摘要:

A systematic optimization of the components of our polarized electron source has markedly improved its long term stability over earlier versions. The major factors shortening the lifetime of the source have been identified. The essential parts of the spin polarized electron source, such as the vacuum system, crystal holder, cleaving mechanism, caesium dispenser, oxygen admittance tube, and computer control activation features are discussed. The lifetime of the source now exceeds 500 h with a constant polarization of 28.5&percent;. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147979

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A beam chopping system for a cyclotron is in operation at the JAERI cyclotron facility. A combination of a pulse voltage chopper in the injection line and a sinusoidal voltage chopper after the exit of the cyclotron is adopted to produce beam pulses spaced at 1 &mgr;s–1 ms intervals from natural cyclotron beams. The chopping system was designed according to a simple formulation of the chopping process in which the multiturn extraction was taken into account. Performance of the chopping system was experimentally proved to satisfy requirements of the design. In actual operation to produce beam pulses at long intervals, however, the number of the multiturn extraction is usually larger than the assumed value in the design because of a large phase acceptance of the cyclotron. Careful tuning of the acceleration phase width or the base magnetic field of the cyclotron is necessary to reduce it. It is essential to strictly define the acceleration phase of injected beams in the central region of the cyclotron to improve this situation. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147980

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Two natural diamond detectors (NDDs) operating at room temperature were used for Fusion Neutronics Source (FNS) deuterium–tritium (DT) neutron spectra measurements at different points around the tritium target and for different deuteron beam energies. Energy resolution of both NDDs were measured, with values 1.95&percent; and 2.8&percent;. Due to the higher energy resolution of one of the two NDDs studied it was possible to measure the shape of the DT neutron energy distribution and its broadening due to deuteron scattering inside the target. The influence of pulse pileup on the energy resolution of the combined system (NDD+electronics) at count rates up to 3.8×105counts/s was investigated. A 3.58&percent; energy resolution for the spectrometric system based on NDD and a 0.25 &mgr;s shaping time amplifier has been measured at a count rate of 5.7×105counts/s. It is shown that special development of a fast pulse signal processor is necessary for NDD based spectrometry at count rates of approximately 106counts/s. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148001

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We describe an instrument used to measure the light transmitted through a large scalelength plasma. Light that passes through the plasma scatters diffusely from a frosted silica scatter plate. An optical system images this scattered light onto several detectors which measure its spatial and temporal characteristics. Low and high dispersion spectral measurements of the transmitted light are made using optical fiber collectors placed behind the scatter plate. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147981

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A filter using a transmission line formed by a cascade connection of invertedL-type networks has been developed to reject the distortion of the probe characteristics by rf (radio-frequency) noise. Each inverseLnetwork consists of two coaxial cables with the same physical constant and length. The filter can remove discrete frequency components including the fundamental and harmonic components, the cut-off frequencies being determined by the distributed circuit constant and the length of the cables. By inserting different kinds of the network in cascade, many noise components associated with the rf frequency can be eliminated at the end section of the filter. Experiments have been performed in rf plasmas by inserting three kinds of invertedLnetworks with the frequencyf(13.56 MHz),2 fand4fas the cut-off frequency. Distortion free probe characteristics have been obtained, from which accurate determination of plasma parameter such as the electron energy distribution is possible. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147982

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Crystal and synthetic multilayer diffractors, deployed either as flat Bragg reflectors, or curved, as in the Johann configuration, are used to study the spectrum of COMPASS-D and other tokamaks in the wavelength region of 1–100 Å. In this article, we concentrate on the measurement of absolute photon fluxes and the derivation of volume emissivities of the lines and continua in the x-ray region. The sensitivities of these instruments to absolute photon flux have been constructedab initiofrom the individual component efficiencies, including published values of the diffractor reflectivities, which have been checked or supplemented by measurements using a double-axis goniometer or from line branching ratios. For those tokamak plasmas, where the elemental abundances and effective ion charge are documented, the x-ray continuum intensity itself has been used as a calibration source to derive absolute instrument sensitivity, in reasonable agreement with theab initiomethod. In the COMPASS-D Tokamak, changes in the effective ion charge state,Zeff, have been derived for different operating conditions, from the absolute intensity of the continuum at ∼4 Å. From the radiances of the line emission, changes in the absolute level of impurities following “boronization” of the vacuum vessel have also been documented. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147983

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The authors have studied a system, consisting of superconducting and ferromagnetic cylinders, and a magnetic field sensor for selectively detecting a magnetic dipole parallel to the extension of the axis of the cylinders. The superconducting cylinder has an open slit in its side so that the magnetic field from the dipole can be measured selectively according to its diamagnetic characteristics. The magnetic fields detected by the sensor are estimated with the aid of magnetic field analysis. It may be possible to use the system for positioning of one or two parallel dipoles. The system will be useful for nondestructive testing of metallic materials. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147984

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This article presents a trial for deriving a thermal transfer model of a thermostat housing a heat source generating several watts and achieving high temperature stabilization. It is intended for investigating the open-loop linearity of operational amplifiers labeled as high precision or low noise and their noise characteristics. This thermostat is built up with a double-jacket constructed with a copper plate of 10 mm thickness and an approach of deriving a lumped parameter model to each jacket on the temperature control is presented. The temperature stability of the order of3×10−5°C per 1°C temperature change in the air outside in 1 h is realized in the inner jacket. The linearity is measurable and it is clarified that amplifiers are classified into three groups. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147985

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The role of speckles in generating erroneous laser vibrometer signals in the case of a beam undergoing flexural and longitudinal motion is investigated. As illustrated by experimental results, spurious signals, brought about predominantly by flexural motion in this case, can be removed by increasing the speckle size at the photodetector plane. The approach can provide a simple but effective remedy to the pseudovibration problem. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147986

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have developed a practical heating holder for the field-emission scanning electron microscope (FESEM, JSM-6000F) to study and apply the specimen heated and electron beam induced conductivity. The design is described in detail. A surface temperature up to 943 K is achieved. The temperature fluctuation is less than 0.5&percent;/h at about 20 min after the heating up to 943 K, and the thermal drift is suppressed to less than 5 nm/min up to 873 K. The temperature of the observation area is proportional to the input power of the heater up to about 700 K. The charging on a nonconducting surface such as porous pipe glass can be prevented at a surface temperature above about 673 K. It is demonstrated that this is useful to the high resolution observations of the nonconducting surfaces. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147987

出版商:AIP    

年代:1997

数据来源: AIP