Ice Cube DOM Calibration Jim Braun April 20

Ice. Cube DOM Calibration Jim Braun April 20, 2005 1

Motivation April 20. 2005 2

DOM-Cal – Big Picture • Application runs on DOM – Can calibrate all DOMs in parallel – Stores calibration data on DOM flash memory DOM hub DOM-Cal Client • Java client – Coordinates calibration – Reads calibration data from DOM – Produces DOM-Cal XML calibration files • Calibrator class reads XML file, applies calibration constants • All code in dom-cal project on glacier – Authors: John Kelley, Jim Braun, Kael Hanson April 20. 2005 Database XML Files Calibrator. java Analysis 3

Calibration Routine • ATWD Calibration – Reconstruct PMT voltage waveform from ATWD data – Requires: • • Voltage calibration of ATWD Measurement of amplifier gain for ch 0, ch 1, and ch 2 Frequency calibration of ATWD Baseline measurement • PMT Gain Calibration – Find relationship between PMT gain and applied voltage • PMT Transit Time Calibration (NEW!) – Find PMT transit time as a function of applied voltage April 20. 2005 4

ATWD Calibration • Bootstrap process! Amplifier ch 2 Calibration Muons Mainboard LED April 20. 2005 Amplifier ch 1 Calibration Amplifier ch 0 Calibration Baseline Calibration ATWD Frequency Calibration Pulser Calibration ATWD Voltage Calibration f = 20 MHz V = 0. 0001220 x (0. 4 x disc_dac – 0. 1 x bias_dac) V = 5 x bias_dac / 4096 5

Pulser Calibration • Determine relationship between pulser DAC setting and peak voltage – Use known relationship between discriminator DAC and voltage – Set discriminator DAC, adjust pulser DAC until 50% of pulses cross discriminator threshold – At this point, the pulser peak voltage corresponds to known discriminator voltage. – Peak voltage distribution is very narrow April 20. 2005 6

Pulser Calibration • Repeat for ~10 discriminator voltages • Relationship is very linear • Now know pulser peak voltage given DAC setting • Will use this relationship in amplifier calibration April 20. 2005 7

ATWD Voltage Calibration • Determine relationship between ATWD value and signal voltage • Use known bias DAC voltage relationship – Bias is independent of amplifier gain – Set bias, record average ATWD value • For each bin (0 -127) of each signal channel (0 -2) of each ATWD (0 -1) • O(100) samples – Apply linear fit to ATWD value vs. voltage data • Pedestal patterns are eliminated April 20. 2005 8

ATWD Voltage Calibration • Now know voltage of any ATWD bin given a channel number, bin number, and value • Requires 768 linear fits! • ATWD response not entirely linear • Need to calculate and subtract small baseline offset for each channel during precision measurements April 20. 2005 9

Baseline Calibration • New in DOM-Cal 5. 0 • Measures average baseline offset for each ATWD channel • Need to measure baseline whenever the internal state of the DOM changes • Known to affect baseline: – Analog multiplexer – Mainboard LED power supply – PMT high voltage • Affects low gain channel the most – Main source of Hagar’s ch 1: ch 2 charge discrepancy April 20. 2005 10

Baseline Calibration • We care most about affect of high voltage and residual baseline from imperfect ATWD calibration • Take baseline data both with HV off and HV at values spanning DOM operating points • Store all data points • Use baseline value closest to operational HV when calibrating Test. DAQ data • For gain calibration, domcal chooses only the voltages where baseline calibration points exist April 20. 2005 11

Amplifier Calibration • Calibrate high gain channel (0) with pulser – Pulser too weak to accurately calibrate lower gain channels • Set pulser peak to a known voltage, record peak voltage after amplification in ch 0 – Use ATWD ch 0 calibration data to find peak voltage • Maximize ATWD sampling speed to better localize peak • Record mean and error of O(250) ch 0 peaks • Ratio of mean voltage and known pulser voltage yields amplification factor April 20. 2005 12

Amplifier Calibration • Need source of high amplitude pulses to calibrate ch 1 and ch 2 amplifiers • Use PMT signals! – new in DOM-Cal 5. 0 – Muons work well at surface – Mainboard LED needed in deep ice • LED power supply shifts baseline, need to recalibrate • For ch 1: – Select pulses which have an ATWD peak value of 600 -800 counts • Too few ch 0 counts -- too much error in ch 1 peak voltage • Too many ch 0 counts -- ch 0 nonlinearity becomes significant April 20. 2005 13

