Volume 12, Issue 9, September 1941
Index of content:
12(1941); http://dx.doi.org/10.1063/1.1769916View Description Hide Description
Small steel rotors have been suspended by an axial magnetic suspension using inductance control to effect vertical stabilization. They have been spun in vacuum by means of a rotating magnetic field having a frequency of the order of 100 kilocycles. Rod rotors tended to precess in the absence of horizontal damping. This was remedied by placing a copper block just above the upper end of the rod. A tapered length of drill rod ⅞″ long (max. diam. ) reached 36,000 r.p.s. before bending double due to the effect of centrifugal force. Steel balls have the advantage of no precession; however, on starting to spin they soon built up a circular orbital motion of increasing amplitude. A damping needle situated outside the vacuum system and immersed in oil was found to eliminate this motion satisfactorily. A diam. ball has been spun to 110,000 r.p.s. This corresponds to a centripetal acceleration at the periphery of 58×106 gravity. The rate of free deceleration at 106,000 r.p.s. was about 1 percent per hour. Rotational speed was measured by observing the rotor in stroboscopic light whose frequency could be matched with the speed of the rotor.
12(1941); http://dx.doi.org/10.1063/1.1769917View Description Hide Description
The complete constructional details for a 180° Dempster type mass spectrometer are given. The ions have a radius of curvature of 15 cm, and are accelerated through a potential of 2000 volts. Circuit diagrams for the voltage stabilizers and magnet current stabilizer are included.
12(1941); http://dx.doi.org/10.1063/1.1769918View Description Hide Description
This paper describes a discriminator circuit which automatically compensates for the changes due to thermal effects in the capacitive and inductive reactances of a quarter‐wave‐length dee line of a cyclotron. The unit thereby contributes to smoother power input.
12(1941); http://dx.doi.org/10.1063/1.1769919View Description Hide Description
An amplifier which is based on the scheme of heterodyning the signal to be measured with a locking‐in voltage of the same frequency, as proposed originally by Cosens, is described and its characteristics are discussed. The particular design used, with the locking‐in voltage applied to the screen grids of two pentodes, possesses a distinct advantage over earlier instruments because the tubes operate on a linear portion of their transfer characteristics, reducing harmonic response, and also because the main power supply is direct current, so that there is little drain on the control supply. It is found that the response band can be given a width of the order of one cycle per second without undue inconvenience or expense.