摘要:

This paper reviews the development, history, theoretical basis, and experimental performance of solid‐state hydrogen detectors under flow‐through conditions available to date such as pyroelectric, piezoelectric, fiber optic, and electrochemical devices. Semiconductor hydrogen detectors will only be reviewed briefly, as excellent reviews on this subject already exist. In view of the fact that almost all the devices that will be discussed later in this paper use Pd as a hydrogen trap, we devote a subsection to examining the role of palladium as a catalyst as well as some of the characteristics of the Pd‐H2system. Non‐solid‐state hydrogen sensors, such as the flame ionization detector are not the object of this review. A useful feature of this review is a comparison of operating characteristics of each device in a general table in Sec. VII. In that section a general discussion is presented, including a critical comparison of the capabilities and parameters of various solid‐state hydrogen sensors in the form of a table showing data collected from the literature. The Pd‐fiber optic sensor is the most sensitive optical device operating at room temperature. The Pd‐photopyroelectric sensor appears to be most economical and second best in sensitivity at room temperature; it has the best potential for high signal‐to‐noise operation at the widest temperature range, down to cryogenic temperatures. The Pd‐field effect transistor devices exhibit the second highest sensitivity at elevated temperatures.

ISSN:0021-8979    

DOI:10.1063/1.346398

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In order to calibrate a time‐of‐flight mass spectrometer which is to be flown in the solar wind we have investigated the charge exchange properties of low‐energy ions in thin carbon foils. We have used incident ions of He, C, N, O, Ne, and Ar with energies in the range 0.5–2 keV/nucleon to measure charge‐state distribution, residual energy, and angular distribution after transmission through thin (1–6 &mgr;g/cm2) carbon foils. Within such foils an equilibrium between ionization and recombination of the projectile is rapidly established and, consequently, the charge state of the emerging particle depends essentially on its residual velocity. A comparison of the charge exchange properties of22Ne with20Ne demonstrates that indeed the velocity (and not the energy) of the emerging particle determines its final charge. Comparing properties of different elements one observes an indication of an electron shell effect. Predictions for the energy loss of ions within the carbon foils made with thetrimcode [J. F. Ziegler, computer codetrim‐88 (IBM‐Research, Yorktown, NY, 1987)] are in good agreement with the experimental results presented in this paper.

ISSN:0021-8979    

DOI:10.1063/1.346478

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We present the first experimental results of a uniformly insulated extraction applied‐B ion diode. The diode typically attained beam generating efficiencies of 70% at the time of peak beam power. This is a significant improvement over previous extraction applied‐B ion diodes, demonstrating the importance of uniform insulation as suggested by theory [J. Appl. Phys.59, 2685 (1986)]. Furthermore, we found that the beam current is nearly independent of the ion‐emitting area down to a minimum area. At the minimum area, the beam current density was enhanced by 150 times the monopolar Child–Langmuir value. This data supports a recently proposed theory [Phys. Rev. Lett.59, 2295 (1987)] that predicts large enhancements due to the electron diamagnetic effect on the virtual cathode.

ISSN:0021-8979    

DOI:10.1063/1.346479

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Experimental results for a high‐brightness electron‐beam source are compared to results of numerical and analytic calculations. The 4‐MV, 5‐kA beam is generated from a velvet cathode and focused by a solenoidal magnet. Data for the diode impedance and the beam focusing length and spot size agree well with numerical simulations. The minimum spot size is consistent with a normalized Lapostolle emittance of 0.12 cm rad, yielding a brightness of 3.5×108A/m2 rad2. Transverse beam oscillations are observed in streak photographs and are thought to be caused by electromagnetic dipole modes in the diode cavity. The oscillation amplitude is significantly reduced by making the current rise more slowly.

ISSN:0021-8979    

DOI:10.1063/1.346480

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The F2concentration , laser output power , laser pulse duration, and laser beam patterns of discharge pumped KrF excimer laser are measured at high repetition rate during long‐term operation. The effects of the F2concentration on the laser output characteristics are analyzed.

