High Radiation Density Research Articles

Transport analysis of high radiation and high density plasmas in the ASDEX Upgrade tokamak

Transport analysis of high radiation and high density plasmas in the ASDEX Upgrade tokamak

Excited OH+, H2O+, and H3O+in NGC 4418 and Arp 220

We report on Herschel/PACS observations of absorption lines of OH+, H2O+ and H3O+ in NGC 4418 and Arp 220. Excited lines of OH+ and H2O+ with E_lower of at least 285 and \sim200 K, respectively, are detected in both sources, indicating radiative pumping and location in the high radiation density environment of the nuclear regions. Abundance ratios OH+/H2O+ of 1-2.5 are estimated in the nuclei of both sources. The inferred OH+ column and abundance relative to H nuclei are (0.5-1)x10^{16} cm-2 and \sim2x10^{-8}, respectively. Additionally, in Arp 220, an extended low excitation component around the nuclear region is found to have OH+/H2O+\sim5-10. H3O+ is detected in both sources with N(H3O+)\sim(0.5-2)x10^{16} cm-2, and in Arp 220 the pure inversion, metastable lines indicate a high rotational temperature of ~500 K, indicative of formation pumping and/or hot gas. Simple chemical models favor an ionization sequence dominated by H+ - O+ - OH+ - H2O+ - H3O+, and we also argue that the H+ production is most likely dominated by X-ray/cosmic ray ionization. The full set of observations and models leads us to propose that the molecular ions arise in a relatively low density (\gtrsim10^4 cm-3) interclump medium, in which case the ionization rate per H nucleus (including secondary ionizations) is zeta>10^{-13} s-1, a lower limit that is severalx10^2 times the highest rate estimates for Galactic regions. In Arp 220, our lower limit for zeta is compatible with estimates for the cosmic ray energy density inferred previously from the supernova rate and synchrotron radio emission, and also with the expected ionization rate produced by X-rays. In NGC 4418, we argue that X-ray ionization due to an AGN is responsible for the molecular ion production.

Influence of neutron radiation on breakdown voltage of silicon voltage limiter

Experimental study of silicon voltage limiters’ breakdown voltage dependence on neutron radiation was conducted. It revealed that with increase of radiation density from 0.1×1014 to 2×1015 N/cm2 the breakdown voltage monotonously increases: the smaller the breakdown voltage, the higher radiation density is needed to provide nominal breakdown voltage. Test curves which may be used for stabilization (normalization) of the breakdown voltage for samples with technological variations are suggested.

Imide Photodissociation Investigated by X-ray Absorption Spectroscopy

X-ray absorption spectroscopy is used to investigate the photodissociation of the imides PMDI (pyromellitic diimide) and SSMCC (sulfosuccinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate). PMDI contains only one type of imide, and its photodissociation can be explained by a simple conversion from imide to a mix of imine and nitrile after desorption of the oxygens from the imide. SSMCC contains two different imides. One reacts like PMDI, the other in a more complex multistep process. Eventually, N(2) is formed in the bulk of the sample at high radiation density. The sequence of reactions is inferred from the π* peaks in total electron yield and fluorescence yield absorption spectra at the N 1s and O 1s edges. First-order rate equations are used to model the evolution of the peak areas versus radiation dose.

The electron injection spectrum determined by anomalous excesses in cosmic ray, gamma ray, and microwave data

Recent cosmic ray, gamma ray, and microwave signals observed by Fermi, PAMELA, and WMAP indicate an unexpected primary source of ${e}^{+}{e}^{\ensuremath{-}}$ at 10--1000 GeV. We fit these data to ``standard backgrounds'' plus a new source, assumed to be a separable function of position and energy. For the spatial part, we consider three cases: annihilating dark matter, decaying dark matter, and pulsars. In each case, we use GALPROP to inject energy in log-spaced energy bins and compute the expected cosmic ray and photon signals for each bin. We then fit a linear combination of energy bins, plus backgrounds, to the data. We use a nonparametric fit, with no prior constraints on the spectrum except smoothness and non-negativity. In addition, we consider arbitrary modifications to the energy spectrum of the ordinary primary source function, fixing its spatial part, finding this alone to be inadequate to explain the PAMELA or WMAP signals. We explore variations in the fits due to choice of magnetic field, primary electron injection index, spatial profiles, propagation parameters, and fit regularization method. Dark matter annihilation fits well, where our fit finds a mass of $\ensuremath{\sim}1\text{ }\text{ }\mathrm{TeV}$ and a boost factor times energy fraction of $\ensuremath{\sim}70$. While it is possible for dark matter decay and pulsars to fit the data, unconventionally high magnetic fields and radiation densities are required near the Galactic center to counter the relative shallowness of the assumed spatial profiles. We also fit to linear combinations of these three scenarios, though the fit is much less constrained.

