Experimental Technology and Management

束流定位探测器可以用来监测加速器束流的位置、强度、束斑大小等信息，是粒子加速器中重要的组成部分。Topmetal是一种采用半导体CMOS工艺生产的硅像素芯片，具有噪声低、位置分辨率高等特点。该研究利用硅像素芯片Topmetal作为气体探测器的电荷收集电极设计了非阻挡式束流定位探测器。为了研究束流定位探测器的性能，设计了一套读出电子学系统，并利用²⁴¹Am α源和重离子束流进行了实验研究。实验结果表明，该电子学系统工作正常，探测器能够正常观察到粒子径迹。该实验研究为高位置分辨束流定位探测器提供了一种新的思路。

[Objective] A beam position monitor is an important component in a particle accelerator, enabling real-time measurement and characterization of beam parameters, such as position, intensity, spot size, and other information about the beam. These measurements are essential for optimizing the accelerator performance, ensuring beam stability, and conducting high-precision experiments. Traditional beam position monitors often rely on scintillators, wire chambers, or semiconductor detectors, each with inherent limitations in resolution, noise, or radiation hardness. To address these challenges, this paper explores the use of Topmetal, a low-noise and high-resolution silicon pixel sensor fabricated using complementary metal–oxide–semiconductor(CMOS) technology, as the charge collection electrode in a gas-based beam monitor. [Methods] The proposed beam monitor integrates a Topmetal sensor into a gas detector structure, where ionizing particles generate electron–ion pairs in the gas chamber. The ionized electrons drift toward the Topmetal pixel array under the influence of an applied electric field and are sensed and read by Topmetal. The position of the beam particles was calculated based on the signal distribution on the pixel array. A dedicated readout electronics system was designed to process the signals from the beam monitor, which consists of front-and back-end electronics. The front-end electronics consists of a Topmetal bonding board and a motherboard. To increase the sensitive area of the detector, four Topmetal-II chips were installed in one row on the bonding board. The motherboard mainly implements four functions: power supply for the chips, bias voltage provision, control signal fan-out, and analog output buffering. The back-end electronics were designed based on a Xilinx Kintex-7 series field-programmable gate array, which was mainly responsible for Topmetal-II chip configuration, receiving analog output signals for analog-to-digital conversion, data packaging and caching, data transmission, and other functions. The readout electronics system was designed with low noise, fast signal digitization, and efficient data acquisition. To validate the feasibility and evaluate the performance of the beam position monitor, tests using ²⁴¹Am α-particles and heavy ion beams were conducted in addition to the electronic tests. [Results] The tests proved that all the designed functions of the readout electronics system worked as expected. For the downlink, the readout electronics system can correctly configure the Topmetal chip, whereas for the uplink, it can read out the data of the chip and transmit the data to the computer through the ethernet. The ²⁴¹Am α particles test revealed that the whole detector system of the beam position monitor, including the high-voltage system, gas system, and electronic system, worked as expected, and the detector could successfully register individual α particles. The beam tests demonstrated that the detector could work stably under the beam environment and resolve individual beam particles with the beam flux of 10⁴–10⁶ pps. With each pixel size of 83 μm×83 μm, the Topmetal-based beam monitor can achieve excellent position resolution, making it suitable for high-precision beam diagnostics. Furthermore, the detector's gas-based design offers flexibility in adjusting the sensitivity and dynamic range by varying the gas mixture and pressure. [Conclusions] This paper provides a new approach for high-position-resolution beam position monitoring, combining the advantages of CMOS pixel sensors and gas detectors. The Topmetal-based system offers excellent spatial resolution compared with traditional beam position monitors, along with low noise and radiation tolerance. Future work will focus on improving the rate capability of detectors for high-intensity beam applications and exploiting gas amplification mechanisms. The successful implementation of this technology could significantly enhance beam diagnostics in the accelerators, particularly in applications requiring micron-level precision, such as synchrotron light sources, medical proton and ion therapy, and particle and nuclear physics experiments.