 I am Rohini Mirgu working as associate professor at Walshian Institute of Technology and topic is magnetron is construction and working. Learning outcomes at the end of this video you will be able to draw and explain construction of cavity magnetron. You will be able to justify the statement how magnetron works as an oscillator. The contents are introduction to the magnetron, types of magnetrons, the construction of cavity magnetron and working of cavity magnetron and summary of whatever we have explained in this video. Magnetron is a self-excited oscillator. It is a cross-filled tube called M-type tube. The direction of electric field that accelerates the electron beam is perpendicular to the axis of magnetic field. That means electric field and magnetic field are perpendicular to each other so that magnetron is called as cross-filled tube. Magnetrons are used in radar transmitters and in microwave ovens. So one of the famous application of magnetron is in microwave ovens. Magnetrons are characterized by high peak power, small size, efficient operation and low operating voltage. Types of magnetrons, split anode or negative resistance magnetron that is the first type. Second is cyclotron, frequency magnetron, third is traveling wave or cavity magnetron. Can you write the answer to the question what is the meaning of negative resistance? Negative resistance in electronics, negative resistance NR is the property of some electrical circuits and devices in which an increase in voltage across the device terminals results in decrease in electric current through it. That means voltage is increasing, expected is current should also increase but in this case if voltage is increasing current will be reducing. Some special such devices are there those are called as negative resistance devices. This property is used in electronic oscillators and amplifiers at microwave frequencies. Split anode or negative resistance magnetron. This magnetron make use of negative resistance between two anode segments. It has low efficiency and useful for frequencies which are less than 500 megahertz. What is the meaning of cyclotron, cyclotron frequency magnetron? So can you write the answer for the question what is the meaning of cyclotron? So here is the answer. A cyclotron is a type of particle accelerator in which charged particles accelerate outwards from the center along a spiral path. And particles are taking a spiral path and that path is called as a cyclotron. So cyclotron frequency magnetron the frequency of operation depends on synchronism between the alternating component of electric field and electrons oscillating in a direction parallel to this field. It is useful for frequencies greater than 100 megahertz. What is a microwave cavity, traveling wave or a cavity magnetron? So can you tell what is a microwave cavity? The answer is a microwave cavity is a closed metal structure. The cavity confines electromagnetic fields in the microwave spectrum and acts as a special type of resonator. The structure is either hollow or filled with dielectric material. Cavity or traveling wave magnetron it works on the principle of interaction of electrons with rotating electromagnetic field of constant velocity. Now we are going to see in detail the cavity magnetron, its construction and working. The components in the construction are cathode, anode cavities, Peruvian magnets producing magnetic field, RF out using coupling probe. Cavity magnetron you can see here this is a cavity magnetron. As we say there is a cathode at the center surrounding to this are the anode cavities these are the anode blocks you can see these are the circular cavities around it. This is the RF out coaxial cable with which we are taking output RF out and perpendicular is the magnetic field. Magnetic field is perpendicular to the direction of electric field. So now you can see here at the center there is a cavity this is the anode and north and south poles that means magnetic field is perpendicular and radial will be the electric field. So it is called as a cross-filled tube. So here the same diagram is shown at the center there is a cathode surrounding is the anode cavities these are the cooling fans and here you can see the magnets these magnets are producing the magnetic field and from here microwave energy is taken out and here you can see the interaction is taking place of with the electron and the RF field. Magnetic magnetron working electron trajectories in the absence of magnetic field B equal to 0. When no magnetic field is applied and only voltage is applied between anode and cathode the electrons are emitted from cathode and moving towards anode by straight path. When we when we apply a small magnetic field which is B less than BC the electron instead of moving along the straight path will take a curvature as shown by path B and this space between anode and cathode is called as the interaction space these are the anode cavities this is a cathode. So it is taking a curvature path for applied magnetic field which is B less than BC. Now here the importance comes of B equal to BC which is called as a cut-off magnetic flux density where the electron is emitted from cathode moving towards the anode taking a longer distance and touching the anode and returning back. So electrons stays for more time in the interaction space and these electrons we want for oscillations these electrons help in oscillations. So we apply B equal to BC in order to produce oscillations in the magnetron. If we increase the magnetic flux density beyond BC, B greater than BC the electron curves curvature is more and it bends and will return back early to the cathode and such electrons are of no use these electrons causes back heating. We do not want such type of electrons which are not helpful for oscillation. For oscillation the helpful electrons are these one. So electron trajectories are again shown here the electron taking straight path when B equal to 0 when small amount of B is applied B less than BC the electron is taking this path when B equal to BC the electron is taking this red colored path and when B greater than BC the electron is taking this path back heating. So we do not want all these electrons we expect mostly the electrons which are taking this red colored path. There is a small amount of RF field available inside the interaction space and the electron is emitted from cathode moving towards anode and when this electron is trying to move towards anode if you are taking a smaller path and again returning back this electron is not interacting at all with the RF here but the electron which is taking longer path is interacting with the RF field in such a way that the electron gives its energy to RF field. As the electron gives its energy to RF field the oscillation starts inside the cavity and the cavity oscillates. So these electrons are called favorable electrons which are taking longer path and giving its energy to RF whereas the electrons which are not provide a helping in the oscillations are called as unfavorable electrons. All such favorable electrons forms electron cloud or spoke. All such favorable electrons form electron cloud or spoke but for the two anodes one electron cloud is formed like for alternating anode cavities one electron cloud or a spoke is formed and all this electron clouds or spokes rotates inside the interaction space. And this is called as a phase focusing effect. In summary this is the magnetron how it actually looks like. In summary the electrons are emitted by cathode they move towards anode. The interaction takes place in the interaction space. The interaction between the electron and the RF field takes place. Interaction between electron and RF field takes place in such a way that all favorable electrons form electron bunch or spoke. These bunches rotate in the interaction space as these bunches rotate in the interaction space as we have shown here as these bunches rotate in the interaction space this is called as phase focusing effect. So set in by this method the magnetron oscillates and magnetron works as an oscillator. The basic application of magnetron is in microwave ovens really helpful as a microwave source in microwave ovens. These are the references used. Thank you for listening my video.