The lasing of the first free-electron laser (FEL) in the world was successfully carried out in 1977, so the history of FELs as a light source is not so long. But FELs are now utilized for research in many scientific and engineering fields owing to such characteristics as tunability of the wavelength, and short pulse and high peak power, which is difficult utilizing a common light source. Research for industrial applications has also been carried out in some fields, such as life sciences, semiconductors, nano-scale measurement, and others. The task for the industrial use of FEL is the realization of high energy efficiency and high optical power. As a means of promoting realization, the combining of an FEL and superconducting linac is now under development in order to overcome the thermal limitations of normal-conducting linacs. Further, since tuning the wavelength is carried out by changing the magnetic density of the undulator, which is now induced by moving part of the stack of permanent magnets, there is uneasiness in the moving part and partial magnetic depression by irradiation. If the superconducting coil is applied for the undulator, it is believed that wavelength tunability will improve in terms of reliance and usability. As a result, the collaboration between superconducting/cryogenic engineers and FEL engineers is very fruitful because superconducting FEL is essential for industrial use.
Numerical simulation has been performed to analyze the heat and fluid flow in pulse tubes and to clarify the working principle of refrigeration in basic pulse-tube refrigerators. Transient axisymmetric two-dimensional equations of continuity, momentum and energy were solved utilizing the TVD method. A physical model combining the pulse tube with the wall and regenerator is used for numerical simulation. The pulse tube for this study is a stainless-steel pipe of 150mm in length, 5mm in inner diameter and 1mm in thickness, and contains a heat exchanger of 30mm in length. The dimensions of the regenerator are 60mm in length and 12.5mm in inner diameter. Woven 200 mesh wire screens of copper are used as the regenerator material. Air is selected as the working gas. Heat exchange between the pulse-tube wall and the working gas in the pulse tube is assumed to be convective heat transfer. In this paper, we analyze the transient behaviors of pressure and gas temperature, traces and temperature changes of the gas elements in the pulse tube and heat transfer between the working gas and tube wall.