ISSN:0021-8979    

DOI:10.1063/1.346481

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The HAWK facility has been developed as a tool to investigate the kinetics of electron‐beam‐pumped lasers at a pressure of 1 atm for pump rates of 0.040–1 kW/cm3and pump times of 0.05–1 ms. The highly collimated (1 cm FWHM within the lasing medium) relativistic electron beam propagates through fast valves that separate the accelerator vacuum from a 2‐m‐long vacuum isolation section, a 0.4‐m‐long gas‐filled buffer section, and 0.7 m along a lambda‐geometry laser cell. A 6.5 kG magnetic field confines the 1‐MeV electron beam laterally and guides it around a 30° bend into the 3.3‐cm‐diam laser cell. A magnetic mirror at the far end of the laser cell reflects a large portion of the transmitted electron beam, thereby protecting the laser optics from the electron beam and making the axial deposition more uniform. In this paper we describe modeling of the electron beam energy deposition in HAWK using the three‐dimensional Monte Carlo electron/photon transport codeacceptmand compare our results with the measured energy deposition. These numerical simulations were begun during the design phase to define the operational range of the facility. There is good agreement between the calculated energy deposition in the laser cell and the deposition inferred from measurements with a segmented, totally stopping calorimeter at different axial locations in cases where hydrodynamic effects are unimportant. ln cases where these effects are important, however, the calculations can predict too large an amount of energy deposited in the laser gas. The numerical simulations are being used to infer the radial and axial deposition profiles of the electron beam energy as an aid in determining the electron‐beam‐pumped laser performance.

ISSN:0021-8979    

DOI:10.1063/1.346482

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We describe in detail the design and performance of a multikilowatt Pockels cell for use in high average power laser systems. The Pockels cell is a gas‐cooled, transversely excited electro‐optic switch based on KD*P as the electro‐optic material. Matched pairs of crystals with different crystallographic orientations are used to make the switch performance insensitive to the operating point and ambient temperature. Excellent switching performance and low‐wave‐front distortion have been achieved at average power levels in excess of 1 kW.

ISSN:0021-8979    

DOI:10.1063/1.346483

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Near‐ and far‐field patterns, lasing efficiency, and spectra of twin‐stripe lasers as a function of the injected current ratio were systematically examined with particular interest in their dependence on the carrier spreading which was controlled by the interstripe etched depth. As for lasers lightly etched not deeper than 0.5 &mgr;m to the active layer, the near‐field peak shifts with current ratio at a higher rate for deeper etching, which leads to the more drastic change of the lasing efficiency. At the same time, the peak direction of the far‐field pattern and the peak wavelength also changes at a higher rate for deeper etching. The dependence of these characteristics on the etching depth can be attributed to the higher current isolation for deeper etching. These results mean that laser beam deflection and nonlinear light‐current characteristics, which are particularly important for information processing, can be controlled by the interstripe etched depth. As for lasers deeply etched down to 0.3 &mgr;m to the active layer, the regions below the stripes lases independently from each other which are ascribed to both the strong isolation of carriers and the considerable dip in the built‐in index in the interstripe region.

ISSN:0021-8979    

DOI:10.1063/1.346484

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The electron density in electron‐beam irradiated Ar/HCl gas mixtures has been measured by time‐resolved infrared interferometry at 9.6 &mgr;m, using a Mach‐Zehnder interferometer. Measurements were performed fore‐beam irradiated gas mixtures with various HCl concentrations between 0.05% and 5.0%, and total gas pressures between 0.5 and 4.0 atm. Thee‐beam pulse was 350 ns long and at an energy of 150 keV. Thee‐beam current density was varied between 25 and 14 mA/cm2. The measured electron‐density pulse had a characteristic shape with a maximum at the first 100 ns, followed by a drop toward the end of thee‐beam pulse. The values of the electron density at the maximum and at the end of thee‐beam pulse varied slowly as a function of HCl concentration. The experimental results were modeled by incorporating a simplified kinetic code into theelendifBoltzmann code, which calculated the electron energy‐distribution function. The code calculations took into account the effect of the large cross sections for vibrational and rotational excitation of HCl molecules by electron impact. The main conclusion of the analysis is that these cross sections reduce the electron average energy below 0.5 eV for HCl concentrations higher than 0.1%. This conclusion and the results of the code calculations are qualitatively consistent with the experimental observations. But no quantitative agreement was obtained between the code predictions and the experimental results. Possible reasons for this disagreement are discussed.

ISSN:0021-8979    

DOI:10.1063/1.346485

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Detailed measurements of the time‐dependent electron density, xenon excited‐state densities, and total HCl depletion have been recently made in electron‐beam‐ (e‐beam‐) pumped XeCl. This paper presents the results of extensive computer modeling of these experiments and detailed comparisons with the measured results. The model used includes updated HCl reaction cross sections and an enlarged xenon excited‐state manifold. A reduced Boltzmann equation is used to calculate the high‐energy electron‐energy distribution function, and the low‐energy distribution function assumes a quasi‐Maxwellian distribution. These changes are upgrades to prior models. The model accurately predicts the total HCl depletion, the time‐dependent electron density for initial HCl concentrations ≥0.16% (4.8 Torr), and the time‐dependent xenon excited‐state densities for lean (&bartil;0.04%) initial HCl concentration cases. The model tends to underpredict the rate of electron‐density growth after the electron density begins to run away. Since depletion of HCl is a key factor in understanding the kinetics data, possible mechanisms that can contribute to this process are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.346486

出版商:AIP    

年代:1990

数据来源: AIP