LAUSR

The linearity of charge response is an important feature of photomultiplier tubes (PMTs) for physics measurements, especially the newly developed 20'' microchannel plate (MCP) PMT (MCP-PMT). In this paper, in addition to the traditional method of double light sources, we applied another relative method of 20'' PMT to 3'' PMT comparison to measure the linearity of the 20'' dynode and MCP PMTs in pulse mode using a waveform digitizer. The measurements show a good linear response of the two types of 20'' PMTs to 1000 photoelectrons (p.e.). The correlations of the amplitude, rise-time, fall-time, FWHM, baseline recovery, overshoot, and the amplitude ratio of late-puse of the 20'' PMTs were derived from the waveform analysis, where the MCP-PMT shows very different features compared to the 20'' dynode-PMT.