Heaters Operate Reliably in Liquid Nitrogen Environment


A large university conducting fusion research required heaters for their plasma fusion reactor. The function of the heaters would be to regulate and monitor the vessel between -60 and 32°F (-50 and 0°C) during normal plasma operation, and to bake the vessel to 300°F (150°C) after each cycle. Due to a liquid nitrogen environment around the vessel, the heaters and adhesive had to function reliably at temperatures as low as -310°F (-190°C).

Another requirement was that the heaters had to meet certain thickness requirements due to very limited space. Also, since access to the heaters would be severely limited, the heaters must be highly reliable.


Watlow engineers recommended polyimide heaters due to their low temperature capabilities and thin construction.

The reactor vessel is more than two stories tall, and six feet in diameter. A total of 375 polyimide heaters in more than 25 sizes and shapes were required to cover the outside surface. To insure long heater life in the vessel, Watlow implemented redundant heating elements and thermocouples in each polyimide heater.

Watlow's ability to meet unusual temperature requirements and provide even heating, as well as unlimited custom shapes and sizes, were important factors in solving this unique application.