摘要:

The numerical solution of potential problems of the Dirichlet type based on Fredholm integral equations is considered. The method is illustrated for the case of a unit sphere. In solving the integral equations there are advantages in extrapolating in the order of Gaussian quadrature, and this is done by introducing an empirical formula for curve fitting purposes. An iterative solution which overcomes the peaked nature of the kernel in the integral equations is also considered, together with a discussion of convergence and error accumulation.

ISSN:0021-8979    

DOI:10.1063/1.331306

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The numerical solution of the Fredholm integral equation of the first kind is formulated so that the source of instability is identified and can be isolated. The problem is regarded as a minimization with no constraints on the solution. It is shown that the introduction of instability depends on the path taken from the initial to the final estimate of the solution. The initial estimate is the given data, and the path which avoids instabilities is that which requires monotonic variation of these data. The method is applied to the deconvolution of noisy spectra and a more objective procedure results than has been previously obtained. Detailed applications and comparisons with previous methods are given.

ISSN:0021-8979    

DOI:10.1063/1.331307

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A magnetically insulated light ion diode which has produced an ion beam with total current exceeding 400 kA for 25 ns and generated a proton current density approaching 500 kA/cm2is described. This intense beam current is achieved in a noncurrent neutralized mode via geometric focusing and a balance between self‐magnetic field and space‐charge forces. A number of techniques are described which have been used to diagnose the beam production, transport, and focusing. These include observation ofK&agr;emission due to beam‐induced atomic excitation, prompt‐&ggr; radiation due to beam‐induced nuclear reactions, and thermal emission due to beam‐target heating.

ISSN:0021-8979    

DOI:10.1063/1.331308

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

In 1967, R. L. Hirsch [J. Appl. Phys. 38, 4522 (1967)] reported neutron production rates of 1010neutrons per second from an electrostatic inertial confinement device. The device consisted of six ion guns injecting deuterium or a mixture of deuterium and tritium ions into an evacuated cathode chamber at 30–150 keV. No previous theoretical model for this experiment has adequately explained the observed neutron fluxes. A new model that includes the effects of charge exchange and ionization in the ion guns is analyzed. This model predicts three main features of the observed neutron flux: Neutron output proportional to gun current, neutron production localized at the center of the evacuated chamber, and neutron production decreasing with increasing neutral background gas density. Previous analysis modelled the ion guns as being monoenergetic. In this study, the ion gun output is modelled as a mixture of ions and fast neutrals with energies ranging from zero to the maximum gun energy. Using this theoretical model, a survey of the possible operating parameters indicates that the device was probably operated at or near the most efficient combined values of voltage and background pressure. Applications of the theory to other devices are discussed.

ISSN:0021-8979    

DOI:10.1063/1.331309

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A study of the composition and energy distribution of a beam of ions obtained from an Al liquid metal ion source supports the field evaporation mechanism for ion formation at low currents. The beam composition varies as Al+≫Al++≳A+ 2≳ Al+ 3≳ Al+ 4≳ Al+ 5and the energy spread &Dgr;Evaries as Al++<Al+≪Al+ 5< Al+ 4< Al+ 3<Al+ 2. Both &Dgr;Eand the ratio of Al+n/ Al+increase with total current. Because of the strong mass dependence of &Dgr;E, Al+exhibits an angular intensity twice as large as Ga+for &Dgr;Evalues between 5 and 10 eV.

ISSN:0021-8979    

DOI:10.1063/1.331310

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

This paper considers of a coordinate‐free approach to wave propagation in anisotropic media. Based on the direct manipulation of vectors, dyadics, and their invariants, the approach eliminates the use of coordinate systems. It facilitates solutions and provides results in a greater generality. The paper contains the following results in coordinate‐free forms: The formulation of eigenvalue problems, the dispersion equation, the polarization of waves in magnetic crystals, and the determination of the directions of field vectors.

