摘要:

The development of a captive sample microreactor, its integration into a video microscopy system, and its use for studies on coal pyrolysis are presented. The reactor can operate as a high‐temperature microscope hot stage allowing for direct viewing of the pyrolysis process under an optical microscope equipped with a video camera. By using a microcomputer and specialized video equipment, process information such as elapsed time and reactor temperature are superimposed in alphanumeric form on the video signal. Complete histories of fast experiments can thus be stored on videotape for postprocessing and analysis of transient phenomena. The reactor is controlled via a microcomputer with custom‐built analog interfaces. A digital algorithm combining internal model control and feedback control is implemented for accurate programming of the reactor temperature. Heating rates as high as 1000 °C/s can be achieved with good reproducibility. Some experimental results are presented to outline the capabilities of the apparatus and to suggest other potential applications.

ISSN:0034-6748    

DOI:10.1063/1.1140261

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A microscope‐based fluorescence correlation apparatus for diffusivity measurements is described. The use of optical fibers offers not only the advantage of setup flexibility but also an improved quality of the illuminating beam. The achieved beam radius is as small as 0.4 &mgr;m, and the size of the observed volume amounts to only 10 &mgr;m3. The measured correlation functions obtained for noninteracting particles having diffusion coefficients in a large range form 10−12to 5×10−10m2/s are very well fitted by the theoretically expected hyperbolas.

ISSN:0034-6748    

DOI:10.1063/1.1139837

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A prototype instrument for making contactless measurements of free carrier concentration as a function of the surface coordinates has been developed. The instrument requires minimal sample preparation and the measurements are nondestructive. Measurements are based upon the free carrier absorption of photons at a wavelength of 10.6 &mgr;m. The measurement sensitivity is determined by the ability to resolve small variations in the transmitted wave. These variations can be significantly influenced by changes in sample thickness. A scheme has been devised which eliminates thickness variations by rotating the sample through small angles to achieve a transmission maximum at each data point. Preliminary results indicate that system drift limits the sensitivity of the prototype system to measurements of the order of 1015free carriers per cm3. Data on CdS samples indicate accurate measurements for free electron densities greater that 1016cm−3. Refinements in the instrument should reduce this level to 1014cm−3or less.

ISSN:0034-6748    

DOI:10.1063/1.1139838

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Large area 10×40‐cm Lawrence Berkeley Laboratory ‘‘field‐free’’ ion sources were used during the first 2.5 yr of the neutral beam injection heating experiment on the tokamak fusion test reactor. Although these ion sources were located inside magnetic shielding structures, interference from tokamak magnetic fields prevented beam operation under certain conditions when using hydrogen. The fields causing this interference have been studied, and modifications which allow operation of such sources in these fields have been made.

ISSN:0034-6748    

DOI:10.1063/1.1139839

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A time‐of‐flight analyzer has successfully been used to measure the extracted charge‐state distribution and impurity level of an ECRH mirror plasma. End‐loss temperatures for each ion species have been determined from the rise time of the analyzer output pulses. Ions entering the line‐of‐sight device are first accelerated by a two‐aperture lens and are then focused with an einzel lens. Electrostatic deflection plates chop the ion beam into short pulses which travel down a 1.20‐m tube to an electron multiplier. Ion spectra are typically summed at a rate of 1 kHz using a hardware signal averager.

ISSN:0034-6748    

DOI:10.1063/1.1139840

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A method is presented which allows a determination of electron density profiles in the plasma boundary of a fusion device up to some 1013cm−3within about 100 &mgr;s. For this purpose, the complete attenuation of an injected lithium beam is determined by measuring its optical emission profile. The beam is generated by a ruby laser, which ablates small portions of a LiF coating with a thickness of about 1000 A˚ from the rear side of a glass substrate. The produced lithium atoms have velocities of 1×106cm/s and can penetrate into the plasma untilne×l≊1×1013cm−2. For the measurement of the optical emission profile of the excited lithium atoms, a silicon photodiode array camera is used. The emission profile is then converted into an electron density profile with the help of the ionization rate for lithium atoms by electron impact.

ISSN:0034-6748    

DOI:10.1063/1.1139841

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The fluence of high‐energy (>14 MeV) ‘‘secondary’’ neutrons, produced in D–T reactions involving suprathermal fuel ions created by elastic scattering with 14‐MeV ‘‘primary’’ neutrons, yields information about the fuel density‐radius product (&rgr;R) and the hydrodynamic stability of inertial‐confinement fusion (ICF) targets. The suprathermal ions, produced in proportion to the fuel &rgr;R, create secondary neutrons with energies ≤30 MeV when fusing with a thermal ion. The ratio of secondary to primary neutrons determines the mean fuel &rgr;R. Since secondary neutrons, which are mainly formed near the fuel tamper interface with energies >24 MeV, are radially directed, the detection of their angular distribution provides a unique measurement of the deviation from spherical geometry of the fuel &rgr;R. Valid for fuel &rgr;R>0.1 g/cm2and D–T yield above 1014, this diagnostic would be valuable in upcoming ICF experiments.

ISSN:0034-6748    

DOI:10.1063/1.1139842

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

High‐precision Hall probes and B‐dot probes are described. These probes are designed to measure magnetic field changes of a few gauss on a time scale of 2–3 s in a 5‐kG background field. A digital, drift‐free sample‐and‐hold circuit is used with the Hall probe to subtract the vacuum field.

ISSN:0034-6748    

DOI:10.1063/1.1139843

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A low‐pressure pneumatically controlled stressing mechanism for investigating the effects of uniaxial stress on the magnetostrictive and magnetomechanical behavior of 2% Mn pipeline steel is described. The apparatus uses microcomputer control and data logging. It has been developed to allow convenient stress cycling so that reversible and irreversible changes can be separated. Irreversible stress‐induced changes in magnetization are toward the anhysteretic, in accordance with Jiles–Atherton theory. Reversible magnetomechanical effects may be correlated with reversible magnetostrictive effects.

ISSN:0034-6748    

DOI:10.1063/1.1139844

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

High resolution in a cryogenic current comparator (CCC) can be attained with an unmodified commercial SQUID by involving geometrical aspects in the design considerations. A description of a CCC is given whose measured sensitivity (one flux quantum &fgr;0per 2.7‐&mgr;A turn) agrees well with the calculated value, being high enough to meet the requirements for high‐precision measurements of the quantized Hall resistance.

ISSN:0034-6748    

DOI:10.1063/1.1139845

出版商:AIP    

年代:1988

数据来源: AIP