## 1 Introduction
Similarly, plasma technology is used to clean or alter the surface properties of materials to achieve special functions and effects in the semiconductor packaging and textile industries. In the case of diamond film deposition, the carbon atoms required for diamond growth are produced in the plasma of a specific gas mixture. Once a graphite bond forms on the surface, the hydrogen atoms generated in the plasma can bond to the carbon atoms of the graphite bond to react with the etching process. With a high-purity coating, good electrical coupling, and high energy concentration, microwave plasma is widely used in the deposition of diamond films. In general, plasma is a complex system involving nonlinear particle dynamics, physical interactions, and chemical reactions on multiple-spatial and time scales. Experimenting with an MPJCVD for diamond film fabrication by trial and error is not only time-consuming but also costly. With the advancement of modern computers, plasma modeling has become a valuable and necessary tool for understanding plasma physics and has contributed to the research and development of a variety of plasma reactors and their performance improvement and conditioning [31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41]. [PERSON] et al. [32] developed a 2D axisymmetric model of the MPECVD system using the multiphysics solver COMSOL, a finite element method (FEM) based solver that combines the Maxwell solver and the heat transfer solver. The numerical simulation was employed to study the effect of parameters such as reactor geometry, microwave power, and gas pressure. The results showed that the gas temperature is weakly dependent on power but strongly dependent on gas pressure. [PERSON] et al. [39] also proposed a numerical simulation using COMSOL to model the electric field and plasma-density distributions in the MPECVD. A 2.45 GHz microwave plasma reactor with TM\({}_{021}\) mode was then physically built, which is based on their simulation result. Uniform single-crystal diamond films can be successfully grown on the substrate. [PERSON] et al. [40] showed how total pressure and microwave power affect the electrical conductivity of nitrogen atoms' grain boundaries when incorporated into ultrananocrystalline diamond (UNCD) films grown by MPECVD. The result showed that the film thickness decreased as a function of growth pressure. It was also found that the electrical conductivity of UNCD films increases once the microwave power and total plasma pressure increase in the film growth process. The maximum electrical conductivity for the UNCD film grown was found at a total pressure of 100 mbar and 4.5 kW microwave power. [PERSON] et al. [41] constructed a two-dimensional axisymmetric numerical model using COMSOL to investigate the effect of positive bias and deposition pressure on the properties of plasma flow inside the deposition chamber during the bias-enhanced MPECVD process. It was shown that as the deposition pressure increases, the temperature of the electrons in the deposition chamber increases as well, locally. The maximum value of the pressure was found to be approximately 30 Torr. Different studies have shown that the effects of pressure and power are crucial for film growth, and plasma modeling plays an important role in supporting experimental processes. In this work, we report the successful reconditioning of our homemade MPJCVD system for developing diamond films using three-dimensional plasma fluid modeling. The whole system has been modeled under varying parameters, including the reactor geometry, microwave power, and working gas pressure, in order to optimize its operating conditions. Using an operating condition identical to the optimized simulation results, the MPJCVD system successfully fabricates a diamond-thin film on a graphite substrate. We introduce the system configuration and its reconditioning in Section 2, present the detailed formulation and numerical modeling in Section 3, the simulation results and optimization in Section 4, and the experimental results in Section 5.