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High frequency electron beam modulation

To define the preliminary design of a Microwave vacuum amplifier, calculations of some parameters to design a diode and triode test vehicles have been done.

The mains parameters calculated were:
- the emitter-grid capacitance of the cathode/grid system.
- the electron transit time between cathode and grid.
- the distribution of the RF electrical field in a RF diode working at frequency of 1.5Ghz and in a RF triode working at 32Ghz.
- the geometrical characteristics of the input and output cavity of the 32GHz triode.
- the equivalent circuits of the input and output cavity.

First, the electron emission of the CNT cathodes has been measured in a RF diode having a resonance frequency of 1.5 GHz. In this device a 1.5GHz electrical field of 35MV/m is created in front of the CNT cathode when a 3kW peak power (duty cycle 1%) is injected in the cavity. Then,it has been measured an average emission current density of 1.5A/cm2 corresponding to a peak current density of 15 A/cm2.

Second, the electron emission of the CNT cathodes has been measured in the 32Ghz triode vehicle. In this device a DC electrical field of ~ 30MV/m is created in front of the CNT cathode by a DC polarisation of a grid. The field modulation is created by injection of a 32GHz RF signal of a few watts in the input cavity. A current density of 0.15A/cm2 modulated at 32GHz was measured in the output cavity.

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