In a two cavity Klystron the secondary cavity is called
Catcher
The two cavities are named for what they do to the beam: the first bunches it, the second catches it — so the secondary cavity is the catcher, option 4.
| Position | Name | Function |
|---|---|---|
| First cavity | Buncher | Input signal velocity-modulates the beam |
| Between them | Drift space | Velocity modulation becomes density modulation |
| Second cavity | Catcher | Bunches induce the amplified output |
What happens at each. At the buncher gap the RF input alternately speeds up and slows down electrons as they cross. No power is drawn from the beam here — the beam current is still uniform, only the velocities differ. During the field-free drift that follows, faster electrons catch up with slower ones ahead of them, and the beam arranges itself into dense bunches. Arriving at the catcher gap, that strongly varying current induces a large RF voltage in the resonant cavity, and the output is taken from there.
Why the order cannot be reversed. Bunching takes time to develop, so the drift length is chosen to make the bunches tightest just as they reach the catcher. Put the catcher first and there would be no bunches to catch — the beam current entering it would be perfectly smooth and would induce nothing.
Where the amplification comes from. Not from the input signal, which merely organises the electrons, but from the DC beam supply. Bunches arrive at the catcher gap in the retarding phase of the induced field, are decelerated, and surrender kinetic energy to the cavity; what remains of the beam passes on to the collector.
Why the other options fail. "Buncher" names the first cavity. "Velocity modulation" is the process the buncher performs, not the name of a cavity. "Coupled cavity" belongs to a different tube altogether — the coupled-cavity TWT, in which a chain of cavities replaces the helix as a slow-wave structure.
An extension the terminology supports : adding intermediate cavities between buncher and catcher gives the multicavity klystron, each one re-bunching the beam more tightly, so gain rises from around 20 dB for two cavities to 50 or 60 dB for four or five.
Hence, the secondary cavity is the catcher.
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.
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