摘要:

A double magnetic suspension is described in which the lower rotor is magnetically suspended from the upper rotor which in turn is magnetically suspended. The upper rotor may be made to surround the lower (or inner) rotor. Consequently, the effective magnetic suspension and vacuum chamber surrounding the inner rotor may be made to spin at approximately the same speed as the inner rotor (or within a few rps). This greatly reduces the rotor's deceleration when it is coasting freely.

ISSN:0034-6748    

DOI:10.1063/1.1718136

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Pulse transformers capable of matching the low impedance load characteristics of integrated circuits are discussed. Experimental models constructed by winding transmission lines on cores were found to pass pulses with rise times between 1 and 2 nsec and with little droop for pulses of 300‐nsec width. A transformer in liquid helium transmitted a 1‐&mgr;sec pulse with less than 10% droop.

ISSN:0034-6748    

DOI:10.1063/1.1718137

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The excellent sensitivity of a permanent‐magnet type magnetic suspension balance was utilized in a simple method for measuring the resistivities of bulk quantities of metals and alloys, based on the Arago effect. An estimated accuracy of 2% was obtained on samples 2.85 cm in diameter in the range 10−4to 10−6&OHgr;‐cm. Skin effects were negligible in samples this size, as the frequency of the excitation field was less than 1 cps.

ISSN:0034-6748    

DOI:10.1063/1.1718138

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The design, construction, and theory of a light probe for the measurement of turbulent concentration fluctuations are given. Consideration is given to the measurement of the mean concentration, as well as the necessary corrections for noise. The limitations associated with the sample volume size, frequency response, and signal‐to‐noise ratio are discussed. Recommendations for improvement beyond the present sample volume of 5.6×10−4cc, and a frequency response of 10 000 cps are given.

ISSN:0034-6748    

DOI:10.1063/1.1718139

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

It has been observed that the forward voltage drop, at constant forward current, of a GaAs diffused p‐n junction varies almost linearly with temperature from 2.0°K to above 300°K. Since carrier ``freeze‐out'' at low temperatures is not observed, these junctions make excellent cryometers. In addition, these diodes exhibit good repeatability on temperature cycling and an insensitivity to magnetic fields. The sensitivity of the devices measured near room temperature is &Dgr;V/&Dgr;T≈−3.5 mV/°C,If=0.1 &mgr;A; &Dgr;V/&Dgr;T≈−2.0 mV/°C,If=1.0 mA. The sensitivity decreases slowly toward lower temperatures and at liquid helium is −1.5 mV/°C and is essentially independent of current. This high and nearly uniform sensitivity over such a wide temperature range is unique among low temperature thermometers. The shape of the temperature‐voltage characteristic, with current as a parameter, is explained quite satisfactorily forT>50°K by assuming that the device conducts primarily recombination‐generation currents, according to the theory of Sah, Noyce, and Shockley. Below 50°K certain deviations from this theory occur, but the applicability of the devices to thermometry is not affected. It appears likely that these devices are capable of a temperature resolution of at least ±0.01°C over the entire range investigated, using ordinary current sources and precision potentiometers.

ISSN:0034-6748    

DOI:10.1063/1.1718140

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The theory of the deflecting or hybrid electromagnetic mode in an iris‐loaded waveguide is presented. The dispersion diagrams of the two lowest passbands are computed and compared with experimental data. TM1and TE1modes are no longer independent solutions of Maxwell's equations if the phase velocity equals the velocity of light. In this case the most general field expressions require the use of hybrid solutions, which are derived from Hertzian vectors with transverse components. The hybrid solutions, in contrast to transverse solutions, are able to give a transverse deflection to synchronous, ultrarelativistic particles. The fields in the slot region and the center region of the iris‐loaded waveguide are represented as Fourier series. Matching the four tangential field components results ultimately in an infinite matrix. A vanishing determinant constitutes the relationship between wave number, phase velocity, and geometry. A simple first‐order approximation is derived and interpreted.

ISSN:0034-6748    

DOI:10.1063/1.1718141

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A control system is described for regulating the temperature‐limited emission current from the filament of an ionization gauge tube. A dc transistor circuit is used with a lamp and a photosensitive resistor to provide electrical isolation between the control and the controlled circuits. Emission currents from 10 to 0.5 mA can be maintained with a stability of better than 0.05% with the system.

ISSN:0034-6748    

DOI:10.1063/1.1718142

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A differential calorimeter operating by the method of quantitative differential thermal analysis was developed to study stored‐energy release spectra in metals. The method involves the heating of a test specimen and a fully annealed reference specimen by heat transfer from a uniformly heated calorimeter block programmed to a reproducible increase in temperature with time. The initial stored‐energy release run is followed by a base‐line run under identical conditions to compensate for differences in thermal coupling of the specimens to the block. The most stable conditions of thermal coupling have been obtained by the use of cells to contain the specimens and by continuous purification of the helium used as a thermal‐exchange gas. Calibration experiments on the heat of fusion of lead were carried out to evaluate the thermal coupling between specimens and to confirm the calorimetric technique. Typical results for high purity copper deformed in compression are given to demonstrate the existence of an appreciable grain‐size effect on the stored‐energy release; the precision is approximately ±0.4 cal/g‐atom for total stored energies of the order of 5 cal/g‐atom.

ISSN:0034-6748    

DOI:10.1063/1.1718143

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

This paper describes several versions of a single, simple device to provide rotary and linear motion within a vacuum chamber without causing even a temporary rise in pressure. Through the use of metal gaskets, bellows, seals, and magnetic couplings, many difficulties arising from the transmission of rotary and linear motion through vacuum‐chamber walls are overcome. In the device described, freedom of rotation is unlimited in either direction, but linear movement is limited to 2 in. Actually, stroke limits are determined by choice of bellows and space considerations. The device makes use of magnetic coupling for the rotary component, and a bellows‐sealed, lead‐screw mechanism controls linear movement.

ISSN:0034-6748    

DOI:10.1063/1.1718144

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

An improved acid polishing machine for dislocation‐free polishing of copper is reported and its operation described. The main improvements are a compact axial tilt device, provision for rapid interruption of the polishing and inspection of the sample, and a more rigid shaft confinement and alignment. Some useful aids in the chemical polishing techniques are also reported.

ISSN:0034-6748    

DOI:10.1063/1.1718145

出版商:AIP    

年代:1963

数据来源: AIP