1. Development of µHV (miniature HV supplies) at Nikhef Henk Boterenbrood, Harry van der Graaf, Henk Groenstege, Ruud Kluit, Fred Hartjes and Jaap Kuijt RD51 Collaboration workshop Freiburg, 25 May 2010

2. Why developing HV power supplies? uGetting a HV supply that is dedicated for gaseous detectors lFast trip in sub µA region lAccurate current measurement in nA region lSmall unit, not too expensive lFast remote control lGently ramping to target voltage uIn addition, for large scale HEP experiments, one would like having these units close to the detectors in the hot region lNon-magnetic lMinimal mass lRadhard lLow noise emittance 2

3. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Developing two designs 1.Mini HV for use in the lab, testbeams etc lPractical in use, relatively small, not completely antimagnetic nBut NO inductors, transformers 2.Micro HV for use near the detectors in a big experiment lVery low mass, non-magnetic, radhard (until 1000 Mrad/ 10 7 Gy) uPresently we are developing mini HV 3

4. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Preliminary specs of mini HV, version 2 uOutput ~ -3 to -1000V @ 1.8 µA max lSteps of 73.6 mV uRipple 2 mV p-p @ 1 µA expected uRamping: initially linear, followed by exponential approach to target voltage lLinear part adjustable in units of 73.6 mV/s uCurrent measurement in 56 pA units uCommunication by CANopen protocol uSingle RJ45 cable for CAN communication and supply lCan be daisy chained uCast aluminium box 112 x 60 mm, 31 mm high lSHV out 4

5. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes CANopen communication to multiple mini HVs 5 uSingle RJ45 cable to supply everything

6. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Block diagram of single mini HV unit 6 ? uChop frequency may be modified uTrip by CAN logic processor, depending on voltage ramp lE.g. Trip 5 nA @ ramp 1V/s uVoltage feedback from dummy diode circuit

7. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Cockcroft-Walton circuit uIn principle no feedback at end of diode chain, only from first diode circuit uAdvantages lAccurate measurement of output current in nA region lSensitive trip possible uDisadvantage lRegulation less direct, depending on diode characteristics uOutput capacitance ~ 5 nF 7

8. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Fast ramping possible uMeasured rise time without slope adjustment ~ 100 ms (from 0 to -480V) lNo overshoot 8

9. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Simulation of smooth ramping uLinear rise adjustable in steps of -73.6 mV/s uFollowed by exponential approach to target voltage uSlope parameters controlled by CANopen commands lLinear slope lStart exponential part 9

10. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes CANopen Object Dictionary prepared 10

11. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Test results of two prototypes of mini HV version 1 uNote: version 2 (in development) may have different performance 11

12. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Output voltage vs DAC value uUnit 1.2 uGood linear behaviour over full range uVoltage can be regulated in steps of 73.6 mV 12

13. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Detail at low voltage uStarting from ~ -3V on 13

14. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Current measurement uUnit 1.2 uSteps of ~ 56 pA uCertain deviation from linear response uRMS ~ 50 pA lMeasured at -500 V and 500 nA 14

15. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Voltage regulation uUnit 1.2 uOutput impedance ~ 10 MΩ for currents > 200 nA u~ 10V higher output voltage for currents in few nA range compared to 200 nA lUsing two different types of diodes l=> Mismatch of diode characteristics 15

16. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Voltage regulation for Unit 1.1 uBasically no mismatch of diode characteristics l=> output impedance zero for currents > 150 nA l=> ~ 2V higher output voltage for currents in few nA range uRemaining inaccuracy might be partly cured lby adding bleeder resistors like 50 GΩ per cascade stage lMaking correction in CAN processor uAlternative: voltage feedback lBut resistor may be less stable lRegulation pretty slow 16

17. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Assembly in cast aluminium box 17

18. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Planned time schedule mini HV unit uVersion 1 ready l2 prototypes (-500 and -1000V lNot suited for series production uVersion 2 in development lSchematic to be finished lLayout PCB to be made lProduction and assembly PCB lAssembly HV box uStarting with producing 5 prototypes lPlanned to be ready mid October lProduction setup for 25 units 18

19. RD51 collaboration Workshop, Freiburg, May 25, 2010Fred Hartjes Conclusions uGlobal design for mini HV now settled lBut still quite some detailing to be done uStabilize voltage lBy individual calibration curve lBy using voltage feedback from bleeder resistor uCould start in autumn with some series production (~20 units) uWe might consider also more outputs lLike for GEM grids, omitting resistor chain l=> bit larger housing uPlan starting producing series of 20 in October 2010 19