Traveling Wave Tube 

 
Traveling wave tubes are used in many space and military applications where communication over a large distance is needed. These tubes basically take the generated signal and amplify it so that it can be properly received. Some of the space applications include satellites which are launched into orbit and then required to send information back to earth as it travels the universe. Some of the military applications include radar communication with missiles and aircraft. All of these applications require permanent magnets that must be held to tight tolerances and field strengths in order to properly maintain the generated signals to be amplified. It is also important to choose the proper magnetic material in order for it to withstand the possible harsh environments of space. Also, assembling the permanent magnets is crucial to ensure the traveling wave tubes operate as required and do not require servicing.