foil technique and an optical pyrometry diagnostic: The ablation pressure was inferred from the velocity measurements. The uniformity of the acceleration was shown to be controlled by the hot spots in the focal spot, and the importance of studying the smoothing of laser inhomogeneities for accelerated targets with large ablated fractions was emphasized. The observed dependence of the backside temperature as a function of the initial foil thickness is discussed in the light of shock wave heating and radiative heating.

Spectra of Seyfert galaxies and Seyfert galaxy candidates

view Abstract Citations (130) References (58) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectra of Seyfert galaxies and Seyfert galaxy candidates. Osterbrock, D. E. ; Dahari, O. Abstract New spectral classifications of a number of Seyfert galaxies, as well as of other objects that are not but were earlier suspected of being Seyfert galaxies, are presented. Measured redshifts for all these objects are also given. Mrk 266 SW and Mrk 1066, two galaxies near the lower end of the Seyfert 2's and close to Liners (low-ionization nuclear emission-line regions), are studied spectrophotometrically. Their relative emission-line spectra agree much better with published models for photoionization by a low-luminosity power-law-like radiation source than by shock-wave heating. The spectra of Mrk 883 and Mrk 1320, which are borderline Seyfert galaxies, of Mrk 984, a double emission-line galaxy, and Mrk 1459, a galaxy photoionized by a hot-star population, are briefly discussed. Publication: The Astrophysical Journal Pub Date: October 1983 DOI: 10.1086/161385 Bibcode: 1983ApJ...273..478O Keywords: Emission Spectra; Galactic Nuclei; Red Shift; Seyfert Galaxies; Spectrophotometry; Astronomical Models; Forbidden Bands; H Lines; Photoionization; Astrophysics full text sources ADS | data products NED (82) SIMBAD (79)

CLASSIFICATION PARAMETERS FOR THE EMISSION-LINE SPECTRA OF EXTRAGALACTIC OBJECTS.

ABSTRACT An investigation is made of the merits of various emission-line intensity ratios for classifying the spectra of extragalactic objects. It is shown empirically that several combinations of easily-measured lines can be used to separate objects into one of four categories according to the principal excitation mechanism: normal H II regions, planetary nebulae, objects photoionized by a power-law continuum, and objects excited by shock-wave heating. A two-dimensional quantitative classification scheme is suggested.

Studies on the applicability of slit metal vessels in fast theta-pinch discharges

The applicability of slit metal vessels for fast magnetic plasma compression was experimentally investigated. The results were encouraging for small diameter vessels when the time needed for plasma compression was not significantly longer than the time for the development of the limiting shortcircuiting arcs across the slit gaps. Applicability of large diameter slit metal vessels was only achieved after superposition of magnetic bias fields. The limiting effects were identified and the condition for the necessary bias field is presented. It is shown further that satisfactory efficiencies of shockwave heating in slit metal vessels can be achieved only if apart from superposition of bias fields the width of the metal strips is reduced to the order of centimeter.

Pressure fluctuations and heating of a gas by the inflow of a supersonic jet into a cylindrical cavity

The formation of pressure fluctuations at the inflow of a jet into a cavity (or the so-called resonance tube) was first observed by Hartmann. Further investigations showed that at the same time there is a heating of the gas in the cavity [1, 2]. It was established in [1, 2] that at subsonic and slightly supersonic velocities (M < 2.0) the cavity air can be heated up to 500–700 °K. Further investigations [4, 6] showed that by using monatomic gases inside the cavity one can reach even higher temperatures (T ≈ 800–900 °K). The resonance tubes find an application as powerful sound sources. There is also a possibility of their use in thermochemistry, and for the plasma production [6], In the literature, there is an absence of data on the resonance tube characteristics for large Mach numbers. In the present work we investigate the resonance tubes for M = 3.2–4.0. These investigations have shown that pressure oscillations can occur at these Mach numbers with the peak-to-peak amplitude of ΔP ≈ 0.4·Po, where Po is the total pressure in the inflowing jet. Depending on the clearance between the nozzle and the cavity, both low- and high-frequency oscillations can be set up. It is established that the most intense shock-wave heating of the gas takes place at high-frequency fluctuations, although their amplitude is smaller in comparison with the low-frequency ones. It is shown that the cold air inside the cavity can be heated by means of the fluctuations up to T ≈ 1600 °K or more.

Electron Temperature in the Elliptical Galaxy NGC 1052

Image-dissector scanner observations of the emission-line spectrum of NGC 1052 are discussed. The scan of the elliptical galaxy NGC 584 is used to remove the integrated stellar absorption-line features from the spectrum of NGC 1052. The O iii lines indicate Tapprox. =33,000 K. The observed line intensities are consistent with shock-wave heating models by Cox. (AIP)

The Optical Emission-Line Spectrum of Cygnus a

view Abstract Citations (177) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Optical Emission-Line Spectrum of Cygnus a Osterbrock, Donald E. ; Miller, Joseph S. Abstract Spectrophotometric measurements are reported of the radio galaxy 3C 405 = Cyg A, made using the image- tube image-dissector scanner on the Lick 120-inch (3 m) telescope. The measurements were reduced to energy units by comparison with scans of standard stars made with the same system on the same nights. The emission lines and continuum were measured in the spectral region AA3346-673 1 (in the rest system of Cyg A). The interstellar extinction was determined from the measured Balmer-line ratios, assuming a Case B recombination spectrum and the standard Whitford reddening curve, and the measured line and continuum strengths were corrected for this extinction. The corrected line strengths are discussed for the information they contain on the physical conditions and the energy-input mechanism to the ionized gas. Photoionization by stars is ruled out by the great strength of [0 1], [N I], and [S ii]. Shock-wave heating is ruled out by the [0 iii] temperature, unless a large amount of ultraviolet ionizing radiation is emitted in the shock. Published calculations of photo- ionization by a synchrotron spectrum, extending far into the ultraviolet, approximately match the observed emission-line spectrum. Likewise, the observed Crab Nebula spectrum approximately matches Cyg A, except for abundance differences, in agreement with the idea that Cyg A is photoionized by a power-law spectrum. Subject headings: radio sources - galaxies, individual - galactic nuclei - spectrophotometry Publication: The Astrophysical Journal Pub Date: May 1975 DOI: 10.1086/153541 Bibcode: 1975ApJ...197..535O full text sources ADS | data products SIMBAD (10) NED (1)