The correct sequence of sub-systems of Klystron amplifiers as they appear in the direction of flow of electron beam is
Cathode, Buncher cavity, Catcher cavity, collector
The beam must start at the cathode and end at the collector, which alone eliminates three of the four options and leaves cathode, buncher cavity, catcher cavity, collector — option 3.
| Order | Element | Function |
|---|---|---|
| 1 | Cathode | Emits the electron beam, accelerated by the anode |
| 2 | Buncher cavity | Input signal velocity-modulates the beam |
| — | Drift space | Velocity modulation becomes density modulation |
| 3 | Catcher cavity | Bunches induce the amplified output |
| 4 | Collector | Absorbs the spent beam |
The physics of the two cavities is what fixes their order. At the buncher, the RF input alternately accelerates and retards electrons as they cross the gap — this is velocity modulation, and it changes no currents yet, so no power is extracted there. The beam then coasts through a field-free drift space, and because faster electrons overtake slower ones ahead of them, the beam arranges itself into dense bunches. Only then, at the catcher, does the beam carry a strong RF current component that can induce a large voltage in a resonant cavity.
Time is the reason the two cannot be swapped. Bunching takes time to develop; the drift length is chosen so that the bunches are tightest exactly as they arrive at the catcher gap. Put the catcher first and there are no bunches to catch.
Where the amplification comes from. The DC beam supply provides the energy; the input signal only organises the electrons so that their kinetic energy can be surrendered coherently at the catcher. Electrons arrive there in the retarding phase, give up energy to the cavity field, and pass on with what remains to the collector, which is water- or air-cooled since it dissipates the beam power not converted to RF.
Why not an ordinary tube at microwave frequencies : in a triode the transit time across the grid becomes comparable with a period above about 1 GHz, and the device stops working. The klystron turns that same transit time into the operating principle rather than a limitation — which is why klystrons deliver megawatts at gigahertz frequencies in radar and particle accelerators.
Hence, the sequence is cathode, buncher cavity, catcher cavity, collector.
Similar Questions
There are three general purpose microwave tubes. The first is ordinary gridded tube, having electrodes like vacuum tube diode and triodes. The second type are those in which interaction between the electron beam and RF field takes place. The klystron is the example of the second type of microwave tubes. The third category of the device is one in which interaction between an RF field and electron beam is continuous. TWT (Travelling Wave Tube) is the example of this category.
Read the paragraph and answer the questions :
Microwave tubes are used as microwave amplifiers and oscillators. Three general type of microwave tubes in which third type tubes are important because in these tubes there is an interaction between an electron and an RF field is continuous. The Travelling Wave Tube (TWT) is the prime example of this interaction. It is an amplifier, whose oscillator counter part is called Backward Wave Oscillator (BWO). The second sub-group consists of tubes in which a magnetic field ensures a constant electron beam – RF field interaction, and this is complemented by the Cross-Field Amplifier (CFA). Multicavity Klystron is used as high and very high power amplifiers in the UHF and microwave ranges. The frequency range covered is from about 250 MHz to over 95 GHz. The reflex-Klystron is a low power microwave oscillator. It is assumed that oscillations are started by switching transients. For oscillations to be maintained the transient time in the repeller space cycle is given as \(T=\left(n+\dfrac{3}{4}\right)\) where n is an integer, each value of n is said to correspond to different reflex klystron mode. Reflex Klystrons with integral cavities are available in the frequency range 4 to 200 GHz.
Assertion (A) : TWTA is a narrow band device and has a helical structure and it is used as amplifier and oscillator.
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