摘要:

We describe a unique apparatus that simultaneously measures the laboratory energy and angles of several charged particles formed in a single beam. The ability to separate and detect particles of opposite polarity allows one to measure them in coincidence. Equations for the trajectories of the particles are derived and discussed in detail. The expressions for the corresponding resolution of the detected particles are also presented. Data produced in recent experiments illustrate some of the analyzer’s more important features.

ISSN:0034-6748    

DOI:10.1063/1.1144782

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The small‐angle source (SAS), 4X source, and 8X source are Penning surface‐plasma sources that produce high‐current, high‐brightness H−ion beams for accelerator applications. The scaling from the SAS (1X source) to the 4X source, and from the 4X source to the 8X source is at least as good as predicted by the scaling laws. In many instances, the scaling is better than predicted, particularly in the critical area of the efficiency with which H−ions are produced per unit of discharge power. Using &zgr;=jH−/FC, whereFCis the cathode power density load, &zgr;4X≊2&zgr;SASand &zgr;8X≊1.5&zgr;4X. ThejH−scaling is at least as good as predicted by the scaling laws—we have been able to produce the predicted H−current in both the 4X and the 8X sources. The SAS was scaled up in size to the 4X source, and the 4X source was scaled up in size to the 8X source, on the assumption that the effectivekTH−=5 eV. We also assume that the effectivekTH−=the effectivekTD−. These temperature scalings appear to be obeyed. The D−current scaling appears to be even better than assumed, namely,jD−≊jH−.

ISSN:0034-6748    

DOI:10.1063/1.1144783

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A laser‐induced fluorescence (LIF) method for spatially resolved fragment detection and characterization in the radiation field of a photolysis laser is described. Measurements of the radiation field of a focused beam showed up highly inhomogeneous irradiation conditions, resulting in a strong local dependence of the laser‐induced processes. The spatial resolution of the method is based on stepping‐motor‐controlled motion of the focusing lens of the photolysis laser versus the probe laser focused to a diameter (1/e2) of 58 &mgr;m. This diameter corresponds to the spatial inhomogeneities of the quantities studied in this article. However, the monitored volume (5.3×10−6cm3) also represents a compromise between acceptable S/N ratio and spectral resolution. The advantages and limits of this spatially resolved fluorescence (SRF) technique are discussed. Owing to its simplicity it can be readily implemented in existing laser photolysis equipment with conventional LIF detection. This method is currently being applied to the study of IR laser chemical reactions. A few examples illustrate the range of applicability of the method by providing information on the fluence dependence of product formation, on mass transport kinetics of molecular species in the context of heterogeneous laser processing, and on the internal energy distribution of the dissociation products. They show the much higher information content of SRF measurements as compared with conventional LIF measurements.

ISSN:0034-6748    

DOI:10.1063/1.1144784

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Taking advantage of the iron core of the Saha Institute of Nuclear Physics (SINP) tokamak, a single turn primary coil was used to generate low power ohmically excited audio‐frequency hydrogen plasma to clean the SINP tokamak vacuum vessel of adsorbed gases. This scheme allowed us to easily use available low voltage power transistors and other existing power supply components to generate audio‐frequency voltage. Using this scheme the discharge cleaning system was tested successfully in a short period of 2–3 months. The system has been utilized to carry out initial discharge cleaning of the vessel as well as daily cleaning to achieve full designed parameters of our tokamak.

ISSN:0034-6748    

DOI:10.1063/1.1144785

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A ‘‘reference cell’’ for generating radio‐frequency (rf) glow discharges in gases at a frequency of 13.56 MHz is described. The reference cell provides an experimental platform for comparing plasma measurements carried out in a common reactor geometry by different experimental groups, thereby enhancing the transfer of knowledge and insight gained in rf discharge studies. The results of performing ostensibly identical measurements on six of these cells in five different laboratories are analyzed and discussed. Measurements were made of plasma voltage and current characteristics for discharges in pure argon at specified values of applied voltages, gas pressures, and gas flow rates. Data are presented on relevant electrical quantities derived from Fourier analysis of the voltage and current wave forms. Amplitudes, phase shifts, self‐bias voltages, and power dissipation were measured. Each of the cells was characterized in terms of its measured internal reactive components. Comparing results from different cells provides an indication of the degree of precision needed to define the electrical configuration and operating parameters in order to achieve identical performance at various laboratories. The results show, for example, that the external circuit, including the reactive components of the rf power source, can significantly influence the discharge. Results obtained in reference cells with identical rf power sources demonstrate that considerable progress has been made in developing a phenomenological understanding of the conditions needed to obtain reproducible discharge conditions in independent reference cells.

