摘要:

A new class of heat engine is analyzed in which the working fluid operates in a dissipative process, never in equilibrium. The conditions are found for stability and for the generation of work. Then the optimal path is found for operating the general dissipative engine by means of optimal control theory. The optimal cycle consists of arcs of constant power and of approximately instantaneous adiabats. If the heat flow is a function of temperature only, then the constant power arcs become isotherms. An upper bound is found to the power output. Two examples are worked out in detail: a light‐driven dissipative engine whose absorption is a step function of temperature, and a light‐driven dissipative engine whose working fluid undergoes a chemical reaction (isomerization), absorbing light in the isomeric form favored at high temperatures.

ISSN:0021-8979    

DOI:10.1063/1.332598

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Laser driven fusion requires a high degree of uniformity in laser energy deposition in order to achieve the high density compressions required for sustaining a thermonuclear burn. The characteristic nonuniformities produced by laser irradiation, with multiple overlapping beams, are examined for a variety of laser‐target configurations. Conditions are found for which the rms variation in uniformity is less than 1%. The analysis is facilitated by separating the contributions from (1) the geometrical effects related to the number and orientation of the laser beams and (2) the details of ray trajectories for the overlapping beams. Emphasis is placed on the wavelength of the nonuniformities in addition to their magnitudes, as the shorter wavelength nonuniformities are more easily smoothed by thermal condution within the target. It is demonstrated how the geometrical symmetry of the laser system effectively eliminates the longer wavelengths, and how shorter wavelength nonuniformities can be ‘‘tuned out’’ by varying parameters such as the focal position and the radial intensity profile of the beam. The distance required for adequate thermal smoothing of the irradiation nonuniformities is found to be 2 to 3 times smaller than previously estimated due mainly to the relatively small spatial wavelength of the nonuniformities. This is a consequence of the geometrical symmetry of the laser system and is relatively insensitive to the details of overlapping beams. The results are particularly important for irradiation with short wavelength laser light (e.g., 0.35 &mgr;m), as the small smoothing distances anticipated for moderate laser intensities are found to produce adequate attenuation of the calculated nonuniformities.

ISSN:0021-8979    

DOI:10.1063/1.332599

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A linear numerical analysis of the converging guide accelerator incorporating a radially inhomogeneous beam equilibrium and finite axial magnetic field is conducted. It is shown that these characteristics cannot explain the latest experimental results involving large amplitude waves. The slow phase velocity of these waves rely on nonlinear effects. A study of the adiabatic variation of wave amplitude in the accelerator indicates the importance of using high frequency waves for efficient operation.

ISSN:0021-8979    

DOI:10.1063/1.332600

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Energy spectra of 24.8‐MeV electrons after emerging from C, Al, Cu, and Pb were measured at 0°, 5°, 15°, 30°, 60°, 120°, and 150°. The material thickness ranged from ∼1 to ∼3.6 g/cm2. Total energy spectra, defined as 2&pgr; ∫&pgr;0 f(E,&thgr;)dE sin &thgr;d&thgr;, were composed from these observed energy spectra. Average energy loss was calculated from the total energy spectrum for each material. By plotting the experimental data including the one obtained by Ziegler, an empirical equation estimating the average energy loss per unit path length was obtained. The most probable energy losses at 0° for C and Pb agree well with theoretical predictions, while those for Al and Cu are generally larger than calculated values by ∼6–7%. Discrepancy between the experimental and calculated values of the full width off(E,0°) at half‐maximum due to electron straggling becomes smaller asZincreases.

ISSN:0021-8979    

DOI:10.1063/1.332601

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Pulsed resonant optogalvanic effect is investigated in a neon hollow cathode discharges utilizing a nitrogen pumped dye laser. We have studied by the pulsed technique transient effects in the discharge plasma such as fast relaxation of level population density and population inversion. The experimental results are correlated with a four states phenomenological model of the pulsed optogalvanic effect taking into account lumped relevant levels of the 3sand 3pmanifolds of neon. The time integration of the pulsed optogalvanic siganls (OGS) yields the previously measured cw signals and explains their sign changes.

