Performance Test and Circuit Simulation for R12699-406-M4 Photomultiplier Tube Base

TL;DR

The paper addresses the need for wide dynamic-range PMT readout in next-generation liquid xenon detectors, aiming to cover energies up to $2.5\mathrm{MeV}$ NLDBD while preserving SPE sensitivity. It combines bench tests and LTSpice circuit modeling to study the R12699-406-M4 PMT base, focusing on desaturation capacitors to mitigate saturation and suppression effects. The results identify BASE-2 (four desaturation capacitors) as meeting the detector requirements and demonstrate that a data-driven circuit model can reproduce observed waveforms, guiding base design and potential data-analysis corrections. Overall, this integrated approach improves detector dynamic range and provides a practical framework for saturation/suppression correction in PandaX-xT and similar experiments.

Abstract

The next-generation liquid xenon experiments like PandaX-xT target an energy range from sub-keV to multi-MeV to address the requirement of multiple physics searches. The Hamamatsu R12699-406-M4 photomultiplier tubes (PMTs) were developed and selected as photon sensors for PandaX-xT. Their voltage-divider base is optimized for a broad dynamic range, from single-photoelectron (SPE) sensitivity to 30~nC collected charge (matching the 2.5~MeV Q-value of $^{136}$Xe neutrinoless double beta decay~(NLDBD)). Using a dedicated test bench, we characterize the saturation and suppression responses of R12699-406-M4 PMTs with this base design. Based on measured PMT-base responses, we develop a circuit simulation model that accurately reproduces the physical mechanisms underlying these effects with key parameters tuned via experimental data. The combined simulation and bench-test approach guides base design and optimization, enabling improved detector dynamic range and supporting future saturation and suppression correction studies in data analysis.

Figures (16)

• Figure 1: The picture of 2-inch R12699 PMT. The square PMT integrates four identical 1-inch detection channels within a single housing.
• Figure 2: The designed base circuit of the R12699 PMT, illustrating the electron flow and currents during operation. Please refer the text for detailed information.
• Figure 3: (a) Schematic of the bench-test setup. (b) Picture of the test setup. The base PCB accommodates a 3$\times$3 PMT array. 5 PMTs are placed inside, including 1 test PMT and 4 monitors.
• Figure 4: PMT waveforms from bench test. The orange and blue waveforms represent the recorded signal from the test PMT and the reconstructed input signal from the monitor PMT, respectively. (a) the observed charge $Q^{obs}$ matches the true input charge $Q^{t}$, (b) shows Signal with severe saturation effect.
• Figure 5: The saturation response curves of PMT-A with different base circuits. The black markers denote the two specific cases presented in Fig. \ref{['fig:sat_wave']}.