Amplifier Calibration • For ch 1: – Record ratio of ch 1 peak voltage to ch 0 peak voltage for O(250) iterations – We know ch 0 gain, so ch 1 gain is given by the product of ch 0 gain and voltage ratio. • For ch 2 – We now know ch 1 gain, use previous procedure to find ch 2 gain – Slow with muons (<1 Hz) – Slow when discriminator rate is high – Use LED if necessary April 20. 2005 14

ATWD Frequency Calibration • Select mainboard oscillator in ATWD analog multiplexer channel (channel 3) • At various sampling speed DAC values, count number of bins between positive zero crossings in ATWD waveform • Average O(100) clock waveforms • Assuming oscillator operates in spec @ 20 MHz, ATWD frequency is given by 20 MHz * #bins • Not quite linear – newer version will sample closer to 850 DAC value April 20. 2005 15

Gain Calibration • Capture PMT single photoelectron pulses in ATWD – Glass radioactivity emits enough light • Apply ATWD calibration to get PMT V(t) waveform • I(t) given by V(t)/50 W • I(t) pulse integrated from – 4 bins to +8 bins of pulse maximum (~-14 ns - +28 ns), yielding SPE charge • Repeat O(5000) times, histogram charge data, and apply nonlinear fit April 20. 2005 16

Gain Calibration Fit Exponential + Gaussian Single-Photoelectron Peak Noise Discriminator Edge Muons, etc. Charge (p. C) April 20. 2005 17

Gain Calibration Repeat from 1200 V to 1900 V in 100 V intervals 1400 V 1500 V 1600 V 1700 V April 20. 2005 18

Gain Calibration Gain (charge / e) Mean SPE charge vs. voltage is a power law Linear log - log fit yields operating point Voltage The number of photoelectrons for any pulse at a given HV is now determined April 20. 2005 19

Java Client • In dom-cal project on glacier – Main class: icecube. daq. domcal. DOMCal • Run with no args for usage instructions • Reads calibration data from DOM flash – Stores calibration data in local XML files – Stores data in domprodtest database • Can initiate calibration • Can run calibrations on many DOMs and DOM hubs in parallel • Most will never need to use the java client April 20. 2005 20

DOM-Cal XML Files • Hopefully, users won’t need to know much about the XML files or database structure either! – Access provided through calibration applications • XML files are reasonably easy to read if needed – Contain: • • • DOM hardware ID (No name…. . sorry Mark) Temperature Date DAC settings and ADC readings Calibration information – Linear fit data – Baseline data – Gain histogram data April 20. 2005 21

DOM-Cal Calibrator • Icecube. daq. domcal. Calibrator java class provides access to calibration data. – I 3 DOMCalibration equivalent object in Ice. Tray • Create a Calibrator for each DOM: – new Calibrator(XML_File); • Most important routine: – atwd. Calibrate. To. Pmt. Sig() • Takes an array of raw ATWD data and applies calibration to yield true voltage signal • Other methods to access raw data, described in javadoc – http: //www. amanda. wisc. edu/jbraun/domcaldoc/ April 20. 2005 22

DOM-Cal Results • Currently running DOMCal v 4. 3 at pole • Baseline shift apparent in data from String 21 and from last year’s FAT runs • Analog multiplexer enabled in all string-21 runs – just recently disabled April 20. 2005 23

DOM-Cal Results • DOM-Cal 5. 0 results are encouraging • Baseline calibrated to zero for all channels • No analog multiplexer effects • Amplifier gains now calculated much more accurately • Pulse heights now agree between all three ATWD channels April 20. 2005 24

DOM-Cal Results • The bad news – Probably won’t see much gain when analyzing String 21 data, even with DOM-Cal 5. 0 • Local coincidence readout rate is a few Hz • Interval is long enough for baseline to drift • Hopefully there is a firmware fix! April 20. 2005 25

DOM-Cal 6. 0++ • Other features DOM-Cal may deal with: – PMT transit time – almost finished! – Signal droop • Evidence time constant can be easily measured (Chris W. ) – Ch 0 time offset, bandwidth limitation April 20. 2005 26