Spiral traveling wave tube, a kind of broad band microwave tube, has been widely used in the field of aviation and satellite communication system, radar system and electronic warfare system, showing an irreplaceable role in modern military electronic equipment. 

Spiral traveling wave tube wires are often made of tungsten that has high strength, high hardness, high melting point and good mechanical strength. A low loss film material is plated on the inside and outside surfaces of tungsten helices made of tungsten. It is used to reduce the high frequency loss of tungsten spiral wires, and it’s called tungsten spiral gold plating.

 

 

Helical slow wave system is the key component of energy exchange helix traveling wave tube, which directly affects the stability and reliability of traveling-wave tube (TWT). In slow wave systems, the heat is generated mainly by high-frequency loss of the helix and electron bombardment. With the improvements of magnitude and frequency of TWT, the significant increase of high-frequency losses of the key component helix would bring great pressure to the TWT's high frequency heat dissipation, especially in the millimeter wave band. The high frequency loss of the tungsten helix seriously affects the output power and the stability of the TWT. In order to reduce the high frequency loss of tungsten spiral wire, the low loss thin film material, like gold-plated film, is usually plated on the inside and outside surface of tungsten spiral wire.

 

Special attention must be paid when the tungsten spiral is gold plated. If the surface of the tungsten helix is plated directly, the bonding between the two is not good. The pretreatment method of adding transition layer copper can improve the bonding property of the gold plating layer and the tungsten matrix, and the surface of the gold plating layer is flat, smooth and compact with the grain small and even. But if the pre-coating is too thin, it will cause the surface of the helix is partly exposed. On the contrary, if the pre-coating is too thick, the gold plating layer will peel, or drop. The transition layer should be controlled at the proper thickness, then it could get better quality of gold plating layer.