ACTIVE DIVIDER for anode currents up to 10 microamps LPC Clermont Jan. 2010

The present divider

Change of the gain with a DC current

The goals : To maintain stable inter-dynode voltages when the anode current increases Using high voltage SMD transistors Keeping the same voltage distribution as before Keeping the same current in the divider (possibly compatible with the present HV system ?)

SIMULATION PMT simulated by current sources controlled by functions F(x) depending of :  the secondary emission coefficient (linear approximation) the inter-dynode voltage We look at the changes in the inter-dynode voltages as a function of the anode current .

Voltage variations on the last stages For a change from 0 to 10 microamps with HV=-700V and G=10**5 d5 -d6 d6-d7 d7-d8 d8-GND 43 V 88 V 130 V 86 V Variation s 0.19 V 0.27 V 1.14 V 2.96 V PASSIVE DIVIDER d5 -d6 d6-d7 d7-d8 d8-GND 44 V 87 V 128 V 86 V Variations 0.03 V 0.08 V 0.12 V ACTIVE DIVIDER

This simulates only the behavior of the divider (not taking in account the linearity of the photomultiplier itself). We need only to add 3 transistors

The new divider

inter-dynodes variations : measures with different anode DC currents

anode-d8 voltage (V) versus anode current (µA) Active divider Passive divider

CONCLUSION the active divider is efficient even for much higher currents than 10 µA The next steps : *Cabling of 20 dividers and (pulse + DC current) behavior with one PMT * radiation hardness (evolution of the gain of the transistors)