摘要:

The principle of spin analysis by means of measurement of the spin dependent absorption of a polarized electron beam is presented. The spin dependent signal is enhanced relative to the spin averaged signal at an energy near which the secondary yield is unity. Both the collected charge method and the zero‐crossing method are described for situations where the polarization can and cannot be reversed. A statistical analysis of the uncertainty in the polarization determination by each method is given. Annealed, evaporated Au films are shown to be suitable for the detecting surface of this spin detector. The figure of merit is derived and found for Au films to be comparable to the very best Mott detectors, but the electron optical acceptance is smaller. The applications for which this simple compact spin detector are especially suited are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1136472

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The performance of the Heliotron‐E neutral beam system, composed of intense cylindrical magnetic multipole bucket sources and beam line facilities, has been investigated. The investigation of the influence of the filament shape on the arc discharge stability shows that a wide‐hairpin shaped filament results in more stable arc discharge without increasing the arc voltage than does a narrow‐hairpin filament. An electrolytic polishing process has been tested for surface treatment of the Molybdenum grid and found to be very effective in reducing the number of conditioning shots. Beam extraction experiments show that a single bucket source can deliver the total beam current of 35 A at the accelerating voltage of 30 kV with the corresponding power transmission efficiency of more than 85% at the focal point of the grid curvature, the minimum beam divergence is less than 1.15° and the proton yield of the source is above 85%. Measurements of the equivalent gas line density in the neutralizer cell suggest the existence of the gas flow process different from a standard vacuum model.

ISSN:0034-6748    

DOI:10.1063/1.1136473

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Hydrogen ion species and discharge characteristics have been compared for two different magnet geometries in a multicusp ion source. One magnet configuration indicated that the H2+ion percentage in the extracted beam could be reduced by eliminating the high energy ionizing electrons near the ion extraction region. To accomplish this and maintain the desired features of both magnet geometries, a magnetic filter was installed near the source exit. With this combined arrangement, we found that the H+ion percentage and discharge condition were much improved and a more uniform density profile across the extraction plane was achieved. The atomic species fraction can then be further enhanced by the addition of low‐energy (∼16 eV) primary electrons into the source plasma chamber.

ISSN:0034-6748    

DOI:10.1063/1.1136474

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Experiments have been performed on a hollow cathode discharge to test the feasibility of an efficient H—production. When a negatively biased converter electrode was placed in the plasma column of the discharge, a current density of up to 2.7 A/cm2was recorded. Strong evidence was found for an H—surface production with a lower limit of about 0.3 A/cm2at the converter.

ISSN:0034-6748    

DOI:10.1063/1.1136475

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The response of a large area (4.6×13 cm) multianode channel electron multiplier array (CEMA) detector to energetic neutrons was investigated. The measured neutron detection efficiencies of the chevron microchannel plate (MCP) were 1.7×10−3and 6.4×10−3counts/neutron, respectively, for 2.5 MeV‐DD and 14 MeV‐DT neutrons. The apparently higher efficiency observed for the 14 MeV neutrons is attributed to neutron‐induced background gamma radiation.

ISSN:0034-6748    

DOI:10.1063/1.1136476

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

We describe a fast electromagnetic valve for generation of a pulsed supersonic molecular beam. The valve produces 70 &mgr;s pulses with typical intensities in the neighborhood of 1×1022molecules sr−1 s−1at frequencies to 35 Hz. It is triggered by a low voltage–low current pulsed power supply which activates externally‐mounted coils, minimizing problems of heat dissipation and electrical and magnetic interference. It also features a corrosion resistant gas reservoir isolated from the driving mechanism by a stainless steel bellows.

ISSN:0034-6748    

DOI:10.1063/1.1136477

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Tunable dye lasers pumped by a transversely excited atmospheric pressure nitrogen laser have been constructed and operated at the repetition rate up to 1.2 kHz with spectral resolution of 0.2 nm. The high repetition rate of the nitrogen laser is made possible through the use of a closed‐cycle transverse gas flow system. The tunable dye lasers are combined with a time‐correlated single photon counting system for the purpose of measuring nanosecond fluorescence decay. The dye laser pulse, which has an intrinsic <400 ps FWHM, is 740 ps when measured by this laser fluorimeter. This value appears to be characteristic of the transit time spread in the photomultiplier tube. The fluorescence decay curve of fluorescein could be measured at a concentration of 3.2×10−11M with a fluorescence spectral resolution of 0.5 nm. The fluorescence lifetimes of fluorescein and benzo(a)pyrene were determined to be 5.05±0.05 and 44.18±0.05 ns, respectively. Comparisons with cavity‐dumped and mode‐locked dye laser excitation systems are described, with emphasis on application to spectroscopic studies.

ISSN:0034-6748    

DOI:10.1063/1.1136478

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A multipass vernier tandem Fabry–Perot interferometer is easily constructed and aligned when the two scanning mirrors are mounted on a common scanning stage. Using such a system we obtain an ultimate resolution of 10−3cm−1and a maximum scanning range, free of overlapping orders, of ≳50 cm−1. Using a 5 plus 4 pass arrangement a contrast ≫10 is obtained which, together with a high overall luminosity, permits simultaneous resolution of both weak spectral features near zero energy shift and low‐frequency Raman bands. In addition to constructional details of this system we discuss the alignment procedure for uniform transmission in tandem operation, and demonstrate how the alignment requirments ultimately limit the performance of any tandem system to an ’’effective finesse’’ of <1000. Spectra showing surface waves in silicon and shear waves in polystyrene illustrate the power of this technique.

ISSN:0034-6748    

DOI:10.1063/1.1136479

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A low surface resistivity, semitransparent photocathode consisting of a palladium–silver–oxygen–cesium layer has been developed. It has been shown to have near infrared (NIR) response which extends to cut‐off wavelengths ∼1.5 &mgr;m. The processing scheme and its effect on the photoemission characteristics of this photocathode are described.

ISSN:0034-6748    

DOI:10.1063/1.1136480

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The efficiency of channel electron multipliers (CEM) falls drastically at energies of the incident electrons greater than a few KeV. For conversion Electron Mo¨ssbauer Spectroscopy (CEMS) the conversion electron energies are far greater than a few KeV, and the CEM efficiency at 7 KeV, for example, is about 10% determined in our laboratory. The efficiency can be improved by increasing the secondary electron yield of the detector cone. To find a coating material, a study of relative secondary electron yields was carried out using a scanning microscope. The results of the study indicate that the detector efficiency should improve by more than a factor of 3 when the cone is coated with MgO. Experimentally, the efficiency of the coated detector is in fact more than 3 times that of the uncoated detector.

ISSN:0034-6748    

DOI:10.1063/1.1136481

出版商:AIP    

年代:1981

数据来源: AIP