QCD corrections to QED vacuum polarization

We compute QCD corrections to QED calculations for vacuum polarization in background magnetic fields. Formally, the diagram for virtual eē loops is identical to the one for virtual qq̄ loops. However, due to confinement, or to the growth of αs as p2 decreases, a direct calculation of the diagram is not allowed. At large p2 we consider the virtual qq̄ diagram, in the intermediate region we discuss the role of the contribution of quark condensates 〈qq̄〉 and at the low-energy limit we consider the π0, as well as charged pion π+π- loops. Although these effects seem to be out of the measurement accuracy of photon–photon laboratory experiments, they may be relevant for γ-ray burst propagation. In particular, for emissions from the center of the galaxy (8.5 kpc), we show that mixing between the neutral pseudo-scalar pion π0 and photons renders a deviation from the power-law spectrum in the TeV range. For scalar quark condensates 〈qq̄〉 and virtual qq̄ loops are relevant only for very high radiation density ∼300 MeV/fm3 and very strong magnetic fields of order ∼1014 T.

High‐excitation OH and H2O Lines in Markarian 231: The Molecular Signatures of Compact Far‐infrared Continuum Sources

The ISO LWS far-infrared spectrum of the ultraluminous galaxy Mrk 231 shows OH and H2O lines in absorption from energy levels up to 300 K above the ground state, and emission in the [O I] 63 μm and [C II] 158 μm lines. Our analysis shows that OH and H2O are radiatively pumped by the far-infrared continuum emission of the galaxy. The absorptions in the high-excitation lines require high far-infrared radiation densities, allowing us to constrain the properties of the underlying continuum source. The bulk of the far-infrared continuum arises from a warm (Tdust = 70–100 K), optically thick (τ100μ m = 1–2) medium of effective diameter 200-400 pc. In our best-fit model of total luminosity LIR, the observed OH and H2O high-lying lines arise from a luminous (L/LIR ~ 0.56) region with radius ~100 pc. The high surface brightness of this component suggests that its infrared emission is dominated by the AGN. The derived column densities N(OH) 1017 cm−2 and N(H2O) 6 × 1016 cm−2 may indicate X-ray dominated region (XDR) chemistry, although significant starburst chemistry cannot be ruled out. The lower-lying OH, [C II] 158 μm, and [O I] 63 μm lines arise from a more extended (~350 pc) starburst region. We show that the [C II] deficit in Mrk 231 is compatible with a high average abundance of C+ because of an extreme overall luminosity to gas mass ratio. Therefore, a [C II] deficit may indicate a significant contribution to the luminosity by an AGN, and/or by extremely efficient star formation.

Behaviors of impurity and hydrogen recycling on the HT-7 tokamak

Behaviors of impurity and hydrogen recycling are investigated based on passive spectroscopy measurement on HT-7. During LHCD long pulse discharges, impurity and hydrogen recycling shows complicated aspects in different phases depending on wall properties. An uncontrollable density increase is observed, correlated with impurity concentrations, injected energy and local heat flux on the limiter. Under certain conditions, high impurity radiation and uncontrollable density can reduce LHCD efficiency and thus lead to discharge termination. To reduce impurity levels, RF wall conditioning was applied. After boronization, high hydrogen emission led to uncontrollable density rise. When the H/(H+D) ratio was reduced to less than 25%, the electron density was easily controlled. The longest discharge up to 306s with central electron temperature Te(0)∼1.0keV and central electron density ne(0)∼0.8×1019m−3 was achieved. The evolution of recycling behavior has been investigated during long pulse discharges in terms of H/(H+D) ratio and the edge-recycling coefficient R.

Impurity and density behaviours during long pulse discharges in HT-7

Intrinsic plasma impurity behaviours are surveyed by passive spectroscopy in different operation conditions, but with emphasis on long pulse discharges in the HT-7 tokamak. Some complicated behaviours and time evolution are shown for carbon and oxygen impurities resulting from plasma–wall interactions. Uncontrollable increase in density is observed, correlated with impurity concentrations, injected energy and local heat flux on limiter. Under certain conditions, high impurity radiation and uncontrollable density can reduce LHCD efficiency and thus lead to discharge terminations. A major aim of RF wall conditioning is to reduce impurity levels in the plasma. Furthermore, a new operation mode has been successfully developed, by means of LHCD power feedback control, to obtain full non-inductive current driven and long duration plasma. As a result, the longest pulse discharge with a Te(0) ∼ 1.0 keV, ne(0) ∼ 0.75 × 1019 m3 has been achieved with a duration of over 306 s.

Ferroelectric and Pyroelectric Properties of Sol-Gel Derived PbCaTiO3 Thin Films Using Low-Temperature Annealing

PCT7030 (Pb0.7Ca0.3TiO3, PCT7030) films have been prepared by a sol-gel method on platinum-coated Si substrate. PCT7030 films were treated at different radiation densities using CO2 laser annealing to obtain good ferroelectric properties without causing thermal deterioration of the underlying layer. In addition, metallic oxide LaSrMnO3 buffer layer was employed to improve the electrical properties of PCT7030 films. From XRD measurements, we found that fully perovskite phase of PCT7030 films could be obtained at a radiation density below 572 W/cm2. On the other hand, perovskite phase of PCT7030 films with co-existing TiOx were observed for specimens treated at a higher radiation density. The correspondent P-E curves of PCT7030 films with entirely perovskite phase exhibited saturated hysteresis loops and the specimens possessing perovskite PCT7030 and co-existing TiOx phase showed serious leakage. Microstructural investigations imply that grain size increases with increasing radiation density, and voids may evolve on the grain boundaries when high radiation density was employed, indicating that atomic species evaporation of PCT7030 films or coarsening-induced voids may be produced at an over-annealing condition and therefore electrical properties were deteriorated. In the pyroelectric measurement, pyroelectric coefficient of CO2 laser-annealed PCT7030 films varied as a function of calcium content and a pyroelectric coefficient maximum were obtained at a composition near PCT7030, indicating that low temperature laser-annealing process can be employed in ferroelectric and pyroelectric thin film preparation.

High radiation and high density experiments in JT-60U

In order to obtain improved confinement plasmas with highradiation at high density, Ar gas was injected into ELMy H modeplasmas in JT-60U. A confinement improvement of HH98(y,2) ≈ 1 wasobtained with a high radiation loss power fraction (∼80%) at anelectron density of ∼0.65nGW. The HH factor was about 50% higherthan that in plasmas without Ar injection.

The Mid-Infrared Properties of Nearby Spiral Galaxies

The galaxies (~ 40) presented here are part of three ISOCAM guaranteed time programs. Observations consist of raster maps performed with a sampling of 3 and 6 arcsecond per pixel, in the 6.75 μm (LW2) and 15 μm (LW3) bands. The 6.75 μm band samples mostly emission from a blend of aromatic bands, while the 15 μm band is more complex since it generally samples aromatic bands and an associated continuum as well, but can also receive a significant, or even dominant, contribution from a sharply rising continuum emitted by small grains in HII regions or high radiation density environments.

Numerical Simulations of Fe ii Emission Spectra

This paper describes the techniques that we have used to incorporate a large-scale model of the Fe+ ion 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 fluorescence, collisional effects, and the heating-cooling effects 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 fits to temperature-dependent collision strengths where possible, in many cases the uncertain approximation 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, flux, microturbulent velocity, the Fe abundance, and Lyα 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.

CPC solar collectors with multichannel absorber

Stationary CPC solar collectors with symmetric and asymmetric mirrors have been studied and tested. In these collectors the distribution of solar radiation on the absorber surface is not uniform, with areas of low and high intensity, variable and depending on the position of the Sun relative to the collector. This effect can be used to improve the efficiency of the collector if the absorber is flat and divided in several sections, which form the channels of fluid flow. By selecting the channels with the higher radiation density, the working fluid can be heated to higher operating temperatures. Here we present work on the optical analysis and experimental tests on models consisting of four channel absorbers. The results show that efficient operation at temperatures in the range of 100–200°C can be achieved with relatively simple types of concentrating solar collectors.

