| 摘要 |
<p>579,371. Discharge apparatus. STANDARD TELEPHONES & CABLES, Ltd. June 11, 1943, No. 9486. Convention date, June 15, 1942. [Class 39 (i)] Spreading of an electron beam by space charge repulsion within a long conducting tube 14, such as the drift space of a velocity-modulation device, is prevented by trapping within the tube a sufficient number of positive ions to neutralize the space charge of the electrons. It is shown that there is sufficient gas present, even in commercial vacua of 10<-6> to 10<-9> mms. of mercury, to produce a sufficient number of ions, and the previous failure of gas focusing at those pressures is stated to have been due to the leakage of positive ions from the ends of the tube under the influence of the negative gradient existing between the edge and the centre of the beam. If one or both of the electrodes 13, 15 is held at a positive voltage slightly greater than this negative gradient, the leakage is prevented and the space charge of the beam is neutralized. The end facing electrode 13 is most prone to leakage, owing to the proximity of the cathode 10 and first anode 11. As shown, both electrodes are joined together to a source V3, which may be a battery or a dropping resistance operating on the electron current collected by electrode 14. V3 is 10-15 volts for a 6000 volt, 50 milliamp. beam, but nearly 1000 volts for a 5 amp. bearii ; it is proportional to the current and inversely proportional to the voltage. At high vacua, care must be taken that the envelope is of sufficient size to provide an adequate volume of gas, according 'to a formula which is given ; at such vacua almost all the gas molecules will be concentrated as ions in tube 14, the rest of the envelope being nearly empty.</p> |
