Design, microfabrication and measurement of cooling arm for fusion energy source application

The novel cooling arm plays an important role in thermal transfer in the production process of fusion energy. Its structure is designed and simulated by a finite element method. The result shows that the structure with two branches can obtain a temperature difference less than 1 mK among the grip surfaces of all the fingers. A (111) crystal orientation silicon is deployed to fabricate the cooling arm, because of its isotropic Young´s modulus. The thermal conductivity of this material is measured by a Gifford-McMahon (GM) cooler. The result shows it has large thermal conductivity at cryogenic temperature, which excellently contributes to heat transfer. The cooling arm is obtained by a microfabrication process. With a uniform pattern width mask and optimised deep reactive ion etching process recipe, a nearly 90° vertical sidewall is obtained. The temperature distribution of the cooling arm is also measured by a GM cooler, and the result shows that the maximum temperature deviation is 0.48 mK among the 16 fingers. There is a good agreement between finite element analysis and the experimental result.