Cone Target Research Articles

Resputtering effects during magnetron sputtering of YBaCuO

The process of mass transfer from target to substrate during single-target magnetron sputtering has been investigated. The deviation of the film stoichiometry from the target composition has been shown to arise because of film resputtering by neutral recharged atoms rather than ions. The scattering angle of such atoms is about 20°. Two sputtering systems of different geometries have been used to suppress the resputtering effect: one with a conical target and the other with two opposite targets. Films of stoichiometric composition and predictable thickness have been obtained on substrates of large diameter with the aid of these two systems.

Observation of Kα. X-ray satellites from a target heated by an intense ion beam

We have made the first observation of Kα X-ray satellites from a target heated by an intense ion beam. The satellites are produced when thermal ionization due to beam heating is accompanied by inner-shell ionization from beam ion impact. The Particle Beam Fusion Accelerator II was used to irradiate a conical aluminum target with a proton beam. The nominal beam parameters were 50–75 kJ in a 1-cm spot, 15–20-ns pulse length, and 4–5-MeV protons at peak power. An elliptical crystal X-ray spectrograph inside a 1000-kg tungsten shield was used to record the spectra. The peak ion stage reached by the aluminum target was +8. Collisional radiative calculations were performed, which indicate a peak electron temperature of 20–60 eV.

XUV radiation from gold exploding pusher targets irradiated with protons

In 1982, proton beam experiments were carried out on the PROTO I accelerator with up to 0.65 TW/cm 2 incident on gold exploding pusher targets. The total proton energy incident on the target was as high as 2.8 kJ, with up to 1.32 kJ deposited in 2.5-μm-thick gold cones, giving a specific power deposition as high as 27 TW/g for 1.5 MeV incident proton energy. XUV radiation (10 eV -2.5 keV) from the gold conical exploding pusher targets was measured with x-ray diodes (XRDs) and PIN solid state diodes. High resolution, time integrated XUV radiation measurements (60–400 eV) were also obtained with a 1-meter grazing incidence spectrograph. The radiation from these targets consisted of three major components: (1) XUV radiation from a high density but low temperature plasma radiation at the inner surface of the conical exploding pusher target, (2) high energy XUV radiation from a low density, high temperature plasma produced by the stagnation of the pusher material on axis, and (3) 2.1–2.2 keV gold Mα, β inner-shell line radiation from the inside surface of the target. The equivalent brightness temperatures at the inner surface of the conical targets were between 18 and 32 eV, assuming a 0.07 cm 2 emission area.

Calculation of the viscous heating of a plasma compressed by a percussion plate in a conical target

A technique for calculating the problem is described and the results of calculations are given, where the need for a solution arose after unsuccessful attempts to take into account the experimental data within the frame-work of the Euler equations. The essentially new element in this method is the implicit scheme in Lagrangian variables with non-rectangular nets.

Studies of thin foils acceleration by pulsed laser beam

Experimental studies of the ablative acceleration of thin foils as carried out on the “Mishen” device (Nd laser, λ = 1·06μm, 3 nsec pulses) are reported. The plasma corona in the range of power densities 1013–1014 W/cm2 is shown to absorb 80–90% of the laser beam energy, the classical collisional absorption mechanism being the main one. Jet-like and filamentary structures are observed in the laser-plasma interaction; however, the main plasma parameters are found to be independent of the presence (or absence) of such structures. The measured hydrodynamic efficiency of stable ablative acceleration in plane geometry is ≲5%. The production of high-speed cumulative jets with irradiated thin-wall hollow conical targets is reported as an example of a non-traditional ablative acceleration geometry.

Pathways in type-B (U-shaped) metacontrast.

Rod and cone targets were crossed, in every combination, with rod and cone masks in flanking-bars metacontrast. Strong type-B (U-shaped) metacontrast was obtained in each condition, contrary to the claim that rod and cone masking are independent. In each condition, visibility declined steadily with stimulus-onset asynchrony (SOA) in trials in which target and mask appeared to be simultaneous, and increased with SOA in trials in which they appeared to be successive. The 'U' results from collapsing across these different types of trials, which may reflect distinct monotonic processes in masking. Under the light adaptation conditions used the time, Tmax, at which metacontrast was at a maximum was delayed by about 25 ms if rods, rather than cones, detected the target. Whether rods or cones detected the mask hardly altered Tmax.

