Transit time tube

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With drift tube is referred to in the radio frequency art electron tubes for microwave GENERATION or amplification, whose working principle is based on the transit time of the electrons.

  • As crossed-field tubes (engl., And cross-field amplifier cross field amplifier , short CFA) those are referred to runtime tubes in which an additional perpendicular strong magnetic field is the electric field.
  • With linear beam tubes , an additional magnetic field is only used to focus the electron beam, except for the gyrotron .
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In radio tubes and cathode ray tubes , among other things , the density of the electron flow is controlled (density control). With these, the electrode voltage hardly changes during the electron transit time between them. However, the distances between the electrodes cannot be made as small as desired, so that density control can no longer be used at high frequencies.

In the case of time-of-flight tubes , on the other hand, this time-of-flight effect is used in a targeted manner:
a control field initially provides for a speed modulation of the electron flow. After a certain running time , this results in a density modulation , i. That is, thinner and denser areas are formed in the electron flow because faster electrons overtake slower ones. If electrodes are arranged in this area, HF energy can be extracted from them through the capacitive effect of the electron space charge.

The electrodes can be in the form of wire coils, perforated cavity resonators or slots.

Systematics and application

The following tubes belong to the runtime tubes:

  • Cross-field tubes
    • Amplitron : an amplifier tube similar to a magnetron; Stabilotron : back-coupled Amplitron
    • Magnetron : powerful microwave generator, in radars and in microwave ovens
  • Linear beam tubes
    • Klystron : so-called drift tube, to amplify high powers (multi-chamber klystron) or as an oscillator (reflex klystron)
    • Traveling wave tube , also running wave tube : for amplification in radio astronomy and for satellite communication
    • Carcinotron (backward wave tube ): Oscillator, has a helix similar to a traveling wave tube
    • Gyrotron : powerful microwave generator down to the millimeter wave range; it requires a magnetic field and an electron beam with relativistic speed

The following table compares the characteristic parameters of the transit time tubes used in radar technology (pulse lengths in the microsecond range). Although the disc triode is not a time-of-flight tube, it has been included in this table for comparison.

  Klystron Traveling wave tube Magnetron Carcinotron Disc triode
Frequency range up to 10 GHz up to 20 GHz up to 20 GHz up to 5 GHz up to approx. 1.5 GHz
Bandwidth 2 - 4% 10-20% a few MHz 2 GHz 30-50%
Output power up to 50 MW up to 1 MW up to 10 MW 1 w up to 1 MW
Power amplification up to 60 dB up to 50 dB     up to 20 dB
function narrowband power amplifier broadband, low-noise amplifier Power oscillator with a transmission frequency controlled oscillator (VFO) Amplifier, oscillator