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Description
This work investigates rate effects in a photoelectric resistive plate chamber (Photo-RPC) operated in single-photoelectron mode, focusing on the role of electrode bulk resistivity and the underlying mechanism of timing degradation. The detector has a 215 μm gas gap filled with R134a/SF6/i-C4H10 (90/5/5), and a 355 nm femtosecond pulsed laser is used to control the incident photoelectron rate. Glass electrodes with different bulk resistivities are tested to compare gain stability and timing performance. The results show that lower-resistivity electrodes suppress gain reduction and extend the available rate range. A key observation is that, even at the same average gain, the time resolution under high-rate operation is worse than that obtained at low rate by reducing the applied voltage, indicating an additional degradation mechanism beyond the decrease in the average effective field. To explain this effect, a stochastic local voltage-drop model is developed based on local avalanche-charge accumulation and charge relaxation in the resistive electrode. The model shows that random intervals between successive events cause event-by-event fluctuations in local effective field, Townsend coefficient, and electron drift velocity, introducing extra timing jitter. Experimental-data resampling and Garfield++ simulations reproduce the measured gain loss and timing degradation, validating the proposed model.