There are two types of direct current thermal plasma jet based on flow status: turbulent plasma jet and laminar plasma jet. Laminar plasma jet has more advantages for high-precision applications than turbulent jet. Previous researches have been done to study factors that influence the jet characteristics for particular applications. However, more researches should be done to understand the influences of the anode structures on the jet characteristics. Therefore, this paper aims to study the jet characteristics of the laminar plasma torch with different anode structures experimentally. The experimental setup and methods are explained in detail in section 2. Then, results with different anode structures are examined and discussed. The experimental results show that different anode structure results in different jet characteristics, which is beneficial for the design of the laminar plasma torch. To conclude, a bigger diameter of the anode is beneficial for obtaining a higher arc voltage and thermal efficiency, nevertheless, a medium jet length and an anode with a smaller diameter is not recommended because of the low jet length. Furthermore, an anode with semicircular grooves on the inner surface can generate a more stable and long laminar plasma jet with a lower arc voltage but more intense erosion.

Due to its favorable temperature and velocity distributions, a lamina plasma jet, generated by a laminar plasma torch (LPT), is superior to a turbulent plasma jet on some applications. However, most of the reported LPTs usually work at a relatively low output power with a relatively low arc voltage and thermal efficiency, limiting its capability in the applications such as the surface hardening, synthesis of nanoparticles, remanufacturing of large components, and so on. Therefore, this article aims at designing an LPT with medium level output power and a relatively low arc current but a high thermal efficiency. The characteristics and applications of the proposed LPT have been obtained by experiments. The experimental results show the following characteristics: 1) the mean arc voltage of the proposed LPT is higher than 190 V with a maximum working power larger than 25 kW; 2) its mean thermal efficiency and jet length arrive at 50% and 450 mm, respectively; 3) the experimental data of the proposed LPT were used to fit its theoretical characteristics by using the least squares method. According to these fitted curves, the theoretical characteristics of the proposed LPT at a specified working conditions can be predicted; and 4) in addition, the surface of 45# steel was hardened by using the laminar plasma jet to obtain a hardening surface. The maximum hardness of the treated substrate arrives at about 600 HV, which is three times of the untreated substrate.

Due to their favorable jet characteristics, direct current (dc) thermal plasma torches have been used to meet the different requirements of variety applications. For obtaining more favorable jet characteristics and longer service life, variety design considerations of thermal plasma torches, e.g., cascade anode, multicathodes, and multianodes, have been used and studied by experiments and simulations. However, how the design considerations influence the jet characteristics and how about the coupling relationships of the working conditions should be studied systematically. Therefore, some key design tips have been discussed and applied to optimize a home-made thermal plasma torch first. Then, the experimental setup and methods for obtaining the jet characteristics of the optimized plasma torch have been introduced in detail. Finally, the experimental jet characteristics of the optimized plasma torch and the coupling relationships of the working conditions have been obtained and discussed. The study results show that: 1) the thermal plasma torch could obtain good jet characteristics and long service life by adopting the design tips and 2) the coupling relationships of the working conditions have been obtained and discussed, which could be helpful for predicting the jet characteristics of a thermal plasma torch.