Update on Trigger Configuration for Special Runs and Early Bunch Train Running David Strom Updated version 28 April 2015

Background  SCT and IBL have fixed frequency vetoes (FFTV) that are designed to prevent running at fixed frequency  These vetoes were introduced to avoid the fate of CDF where a test run broke many of the modules in their detector  Effects of current implicated in DBM failures (but probably not a resonant effect and not related to the magnetic field)  Current FFTV can easily be evaded even though the power at a given frequency can be much higher than it might be for configuration that would fire it, such as a single colliding bunch in the machine  New DAQ system can read detector at a higher rate than in Run 1 (e.g. the survival of the SCT in Run 1 not a guarantee of safety in Run 2)  Need to independently check IBL and SCT safety for Run 2

What conditions are dangerous for wire bonds?  The Lorentz force on a wire is  The force is perpendicular to magnetic field and the direction of the wire bond  Resonant excitation has been observed in the lab when the force Lorentz force is perpendicular to the plane that contains the wire bond.  In ATLAS such a wire bond would need to be oriented along a radial line perpendicular to the beam  Wires bond located in the dangerous direction in ATLAS are in forward region of SCT and in the DBM. IBL wire bonds have almost no radial component.  In laboratory tests wire bonds have been broken in a 2 T field with a current of 100mA when the current is varied with square wave at the resonant frequency of the wire.  With currents of 20mA at resonance, plastic deformation of the wires is observed.  For this presentation assume that damage could occur at currents as low as 10mA (at resonance) and normalize all results to the first harmonic of 11kHz 10mA square wave with 50% duty cycle.  Wires with shorter lengths have a higher resonant frequencies. The effect of wire length, including the decrease in overall force with shorter lengths, is not accounted for in the following.  Behavior of wire bonds that have been subject to corrosion such as those in the IBL have not been studied and may have a lower damage threshold.

Example of a measured IBL resonance curve  Width is approximately 100 Hz  We therefore plot power as the current amplitude squared/100Hz normalized to 10mA square wave

All “power” measurements normalized to 10mA square wave  Limit for putative damage  Reference “damage threshold”  Safety factor is ratio to damage threshold measured in dB Normalization of first harmonic set to unity Power = |current amplitude| 2 /100 Hz 100Hz bin width

Power for reliably breaking wires +20 dB more than damage threshold

IBL model for L1 Accepts  Normalize all plots to power for 10mA 50% duty cycle square wave at a rate of 11kHz  Define safety factor relative to this: Safety factor = 10Log 10 (P example /P square-wave )  Other assumptions for IBL analysis:  It is assumed that only dangerous currents are related to L1 Accepts (L1A) that cause the IBL FE to search for hits.  Assume that an L1A causes a 20mA current to flow for 125ns (2.5nC) (upper limit). See next slides.  To break wires a current of 100mA is needed for a significant fraction of the duty cycle.  Assume that simple dead time protects L1A from piling up in the IBL FE.  All IBL time series plots show time of needed to process L1As  Assume this is always done during simple deadtime (125ns)

IBL estimation of charge per L1A

Charge per L1A is ~40nC/16 ~ 2.5nC

November 2012 vdM Scan  An example of a vdM scan is run from 22 Nov  LHC had 29 bunches in the machine  We triggered on bunches 1, 2361, 2881 (This is bunch group “7” and called “unpaired” but was in fact a selection of the colliding BCIDs)  Even at 100% occupancy current FFTV will not fire because of spacing

Bunch group 594 (run )  URL for BG is  Trigger for vdM stream consisted of  L1_MBTS_2_BGRP7 (any two MBTS scintillators in BG 7)  L1_MBTS_2_UNPAIRED_ISO (any two MBTS scintillators in BG 4)  These triggers were unprescaled as can be seen in the prescale evolution: (select MBTS in search box to display)

Maximum mu value was ~0.8  Expect that MBTS_2 would have ~50% efficiency, so maximum occupancy was less than 50%  Total rate at which SCT and pixel were readout in this three bunches was 13.5kHz. There were additional random triggers rate of ~6.6kHz on the 29 filled bunches.

IBL example – single bunch N.B. simulation uses 712, 125ns buckets Time series of L1A activity Bin width corresponds to typical wire resonance width IBL -40 dB safety factor

IBL examples – adding randoms doesn’t change power -40 dB safety factor Includes abort gap, could cancel effect of single bunch if it is near abort gap

IBL normal running (independent of μ) Normal running a factor of 10 better than single bunch in machine (-50dB safety) IBL

Conditions of 2012 vdM scan (13.5kHz max) LCH BCIDs: 1,2361, % trigger occupancy 5kHz cyclical prescale Similar to single bunch, -40 dB safety IBL

Request for 2015 vdM scan (33kHz rate) Trigger on every selected BCID Includes extra 2012 randoms Factor of ~4 worse than Nov 2012 vdM IBL -34 dB safety

