Abstract
We report here on a set of experiments that focus on measuring the timing performance of the Photonis miniPlanacon XPM85212/A1-S microchannel plate photomultiplier tubes along with the detector response at high event rates. The detector has a single photoelectron timing resolution of 30 ps at low rates (10 kHz).
We show that both the gain and the timing start to deteriorate around 1 MHz with 20 photoelectrons per channel at 104 target gain, giving the current per unit of area limits of 1.38 mu A/cm(2) and 2.38 mu A/cm(2) for the two tested devices. Photo-multiplier tubes with lower micro-channel plate resistivity exhibit a better rate capability due to the faster replenishment of the charge inside the microchannels.
As we demonstrate, another method to improve the rate capability is to operate the photon detector tubes at a lower gain by reducing the supply voltage and compensating for the loss of amplitude by an additional amplification stage at the expense of the achieved timing resolution. The tube active area over which the beam is spread also plays a role since the same amount of light yields a better rate capability when spread over a larger area.
The tubes exposed to high event rates showed an uncharacteristically slow recovery back to its initial gain with 80% of the initial gain recovered only after several tens of minutes.