Numerical study of compression and heating of conical targets

This paper presents some results of two-dimensional calculations (using Euler variables) of conical targets, performed on the basis of the coservative variant of the grid characteristic method. The mathematical model of the physical processes occurring in the high temperature plasma includes absorption of external laser radiation, the hydrodynamic motion, electron thermal conductivity, and electronion collision relaxation. The basic system of two-dimensional non-steady-state equations for the two-temperature plasma is presented and supplemented by an equation for the mass concentration of one of the components of the two-component mixture of ideal gases.

Frequency independent ultrasound contrast-detail analysis

An ultrasound contrast-detail phantom has been developed to evaluate the image quality of diagnostic ultrasound imaging systems. The phantom includes eight conical targets whose B-mode images show disk lesions such that the object contrast of each lesion relative to background is independent of the imaging device or transducer frequency/spectrum. By maintaining conditions for Rayleigh scattering and Rayleigh speckle statistics in the phantom gel, the object contrast of each lesion depends only on the scatterer concentration in the lesion relative to the scatterer concentration in the background. Experimental data confirmed this frequency independence. Results of contrast-detail performance of an ultrasound imaging system are shown, and a standard technique for error analysis of contrast-detail data is described.

Experimental Study of Alternative Implosion Concepts for Particle Beam ICF

The plasma jet formation experiments on cylindrical Au target applying a focused REB generated by REIDEN III were performed. The clear evidence of jet formation was shown by N 2 laser shadowgrams and damages remained on the target holders. The velocity and the energy density enhancement in jet was observed. In the conical cavity target irradiation, the areal mass density of the foil was increased as the results of the areal plasma convergence in the cavity.

A contrast‐detail analysis of diagnostic ultrasound imaging

For diagnostic ultrasound imaging, as in computed tomography, a feature of prime importance is the detection of focal lesions of varying size and contrast (echo amplitude) from surrounding tissue. This study describes a new tissue-stimulating phantom which has been used to measure the threshold detection of varying contrast, simulated lesions. The phantom consists of a block of tissue-mimicking gelatin which contains a row of conical targets at a depth of 7 cm. Each cone contains a different tissue-mimicking material so that the echo amplitude of the cones relative to the background material covers a dynamic range of 20 dB. Cross-sectional B-scans, perpendicular to the lengths of the cones, result in images of disks of constant diameter but varying contrast. Parallel cross-sectional scans yield "lesions" varying in diameter from 20 to 1 mm. Relative contrast of the cones vs background tissue is obtained by varying scattering particle sizes from 90 to 300 microns. Ultrasound B-scans of the phantom were examined by medical physicist observers to determine threshold detection of lesions as a function of size and contrast. The results indicate that detection of high contrast targets is limited by the imaging system's spatial resolution. Detection of low contrast targets is limited by the image speckle, i.e., coherent noise.

Brightness interactions between rods and cones.

Two parafoveal test targets with different spectral compositions were matched in brightness to a fixed-luminance foveal reference target under scotopic adaptation conditions. The idea of the experiment was to find a reference luminance for which one of the matching test targets stimulated only rods while the other stimulated both rods and cones. If brightness was proportional to the linear sum of rod and cone responses, then the luminance of the matching rod+cone target would be predictably closer to rod threshold than would that of the rod target. The results were complicated by evidence that rod responses to the test targets selectively enhanced weak chromatic signals. Nevertheless, it was possible to show that cone activity never reduced the matching luminance as much as predicted by the additivity hypothesis, and sometimes even increased it. These findings suggest that cone activity can suppress brightness signals from rods.

