4 FEU-84-3 PMTS with Cockcroft-Walton bases were mounted in a block of high density polyethylene. The spacing between the PMTs is the same as intended for the PMT-Cell-Wall. The PMTs were run with the CW-base set to 2000V. There was enough light leakage to generate signals. The temperature was measured inside the bore in the plastic next to the PMT. Now temperature increase was measured when operating the PMTs.
In a second measurement a small hole has been drilled into the shell of the CW-base and the temperature sensor inserted into the base itself. In this case a temperature rise of about 2.5 degree C has been observed. The temperature rise happened over the time scale of one hour and then leveled out.
Scope shot from one PMT showing the signal shapes:
Scope shot from one PMT showing noise level from the base: