 I am talking on two-cavity-clistron construction and working, myself Dr. Rohini Mergu, working as associate professor at Vulture Institute of Technology, Sulapu. Let us look for two-cavity-clistron. Learning outcome, at the end of this video you will be able to draw and explain construction of two-cavity-clistron amplifier, you will be able to sketch the Applegate diagram and explain the working of two-cavity-clistron amplifier with the help of Applegate diagram. Contains, these are the contents of my video, introduction. Clistron is a microwave active device. It is invented by Russell Varian and S.P. Varian at Stanford University in 1939. It is an amplifier tube used to amplify weak microwave energy, which is provided by radio frequency exciter. So this weak microwave energy can be amplified using Clistron amplifier to a high power level for radar transmitter. So in radar transmitters, the amplifier used is a Clistron. It is characterized by a high power, large size, high stability, high gain, high operating voltages. It is a linear beam tube called O-type tube. Linear beam tube has having the, why it is called as a linear beam tube because the direction of electric field accelerates the electron beam. Clistron has applications in Doppler radar, Wether radar, pulse compression applications. First let us look at what is a microwave cavity. Microwave cavity, 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. Construction, in the construction it includes the electron gun, cathode, collector, focusing anodes, two cavities which are namely buncher and catcher cavity, a drift space, RF-in at buncher cavity and RF-out at catcher cavity. So look at the diagram, this is the diagram of the two cavity Clistron amplifier. This is cavity one, this is cavity two. The first cavity is called as a buncher cavity, second cavity is called as a catcher cavity. The small microwave energy which is need to be amplified is given to the buncher cavity with RF-in here and the amplified microwave energy is taken from the catcher cavity which is microwave output here. This is the heater and this is the cathode. From cathode the electrons are emitted and moving towards collector. These are the focusing anodes. You can see here the supply is shown with negative and positive towards the anode. The distance between the two cavities is called as the drift space. So what happens in between these two cavities is the velocity modulation process. The density of electrons is going to change that I am going to talk further in the working of two cavity Clistron amplifier working. Electrons are emitted by cathode as I shown here. The electrons are emitted from cathode and moving towards the collector, collected by the collector. There are two cavities as I have shown, buncher cavity and catcher cavity. Drift space is the space between the two cavities and the interaction between the RF signal and electrons takes place in the drift space. Velocity modulation takes place at buncher cavity and current modulation takes place at catcher cavity. So here velocity modulation takes place in this drift space and at the catcher cavity current modulation takes place. And electron bunching process can be explained by the Applegate diagram which I am showing further. There are the two cavities and this is the drift space between the two. The interaction takes place between these two here. This is the RF cycle which is provided here and the amplified output is obtained at this point. Now this is the Applegate diagram. This is RF input provided at the input cavity which is also called as a buncher cavity and RF output is obtained at catcher cavity. So this is the electrons. The electrons are emitted at the reference or at the zeroth of the RF cycle are called reference electron which moves with some reference velocity v equal to v0 and reaches at the buncher cavity sorry reaches at the these electron reaches at the catcher cavity at this point. The electron which is emitted late after reference electron is called as a late electron which moves with some increased velocity. Why the velocity is increased because the it is emitted at the positive cycle of the RF. So which moves with the velocity greater than v greater than v0 this is the case. Now the electron which is emitted early is called as the EE that is the early electron it is emitted with the when the negative RF is going on. So that time the electron emitted moves with the reduced velocity v less than v0 all these electrons meet at a single point. Whether there are only three electrons? No. There are number of electrons emitted during this part of the RF cycle and all these electrons meet at a single point which is called as electron bunch and the this part of the RF is called as the bunching limit. So the process of change of velocity of electron in accordance with the sinusoidal input applied is called velocity modulation of electron beam. The electric field is directed towards the right the electric field directed towards the right the electrons entering from left side moves towards collector. Electrons are entering from left and moving towards collector all the small dots you can see these are the electrons. This is my position of buncher cavity this is the position of catcher cavity. The velocity modulation taking place electron bunching starts now you can see the thick electrons here they are coming closer they are forming the bunches. So this is electron bunching has started. Now you can see more number of bunches are formed the electron bunches are formed and these electron bunches are moving towards catcher cavity right. Now all these electrons are catched by the catcher cavity so it is called as a name as catcher cavity. So the electron bunches passes through the catcher cavity inducing sinusoidal oscillations the magnitude of oscillations produced will depend on the amount of bunching that has taken place depending on the amount of bunching the sinusoidal oscillations produced will depend. Current modulation the pulsating stream of electrons pass through the catcher cavity and excite oscillations in the output cavity which is catcher cavity. So this pulsating stream of electrons or the density of pulsating stream of electrons produces current modulation and the density of electrons reaching the catcher cavity vary cyclically with time hence the process is called current modulation. The drift space converts velocity modulation into current modulation summary. This is actually how the magnetron sorry how the 2-cavity clistron is there is shown here. From here the electrons are emitted electrons are moving towards the collector the electron bunches are forming here the electron gun produces flow of electrons the electron gun is producing flow of electrons. The bunching cavities regulate the speed of electrons and electrons alive in the bunches at the output of the catcher cavity. So here bunching formation is start and electron bunches will be reaching at the catcher cavity. The bunches of electrons excite the oscillations or excite the microwave in the output cavity of the clistron. This is the output cavity or catcher cavity where oscillations are excited. So the small microwave energy is getting amplified here and can be taken out from this end. Thus we get amplified RF output at the catcher cavity. The microwaves flow into the waveguide which transports them to the collector. This microwave is flowing further and is moved towards collector and the electron beam is stopped here absorbed by the collector. This is actually how the two-cavity clistron amplifier looks that is shown here. From here amplified output can be taken where is the here is the small amount of RF input can be given that is shown here this high amplified output obtained here and small input provided here. These are the references used for preparing this video. Microwave devices and circuits by Samuel Leo and Microwave and Radar Engineering by M. Kulkarni. Thank you.