摘要:

Three‐dimensional codes for calculations of a stray magnetic field of iron core of a toroidal plasma confinement system have been developed. The calculated results agree well with the measured ones. It is found that up‐and‐down asymmetry of the iron‐core gap deforms the stray field asymmetrically when the primary coil current is not equal to the plasma current and that anisotropy of permeability of the iron core does not have a large influence on the field.

ISSN:0021-8979    

DOI:10.1063/1.336324

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The energy absorption and decomposition of PH3in a focused CO2laser beam exhibit a threshold nature. The effect of laser frequency, pulse energy, pressure of PH3, and the presence of a foreign gas (neon) on the energy absorption and decomposition threshold were studied. The absorption of radiation increases sharply at threshold and is always accompanied by a visible luminescence. All the experimental facts can be explained in terms of an electron avalanche process, driven by inverse bremsstrahlung absorption of energy from the field of a focused IR laser beam. The simplified phenomenological theory of the dielectric breakdown of gases was applied to the explanation of the threshold phenomena. The decomposition of phosphine was studied as a function of laser frequency, pressure of PH3, and in the presence of foreign gases. The only products of the decomposition found were H2in the gas phase and a solid deposit PHx. The partition of hydrogen between the gas and solid phases depends on the experimental conditions. A reaction scheme is presented which accounts satisfactorily for the experimental facts.

ISSN:0021-8979    

DOI:10.1063/1.337024

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The relationship between spontaneous and stimulated emission from a variety of AlGaAs‐GaAs double‐heterostructure laser diodes has been studied as a function of temperature over a range of 10–70 °C. The spontaneous emission varied exponentially with temperature, and we introduceT’0(J) as the characteristic temperature of spontaneous emission. As the temperature was changed, the laser threshold and slope efficiency for a device strongly covaried with spontaneous emission. A moderately high correlation (r>0.75) was obtained between the lasing and spontaneous emission slope efficiencies of 20 randomly selected lasers from different suppliers.

ISSN:0021-8979    

DOI:10.1063/1.336325

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A formulation to describe the general expression for the modulation broadening of Lorentzian profile is given analytically by using the Fourier expansion and the residue theorem. It is shown that the specificnth derivative signal can be obtained in a most straightforward manner. The present method is applied to a study of the maximum sensitivity (amplitude versus frequency detuning) of phase‐sensitive detection as a frequency discriminator. For the first derivative signal, maximum discrimination sensitivity can be obtained when the modulation width is set to be 1/2 times of the full width at the half maximum (FWHM) of the profile, while the maximum amplitude (signal‐to‐noise ratio) is obtained when the width is exactly equal to FWHM.

ISSN:0021-8979    

DOI:10.1063/1.336326

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Two important steps in the fabrication of microsphere laser fusion targets have been analyzed by simple mathematical modeling. Volatile‐containing droplets emerging from a nozzle with imposed oscillation first undergo a spontaneous blowing process, driven by the evaporation of volatile solvent which pushes the polymeric shell outward. These hollow particles then enter a refinement zone, where a centering process takes place to eliminate eccentricity between the shell internal and external surfaces. The confined vapor partially permeates to the surroundings, allowing shrinkage of the microspheres in this zone to the desired final dimensions and sphericity. Biaxial extensional flow dominates the rheology of micropshere expansion, whereas detailed dynamics of radial flow results in improved concentricity and sphericity. The effects of viscoelasticity on the rate and stress associated with microsphere expansion have been studied using the Newtonian and Maxwell constitutive equations. Simple analytic results to describe microsphere refinement have been obtained for conditions representative of the centering process where Newtonian behavior prevails as the fluid flow is relatively weak.

