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SNS Beam Loss Monitor Electronics Final Design Review

SNS Beam Loss Monitor Electronics Final Design Review. D. Gassner, R. Witkover Brookhaven National Laboratory. SNS BLM Electronics Outline. Requirements Dose Rate Estimates Gain and Threshold Control Dynamic Range System Block Diagram Cable interface Analog Circuit Schematic

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SNS Beam Loss Monitor Electronics Final Design Review

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  1. SNS Beam Loss Monitor ElectronicsFinal Design Review D. Gassner, R. Witkover Brookhaven National Laboratory SNS BLM Electronics, BNL

  2. SNS BLM Electronics Outline • Requirements • Dose Rate Estimates • Gain and Threshold Control • Dynamic Range • System Block Diagram • Cable interface • Analog Circuit Schematic • Front end Stage • Fast Loss Integrator (MPS Trip) Stage • Viewing Stage • 1 W/m stage • Thermal Drift • VME & Digitizers • Data Acquisition • HV Bias • Summary SNS BLM Electronics, BNL

  3. BLM System Electronics Requirements • Provide measurements of loss for tuning • Protect the machine from high activation due to slow, low-level losses (1W/m criteria) • Protect the machine from radiation damage due to fast high-level losses MPS Input(Beam Permit/Inhibit Link) • Not for personnel protection. SNS BLM Electronics, BNL

  4. Dose Rate Estimates • Slow Loss: 1 W/m criteria • Corresponds to ~10- 4 loss distributed around 248 m Ring. • Beam-off activation approximately 100 mrad/hr at 1 ft. • “Rule of thumb”: Multiply by 1000 to get beam-on dose rate (100R/hr). • Same as 0.5 R/sec during the 1 ms SNS pulse. • Need to resolve 2 decades below, or 1% of 1 W/m. • What is maximum high-end loss? • 1% local loss (of 2 MW) = 20 kW requested. • Pre-integration to extend dynamic range. • Total range is equivalent to 21-bits + sign • Low-end resolution limited by noise and BW, upper end by detector and/or electronics saturation. SNS BLM Electronics, BNL

  5. Required Gain and Threshold Control • Programmable Gain (local & remote) • Beam intensities • Linac and HEBT range: 15-38 mA • Ring increases 103 during macro-pulse • RTBT can vary 103 between single turn, full intensity • Detector shielding by beam line components • Beam energy dependence • Programmable loss limit thresholds • Individual channels • Separate thresholds for Fast and 1 W/m losses • Trip outputs can be masked through MPS for studies SNS BLM Electronics, BNL

  6. Electronics Dynamic Range Fast Response for Beam Abort For 10us rise time, BW would be 35 kHz. (550 pA noise scaled from RHIC) This limits resolution to 30 Rad/hr. Intention is to observe large fast losses ~ 106 Rad/hr Signal Upper Limit 1% of 2MW, in Linac and HEBT, uniformly over pulse = 644uA Lost fast in one place (RTBT) = 644 nC (very large) Lower Limit 1% of 1W/m = 324 pA Total dynamic range of 126dB (324pA – 644uA) Need separate signal paths for Fast and Slow losses. SNS BLM Electronics, BNL

  7. System Block Diagram SNS BLM Electronics, BNL

  8. BLM-Cable Interface • In order to balance rise time due to signal cable length variations, a BLM-Cable interface panel will be included which will hold capacitors at the transition from the coax to mass termination connectors. Example: • Belden 9054 is 16 pf/foot, runs will vary from 75 to 300 feet, yielding 1200 – 4800 pF. • 470 Ohm AFE input R, rise times will vary from 1.2 to 5us (assume 2.2 X RC = rise time) • We can extend the dynamic range for RTBT fast loss signals by pre-integrating the signal by choosing input caps for a 50-100 usec time constant. This would allow us to get to several times 0.1% single point loss without saturating the 1 W/m & Viewing stage electronics. • NOTE: Belden 9054 is a low Tribo-electric cable which significantly reduces noise due to friction. It is essential when measuring signals in the nA or lower region. SNS BLM Electronics, BNL