Luminescence and radiation effects in lithium triborate crystals

LUMINESCENCE AND RADIATION EFFECTS IN LITHIUM TRIBORATE CRYSTALS V. A. Maslov, I. N. Ogorodnikov, L. A. Ol'khovaya, I. N. Antsygin, V. Yu. Ivanov, A. V. Kruzhalov, and A. Yu. Kuznetsov UDC 535.37 In recent years the advent of new nonlinear optical media based on monocrystals of wide-band dielectrics has promoted the development of laser systems with a high radiation density. Their successful use depends, in particular, on resolving the problem of radiation-optical stability under extreme radiation conditions. It is a known fact that the formation of defects due to laser radiation worsens the nonlinear properties of crystals. These processes are rather complicated and are caused by the great number of primary events of formation and evolution of elementary point defects. Even for the best known and most widely used optical media no clear knowledge exists so far on this issue. On the other hand, the present-day level of development of laser technology dictates a search for new highly effective and radiation-resistant nonlinear crystalline media. Thus in late 1980s for the first time bulk crystals of lithium triborate LiB30 5 (LBO) were been synthesized [1-3], which surpass known crystals in threshold optical damage (a 4.1-fold increase in KTP, a 2.25-fold increase in KDP) at comparable nonlinear coefficients. This has placed LBO crystals among highly effective converters of laser radiation, in particular, of the radiation of A12Oa:Ti- lasers [4, 5 ]. By now the main physicochemical [1-3] and nonlinear [4, 5] properties of LBO crystals are studied; however data on radiation-induced defects and their properties are still absent. The appearance of bulk LBO monocrystals and ever-increasing interest in them have necessitated research studies along this line. The present work is devoted to investigation of the radiation defects, recombination processes, and spectral- luminescent properties of LBO crystals. LBO monocrystals of optical quality were grown by the modified solution-melt method with seed pulling in platinum crucibles in one- and two-zone furnaces. To increase the viscosity of the mett, Li2MoO 4 was added to the system Li20-B20 3 [6, 7 ]. Crystals were grown in the temperature range 384-810 ~ with seeding orientations {001} and {110} and the rotational speed of the seeding did not exceed 10 rpm. The mean size of the grown crystals amounted to 50 “ 40 “ 25 mm. LBO crystals were identified by x-ray analysis. The main crystallographic parameters of LBO were consistent with those in [8 ]. The luminescence of LBO crystals and its kinetics were investigated using an automated setup intended for analysis of the radiative-optical properties of solids (an MDR-2 monochromator, an FEU-106 photomultiplier tube operating in a regime of counting photons) [9 ] upon excitation by x-radiation (a URS-55 unit, Cu-anticathode, U = 40 kV, I = 10 mA) or by an electron beam (an MIRA-2D device, I = 1 A.cm -2, Zpuls e -- 10 nsec). Thermoactivation studies within the temperature range 77-600 K of practical importance were conducted using an automated unit [10 ] with x-radiation excitation of crystals. EPR spectra were measured in a modified X-band radiospectrometer RE- 1302 at two fixed temperatures (77 and 290 K). As an excitation source, use was made of a URS-55 x-ray unit and a RADAN-600 pulsed electron accelerator. The spectral-luminescent measurements showed that LBO crystals at 300 K, unlike other nonlinear crystals (e.g., KTP, KDP), show marked shortwave luminescence upon excitation by corpuscular and x-radiation. For example, the spectrum of x-ray luminescence is represented by a wide band with a peak at 4.2 eV and a weak shoulder at 3.4 eV (Fig. 1). The main band is elementary and well approximated by a Gaussian function (the halfheight line Ural Polytechnic Institute, Ekaterinburg Institute of General Physics, Russian Academy of Sciences, Moscow. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 59, Nos. 3-4, pp. 293-298, September-October, 1993. Original article submitted December 25, 1992.

Mid-infrared imaging of Markarian 231 and ARP 220

High angular resolution observations of Arp 220 and Mrk 231 provide images of the nuclei and show that the source of the strong mid-IR emission is confined to regions less than about 0.5 arcsec or 400 pc in diameter in Mrk 231 and less than 1.5 arcsec x 0.9 arcsec or 320 x 530 pc in Arp 220. If much of the far-IR emission also derives from such a small region, the implied radiation densities are quite high, equivalent to one O star per cu pc. Although in normal galaxies the near-IR traces an older population of evolved, cool stars, such high radiation densities in the IR bright galaxies suggest the possibility that the spatial correlation observed between the near-IR, mid-IR, and radio may hold because emission in all three bands is associated with hot interstellar gas and dust.

