This paper presents the design and electrical test results of a low-noise front-end chip (named Topmetal-S) in a High-pressure Time Projection Chamber (TPC) for searching the neutrinoless double beta decay. The Topmetal-S has been fabricated in a 130 nm CMOS technology. The proposed front-end chip consists of a charge collection electrode, a Charge Sensitive Amplifier (CSA) and peripheral circuits. The test results indicate that the CSA features an input linear dynamic range of approximately 6.64 fC, a charge-conversion gain of about 220 mV/fC and an Equivalent Noise Charge (ENC) of approximately 115 e ^- after a digital trapezoidal pulse shaper.

NνDEx is an experiment proposed to search for the neutrinoless double-beta decay of ⁸² Se using a high-pressure gaseous time projection chamber. In Phase-I of the experiment, the NνDEx-100 detector is filled with about 100 kg SeF ₆ . The readout and DAQ systems are crucial components of the experiment. The two-dimensional pixelated readout plane, consisting of approximately 15,000 sensors for charge measurement, is placed at one end-cap of the chamber. The electrode and charge-sensitive preamplifier in each sensor collect drifted ions and amplify the signal, with the analog output transmitted to a digital ASIC, where an internal ADC continuously digitizes the pulse. All digital ASICs on the plane form two routing networks, utilizing four pairs of bidirectional I/Os in each chip. The digitized waveform data from all chips is transmitted towards one edge of the plane via these two networks. Data aggregation modules at the edge aggregate slow parallel data links to fast serial data links, which are then connected to the DAQ system in the back-end. This paper aims to introduce the design and testing of the demonstrator system for the full digital readout chain, including a digital chips array, a data aggregation module and the back-end DAQ system.

Within the project of building a time projection chamber using 100 kg of high-pressure ⁸⁶SeF₆ gas to search for the neutrinoless double-beta decay in the NvDEx collaboration, we are developing a CMOS charge sensor, named Topmetal-S, which is tailored for the experiment to detect the ions without gas amplification. In this work, the performance of the sensor is presented. The equivalent noise charge of the sensor is measured to be about 120 to 140 e^- depending on the operating point, with the charge injection capacitance calibrated against external capacitors. The signal waveforms are investigated with various chip parameters and experimental settings. In addition to electrons, both negatively and positively charged ions could be detected, and their waveforms are studied using air and SF₆ gases. Using the sensor, the mobility of negative ions in ambient air in the atmospheric pressure is measured to be 1.555 ± 0.038 cm² · V^-1 · s^-1. Our study demonstrates that the Topmetal-S chip could be used as the ion detection charge sensor for the experiment. Further work is ongoing to reduce the noise of the sensor and to develop a small readout plane with tens of the sensors.

The cool storage ring (CSR) external-target experiment (CEE) will be the first large-scale nuclear physics experiment at the Heavy Ion Research Facility in Lanzhou (HIRFL). The beam monitor, designed to measure the lateral position of each beam particle, will improve the precision of primary vertex reconstruction otherwise determined by the time projection chamber (TPC) and multi-wire drift chambers (MWDCs). The beam monitor mainly contains two gaseous ionization sub-detectors, each measuring one lateral coordinate of the beam. The design requirements include the spatial resolution of \(<50\) \(\mu\)m, the two-particle separation capability of \(<1\) \(\mu\)s, the rate capability of \(>10^{6}\) pps, and small material budget. It features novel front-end pixel chips for both charge sensing and readout functions. The first prototype, utilizing the common-purpose Topmetal-II-chips, has been developed and tested; the second one, deploying the custom-designed Topmetal-CEEv1 chips, is currently being assembled. In this paper we will present the detector specifications, design and test of the prototypes, in particular the charge sensing and readout chips.

A beam monitor system is being developed for the cool storage ring (CSR) external-target experiment (CEE) at the Heavy Ion Research Facility in Lanzhou (HIRFL). The beam monitor is required to measure the lateral position of each beam particle with spatial resolution less than 50 \(\mu\)m and with beam rates up to 1 MHz. As the beam intensity increases, the build-up of slow-moving positive ions created from the ionization of the detector gas by the beam leads to a significant distortion of the nominal electric field in the drift region. In this work, simulation studies of the beam monitor are performed, in particular the space charge effect and the correction strategy. It shows that the space charge at the nominal drift electric field of 700 V/cm modifies the electric field in the sensitive volume by roughly 5\(\%\) in both the drift and transverse directions. The distortion on the measured position is up to 0.35 mm in the 5\(\sigma\) region of the beam profile. The expected spatial resolution of 500 MeV/u U ion is 34.5 \(\mu\)m considering the pixel noise of 400 \(e^{-}\) and the 100 \(\mu\)m \(\times\) 1 mm pixel size of the charge sensor chip in the selected gas mixture.