ISSN:0021-8979    

DOI:10.1063/1.331382

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

An earlier model developed by others to study the 10.6‐&mgr;m laser transition in CO2has been extended for studying the 16‐&mgr;&mgr; (0200)→(0110) laser transition in cold CO2. The rate equations take into account the rotational relaxation and collisional transfer of population among (0200), (1000), and (0220) levels of CO2. The model has been used to study the effect of various parameters on the 16‐&mgr;m output. It has been found that at higher pressures the collisional relaxation of the (0200) level can be overcome by application of a more powerful 9.6‐&mgr;m pulse to achieve an inversion between the (0200) and (0110) levels of CO2. It is predicted that if transverse excitation is used in these cold mixtures, pulsed powers in excess of 100 kW could be obtained on 16 &mgr;m.

ISSN:0021-8979    

DOI:10.1063/1.331311

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A theoretical analysis based on a conventional CO2gasdynamic laser (GDL) revealed the possibility of 16‐&mgr;m cascade lasing, in which a 9.4‐&mgr;m stimulating beam is internally generated, and subequently a 16‐&mgr;m emission is produced in a cascade manner. In this simulation, cascade‐ type 16‐&mgr;m lasing of 3–10 &mgr;J/cm3energy and 1–1.5 W/cm3power is achievable on theP(15) line of the (0200)—(0110) transition at a position 15 cm downstream from the nozzle throat. Because of its high average power capabilities, without requiring a separate CO2laser as a stimulating beam source, the 16‐&mgr;m cascade operation of a CO2GDL will be practically usable.

ISSN:0021-8979    

DOI:10.1063/1.331334

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The effect of initiator pulse duration on the performance of a pulsed chain reaction chemical laser is investigated using a two‐level vibrational model. Analytic results are presented for a saturated laser in the limits of weak and strong initiation. The initiator is assumed to provide a uniform (e.g., electron beam), parabolic (e.g., flash‐lamp), or power‐law variation of F‐atom production rate F˙Bwith time. Laser performance is presented as a function oftB /te, wheretBandteare initiator and laser pulse times, respectively. In the weak initiation regime, an increase oftB /tefrom zero to one results in a decrement in laser output energy of 20 and 33 (1)/(3) % for a flash‐lamp and electron‐beam initiator, respectively. In the strong initiation regime, an increase oftB /tefrom zero to one results in an energy decrement of only 5 and 10% for a flash‐lamp and electron‐beam initiator, respectively. In each case, the laser‐pulse timeteis increased by a factor of 2 astB /teincreases from zero to one. For strong electron‐beam initiation, peak laser intensity occurs at the end of the initiation pulse whentB /te?2/3, and occurs in the time interval 0.630?t/te?2/3 whentB /te≳2/3.

ISSN:0021-8979    

DOI:10.1063/1.331335

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A general mechanism of self‐stabilization of longitudinal modes in semiconductor lasers is presented. The stabilization is due to the modulation of the inverted population by the beating of the fields of lasing and nonlasing modes, thereby modulating the rate of stimulated emission. This leads to two optical nonlinearities: one causing gain suppression of nonlasing modes and the other causing coupling of pairs of nonlasing modes that are equally separated from the laser line. The two nonlinearities nearly cancel, but their net effect is a weak suppression of the nonlasing modes and stabilization of the lasing mode. Buried optical guide lasers were stabilized in a single longitudinal mode for currents greater than 6mA above threshold. The mode intensity spectra of the lasers were measured over 5 decades and converted to gain spectra, which could be compared with the theory. The gain spectrum is parabolic at threshold. At 20 mA above threshold it remains continuous at the laser line but narrows and becomes structured. The structure is characterized by a dip in the gain and in the mode intensities occurring about 3 modes from the laser line. The laser line also causes a pronounced dip in the gain spectra of the nonlasing first order transverse modes. All of these features can be approximately accounted for by the theory.

ISSN:0021-8979    

DOI:10.1063/1.331290

出版商:AIP    

年代:1982

数据来源: AIP