The Research and Development of New Electronics Systems and Testing on the JNE-1ton Prototype Detector

Technical Summary: Development and Testing of the PDS1500 Electronics System for the Jinping Neutrino Experiment

Problem Statement
The Jinping Neutrino Experiment (JNE), located at the China Jinping Underground Laboratory-II (CJPL-II), is a next-generation neutrino observatory designed to detect solar neutrinos, geoneutrinos, and supernova neutrinos with high precision. The experiment utilizes a 10-meter acrylic sphere containing 500 tons of slow liquid scintillator and approximately 3,000 photomultiplier tubes (PMTs). Unlike previous experiments that relied on charge-time readout modes, JNE requires full waveform acquisition to separate Cherenkov radiation from isotropic scintillation light, enabling precise vertex reconstruction and energy measurement.

This requirement imposes severe technical challenges on the readout electronics: the system must simultaneously digitize analog waveforms from thousands of PMTs within a ~1000 ns window, possess high analog bandwidth, support high trigger rates, minimize processing delays, and maintain continuous data throughput. Furthermore, the system must achieve sub-nanosecond timing synchronization across all channels to ensure accurate event reconstruction in the presence of strong natural radioactive backgrounds. Existing commercial systems, such as the CAEN V1751, face limitations in data loss, baseline stability, and timing drift that may not fully satisfy the stringent requirements of the full-scale JNE detector.

Methodology
To address these challenges, the authors developed a new high-performance readout system, the PDS1500, and validated it using the upgraded JNE-1ton prototype detector (60 PMTs). The methodology involved:

1. System Design: The PDS1500 is a single-crate, 64-channel system comprising:

   • Eight WRX602 Waveform Digitization Boards: Each board features 8 channels of 1 GSa/s sampling with 14-bit physical resolution, utilizing Xilinx Kintex UltraScale FPGAs and ADAM103 ADC mezzanine cards.
   • One TTC308 Trigger and Timing Control Board: Aggregates over-threshold counts to generate global triggers and distributes a 50 MHz synchronous clock.
   • One BP5U10S High-Speed Backplane: Facilitates data transmission and power distribution.
   • One RDX051 PCIe Acquisition Board: Handles data buffering and transmission via an 8-lane PCIe Gen3 interface (64 Gbps bandwidth).
   • Clock Architecture: A deterministic zero-delay clock distribution architecture using LMK04832 jitter cleaners and LMK01801 buffers to ensure phase alignment across all channels.

2. Experimental Validation: The PDS1500 was deployed alongside the commercial CAEN V1751 system on the JNE-1ton prototype. Signals from the PMTs were split and fed into both systems simultaneously to allow for direct, synchronous comparison. The prototype was operated in a slow liquid scintillator environment.

3. Performance Metrics: The study evaluated six key parameters:

   • Data loss rate (using external triggers).
   • Baseline stability (noise levels).
   • Waveform fidelity (using $\chi^2$ analysis of aligned waveforms).
   • Timing drift (measured over five power-cycle restarts using LED calibration).
   • Energy threshold (determined by lowering trigger thresholds).
   • Energy resolution (measured using an AmBe calibration source).

Key Contributions

• Development of PDS1500: The creation of a custom, modular electronics system featuring 1 GSa/s sampling, 14-bit resolution, and a 64 Gbps throughput capability.
• Deterministic Clock Distribution: Implementation of a zero-delay clock architecture that eliminates the phase ambiguity and thermal drift issues common in daisy-chained commercial systems, ensuring absolute trigger consistency.
• Comprehensive Benchmarking: A rigorous side-by-side comparison of the new system against the established CAEN V1751 standard in a real-world experimental environment, providing empirical data on performance gains.

Results
The testing demonstrated that the PDS1500 system meets or exceeds the technical requirements for the JNE experiment:

• Data Integrity: The system achieved zero data loss within the 1000 ns acquisition window, outperforming the CAEN V1751 which exhibited a 49 ns dead time.
• Baseline Stability: The baseline noise of the PDS1500 was reduced to approximately one-third of the CAEN V1751 level, significantly improving measurement accuracy and reducing trigger instability.
• Waveform Fidelity: $\chi^2$ analysis confirmed that the waveforms captured by the PDS1500 are consistent with the CAEN V1751, with the higher 14-bit resolution providing greater waveform detail.
• Timing Drift: Across five power-cycle restarts, the PDS1500 exhibited a clock drift of only 0.3 ns. In contrast, the CAEN V1751 showed a drift of 16 ns. The PDS1500's drift is well below the 1 ns sampling step and the PMT transit time spread (1.8 ns).
• Energy Threshold: The PDS1500 enabled a detection threshold as low as 0.1 MeV (compared to ~0.5 MeV for the CAEN system), facilitating the detection of low-energy solar neutrinos from the $pp$ chain and $^7$Be.
• Energy Resolution: Both systems achieved an energy resolution of approximately 9% for the neutron capture peak. The study notes that this resolution is limited by the intrinsic properties of the 1-ton detector (scintillator light yield and PMT coverage) rather than the electronics' bit depth; thus, the 14-bit resolution did not further improve the overall energy resolution in this specific configuration but provided superior waveform fidelity.

Significance
The paper concludes that the newly developed PDS1500 electronics system fully satisfies the technical requirements for the future full-scale JNE experiment. The modular architecture, high throughput (64 Gbps), and scalability demonstrated by the 64-channel prototype provide a robust foundation for the planned 3,000-channel detector. The system's ability to minimize data loss, reduce baseline noise, and maintain sub-nanosecond timing stability across power cycles addresses the critical challenges of high-precision neutrino physics. The authors assert that these results collectively validate the system's readiness to support the scientific goals of the Jinping Neutrino Experiment, including the precise measurement of solar neutrinos and the search for neutrinoless double-beta decay.