摘要:

A CO2laser‐heated sample holder for an EPR spectrometer capable of temperatures above 1200°C is described. Since only the sample is heated, this system permits rapid temperature changes and rotation of the magnet around the sample. The spectra of MgO containing Fe3+and Cr3+at room temperature and 1200°C are presented.

ISSN:0034-6748    

DOI:10.1063/1.1136246

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Laser beam waveguide propagation in frozen gaseous layers at 4.2 K has been investigated. Propagation lengths of ∼1 cm are observed on metallic mirror substrates. Structures enabling efficient laser injection have been devised. A scattering enhancement factor of 34 in a neon matrix is observed in the waveguide mode, as compared with normal front surface illumination.

ISSN:0034-6748    

DOI:10.1063/1.1136247

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The steering of ion beamlets in a two‐stage accelerator has been measured as functions of both aperture displacement and field intensity ratio between extraction and acceleration regions. Three different types of displacement have been investigated; i.e., displacement of (1) plasma grid, (2) gradient grid, or (3) suppressor grid with respect to the other three grids. In each case, the steering angle is found to be linear with the aperture displacement, and independent of final beam energy and beam current. The variation of steering angle with displacement distance is compared with the value predicted by linear theory using thin lens approximation. It is confirmed that they agree well in the case of (3), while they show appreciable differences in the cases of (1) and (2). This is because the lens effect of the gradient grid is weaker than is predicted by the linear theory. The deterioration of beam optics due to steering has not been observed.

ISSN:0034-6748    

DOI:10.1063/1.1136248

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An ion source using the surface ionization process is described. Elements whose ionization potentials are below or around 6 eV may be ionized in the source. The element vapour to be ionized is passed through one or more rhenium grids on which surface ionization occurs. The source is tested for different elements—lithium, indium, rare earths, uranium—the latter corresponding to the upper limit of the ionization potential range. The properties and performance of the source are studied. Currents from many tens of &mgr;A to many mA have been extracted, depending on the source element.

ISSN:0034-6748    

DOI:10.1063/1.1136249

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The design, construction, operation, and performance of a spin polarized electron source utilizing photoemission from negative electron affinity (NEA) GaAs are presented in detail. A polarization of 43±2% is produced using NEA GaAs (100). The polarization can be easily modulated without affecting other characteristics of the electron beam. The electron beam intensity depends on the intensity of the exciting radiation at 1.6 eV; beam currents of 20 &mgr;A/mW are obtained. The source is electron optically bright; the emittance phase space (energy‐area‐solid angle product) is 0.043 eV mm2sr. The light optics, electron optics, and cathode preparation including the GaAs cleaning and activation to NEA are discussed in depth. The origin of the spin polarization in the photoexcitation process is reviewed and new equations describing the depolarization of photoelectrons in the emission process are derived. Quantum yield and polarization measurements for both NEA and positive electron affinity surfaces are reported. The important considerations for interfacing he polarized electron source to an experiment are illustrated by its application to polarized low energy electron diffraction (PLEED). The advantages of this spin polarization modulated electron gun for PLEED are clearly demonstrated by sample PLEED results for W(100) and ferromagnetic Ni(110). A comparison with other polarized electron sources shows that the GaAs spin polarized electron source offers many advantages for a wide range of applications.

ISSN:0034-6748    

DOI:10.1063/1.1136250

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The guiding of a 300 eV divergent hydrogen ion beam by a surface magnetic field generated by samarium cobalt magnets has been investigated. It was found that magnets arranged in a multi‐ring‐cusp configuration produced the best beam transport efficiency.

ISSN:0034-6748    

DOI:10.1063/1.1136251

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A sensor for the measurement of the level and volume of liquids is described. The device employs an array of point sensors, each of which is sensitive to the large changes in impedance between a conductive liquid and the gas above it. The device, in principle, will function in any liquid medium that can conduct an electric current without significantly perturbing that medium. It has in fact been successfully tested in aqueous solutions with conductivity ranging from 9.0×10−7 &OHgr;−1cm−1to 0.38 &OHgr;−1cm−1. The sensor is activated with either AC or DC applied voltage and used with electronic circuits having linear outputs. The sensor’s output is solution independent and a function of the number of conducting electrodes. The precision of the sensor is controlled by the spacing of its electrode array. The linear output of the sensor has been correlated linearly to solution volume regardless of the shape of the solution tank by the use of unequal spacing between the array electrodes. Several designs of sensors with fixed and adjustable precision are described.

ISSN:0034-6748    

DOI:10.1063/1.1136252

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The design and performance of a compact, high precision, capacitive, vapor‐pressure gauge is described. The gauge was constructed using a thin electrodeposited copper diaphragm.

ISSN:0034-6748    

DOI:10.1063/1.1136254

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The efficiency of detecting H and D atoms (E<1 keV) escaping a plasma has been increased by use of a cesium vapor cell to form negative ions by electron attachment collisions. A 30 cm long heat pipe confines the cesium to a localized region. The resulting negative ions are energy analyzed with a single‐channel, parabolic parallel‐plate analyzer and detected by a channel multiplier. The H0conversion efficiency was 10−2at 100 eV, increasing to 3.8×10−2at 500 eV. For a H0energy of 100 eV, the analyzer is 2.5 orders of magnitude more efficient than a comparable N2stripping cell analyzer. The analyzer has been used to measure ion temperatures as low as 30 eV on the EBT Plasma experiment.

ISSN:0034-6748    

DOI:10.1063/1.1136226

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A new method (electronic cascade impaction) of measuring the particle size distribution of aerosols is presented, and an instrument we call an electronic cascade impactor (ECI) which uses the method is described. Aerosol particles are charged in a unipolar charger and enter a multistage cascade impactor. Each collection stage and the final filter is isolated electrically from other parts of the impactor and connected to an electrometer detector. Particles deposit on the collection stages according to their aerodynamic diameters, and from the associated electrical current the deposition rate onto each stage and the particle size distribution can be determined. Calibration data for the ECI are presented. The ECI has been used to study atmospheric aerosol dynamics in real time, and typical data are given. The ECI has proven to be relialbe in several hundred hours of laboratory and field use and other versions employing the same general method should prove useful in a wide variety of measurement situations.

ISSN:0034-6748    

DOI:10.1063/1.1136227

出版商:AIP    

年代:1980

数据来源: AIP