ISSN:0034-6748    

DOI:10.1063/1.1144770

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The reliability of electrical equipment in high voltage systems can be affected by certain defaults (metallic particles, roughness, etc.) inside the device enclosure. These anomalies may cause a local glow discharge which propagates progressively inside the insulator and which can lead to electrical breakdown. To avoid this end result, corona discharges have to be detected with a system which satisfies some requirements. Actual methods are not well adapted to industrial constraints. An optoelectronic setup, consisting of a fluorescent plastic optical fiber as a light sensor, connected to a simple, low‐cost amplifier, is proposed. Measurements were first carried out in air to demonstrate the feasibility of this detection method, then air was replaced by SF6. Results lead to the delineation of a sensor made of the fluorescent fiber and the associated amplifier.

ISSN:0034-6748    

DOI:10.1063/1.1144771

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We present a complete apparatus for molecule‐surface interaction studies. Three UHV chambers are connected together allowing preparation, characterization, transfer, and experimental investigations with well‐defined surface samples under ultrahigh‐vacuum conditions. A chopped, supersonic molecular beam with well‐controlled profile enters the main UHV chamber where it is scattered by the sample under study. Detection systems have been designed to measure angular and time‐of‐flight distributions and rotational populations of beam particles scattered off the surface sample giving access to the energy exchange between the internal degrees of freedom of the scattered molecules and the surface. The characteristics of our apparatus are reported and experimental tests for nitrogen and argon molecular beams scattered off a graphite surface are shown.

ISSN:0034-6748    

DOI:10.1063/1.1144772

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The design, fabrication, and performance of an inductive transducer for a two‐mode resonant mass gravitational radiation detector is described. The design of the transducer is based on a detailed noise model of the detector. The transducer combines a large dynamic mass, a large loaded quality factor, and transformer impedance matching to an integrated dc superconducting quantum interference device (SQUID). The transducer has been in continuous use on the Louisiana State University detector for two years. Its performance on the antenna is reported. TheQ’s of the two resonant modes measure 6.7×106and 2.3×106at a transducer coupling coefficient of 0.74%. The electricalQranges from 2×105to 9×105and is dependent upon trapped magnetic flux in the transducer. The detector’s dominant noise source is the commercial SQUID amplifier, and not losses in the transducer. The predicted sensitivity of the detector equipped with our transducer agrees well with its measured burst strain sensitivity,h≊6×10−19. The detector’s gravitational burst strain sensitivity could be improved to 1.7×10−19by coupling the transducer to a 200ℏ SQUID, while operating at 4 K.

ISSN:0034-6748    

DOI:10.1063/1.1144773

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We discuss the rich dynamics of an inverted pendulum kept from falling over by an anelastic flexure. The anelastic character of the flexure is dramatically emphasized by the pendulum. We report measurements showing internal friction in one flexure to be independent of frequency over a band of three to four decades. This anelastic behavior in flexures can limit the sensitivity in gravitational wave detectors and in other precision measurements.

ISSN:0034-6748    

DOI:10.1063/1.1144774

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The principles of operation of a new pulsed ultrasonic resonance spectrometer are presented. The system incorporates: (1) the use of electromagnetic‐acoustic transducers (EMATs), (2) a method of obtaining acoustic signals similar to the sampled continuous‐wave scheme described by Bolef and Miller, (3) the Clark method of recording line shapes, and (4) a high power gated rf amplifier and a unique implementation of superheterodyne and quadrature phase sensitive detection circuitry. The result is a spectrometer capable of measuring both shear and longitudinal ultrasonic velocities in very thin samples with much greater reproducibility than other pulse methods. It also has applicability in measuring attenuation and other physical properties such as composite material bonding that can be accessed using ultrasound. Experimental results of tests using EMATs in the 0.1–20 MHz range on thin (1.27 and 2.49 mm thick) aluminum sheets are presented.

ISSN:0034-6748    

DOI:10.1063/1.1144776

出版商:AIP    

年代:1994

数据来源: AIP