  9. Analog Front End 80kHz 80kHz 1.5kHz 1.5kHz SNS BLM Electronics, BNL

  10. Front End Amplifier Stage • Trans-impedance amplifier: • Burr-Brown OPA627BP • low offset voltage, Vos = 100 μV max (un-trimmed) • Drift 0.8uV/0C, max • Bias current, Ib = 1 pA • GBW = 16 MHz. Open loop gain 120dB. • Selectable gain settings: • Normal Linac 62k Ohm • Normal Ring 6.2k Ohm • High Controlled loss 1k Ohm • Noise voltage: gain is set by the resistors Rf and Ri, 6200/470 = 13.2, but the signal is only set by Rf, (IC ideal current source). RHIC noise = 10 pA for 10 Hz BW. Using a 100 kSa/S ADC, BW will be limited to 50 kHz. Scaling between these cases gives an equivalent noise current of 0.71 nA and an output noise voltage of 4.36 μV. Johnson & Amp noise = 4.1 μV. • Thermal Drift: calculated worst case is 100 μV, actual data (better) shown later. • Trim Pot • Protection Diodes SNS BLM Electronics, BNL

  11. Analog Front End SNS BLM Electronics, BNL

  12. Fast Loss Integrator (for MPS) Experience at LANSCE has shown that a beam inhibit signal should be based on integrated dose rather than dose rate. Hardware damage is normally due to amount of energy rather than rate of energy deposited. An integrator will be used to provide a signal to a comparator to generate a signal for the MPS when the programmable reference is exceeded. Response time 10 us (input RC, FE, this stage response.) • Leaky Integrator vs. • Simple • Adequate ? • Non-linear • Residual offset • Gated Integrator • More complex • Gating & Reset • Charge injection • Precise 16.6 ms Circuit components values related to MPS Comparator range (unknown). SNS BLM Electronics, BNL

  13. Analog Front End 80kHz 80kHz SNS BLM Electronics, BNL

  14. Viewing Stage • Features: • Isolation to drive 100kS/s digitizer • Remote gain setting X1, X10 and gain readback. • Change viewing gain without changing MPS trip threshold. • Noise:Calculated 110 μV (< than LSB) with no trim pot this stage. With trim pot, better 20 μV. • Drift: See upcoming plot • Saturation problem in RTBT, solved by: • Added capacitors in Cable Interface, 50-100us time constant • Jumper selectable AFE signal routing • Linac & Ring: routed directly from first stage. • RTBT: routed through integrator. • Should yield several times the 0.1% single point loss without saturating the electronics. SNS BLM Electronics, BNL

  15. Viewing Stage Data Acquisition Data Acquired: • Baseline (1 msec) + BLM signal (1 msec + ion collection time) • Digitizer – 16 bits (incl sign), 100 kSa/s • 2 bytes/sample, 500 bytes/SNS cycle • +/-5 V, LSB = 152.6 μV • Only selected BLM’s send full data (10 max for entire system). • Sum of losses per BLM, per macro-pulse, sent once per second. • Input to waterfall type display. • 1000 point FIFO history at the console level for use in the event of an abort. SNS BLM Electronics, BNL

  16. Analog Front End 80kHz 80kHz 1.5kHz 1.5kHz SNS BLM Electronics, BNL

  17. 1 W/m Stage • Philosophy: • Reduce noise by reducing BW. • 1kHz allows enough settling time so digitizer can acquire baseline. • Reduce amplitude of fast loss spikes so we don’t saturate. • Gain added ( X 10) so we can use 16-bit ADC rather than 24 bit ( see slide ) • 1 W/m loss during the cycle (32.4nA X 6.2k X 10) will yield 2mV. • 1% of 1W/m = 20uV • Trim Pot • Data: Baseline (1 msec) + Beam On (1 msec) + Residual signal (1 msec) • Digitizer: • Slow loss viewing – 16 bits (incl sign), 100 kSa/s • 2 bytes/sample, 600 bytes/SNS cycle • +/-5 V, LSB = 152.6 μV • Data accumulated over 10 second or longer interval • Processed to compare against a 1 W/m reference (alarm) in IOC. • Pre-averaged low-level data will be available as a waterfall, or a strip chart display. SNS BLM Electronics, BNL

