With neat cross sectional constructional details,write effect of magnetic and electric field in magnetron
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1)When magnetic & electric fields act simultaneously upon the electron,its path can have any of a number of shapes dictated by the resistive strengths of the mutually perpendicular electric & magnetic fields. 2)Some of these electron paths are shown in figure in the absence of oscillations in a magnetron in which the electric field is constant and radial and the axial magnetic field can have any number of values. 3)When the magnetic field is zero,the electron goes straight from the cathode to anode accelerating all the time under the force of the radial electric field. 4)This is indicated by path x in figure. 5)When the magnetic field has a small but definite strength ,it will exert a lateral force on the electron,bending its path to the left as shown in figure by path y,that the electrons motion is no longer rectilinear. 6)As the electron approaches the anode its velocity continues to increase radially as it is accelerating. 7)The effect of magnetic field upon it increases also. 8)It is possible to make the magnetic field so strong the electrons will not reach the anode at all. 9)The magnetic field required to return electrons to the cathode after they have just grazed the anode it is called the cut off field.The resulting path is z shown in figure. 10)Knowing the value of the required magnetic field strength is important because this cut off field just reduces anode current to zero in the absence of oscillations. 11)If the magnetic field is stronger still,the electron path as shown will be more curved still and the electrons will return to the cathode even sooner(only to be reemitted) 12)All these paths are naturally changed by the presence of any RF field due to the oscillations but the state of affairs without the RF field must still be appreciated for two reasons. a)First it leads to the understanding of the oscillating magnetron. b)Second it draws attention to the fact that unless a magnetron is oscillating ,all the electrons will be returned to the cathode ,which will overheat and ruin the tube . 13)This happens because in practice the applied magnetic field is greatly in excess of the cutoff field.
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