Fig. 1. Schematics of thermal cycle post-treatment

Fig. 2. Schematic of operation and typical plateau curve of high temperature photomultiplier tubes. (a) Schematic of high temperature photomultiplier tubes in deep-sea oil and gas logging and high temperature photomultiplier tube operation (this figure is from https:∥www.163.com/dy/article/D3H3DCVS0511KHPS.html); (b) typical plateau curve of high temperature photomultiplier tube, where A is the starting point of the plateau and B is the ending point of the plateau

Fig. 3. Plateau curves of original PMT and thermal cycle post-treated PMT. (a) Original PMT; (b) thermal cycle post-treated PMT

Fig. 4. Test curves of count rate stability of PMT maintained at 175 ℃ for 400 h under different working voltages. (a) Original PMT; (b) thermal cycle post-treated PMT

Fig. 5. Change in dark noise and gain of PMT with voltage. (a) Dark noise versus voltage at 175 ℃; (b) gain versus voltage

Fig. 6. Dark noise versus temperature at constant voltage of 1900 V

Fig. 7. Spectral response curves and mechanism diagram of high temperature photomultiplier tubes. (a) Spectral response curve comparison for original PMT and thermal cycle post-treatment PMT; (b) schematic of mechanism of ion feedback noise reduction by thermal cycle post-treatment