## 1 Introduction  
Plasma has been actively applied in industrial fields, such as semiconductor manufacturing and fluorescent lighting. For example, in the field of surface treatment, plasma is used to harden the surface of materials [1] and surface modification [2]. These surface treatments are techniques that change the properties of solid surfaces using the action of the ions and electrons generated by plasma, for which low-pressure plasma has been used. Low-pressure plasmas are generated at low pressures of 1/1000 atm or less, which enables uniform surface treatment; however, this has limitations in terms of the types of treatment objects and throughput. In recent years, it has become possible to stably generate low-temperature plasmas under atmospheric pressure; therefore, these plasmas have been applied in various fields such as medicine, industry, and chemical analysis. For example, in the medical field, they are used for disinfection [3, 4, 5], hemostasis [6], and wound healing [7], and they are used for surface modification in the industrial field [8]. In the field of chemical analysis, they have been utilized for surface adhesion analysis [9] and on-site analysis [10]. To increase the processing effectiveness of atmospheric low-temperature plasma, the energy applied to a unit volume can be increased by means such as discharge [11]. For materials that are resistant to thermal damage, an increase in temperature promotes the reaction with the reactive species, improving the treatment effect. [PERSON] et al. reported the adhesion of PTFE using atmospheric pressure plasma controlled at 260 \({}^{\circ}\)C [12]. A high adhesion effect and radical density were observed in the high temperature plasma by increasing the input power. However, this temperature increase is a problem for heat-sensitive materials, such as biological samples. To solve this problem, cryo-microplasma, in which He gas is cooled by liquid nitrogen before the plasma is generated, was developed [13,14]. [PERSON] et al. developed a temperature-controllable atmospheric plasma source as an advanced plasma jet [15]. They succeeded in controlling the gas temperature of He plasma in the range of \(-\)54-160 \({}^{\circ}\)C by cooling with liquid nitrogen and heating with a heater. Another way to increase the treatment effect of atmospheric low-temperature plasma is to change the gas species of the plasma. [PERSON] et al. evaluated the effect of plasma gas species on the surface treatment effect of polyimide films and found that carbon dioxide plasma was the most effective treatment [16]. Thus, to obtain a high treatment effect without thermal damage to the target in atmospheric low-temperature plasma application, it is necessary to control the gas temperature of the plasma and generate plasmas of various gas species. We developed a multi-gas temperature-controllable plasma jet that can easily control the gas temperature of plasmas of various gas species over a wide range of temperatures. In this study, because the temperature of gases other than He can be controlled, the excessive cooling using liquid nitrogen in the previous study must be avoided. In this study, to control the gas temperature in the plasma, the gas was stagnated in the plasma jet body before plasma generation, and heat exchange was performed. To achieve a wide temperature control range, a plasma jet body was designed and analyzed using computational fluid dynamics (CFD) to improve the temperature control performance. To fabricate a plasma jet body with a complex shape, a metal 3D printer was used. 3D-printing technology has attracted increasing attention in manufacturing, including its use in plasma systems, due to its low cost and high flexibility [17, 18, 19]. Recently, a plasma jet for an endoscope with a diameter of approximately 3 mm produced by a metal 3D printer has been reported [20]. Nitrogen, carbon dioxide, oxygen, and argon plasmas were generated using a multi-gas temperature-controllable plasma jet fabricated using a metal 3D printer.