. The Bell System technical journal . lectron current intothe two beams, the remaining 10 or 15 per cent being lost at the cathode dueto an increase in the space charge which the magnetic field produces. Someof the smaller tubes produce beam currents of more than 5 milliamperes withonly 50 volts on the anode structure, and in some of the tubes with largercathodes beam currents of 50 milliamperes or more are easily magnetic field strengths range from 50 to 300 gauss. 190 RADIAL BEAM VACUUM TUBE m For some applications it is desirable to eliminate one of the two beams andthis may
. The Bell System technical journal . lectron current intothe two beams, the remaining 10 or 15 per cent being lost at the cathode dueto an increase in the space charge which the magnetic field produces. Someof the smaller tubes produce beam currents of more than 5 milliamperes withonly 50 volts on the anode structure, and in some of the tubes with largercathodes beam currents of 50 milliamperes or more are easily magnetic field strengths range from 50 to 300 gauss. 190 RADIAL BEAM VACUUM TUBE m For some applications it is desirable to eliminate one of the two beams andthis may be accomplished by substituting a uniform electrical field in thetube for the cylindrical one described above. The uniform field may beobtained by applying to the anode elements a series of potentials that varyaccording to the sine of the angle taken around the axis. The line joiningthe maximum potentials (+ and —) is maintained parallel to the magneticfield so that on one side of the cathode the potentials are all negative and the. ANODE STRUCTURE Fig. 1.—Elementary tube structure showing focused beams. beam on that side is suppressed. The remaining beam will have somewhatless current than the corresponding one in the cylindrical field but the mag-netic field-strength required for focus is reduced. Cylindrical Electrical Field For the case of the cylindrical electric field the focus is obtained by ap-plying a magnetic field that is strong enough to reduce the radius of curva-ture of the spiral electron trajectories to a small value. There is not ob-tained an electron optical image of the cathode in the usual sense that for 192 BELL SYSTEM TECUXICAL JOURXAL each point on the cathode there is a corresponding point on the image. Tliesharpness of the image may be increased by increasing the strength of themagnetic field and the field required for any degree of focus is not sharplycritical. Figure 2 shows a series of drawings of the various electron images thatwere obtained as
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