摘要:

A technique for calibrating an x‐ray streak camerainsituhas been developed. It has been applied to an x‐ray streak camera installed on a collapsing gas shellZ‐pinch. The calibration was done by simultaneously measuring the emitted x‐rays using a pinhole camera, an InP:Fe photoconductive detector, and the streak camera. The spatial dimension of the streak image was calibrated by integrating the film density over time and fitting the resulting data to the corresponding information taken from an x‐ray pinhole image. The temporal calibration was obtained by similarly fitting the film density from the x‐ray streak image as a function of time integrated over the appropriate part of the spatial dimension with the signal from an InP:Fe photoconductive detector. By using this technique we have found a spatial magnification of the streak camera system consistent with the results derived from the geometrical optics to within 10%. A temporal dispersion of 2.5±0.5 ns/mm was obtained, which is in agreement with the nominal speed of 2.5 ns/mm. This technique also yielded an absolute intensity calibration of the streak camera.

ISSN:0021-8979    

DOI:10.1063/1.336017

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The principal factors which limit the bandwidth and noise temperature of the free‐electron bolometer mixer have been calculated. The minimum mixer contribution to the effective noise temperature is found to be 33Tlatticeunder the conditions of rf match, IF match, and constant current bias. This result is independent of the electron‐lattice energy relaxation time, and can be achieved without significantly degrading the information bandwidth. The best experimental values from the literature are found to be near this predicted performance.

ISSN:0021-8979    

DOI:10.1063/1.336018

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

X rays with a mean energy of ∼50 keV produced by a flash x‐ray source have been used to preionize high‐pressure CO2laser mixtures so as to obtain uniform glow discharges. The x‐ray exposure measured in the active volume was 1–2 mR/pulse with a pulse duration of 100 nsec (FWHM) which permitted specific energy inputs of up to 300 J/l atm. Glow discharges were obtained for a variety of pressures and gas mixtures including some which were helium‐free or in which helium was replaced by argon. Further, a realistic comparison of UV and x‐ray schemes was made under sealed‐off conditions. X‐ray preionization appears to be advantageous and the resulting discharges are shown to tolerate oxygen (up to 2.6%) better. Additives such as xenon or organic compounds were not necessary for obtaining uniform glow discharges.

ISSN:0021-8979    

DOI:10.1063/1.336019

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Analyses of heat spreading, temperature distribution, and resultant cooling effects in a monolithically Peltier‐cooled laser (MPCL) structure are presented. The analyses were obtained by using Laplace’s equation and were made under steady‐state conditions, assuming constant thermal conductivity. In this MPCL structure a metal surface layer surrounds a heat‐generatingp‐nlaser junction. It is shown that by depositing relatively thick metallic cooling plates a 15% temperature reduction and 25% thermal spreading can be achieved. This heat spreading due to the passive cooling is added to the cooling obtained when the Peltier cooler is operated. Experimental measurements of the effect of Peltier cooling reveal a 6.8 °C reduction in junction temperature corresponding to a wavelength shift of as much as 20 A˚.

ISSN:0021-8979    

DOI:10.1063/1.336020

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The coupling of the surface polaritons incident obliquely on a small amplitude grating is investigated. The dispersion characteristics in the neighborhood of the band gap are deduced. The splitting of the dispersion curves of the interacting surface polaritons in the wave‐number space is determined and compared with the available experimental result.

ISSN:0021-8979    

DOI:10.1063/1.336021

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The entire fabrication process of an optical waveguide with a gradient index profile in planar soda‐lime glass substrate was analyzed by using the Nernst–Planck equation for the fluxes of ion species in the glass by considering the effect of an electric current. The derived equations were solved numerically and the effect of the diffusivity ratio of ions and the electric current on the concentration profile of the impurity were discussed. A method for the fabrication of the waveguide was presented and some conditions for getting a parabolic concentration profile of the impurity were presented for Ag–soda‐lime glass substrate system.

ISSN:0021-8979    

DOI:10.1063/1.336022

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

In the use of spark gaps as switching devices, it is desirable to maximize the power delivered to the load and to minimize the power deposited in the switch; that is, it is desirable for the resistance of the switch to be negligible as compared to the load. The hydrodynamic time scale for expansion of the arc in a spark gap and hence for the reduction in its resistance to a small value is tens to hundreds of nanoseconds. Therefore, with current pulses of duration of a few hundred nanoseconds or less, the resistance of the spark gap may be a significant fraction of that of the load. In this paper, we report on measurements that determine the resistance of the arc in a fully diagnosed laser‐triggered spark gap. The spark gap switches a 100‐ns, 1.5‐&OHgr; waterline into a 1.5‐&OHgr; load resistor. A capacitive voltage divider housed within the switch enclosure measures the voltage drop across the switch, a current‐viewing resistor measures the current, and an interferometer measures the diameter of the plasma column, a value required to calculate its inductance. The resistance of the arc is found to remain in excess of 0.1–0.2 &OHgr; for the duration of the current pulse for a variety of switch gas mixtures. The resistance decreases with increasing charging voltage on the waterline at the time of triggering and decreases with decreasing average molecular weight of the gas mixture in which the arc is sustained.

ISSN:0021-8979    

DOI:10.1063/1.336023

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The ion temperature and the energy of gross drift motion of a fully ionized hydrogen plasma with a field‐reversed configuration are measured from the observed Doppler profile of theH&bgr;line from charge exchange neutrals which are generated by a pulsed intense hydrogen beam with energy ∼400 eV. At the beam energy, the generated neutrals are almost hydrogen atoms in the ground state and they emit spectral lines via electron impact excitation. A Monte Carlo analysis shows that the obtained Doppler temperature of the charge exchange neutrals agree with the ion temperature within 6% accuracy. The measured ion temperature and drift energy of the plasma are typically 100 and 10 eV, respectively.

ISSN:0021-8979    

DOI:10.1063/1.336024

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A tandem high‐density hydrogen negative‐ion‐source system is optimized for the purpose of identifying the maximum possible extracted ion current densities. In the first chamber, vibrational excitation occurs by high‐energy electron excitation (E‐Vprocess); in the second chamber negative ions are formed by dissociative attachment. The electron, atom, and molecular densities are varied together with the length of the second chamber. Electron excitation cross sections to theB1∑uandC1∏ustates are calculated as a function of vibrational excitation. The vibrational excitation approaches an asymptotic value as the first‐chamber electron density increases. For a system with scale lengthR=10 cm the optimum extracted current densities occur for gas densities near 1015mol cm−3for first‐chamber electron densities equal to 1013cm−3, and for second‐chamber electron densities in the 4–6×1012cm−3range. For atomic densities equal to one‐tenth the molecular density and for second‐chamber scale lengths as short asZ/R=0.2, extracted current densities are approximately 30 mA cm−2. AsZ/Rdecreases toward 0.1, the current density is doubled. If the atomic density is increased to one‐fifth the molecular density, these current densities are halved; for atomic densities equal to the molecular density, these current densities are reduced by a factor of 6. Applying the system scaling law and varyingRfrom 10 cm toward 1 cm, the extracted current densities tend toward several hundred mA cm−2.

ISSN:0021-8979    

DOI:10.1063/1.336025

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

New data are reported concerning the plasma initiation in front of metallic and dielectric surfaces under the action of pulsed CO2laser radiation.

ISSN:0021-8979    

DOI:10.1063/1.336026

出版商:AIP    

年代:1985

数据来源: AIP