ISSN:0021-8979    

DOI:10.1063/1.336327

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

When water vapor content is increased from 10 to 100 ppmvin SF6at pressures from 200 to 300 kPa, a dramatic enhancement occurs in the mean size of electron avalanches formed near a positive‐point electrode. Although this effect can be attributed to a change in gas composition, it is not due to a change in the ionization rate for the gas. It is proposed that the avalanche enhancement is due primarily to an increase in the probability for initiating electron release from minor negative ions associated with water vapor that collisionally detach more readily at a given field strength than the predominant negative ions associated with SF6. The profiles of the electron avalanche size distributions exhibit a monotonic decrease of probability with increasing number of electrons for avalanches with fewer than 107electrons, but pronounced peaks appear in the distributions as the mean electron number exceeds 107. These peaks are not consistent with the behavior expected from a stochastic model of electron‐avalanche growth in nonuniform electric fields which neglects the influence of space charge.

ISSN:0021-8979    

DOI:10.1063/1.336328

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Laser absorption experiments are described to measure the radial sodium ground‐state distribution in the positive column of a low‐pressure Na‐Ne discharge. The radial electron density distribution is obtained by combining the results with a particle balance. The electron densities at the tube axisne(0) derived in this way are approximately a factor of 2.5 higher than the ones derived from a direct determination with Langmuir probes. Measuring the sodium profiles as a function of the distance to a probe reveals quantitatively the perturbative effect on the plasma of the glass capillary that supports the probe. This partly explains the observed discrepancy inne(0). The electron temperatureTeis deduced from the laser absorption data using the measured electrical conductivity of the plasma. This value ofTeagrees very well with the value as measured with the probe.

ISSN:0021-8979    

DOI:10.1063/1.336329

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The first experimental investigation has been made of the time‐resolved soft x‐ray spectra from an empty highZcavity target irradiated by 0.53‐&mgr;m wavelength laser. The soft x‐ray emission spectra are compared with those from planar targets with respect to temporal and spectral profiles and brightness temperature. Evidence on the radiation confinement and the plasma confinement in the cavity geometry is discussed in conjunction with the energy dissipation flow.

ISSN:0021-8979    

DOI:10.1063/1.336330

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We present some properties of laser‐generated plasma emission in the soft x‐ray region. Detailed spectral distributions are reported for different target materials (C, Mg, Al, Si, Ti, Fe, Ni, Cu, Mo, Ag, Sn, Ta, Au, Pb, and Bi) in the energy range from 100 to 800 eV. Furthermore, we include measurements of the angular distribution, laser power dependence, and source size of the soft x rays. The efficiency for soft x‐ray generation in our energy range peaks at a laser power density of 1012W/cm2, which can be obtained already with standard laser systems. A comparison is made with other x‐ray sources. To demonstrate the unique properties of laser‐generated plasmas as soft x‐ray source, we report the first single‐shot EXAFS measurement in the soft x‐ray region.

ISSN:0021-8979    

DOI:10.1063/1.336331

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Measurements of piezoelectric and pyroelectric activity, density, and x‐ray pole figures were used to study the effect of thermal aging on the state of polarization in polyvinylidene fluoride. A rolled and poled  &bgr;‐phase specimen of polyvinylidene fluoride was subjected to thermal aging which consisted of temperature cycling between room temperature and successively higher maximum temperatures,TMAX, whereTMAXranged from room temperature to 164 °C. We found that the room temperature piezo and pyroelectric activity decreased linearly as a function ofTMAXfrom 75 °C to 164 °C at which temperature the specimen had 30% of its original activity; a linear extrapolation of these data to zero activity yielded a temperatureTc=207 °C. From density measurements at room temperature, crystallinity was calculated and found to remain constant during thermal cycling. X‐ray pole‐figure observations of the (200) (110) composite diffraction of the  &bgr;‐phase crystal showed single‐crystal texture of the rolled specimen and confirmed the six‐site model of dipole orientation. Changes in x‐ray intensity at the six sites on the pole figure, as a function of thermal aging, were associated with the depolarization process which occurs via a 60° rotation of dipoles away from the direction of primary polarization. Based on these data, we propose a model which describes the state of polarization in polyvinylidene fluoride and from which we calculate the fraction of dipoles in the crystalline state contributing to the polarization.

ISSN:0021-8979    

DOI:10.1063/1.336332

出版商:AIP    

年代:1986

数据来源: AIP