A microwave tube amplifier uses an axial magnetic field and a radial electric field. This is a

• The Crossed Field Amplifier (CFA) is a broadband microwave amplifier that can also be used as an oscillator.
• It is a microwave tube amplifier that uses an axial magnetic field and radial electric field
• Its operation is similar in operation to the magnetron and can provide relatively large amounts of power with high efficiency.

Travelling Wave Tube:

• A specialized vacuum tube that is used in electronics to amplify radio frequency (RF) signals in the microwave range. 
• The TWT belongs to a category of "linear beam" tubes, such as the klystron, in which the radio wave is amplified by absorbing power from a beam of electrons as it passes down the tube.
• A major advantage of the TWT over some other microwave tubes is its ability to amplify a wide range of frequencies i.e. a large bandwidth.
• The bandwidth of the helix TWT can be as high as two octaves, while the cavity versions have bandwidths of 10% - 20%.
• Operating frequencies range from 300 MHz to 50 GHz.
• The power gain of the tube is on the order of 40 to 70 decibels, and output power ranges from a few watts to megawatts.