The IRAS bright galaxy sample. V - Multibeam photometry of galaxies with L(IR) greater than 10 to the 11th solar luminosities

Forty-seven galaxies from the IRAS Bright Galaxy Sample with infrared luminosities L_(IR)⩾ 10^(11) L_☉ have been measured at 1.3, 1.65, and 2.2 µm with beam diameters of 17, 33, and 55. These measurements, combined with 5 and 10 observations presented in an earlier paper, provide an opportunity to study the spatial distribution of the near-infrared emission in luminous IRAS galaxies. It is found that the unusually red near-infrared colors known previously for many of these galaxies are confined to the nuclear regions, whereas the outer disk regions have near-infrared colors essentially appropriate for a normal stellar population. Since dust reddening and emission are required to explain the unusual nuclear colors, it follows that the observed effects of dust in these galaxies are also confined primarily to the nuclei. Thus, it is probable that the far-infrared emission, the bulk of the entire luminosity in infrared luminous galaxies, is highly concentrated about the nuclei, and that the physical processes responsible for the unusual properties of infrared luminous galaxies tend to occur within the central regions, with diameters ≾1-3 kpc. The nuclei are found to have considerably higher 2.2 µm luminosities than are found in classical “starburst” nuclei, implying that infrared luminous galaxies are characterized by extremely high radiation densities in their central regions, presumably due to intense star formation activity and/or the presence of a dust-enshrouded quasar. However, the nuclei of the galaxies studied are typically not as luminous at 2.2 µm as classical Seyfert nuclei, which may be partly attributable to extinction from dust at near-infrared wavelengths, particularly for those sources in the sample that have been identified in the literature as having Seyfert nuclei. Finally, the large diameter beam measurements are used to obtain estimates of the total near-infrared emission. It is found that, since most of the infrared luminosity is coming from the nuclei, the global near-infrared properties of infrared luminous galaxies are not good tracers of infrared activity. Also, the contribution from the observed stellar emission to the total observed luminosity is found to be ≾25% for most of the galaxies in the sample, considerably smaller than the value for typical low-luminosity spiral galaxies.

The measurement of subnanosecond fluorescence decay of flavins using time-correlated photon counting and a mode-locked Ar ion laser

A system is described consisting of a mode-locked Ar ion laser and time-resolved photon-counting electronics. The system is capable of measuring fluorescence lifetimes in the subnanosecond time domain. The Ar ion laser is suitable for the excitation of flavins, since the available laser wavelengths encompass the first absorption band of the yellow chromophore. Due to the high radiation density and the short pulse, both the time and wavelength resolution of the fluorescence of very weakly emitting compounds can be measured. Experiments have been described for flavin models exhibiting single and multiple modes of decay. In these examples lifetimes were determined both from deconvolved decay curves and from direct analysis of the tail of the curve, where no interference of the exciting pulse is encountered. Both determinations showed very good agreement. Due to the highly polarized laser light the decay of the emission anisotropy could be measured directly after the exciting pulse. In principle, fast rotational motions might be detected. An anisotropy measurement conducted with a flavoprotein with a noncovalently attached FAD is presented.

Optimization and limiting characteristics of CO2 lasers

It is shown that the limiting characteristics of CO2 lasers are determined mainly by two parameters: the specific power of the electric discharge, referred to the square of the active medium pressure, and the product of the pumping time and the gas pressure. An investigation is made of the dependence of the efficiency and the radiation pulse shape over a wide range of the parameters. For the first time it is noted that the energy from the lower laser level can be given to the upper vibrational states of the symmetric and deformed modes, which allows high radiation density, ∼0.2 J/cm3 · atm, to be achieved, as is shown by calculation. Because of energy redistribution in the asymmetric mode the limiting gain coefficient in C02 lasers is ∼0.12 cm−1.

Coaxial pulse-discharge lamp as a pump source for organic dye lasers

The mechanical strength as well as the electrical and optical characteristics of a coaxial pulse-discharge lamp were determined with a view to using this lamp as a pump source for organic dye lasers capable of emitting coherent light pulses of ~100 J. The conditions under which such a lamp operated most efficiently were determined. Under these conditions, the electrical energy stored in a capacitor bank was introduced rapidly into the lamp discharge and the lamp illuminated uniformly the active medium, ensuring a high pump radiation density throughout the active element.