摘要:

A position sensitive photomultiplier of a new concept is presented which is based on the scaling property of the equation of motion describing electrons moving inside electric and magnetic fields. The idea has been fully supported by a test using a prototype having ten stages of specially designed dynodes. A gain of 105–106, and a spatial resolution of ∼3.4 mm (FWHM) in two‐dimensional space have been obtained. The time resolution is comparable or superior to that of most conventional photomultipliers. An example of data handling of signals coming from divided anode cells showed a possibility of reconstructing impact light position with a precision of a few hundred microns.

ISSN:0034-6748    

DOI:10.1063/1.1136601

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A two‐stage light‐gas gun is used for a variety of dynamic physical‐property measurements at 100 GPa (1 Mbar) pressures. The diagnostic system described here consists of a flash x‐ray system to measure impactor velocity, detectors and electronics to measure shock‐wave velocities with subnanosecond resolution, and data–analysis techniques that permit us to measure the tilt and distortion of the impactor and of the resulting shock front. We describe our methods for safely purging hydrogen gas from the system after each shot.

ISSN:0034-6748    

DOI:10.1063/1.1136602

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A description of the design and construction of the first cw far‐infrared laser‐scattering apparatus for the study of the frequency and wavenumber spectra of plasma density fluctuations is given. Scattering results from both a controlled laboratory plasma and the UCLA Microtor tokamak are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1136603

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A fully ionized plasma consisting of 2×1019D+ions with an average energy of 50 eV is produced by irradiating a free‐falling solidD2pellet with a sequence of two laser pulses. An Nd–glass laser pulse first evaporates the pellet and a CO2laser pulse ionizes and heats the resultingD2cloud. This staged laser process couples about 2/3 of the energy of the 70 ns CO2laser spike into the plasma. The techniques for making, dropping, and irradiating the pellet are discussed in detail. The properties of the resulting plasma are described, and a brief account is given of the cusp containment experiment for which this plasma production method was developed.

ISSN:0034-6748    

DOI:10.1063/1.1136604

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The capabilities of the pulsed Langmuir probe technique have been expanded to operate in charged particle environments having spatial and temporal variations in plasma or reference–electrode potentials. This practice is implemented by logic circuitry which tracks local floating potentials and adjusts automatically the sweep center voltage to guarantee a complete current–voltage characteristic with minimum sweep voltage excursion.

ISSN:0034-6748    

DOI:10.1063/1.1136605

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A variable temperature control unit for NMR spectrometers was modified to improve the accuracy of the temperature setting and to suppress the drift and fluctuation of the sample temperature within ±0.1 °C.

ISSN:0034-6748    

DOI:10.1063/1.1136606

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A pulsed NMR spectrometer for cryogenic use is described. It includes an improved coupling scheme which is suitable for installation in most cryostats. An rf preamplifier has been developed which offers wide bandwidth, high gain, low noise and fast recovery (⩽2 &mgr;s). While the spectrometer was designed for a resonance frequency of 27 MHz, extension from 4–100 MHz is discussed. At 27 MHz the bandwidth of the free‐induction decay is 1 MHz, and the dead time, after the end of the rf pulse, is 3.6 ms. Techniques are presented for reducing the dead time, the noise, and the amplitude of ground loops as well as extending the signal bandwidth and dynamic range.

ISSN:0034-6748    

DOI:10.1063/1.1136607

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A fast recovery, low‐noise receiver designed for use in pulsed NMR, especially high‐resolution multiple‐pulse NMR, is described. This receiver is easy to build from commercially available parts. Passive (but biased) voltage limiters placed before each amplifier in the cascade prevent any of the amplifiers from saturating, so it is only the limiters that ever saturate. Recovery times of 850 ns and 2.35 ms are measured with a 50‐W load and a highQ(Q= 141) resonant sample probe in the circuit, respectively. The receiver has a measured overall noise figure of 6.5 dB, including crossed diodes and filter on the input. An example of the use of the receiver to measure a short proton free‐induction decay at 186.5 MHz is also shown.

ISSN:0034-6748    

DOI:10.1063/1.1136608

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The design and performance of a 24‐channel fluorescence detection system for use in x‐ray absorption spectroscopy are discussed, and comparisons are drawn with other detection systems currently in use. Each channel of the current system consists of a NaI scintillation detector with a filter and collimator arrangement designed to reduce the scatter and filter fluorescence background. Given a sufficiently intense and stable x‐ray source, this apparatus can record a useful EXAFS spectrum for an element (Z⩾23) at 100 ppm concentration in approximately 30 minutes. The new design permits the study of plate‐like samples (such as molybdenum enzyme solutions) unsuitable for previously described slit assemblies. Breaking the detection system up into discrete elements also allows (1) optimization of filter thickness for each direction, (2) use of a weighting scheme to optimize the total S/N, and (3) operation at high total count rates, while retaining the advantages of pulse counting electronics. The relative merits of filters and crystal monchromators are discussed quantitatively, using the two criteria of efficiency and selectivity. It is shown that practical filters and barrel monochromators give similar performance over a 100‐fold concentration range, for a given solid angle, and that the 20‐fold solid angle advantage of the multielement approach makes it the design of choice for many cases. Finally, the construction of an array of solid‐state detectors with the appropriate filters and collimating elements is proposed as a device capable of yielding unprecedented performance in x‐ray absorption spectroscopy.

ISSN:0034-6748    

DOI:10.1063/1.1136591

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The well‐known FFT (Fast Fourier Transform) algorithm of Cooley and Tukey has found widespread application in the field of numerical Fourier transforms and related problems. Nevertheless, the FFT algorithm has to be treated with caution, because in order to avoid aliasing in the frequency domain, it is restricted to the transform of bandlimited functions. A new algorithm has been developed that still has the FFT characteristics, but that is no longer confined to bandlimited functions. The new algorithm has been tested in the case of MBRS (Molecular Beam Relaxation Spectroscopy) linear system analysis.

ISSN:0034-6748    

DOI:10.1063/1.1136592

出版商:AIP    

年代:1981

数据来源: AIP