ISSN:0021-8979    

DOI:10.1063/1.332602

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

In order to be able to use it in time‐of‐flight mass spectrometry, we have tried to find a mirror with as few spherical and chromatic aberrations as possible. We have studied the characteristics of the mirror with charged particles whose initial energy varies by ±1% around a central value and which go through an imaginary input pupil of radius 0.2 &rgr; (&rgr; being the radius of the three cylinders which go to make up the mirror). The best operating conditions are calculated for different source points on the axis, taking into account separate residual chromatic and spherical aberrations, and also in the case of simultaneous chromatic and spherical aberrations. The second part of the paper deals with flight time (internal mirror flight time and object‐image flight time). The data enable us to establish that this convergent mirror plays an essential compensating role; it eliminates not only the initial energy spread effects, but also those of the ion bunch divergence. Consequently, all the above‐mentioned particles have a flight time which is virtually constant.

ISSN:0021-8979    

DOI:10.1063/1.332603

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Diagnostic measurements have been made on a two‐phase flow of carbon particles suspended in nitrogen gas, in conjunction with another experiment. Experimental data on particle size distribution were obtained from scanning electron microscopy of samples, laser extinction, and laser scattering in the flow. Two independent nonintrusive laser measurements indicated ‘‘average’’ particle diameters of 1.5 and 3.4 &mgr;m. Predictive calculations show that these experimental measurements can be used to indicate the degree of agglomeration in the flow and provide restrictive boundaries toapriorisize distributions which are computationally consistent with the observed data.

ISSN:0021-8979    

DOI:10.1063/1.332604

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

This work presents a new type of optical recording medium for a diode laser which is three times more sensitive than a chalcogenide thin film. This medium has a tetralayer structure ofn–hexatriacontane, zinc stearate, Sb2S3and Bi. The Bi layer absorbs a recording light beam and organic layers are ablated by heat evolved in the Bi layer. The high sensitivity characteristic of this medium is attributed to the use of low‐melting‐point material as the ablating layer and the effective use of the incident beam.

ISSN:0021-8979    

DOI:10.1063/1.332586

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A general theoretical consideration is given for the stimulated Raman scattering in a finitely magnetized relativistic electron beam on which the operation of the Raman‐type free‐electron laser is based. After some preliminary discussion, the coupled mode equations are derived which relate the pump wave (assumed to be an electromagnetic wave), the scattered wave and the electron plasma wave (negative‐energy wave). From the coupled mode equations obtained above, the linear growth rate for the scattered and electron plasma waves is found. Then, the energy relations are formulated for the three waves involved in the process of the stimulated Raman scattering, together with the discussion on the energy balance among these waves. A special attention is paid to the behavior of the scattered wave in the vicinity of the cyclotron resonance. Some of the important features brought about by the cyclotron resonance are as follows: (a) According to the conditions imposed on the frequency and wave number of the pump wave, the scattered wave becomes either the electromagnetic wave mode or the electron cyclotron wave mode, or it is not excited. (b) In the presence of a finite static magnetic field, the spatial growth rate for the electromagnetic wave mode takes a maximum value for a particular set of various parameters, and the maximum growth rate becomes one order of magnitude or more as large as the growth rate for the case that there is no static magnetic field applied.

ISSN:0021-8979    

DOI:10.1063/1.332587

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A kinetic model of the sustained discharge Ar/HgBr2laser is developed from an experimental base. The choice of Ar as the buffer gas is supported by measurements of the specific fluorescence and laser efficiency in the buffer mixtures (Ar, Ar+5% Xe, Ne+10% Xe, Ne+10% N2). A computational treatment of the coupled photon and kinetic equations is described. Gain measurements determine a peak HgBr (B‐X) stimulated emission cross section of 1.6×10−16cm2±20% at 502 nm. Absorption measurements between 515 and 530 nm show the presence of a large, broad band absorption tentatively assigned to HgBr+2with a cross section of 2×10−18cm2. An upper bound of 5×10−9cm3 sec−1is placed on the rate constant for electron collisional quenching of the HgBr(B) state. The laser extraction efficiency of 65% is modeled by a lower level collisional deactivation by Ar with a rate constant 6.0×10−12cm3 sec−1. Discharge impedance is measured as a function ofE/Nand the ionizing electron beam current density. Using the new data a good description of laser efficiency is demonstrated if the ratio of HgBr(B‐X) fluorescence power to discharge input electical power is set to 6.1%, for 0.8% HgBr2in Ar atE/N=8×10−17V cm2.

ISSN:0021-8979    

DOI:10.1063/1.332588

出版商:AIP    

年代:1983

数据来源: AIP