1. Status of the development of miniHV at Nikhef Henk Boterenbrood, Harry van der Graaf, Henk Groenstege, Ruud Kluit, Fred Hartjes and Jaap Kuijt 7 th RD51 Collaboration Meeting CERN, 14 April 2011 Small HV modules dedicated to gaseous detectors for laboratory use

2. Why developing HV power supplies? uGetting a HV supply that is dedicated for gaseous detectors lFast trip in nA 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. 7 th RD51 Collaboration Meeting, CERN, April 14, 2011Fred Hartjes Aiming for two designs 1.MiniHV for use in the lab, testbeams etc lPractical in use, relatively small, not completely antimagnetic nBut NO inductors, transformers 2.MicroHV 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 miniHV 3

4. 7 th RD51 Collaboration Meeting, CERN, April 14, 2011Fred Hartjes Philosophy of Nikhef miniHV uGenerally HV power supplies make use of feedback by voltage divider circuit l=> quiescent current of 10 – 100 µA uWith Nikhef miniHV no feedback by voltage divider lBut by dummy Cockcroft-Walton cell lAdditional compensation from measured output current u=> trip and output current measurement in nA region uBleeder circuit using high ohmic resistors (180 GΩ total) for HV signaling l=> I quiescent < 6 nA lUsed for HV indication by an LED l(Not suited for voltage regulation) 4 HV out Feed back 10 – 100 µA < 6 nA Commercial HV power supplies MiniHV

5. 7 th RD51 Collaboration Meeting, CERN, April 14, 2011Fred Hartjes Voltage regulation uRegulation by analogue input voltage (0 – 60V) uVoltage feedback lVia single Cockroft Walton circuit lCurrent compensation by local microprocessor 5

6. 7 th RD51 Collaboration Meeting, CERN, April 14, 2011Fred Hartjes Configuration uUp to 10 HV units connected to single power supply unit uOnly connected by CAN bus lPower supply lines incorporated (+/- 12 V; 60 V) uCAN interface needed (National Instruments or KVASER) uCAN bus ends in passive terminator 6 CAN bus @ 125 kbit/s + power PC + CAN-interface Powersupply unit

7. 7 th RD51 Collaboration Meeting, CERN, April 14, 2011Fred Hartjes Specs of miniHV, version 2 uOutput ~ -3 to -1000V @ ≥ 0 - 5 µA lSteps of ~ 70 mV lVoltage variation from zero to full load: 4 – 6 V nTo be improved uStandard negative output lPositive output in principle possible but needs modified Cockcroft Walton PCB uRipple ~ 100 mV p-p measured uOutput impedance without current compensation ~ 5 MΩ uLED indication for V out exceeding -50V uRamping lCompletely controlled by local microprocessor lInitially linear, followed by exponential approach to target voltage, fully configurable uContaining minor magnetic parts from electronics l=> expected to operate in magnetic field lSupply box is NOT antimagnetic 7 More or less finalised Conform classification

8. 7 th RD51 Collaboration Meeting, CERN, April 14, 2011Fred Hartjes Ramping scheme uControlled by local processor uLinear-1 l0.07 – 4500 V/s lUnits of 0.07 V/s uExponential lStarting between 0 and 100% of required voltage lUnits of 1% uLinear-2 l0.07 – 4500 V/s lUnits of 0.07 V/s 8 Linear-1 Exponential Linear-2

9. 7 th RD51 Collaboration Meeting, CERN, April 14, 2011Fred Hartjes Two different trip actions uWarning limit (nA) in 0 – 65 µA lAction: warning message is sent uTrip limit (nA) in 0 – 65 µA lActual trip only after certain number of overcurrent events (0 – 255) l=> reaction time depends on frequency of the control loop of the local processor nExample: 2 Hz => 0.5 – 128 s lAction: HV supply current is set to zero (no active pull down to zero, the pull down current has to be provided by the detector itself) 9

10. 7 th RD51 Collaboration Meeting, CERN, April 14, 2011Fred Hartjes CANopen Object Dictionary prepared 10

11. 7 th RD51 Collaboration Meeting, CERN, April 14, 2011Fred Hartjes Existing control software uFull control by CAN bus lNo manual control or read-out uControl by stand-alone program lMiniHVmon uLabView control lIn progress lSome communication problems to be solved 11 4 channel control panel

12. 7 th RD51 Collaboration Meeting, CERN, April 14, 2011Fred Hartjes Preliminary performance 12 Calibration routines still in development All voltages and currents negative uActual voltage measured with electrostatic voltmeter (readout lc 1 V) uVoltage stability (0 – 5 µA): ~ 5 V -500 V -1000 V

13. 7 th RD51 Collaboration Meeting, CERN, April 14, 2011Fred Hartjes Prices, availability u5 miniHVs are operational lOnly for Nikhef use u20 miniHVs in preparation lExpected to be finished mid May 2011 lPartly for Nikhef use lPrice not yet fixed, but ~ € 1200 + 19% VAT (Europe) u10 modified power supply units in development (connected to line ground) lExpected to be finished July 2011 lPrice not yet fixed, but ~ € 400 + 19% VAT (Europe) uIn addition a CAN interface is needed (National Instruments or KVASER) l~ € 300 13 Will be exchanged by grounded AC power connection Send me an email if you’re interested F.Hartjes@nikhef.nl Send me an email if you’re interested F.Hartjes@nikhef.nl

14. 7 th RD51 Collaboration Meeting, CERN, April 14, 2011Fred Hartjes GEM grid 1 GEM grid 2 GEM grid 3 V field Ideas for other miniHV modules 1.-2000 V version lDifferent CW PCB but same housing 2.Single MiniHV with ~ 7 outputs (-6000 V?) from Cockroft Walton circuit for triple GEM lRegulating GEM voltages by selecting the desired CW stage nsteps of ~ 50V lBut whole chain may be finely tuned uAdvantage lGetting rid of voltage divider chains or multiple cascaded HV units lLow trip levels possible (nA region) nNo current from voltage divider chain lProblem: how to handle possible pull up currents 14 Send me an email if you’re interested in one of these ideas F.Hartjes@nikhef.nl Send me an email if you’re interested in one of these ideas F.Hartjes@nikhef.nl

15. 7 th RD51 Collaboration Meeting, CERN, April 14, 2011Fred Hartjes Conclusions u5 units Mini HV version 2 (-1000V) now completed and operating well u20 units + power supplies available after summer, partly for groups outside Nikhef lBut a new series can be started at sufficient interest uPositive output possible but needs additinal work (modified cascade board) u-2 kV version well possible but also new cascade PCB required lNot yet designed, will only be considered at sufficient interest uPossible future developments lMore outputs and higher voltage (-6 kV) nGEM grids n=> bit larger housing lNot yet designed, will only be considered at sufficient interest uMore info about mini HV on web page http://www.nikhef.nl/pub/departments/et/high_voltage/index.html 15