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SVTRAD Upgrades: Diamond Sensors and Readout Electronics

This workshop discusses the motivation, problems, and upgrade strategy for the SVTRAD system at SLAC. It focuses on the installation of diamond sensors and the improvement of readout electronics for better radiation monitoring and protection.

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SVTRAD Upgrades: Diamond Sensors and Readout Electronics

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  1. September 22, 2003Background Workshop, SLAC SVTRAD Upgrades M. Bruinsma bruinsma@slac.stanford.edu • Motivation • Diamond sensors • Readout electronics upgrade: SVTRAD1.5 M. Bruinsma

  2. Purpose of SVTRAD • Monitor radiation levels and • Protect the SVT from excessive and avoidable radiation damage: • Acute radiation damage: • P-stops, blocking capacitor breakdown • May occur at acute doses of 1 rad or more • Should be detected within ~ 1 ms: “fast aborts” • Long-term radiation damage: • Leakage current increase in Si bulk • Noise increase, gain reduction in readout electronics • Significant degradation expected after 5Mrad. • SVTRAD should keep total dose of SVT modules below 4Mrad • Time scale: seconds (monitoring) – minutes (“slow aborts”) – years These are two very distinct protection tasks, both done by SVTRAD. M. Bruinsma

  3. Problems with the current system • Uncertainty in pedestal (=‘leakage’=‘dark’) current of PIN diode: • accuracy ~0.1% => 3nA for 3mA dark current ~ radiation current (15mrad/s) • This mainly affects the slow (‘software’) aborts • Secondary problems/limitations – SVTRAD board • mid-plane diode radiation currents only accurate after long averaging • feedback to PEP-II of (mid-plane) radiation levels rather slow (few s) • PIN diode is either ‘abort diode’ or ‘monitoring diode’ • Abort logic not very flexible • Electronic problems (ground fluctuations, etc.) • Board-temperature dependencies • Upgrade strategy: • Replace damaged sensors with CVD diamond sensors in 2005 (=a.s.a.p.) • Upgrade readout electronics in end of 2003 (=a.s.a.p) M. Bruinsma

  4. CVD diamond sensors • From ‘operational’ point of view, diamond sensors are similar to PIN diodes: • similar sizes obtainable (10x10x0.5mm) • similar current levels due to radiation (100-200pC/mrad) • faster response times (ns) • higher bias : 500V for pcCVD diamond, 100 V for scCVD diamond (50V for PIN diodes) • Diamonds have (virtually) no leakage currents, even after irradiation • They are very radiation-hard • Have been installed in BaBar and routinely read out with SVTRAD1 board: • Proven to be suitable alternative • Minor (non-critical) to be understood (current tails, E x B effect) • The use of diamond sensors will eliminate the largest systematic uncertainty of the SVTRAD system M. Bruinsma

  5. Electronics Upgrade: SVTRAD1.5 • Motivation for SVTRAD1.5: • Compatible with future diamond sensor operation (500V bias) • Enhanced functionality, improved diagnostic power & flexibility in abort decisions • Improved precision on temperature- and current-measurement • Elimination of electronics problems of current readout board • Ensure sufficient spare boards for running until 2010 (no working spares) Note: SVTRAD1.5 will not solve the leakage current problem – diamonds will. (but it may reduce it) M. Bruinsma

  6. Conceptual overview of SVTRAD1.5 abort Diode current front-end (opamps, ADCs) display (LEDs) Abort & monitoring logic (FPGA(s) + EPROM) Diodes/diamonds Vbias PEP monit. Idiode fibers on-board thermistors SVT p.s. IOC Itherm MCU + CAN & RS232 Temp. measurement +switch thermistors analog mon. (DACs) temp scope Vtherm JTAG HTEMP M. Bruinsma

  7. Analog outputs for fast monitoring optical fibers, 3 per board Digital SPI interface to (quad) DAC (SCLK, CS, DIN) • ‘SVTRAD-DAC’ module: • ~1kHz update rate per channel • 4 quad DACs with SPI interface • AD5544, 16 bit precision • NIM module • Installed in alcove near PEP-II electronics SVTRAD1.5 SVTRAD1.5 SVTRAD1.5 SVTRAD1.5 • Benefits: • Fast feedback to PEP-II operators • 1kHz rate can be used to study individual injection pulses • 12 analog diode signals (1kHz) to PEP-II SAM: • leakage current subtracted => radiation levels M. Bruinsma

  8. More flexibility in fast abort decisions • All logic integrated into single FPGA: • can make an abort decision based on a combination of sensors (MID,TOP,BOT) • Abort channel current measurement modified from VFC -> ADC: • could include non-linear terms in temperature correction (more precise) • could include time-dependence of radiation levels in abort decision, e.g. prevent abort if radiation levels decreasing • could prevent abort decision if dose rate over threshold not hazardous for acute damage (i.e. << 1rad/ms) (it then becomes mainly a radiation budget issue) abort if dose over threshold:~2.5 rad Dose rate threshold rate: 1000 mrad/s 0 time 2ms M. Bruinsma

  9. Other benefits of front-end upgrade • All diodes are both ‘monitoring’ diodes and ‘abort’ diodes • Better precision on abort channel (monitoring channel the same) • Both ranges completely ‘tunable’: • monitoring range extended (7.8mA -> 15mA) for larger leakage currents • abort range extended (0.5mA->5mA) (may be lowered for better precision) • Faster abort decisions (1ms ->100ms) possible • Better (x100) precision on monitoring of ‘abort channel’ (no rerouting) • Can store history of abort ADC values: • better verification of abort decision • good fast-history of abort channel currents • Not fully-explored option: • Issue fast hardware ‘warning’ signal that would automatically undo latest change in optics before it causes the beams to be aborted. • Additional (optical) output has been added to SVTRAD1.5 to enable this M. Bruinsma

  10. Status, Time schedule & commissioning Electronics upgrade has been endorsed by Review Committee (July 23rd) • Present status of SVTRAD upgrade: • SVTRAD1.5 readout board designed, layout of PCB started • First board ready for testing in November • SVTRAD-DAC module designed, layout done, PCB being produced. • Commissioning strategy: • Lab tests (November/December) • Check contacts, FPGA firmware, calibration with current-source, optimization of temperature corrections, test abort logic, fast history • Tests with installed diodes/diamonds (December/January) • Connect to BE diodes, routed to electronics hut, separate IOC • Long-term stability, check abort decisions, correlate with other sensors • Installation in IR2 during access (first replace BE board, then others) M. Bruinsma

  11. For more information … Review document: BAD339: "SVT Radiation Protection: Upgrade Requirements & Scenarios" Upgrade website (links to talks, documentation, etc): http://www.slac.stanford.edu/BFROOT/www/Detector/SVT/Operations/SVTRAD/UPGRADE/ Design materials of SVTRAD1.5: http://www.slac.stanford.edu/BFROOT/www/Detector/SVT/Operations/SVTRAD/UPGRADE/SVTRAD15/SVTRAD15_design.html Design materials of SVTRAD-DAC: http://www.slac.stanford.edu/BFROOT/www/Detector/SVT/Operations/SVTRAD/UPGRADE/SVTRADDAC/SVTRADDAC_design.html Review materials (talks, etc.): http://www.slac.stanford.edu/BFROOT/www/Detector/SVT/Operations/SVTRAD/UPGRADE/SVTRAD15_Review_Jul2003/ M. Bruinsma

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