Pulsed wire magnetic field measurement on the permanent magnet focusing device of millimeter-wave traveling wave tube

Abstract

In our case, the pulsed wire method is applied to the magnetic field measurement of the permanent magnets in focusing device of millimeter-wave traveling wave tube (TWT). The focusing device using permanent magnets is used to help the electron beam keep shape and make it possible go through the slow-wave circuit, effectively interact with the microwave field and well received by collectors, which makes the measurement become a key factor for the development of the millimeter-wave TWT technique. Furthermore, the wire method can be extended used to magnetic field measurement of the magnet with small via hole. The pulsed wire technique is based on the excitation of the harmonics of a wire vibration by Lorenz forces between current in a wire and the surrounding magnetic field. Knowing the amplitude and the phase of the various harmonics of the wire vibration, one can easily reconstruct the surrounding magnetic field. As sensitive the wire system is, ultrastable supporters, high accurate mechanical adjusters, precise light and electric centering device are installed and relevant parameters are properly chosen. In addition, shorter wire is used to reduce the sag, and a simple and effective wire-position detector providing accuracy up to 1μm is designed and tested. Experiment confirms the theoretical conclusions and shows a positive future of application. The prototype system can show several relevant results, e.g., three-dimensional magnetic intensity distribution, maximum, minimum, and medium magnetic inductions, pole pitch error, etc.