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

2. The present divider

3. Change of the gain with a DC current

4. 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 ?)

5. 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 .

10. 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

12. 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

13. The new divider

16. inter-dynodes variations : measures with different anode DC currents

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

18. 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)