QRLed Driver in Magnetic Field

1. Jaroslav Zalesak Institute of Physics of the ASCR, Prague QRLed Driver inMagnetic Field QRL in Magnetic Field

2. QRL in Magnetic Field Calibration Option 2:LED driver • Non-linearity correction, MIP calibration, Correction temperature variations • Two appr.: electrical or optical signal distribution - One LED / one tile or central driver plus fibres UV LEDs – short light pulses Notched fibers Each illuminates 12 tiles HBU CALIB module Option I QRLD board (ASCR Prague): „Quasi Resonant LED Driver Board“, 6 LEDs / 1 PCB

3. QRL in Magnetic Field QR-LED driver LED1 +12V QRLED 1 Power regulator FIBRES T-calib µC AT91SAM7X256 V-calib LED 6 QRLED 6 • Option with optical fiber distribution • Electronics: multi-channel prototype complete • Optical system: uniformity again competitive • MultichannelLED driver • 1 PCB with the communication module µC, power regulator, 6 channels of QRLed driver • Communication module to PC via CAN bus or I2C • Controlling the amplitude and monitoring temperature and voltages • LED pulse width ~ 5 ns fixed, tunable amplitude up to 50-100 MIPs is controlled by the V-calib signal • 2 LEDs can be monitored by a PIN photodiode

4. QRL in Magnetic Field Magnetic Field Test Setup • week ago tests in mag. field • one week period at solenoid • DESY site up to 4 T available • QRL PCB fixed to movable rod • different positions to measure • 3 LEDs / channels → • 3 optical fibers outside meas. • area, LV supply and CANbus • wires from r/o area

5. QRL in Magnetic Field Data Readout • 3 r/o Photo detector channels: • 2 APDs@ low-gain • 1 PIN diode + amplifiers • 1 Temp sensor @ APD (automatically in r/o only at the end) • LV + HV supplies • Slow control based on LabView • via CAN bus several LV/Temp • control points from PCB recorded • Auto-implemented data transfer from scope (3+1 ch. Ampl) • Independent S/C for Magnet

6. QRL in Magnetic Field Magnetic Field Scan #1 - ‘middle’ • 1st PCB position in the middle solenoid parallel to line of magnet • force, horizontally placed, homogeneous Mag. Field • about 2hours scan 6.5 up/down magnet + 7min stable B • Variations in response @ (in) visible level (PIN x APD T- uncorr.)

7. QRL in Magnetic Field Magnetic Field Scan #2 - ‘slantways’ • 2nd PCB position in the middle solenoid, placed on oblique surface • ‘slantways’ ~25° angle, homogeneous Mag. Field • Variations in response @ (in) visible level (PIN x APD T- uncorr.) • Overall scan ±0.5% difference (a bit more APDs), maybe B steps

8. QRL in Magnetic Field Magnetic Field Scan #3 – ‘outer’ • 3rd PCB position at the end of solenoid – ‘outer’ position, • horizontally placed, no-homogeneous Mag. Field • response seems to rise contrary previous measurements • for highest magnetic field B.

9. QRL in Magnetic Field Magnetic Field – Long-term • Over 8 hours long-term behavior in constant 4T magnetic field • Almost (Temp ~0.1%) constant conditions • Variations in response invisible • Amplitudes < 0.5%; PIN diodes ~0.5% noise level, APD less

10. QRL in Magnetic Field Temperature dependence • Only, at the end of data measurement period automatically • APD temperature sensor in r/o implemented • Correction formulas determined to be applied to data • 2(?,gain/pos. sensor) diff APD dependence, NO PIN dependence

11. QRL in Magnetic Field Conclusion I • Calibration system – option II: electronic part QR LED driver reasonably works incl. Slow control interfaces  can be implemented into EUDET AHCAL prototype • Characteristics and function described in public paper EUDET report 2008-7 • Optical part – notched fibres in preparation → promising results Prague AHCAL group

12. QRL in Magnetic Field Conclusion II, Outlook • Calibration system – QR LED driver in Magnetic field tests:  works very well • meas. system sensitive to < 0.5% variations in response • During constant magnetic field (standard operation conditions) the measurementsare stable (w/o reference to PD temp.) • Expecting one more measurement period • more precise orientations of PCB in mag. field • to avoid temperature dependence P.S. Thanks to DESY staff to allow to make such measurement Note: these days we have obtained one new notched fiber, which seems to fulfill our request on uniformity (light output ± 10%)

13. QRL in Magnetic Field Backup slides

14. QRL in Magnetic Field Option 2: Optical system 2 MIPs 10 MIPs 25 MIPs • Idea: use one fiber for one row of tiles (72) • Problems: • uniformity of distributed light • enough intensity of distributed light • concentration of LED light into one fiber • Two fibres: • Side-emitting - exponential fall of intensity • Notched fibre ‏- better uniformity of distributed light - need to mechanize production - R&D • No optical cross talk seen (< 1-2 %) @ different amplitudes Notched fiber:

15. QRL in Magnetic Field Calibration system • Non-linearity correction, MIP calibration, Correction temperature variations • Use gain monitoring, adjust voltage → see G. Eigen’s talk • Many procedures developed during last year’s analysis, but not finally proven yet • Stability of saturation still an issue -> need dynamic range • Two appr.: electrical or optical signal distribution - One LED / one tile or central driver plus fibres • Differences inside the active gap, but same external interfaces Option 2: LED driver • Electronics: multi-channel prototype complete • Optical system: uniformity again competitive • Integration into active layer still an open issue • MultichannelLED driver • 1 PCB with the communication module µC, power regulator, 6 channels of QRLed driver • Communication module to PC via CAN bus or I2C • Controlling the amplitude and monitoring temperature and voltages • LED pulse width ~ 5 ns fixed, tunable amplitude up to 50-100 MIPs is controlled by the V-calib signal • 2 LEDs can be monitored by a PIN photodiode