## 1 Introduction
The miniaturization of the source body is achieved through the adoption of smaller discharge chambers and permanent magnets. Meanwhile, the miniaturization of the extraction system focuses on reducing the length of the extraction electrode while ensuring its performance. The miniaturization approaches employed by different institutions for ECR ion sources are summarized in Table 4. It can be observed that currently none of these ion sources fully meet the requirements of high-current high-voltage accelerators in terms of source size and performance. Therefore, based on the aforementioned miniaturization schemes for ECR ion sources, we propose an ECR ion source miniaturization approach that can meet the requirements of high-voltage accelerators. This approach combines the miniaturization of both the waveguide transmission system and the source body to achieve the desired outcomes. First, the transmission length of the microwave system was compressed by removing the three-pin tuner and circulator and miniaturizing other waveguide devices. With these enhancements, the total length of the microwave system is less than 300 mm. Second, because the ECR ion source is installed in the accelerator's high-voltage terminal spherical shell, the external dimensions of the ion source magnetic components are limited. More plasma can be generated while ensuring efficient microwave transmission by optimizing the magnetic field distribution and the size of the discharge chamber. \begin{table}
\begin{tabular}{c c} \hline
**Index Parameter** & **Design Indexes** \\ \hline Beam intensity & \(\geq\)20 mA \\ Extraction voltage & 40 kV \\ Proton ratio & \(\geq\)85\% \\ Normalized emittance & \(\leq\)0.25 \(\pi\) mm. mrad \\ External contour size & 600 mm(length) \(\times\) 300 mm(width) \(\times\) 300 mm(high) \\ Maximum magnetic field & 1100 G \\ Vacuum level & \(10^{-5}\) Pa\(-10^{-3}\) Pa \\ Microwave frequency & 2.45 GHz \\ Microwave power & 300 W-500 W \\ \end{tabular}
\end{table} 
Table 2: Design parameters of the ion source system. \begin{table}
\begin{tabular}{c c c c c} \hline
**Organization** & **Ion Source Type** & **Ion Species** &
\begin{tabular}{c} **Extraction** \\ **Voltage (kV)** \\ \end{tabular} & **Beam (mA)** \\ \hline Institute of Plasma & & & & \\ Physics, CAS [6] & Penning ion source & H\({}^{+}\) & 40 & 0.1 \\ Lawrence Berkeley & High frequency & H\({}^{+}\) & 15.5 & 16 \\ National Laboratory [7] & source & & & \\ Peking University [8] & ECR source & H\({}^{+}\) & 50 & 100 \\ CEA/Saclay [9] & ECR source & H\({}^{+}\) & 85 & \textgreater{}100 \\ \hline \end{tabular}
\end{table} 
Table 3: Comparison of proton sources currently operating on accelerator facilities. Figure 2 shows a physical structure model for calculating the transmission of a miniaturized microwave transmission system and a physical structure model of the source body for calculating the discharge inside the discharge chamber. Figure 2a shows the model of the miniaturized microwave transmission system, which mainly consists of a magnetron, an excitation chamber, a high-voltage isolated waveguide, a matched waveguide, and a source body, as shown in Figure 2b. Figure 2b shows the structural diagram of the source body used to calculate the discharge case, which includes a microwave window composed of alumina ceramics and boron nitride, a discharge chamber, a mounting barrel, and permanent magnet rings. These simulations were performed using the COMSOL Multiphysics software, which allowed for a comprehensive analysis of microwave, magnetic, electric, and plasma processes.