  18. Thermal Drift 1 LSB SNS BLM Electronics, BNL

  19. ICS 110B VMIC 3123 HyTec 8401 Offset drift -13 ±9uV/oC -25 ±6uV /oC 67 ±11uV/oC Gain drift 128 ±6 PPM 34 ± 4 PPM 8 ± 7 PPM Simulated slow loss signal measured by a 16 and a 24 bit digitizers (Yongbin Leng) SNS BLM Digitizers 1 W/m loss generates 32.4nA, through 6.2k = 200uV, for 1 ms pulse. Times 10 gain. 1% of 1W/m yields 2 x 10-8 V.S. 1% 1W/m 600 pulses 10 seconds SNS BLM Electronics, BNL

  20. VME Implementation Non-VME, Linear power supplies SNS BLM Electronics, BNL

  21. Data Acquisition and Control • Controls Interface • Readback front end gain jumper setting • Set & Readback Viewing Stage Gain (X1, X10) • Timing for Integrator (MPS) gating • Set loss threshold, fast loss (trip), slow loss (alarm) • Digitized loss data (fast and slow) • Gain and calibration data folded into resolved data. • Set and readback of High Voltage, On/Off bits • System test SNS BLM Electronics, BNL

  22. HV Bias ISEG HV Bias Supply • VME High Voltage Power Supplies in 2 slot width • 1 channel and 2 channel versions in same dimensions • LCD display for voltage or current • variable rate of change of output voltage • switched polarity • integrated protection and control circuits • output overload and short circuit protected • SHV connector on front side • Full control via VMEbus • EPIC’s drivers • $1.2k/channel • Model VHQ 204L, 0-4kV, 1mA SNS BLM Electronics, BNL

  23. SNS BLM System - Summary • BLM Electronics • Provide loss measurements for tuning. Three local gain ranges. • Low level signals (1W/m) • Expected low-end signals within the range proposed system. • Bandwidth limit 1kHz. • Process data over 10 second interval. • Goal 1% of 1W/m. • Higher level signals (larger fast losses) • Wideband (50kHz) viewing. • Additional remote gain control. • Fast RTBT loss signals pre-integrated to extend dynamic range. • Machine Protection (Integrated loss) • 10 μsec response, programmable thresholds and masks. SNS BLM Electronics, BNL

  24. Back-Up Slides • Rack Layout • Analog Front end (Leaky integrator) SNS BLM Electronics, BNL

  25. Rack Layout Location # Ch #FBLM #Crates Note • DTL_Diag:Cab401 5 1 • CCL_Diag:Cab301 12 1 • CCL_Diag:Cab302 12 1 • SCL_Diag:HB13Cab01 29 1 • SCL_Diag:HB1Cab02 30 1 • HEBT_Diag:Cab07 40 3 2 1 • Ring_Diag:Cab05 55 12 2 2 • Ring_Diag:Cab06 44 0 2 3 • RTBT_Diag:Cab04 28 3 1 4 • Note 1: 12 HEBT ch located in Ring racks • Note 2: Includes HEBT ch beyond ground break • Note 3:Includes 12 ch from RTBT before ground beak • Note 4: 12 RTBT ch located in Ring racks SNS BLM Electronics, BNL

  26. Analog Front End (LI) 36Hz 80kHz 80kHz 1.5kHz 1.5kHz SNS BLM Electronics, BNL

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