摘要:

The generation of acoustic waves in metals by pulsed laser irradiation over a wide range of material conditions has been studied. Capacitance transducers have been used to obtain quantitative measurements of the amplitude of bulk acoustic waveforms where the laser beam was directed onto free metal surfaces in the presence and absence of surface plasmas, and onto modified metal surfaces. The application of acoustic wave propagation theory has allowed theoretical waveforms to be determined. By combining data for thermoelastic and normal force sources, waveforms have been produced that follow closely those measured experimentally.

ISSN:0021-8979    

DOI:10.1063/1.331270

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A hydrophone using a liquid delay line oscillator has been developed. The delay line consists of two pairs of interdigital transducers on the same substrate surface and a diaphragm used as a reflecting plate of the sound beam. The interdigital transducer operates as a sound beam radiator or a detector at a liquid‐solid interface. The oscillation frequency is dependent upon the sound pressure level applied to the diaphragm. Performances of the hydrophone are described, including sensitivity and its frequency dependence.

ISSN:0021-8979    

DOI:10.1063/1.331271

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The viscosity of a soda‐lime silica glass was measured at high strain rates. The data show non‐Newtonian viscous flow in this inorganic oxide glass with the viscosity values below the expected Newtonian value. Following the imposition of large, steady strain rates, the observed stress increases with time to a maximum and then decreases to a time‐independent value. A comparison of the viscosity behavior of this glass with the molecular dynamics results in a ’’Lennard‐Jones’’ glass shows a number of points of correspondence and suggests the interpretation of the non‐Newtonian behavior as resulting from structural rearrangements in the material. The combined data show that the sustained, steady‐state stress asymptotically approaches a maximum at very high strain rates. This limiting stress is interpreted as the actual cohesive strength of the material and is calculated to be 1.4×108N/m2(20,000 psi) for the glass under study.

ISSN:0021-8979    

DOI:10.1063/1.331272

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A system of one‐dimensional equations governing the extensional (contour) modes of vibrations in rectangular crystal plates is derived from the Cauchy–Voigt two‐dimensional equations of extensional motion of anisotropic, elastic plates. The system of equations is further divided into two groups of equations governing, separately, the symmetric (contour extensional) and antisymmetric (contour shear) modes of vibrations, by setting the elastic stiffness coefficients &ggr;15= &ggr;35= 0 in order to neglect the coupling effect between the two groups. Closed form solutions of contour extensional vibrations are obtained for rectangular crystal plates satisfying the traction‐free conditions at four edges. Dispersion relation and frequency equation are obtained in explicit form for the first three contour extensional modes. Resonance frequencies, for various contour extensional modes, are computed as a function of the length‐to‐width ratio (a/c) of plates. Predicted results are compared with the detailed measurements for rectangularGTcuts with close agreement. Two‐dimensional vibration patterns have also been calculated at resonances for different values ofa/cratio.

ISSN:0021-8979    

DOI:10.1063/1.331273

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Experimental results are presented from negatively‐biased cylindrical Langmuir probes located in a magnetohydrodynamic (MHD) generator with the flow supersonic and the plasma both in equilibrium and uniform. Voltage‐current characteristics were obtained over a wide range of bias voltages, up to the arcing limit, and these showed that the probes operate in the convection‐sheath mode. Electron densities deduced from the probe measurements are in agreement with values obtained by other methods; the results confirm the applicability of the Langmuir probe as a diagnostic technique in flowing plasmas.

ISSN:0021-8979    

DOI:10.1063/1.331274

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The stability of a charge and current neutralized electron‐ion beam propagating between two planar boundaries is investigated. For equipotential boundaries the beam is, as originally shown by Pierce, electrostatically unstable for electron current densities above a certain limiting value. If, however, the electric field at the upstream boundary is required to vanish, there is no instability. An intermediate case, in which the two boundaries are electrically connected with a finite conductivity plasma, corresponds to the proposed use of neutralized light and heavy ion beams for inertial confinement fusion drivers. Results indicate such beams can propagate either stably or with zero‐frequency Pierce instability growth rates which are probably insignificant. lectric currents; boundary conditions; current density; electric fields; plasma;

ISSN:0021-8979    

DOI:10.1063/1.331275

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The 10 TW BLACKJACK 5 pulse generator has been used to create both plasmas with electron densities on the order of 5×1020cm−3and electron temperatures between 0.5 and 2 keV by imploding cylindrical arrays of fine aluminum, calcium, and titanium wires and ribbons. Visible streak photographs indicate that the wires are ionized by the prepulse and expand to ∼1‐mm diameter before imploding toward the central array axis to form a dense pinch. The individual plasmas assemble on axis at approximately peak current, at which time a 20–25‐ns FWHM pulse ofK‐shell x‐ray radiation is emitted. Emission from H‐, He‐, and Li‐like ionization states has been observed with curved crystal spectrographs, and electron temperatures and densities have been inferred from these measurements. Pinhole photographs show intense emitting regions and kink structures in the plasma column.

ISSN:0021-8979    

DOI:10.1063/1.331276

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Electrostatic plugging is used to improve plasma confinement in a multidipole ion source. A conventional multidipole device is modified by placing positively biased electrodes on both sides of each magnetic line cusp. As the electrode bias voltage is increased from zero, plasma density increases by approximately a factor of 2 and the plasma potential follows the electrode potential. The density enhancement is reduced as neutral pressure is increased or if the electrode‐gap width is decreased. Similar behavior is observed when a negatively biased grid is present. A model which assumes that the main electron‐loss mechanism at high electrode bias is diffusion across the cusp magnetic field lines is shown to be in qualitative agreement with measurements.

ISSN:0021-8979    

DOI:10.1063/1.331277

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Two parallel, relativistic electron streams with different velocities support unstable, exponentially growing space‐charge waves, and efficient electron bunching may be achieved in the submillimeter wavelength range. Injection of the prebunched streams into a static, periodic (wiggler) magnetic field enhances the intensity of the parametrically excited, backscattered electromagnetic wave. Calculations are presented of the amplitude enhancement and of the linear growth rate of the wave in the Raman regime, for the case of two cold, perfectly intermingled electron streams.

ISSN:0021-8979    

DOI:10.1063/1.331278

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The aplication of computer‐imaged microwave holography to plasma diagnostics is mathematically formulated, a system is constructed and performance evaluated, and tested experimentally in a plasma chamber. The initial results of the project indicate potentials of the holographic technique in the area of non‐interference versatility and simplicity of operation.

ISSN:0021-8979    

DOI:10.1063/1.331234

出版商:AIP    

年代:1982

数据来源: AIP