# Development of a Radio-Frequency Quadrupole Accelerator for the HL-2A/2M Tokamak Diagnostic System
## 5 Conclusions  
In this paper, we have described the beam dynamics, RF conditioning, and beam commissioning of a deuteron RFQ for plasma-material interaction on fusion devices. In the beam dynamics design, the combination of a large aperture radial matching section and weak focusing makes beam matching from the LEBT into the RFQ easy. Beam dynamics parameters were optimized to minimize the emittance growth and also to maximize the beam transmission.  
The RFQ was successfully conditioned to the RF power of 55 kW required for deuteron operation, with a sufficient power margin. The inter-vane voltage was calibrated using an X-ray energy measurement technique. An inter-vane voltage of 70 kV can be achieved at a cavity power of 48.6 kW. The intrinsic \(Q\)-value measured by the Ring-Down method after high-power tests is 13,780.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Project**} & \multirow{2}{*}{**Type**} & \multirow{2}{*}{**Frequency**} & \multirow{2}{*}{\begin{tabular}{c} **E\({}_{\text{in}}\)/E\({}_{\text{out}}\)** \\ **(MeV)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Beam** \\ **Current** \\ **(mA)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Inter-vane** \\ **Voltage** \\ **(kV)** \\ \end{tabular} } & \multirow{2}{*}{**Length**} & \multirow{2}{*}{
\begin{tabular}{c} **Power** \\ **(kW)** \\ \end{tabular} } & \multirow{2}{*}{**Status**} \\ \cline{1-1} \cline{6-10}  & & & & & & & & \\ \hline SPIRAL2 & & & & & & & \\
[21; 22; 23] & 4-vane & 88 & 0.04/1.5 & 5 & 100–113 & 5.08 & 180 & cw 1.34 mA He\({}^{2+}\) \\ SARAF [24] & 4-rod & 176 & 0.04/2.54 & 5 & 56 & 3.70 & 186 & cw 1.15 mA D\({}^{+}\) \\ IFMIF [13; 25] & 4-vane & 175 & 0.1/5.0 & 125 & 79–132 & 9.8 & 550 & pulse 125 mA D\({}^{+}\) \\ CMIF [26] & 4-vane & 162.5 & 0.04/3.0 & 10 & 65 & 5.26 & 120 & pulse 7.8 mA \({}^{2}\)H\({}^{+}\) \\
973-RFQ [27] & window & 162.5 & 0.05/1.0 & 50 & 60 & 1.8 & 49 & cw 1.78 mA \({}^{2}\)H\({}^{+}\) \\ this work & 4-vane & 162.5 & 0.04/1.5 & 10 & 70 & 2.2 & 45 & pulse 10 mA \({}^{2}\)H\({}^{+}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Main parameters of the deuteron RFQs in the world.  
The beam commissioning with a \({}^{2}\)H\({}^{+}\) beam demonstrated that the RFQ is performing well with the design parameters. A 10 mA \({}^{2}\)H\({}^{+}\) beam was successfully accelerated up to 1.5 MeV through the RFQ in May 2021. The acceleration of the D\({}^{+}\) beam is programmed to begin as soon as we obtain the safety authority's authorization.  
Conceptualization, P.Z. and Y.L.; methodology, S.L.; software, S.L.; validation, S.L., M.H. and T.W.; formal analysis, Y.X.; investigation, S.L.; resources, Y.W.; data curation, Z.W.; writing--original draft preparation, S.L.; writing--review and editing, P.Z.; visualization, H.L.; supervision, S.G.; project administration, P.Z.; funding acquisition, P.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key Research and Development Program of China (Grant No. 2017 YFE0301306).  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The primary author, [PERSON], would like to thank all the partner labs staff for their deep involvement in the project.  
The authors declare no conflict of interest.