Radar scattering measurements of cones and computation of transient response

The far zone scattered signal amplitude and phase for two small cone and cone-like targets (sharp and spherically blunted) were measured using a ten-harmonic <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20\deg</tex> bistatic radar system. As many as five of the first ten harmonics of 1.085 GHz were transmitted simultaneously. The received vector sum of the harmonics was measured (amplitude and phase) by a network analyzer and stored in a computer. Data were collected as the target moved a half wavelength at the fundamental, and individual data for each harmonic were extracted by Fourier analysis. In either system, empty pedestal (background) data were vectorially subtracted and sphere data were used for system calibration. Data were collected for cones at aspect angles of 0, 10, 20, and 30 degrees for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ka</tex> from 0.1 to nearly 4. The behavior of the data is compared to the Rayleigh theory for the lower frequencies and the geometrical theory of diffraction (GTD) for the higher frequencies. These theories do not overlap, and the data allow us to "fill the gap." The data were Fourier transformed to the time domain, and the time response of the targets is discussed.

Efficiency of conical targets for laser thermonuclear fusion

The advantages and disadvantages of conical targets for laser thermonuclear fusion are considered. An analysis is made of the possibility of reducing the laser power, extending the laser pulse, and increasing the neutron yield, using an ideal conical target with absolutely rigid walls of zero thermal conductivity, compared with a spherical target of equal mass. A simple theory is proposed enabling the influence of the walls on the fusion process in a conical target with a gaseous fuel and a heavy shell to be taken into account. Estimates are given of the energy losses caused by distortion of the walls and heat conduction in them. The influence of these effects on the neutron yield is estimated.

Production of 0.5-TW Proton Pulses with a Spherical Focusing, Magnetically Insulated Diode

The production, focusing, and numerical simulation of a 0.5-TW proton beam is reported. This beam is produced with a spherical, magnetically insulated, ion diode fed symmetrically by the dual-pulse-line Proto I generator. The ions are accelerated with electric fields due to a virtual cathode supported by magnetic field surfaces. Approximately 75% of the diode electrical power is delivered to ions and 25% of the ion beam is focused upon thin, 1-cm-diam, 1-cm-long conical targets to produce the first experimental ion-driven implosions.

Conical targets for implosion studies with a CO2 laser

The design, fabrication, and testing of conical laser fusion targets is described. These are DT-filled conical holes in lead, 190 μm deep and covered with a 132-μm-diam plastic cap. The results of two-dimensional simulations of the cones are displayed. Experimentally, up to 2.8×105 neutrons have been obtained from the exploding pusher implosion of such a target under single-beam CO2 illumination of the cap at 0.13 TW.

Influence of collisions between laser plasma jets in conical targets on the plasma parameters in the final stages of expansion

An investigation was made of the charge, kinetic, and geometric parameters of the ion component of a laser plasma in the final stages of expansion when the radiation was focused into a conical recess in a lead target. The dependences of these parameters on the cone vertex angle were determined and a comparison was made with plane targets. The measurements were made by probe and mass spectrometer techniques. The results suggest that a narrow highly directional plasma jet with a high degree of ionization can be produced by optimizing the target shape and the radiation focusing conditions. A possible mechanism of the influence of collision processes on the resultant plasma parameters is discussed.

Reflection and absorption of electron plasma waves in a bounded plasma

Reflection and absorption of electron plasma waves are studied experimentally in a Q-machine. The waves are reflected from a cold, negatively biased metal plate. The potential of the reflected wave is in phase with that of the incident wave, but the plate absorbs the incident waves when it is biased at a large positive potential. On the other hand, an ionizing hot plate reflects the waves and a phase reversal is observed. A conical target can be used as a wave absorber under some experimental condition.

Near-zone scattering by plates, cylinders, and cones

The near-zone monostatic scattered fields of flat plate, circular cylinder, and finite right circular cone targets are considered in this communication. The near-zone scattered fields were measured using a Scientific-Atlanta precision EM field probe, and the near-zone fields were computed using the geometrical theory of diffraction (GTD). Good agreement between measurements and predictions resulted. These results indicate that the geometrical theory of diffraction is an accurate descriptor of near-zone scattering.

A conical liquid hydrogen target

A conical liquid hydrogen target

Analysis of a conical solar concentrator

The concentration that a conical mirror can theoretically attain is developed for two types of targets; a circular cylindrical target and a conical target. Under the assumption of a one-dimensional sun, the optimum mirror cone 1 2 - angle is determined for both types of targets. At the optimum mirror cone 1 2 - angle , the concentration, assuming a two-dimensional sun, is determined, and the optimum concentration in terms of mirror radii is found for both types of mirrors.