**4.7 Magnetic system**

The purpose of the magnetic system is to generate required axial magnetic field profile needed for the cavity as well as the MIG and collector. For lower frequency operation, non-superconducting air-cooled solenoids are preferred. However, for higher frequency operation (i.e., for gyrotrons operating at W-band or beyond), superconducting magnets are being used. The state-of-the-art magnets employ cryogen free superconducting magnet technology. Which eliminates the need of refilling of liquid helium. Some researchers have reported gyrotrons developed with Samarium-Cobalt (Sm2Co17) permanent magnets and special type of room temperature solenoid made out of copper foil. Such gyrotrons usually operate at higher harmonic mode of interaction.