Alternative, 25kHz (5 bunches with MBTS) No Peak at 11kHz BCID: 1,841,1581,2401, % occupancy IBL -32 dB safety

Early 25ns and 50ns running  LHC will add slowly add bunch trains to the machine as in 2010, 2011, 2012  Apparently these configurations can be more dangerous than vdM scans  SCT survived many runs in 2012 with only a few bunch trains (I will try to locate them)

IBL single saturated bunch train (95kHz) IBL Safety factor -22dB

IBL Single bunch train, ~50% occupancy in train 6kHz rate IBL New FFTV-B would limit to this power Safety factor -50dB

IBL single bunch train, ~25% occupancy in train 3kHz rate (e.g no HLT) Typical enhanced bias data run IBL Safety factor -50dB

Tentative Conclusions for IBL  vdM scans with MBTS trigger in Nov 2012 has a peak at near 11kHz which is factor of 10 worse the “normal running”, but safety factor is still -42 dB  Effect of corrosion is unknown  vdM request for 2015 for reading every BCID has ~4 times higher power in L1A 100Hz bands than the 2012 configuration, safety factor of -34 dB  vdM scans with 5 almost evenly spaced bunches removes 11kHz peak for IBL, safety factor of -32dB at higher frequency  Additional protection is possible for runs with only a few bunch trains. 50% occupancy veto reduces IBL power to “normal running” level (safety improves from -22 dB to -50 dB)

Model for relative power SCT  Normalize all plots to power from 50% duty cycle square wave at 10mA as for IBL  SCT sensitive wire bonds are on readout, so depends on queuing model  Other assumptions:  Readout rate is 40Mb/s  Events have *n bits (where n is the number of hits)  For normal running assume that mean number of hits is = *0.17, Poission distribution  Assume = 0.5 for vdM scans (and offset 53 for 0 hits)  For normal running simulate abort gap but not details of bunch trains.  For normal running implement simple queuing, assuming an infinite buffer  For vdM scans assume detector can always be readout between collisions (minimum spacing of filled bunches is 40 BC = 1μsec )  All time series plots show time readout is active, not necessarily trigger time.

SCT current with a single beam in machine N.B. simulation uses 712, 125ns buckets (same as IBL) Time series of readout activity FFT – normalized to 10mA square wave SCT SCT resonance region starts at 15kHz Safety factor -37 dB

SCT normal running (μ=40) Normal running somewhat worse than a single fixed frequency bunch SCT Safety factor -33 dB at 15kHz

SCT survived 2012 vdM scan (13.5kHz max) LCH BCIDs: 1,2361, % occupancy 5kHz cyclical prescale Peaks in dangerous region, power/100Hz not worse than normal SCT Safety factor -35 dB

Request for 2015 vdM scan (33kHz rate) Trigger on every selected BCID Includes extra 2012 randoms Factor of ~4 worse than Nov 2012 vdM SCT Safety factor -35 dB at 55kHz

Early 25ns and 50ns running  LHC will steadily add bunch trains to the machine as in 2010, 2011, 2012  Apparently these configurations can be the most dangerous for SCT as the following slides show  SCT survived many runs in 2012 with only a few bunch trains (some archeology needed to check what rates were)  See for example:

SCT single saturated bunch train (95kHz) SCT Safety factor -10 dB at 11kHz -20 dB at 22kHz Unlikely configuration, no lumi for ALICE and LHCb Could happen by accident in BG selection, etc.

SCT Single saturated bunch train, ~50% occupancy in train 5.4 kHz rate SCT Safety factor -30 dB Condition s just under veto

BG251

BG 251 with 98kHz rate (~100% occupancy) 98 kHz rate SCT Safety factor -17 dB

BG 251 with 40kHz rate (~50% occupancy) 40 kHz rate SCT Safety factor -26dB Just below veto

SCT Tentative Conclusion  SCT survived 2012 vdM scan and running with single bunch-trains  Lumi group request for 2015 would be a factor 4 worse than the 2012 vdM scan for SCT, but better than single bunch- train running at high rate  Safety factor still is -35dB  Single bunch trains at high trigger rate and high μ are comparatively more dangerous than vdM scans  Unclear what the worst case for SCT in Run 1 was  Adding a 50% veto (FFTV-B) for overlapping bins in the machine would improve the safety factor from -10dB to -30B for a single bunch  FFTV-B has major implications for trigger and running early running scenarios, e.g. the muon alignment run if we can not run at high rate with only a few bunch trains in the machine

Overall Conclusions  IBL and SCT are first order suppressed for two reasons:  Wire orientation: oWire bonds in z direction have no force on the wire oWire bonds in the azimuthal direction have force on wire in the plane of the wire bond oWire bonds in radial direction (only in SCT EC, VDC to VCSEL) are in the dangerous direction, but are short and have resonance at high frequency  Assuming the wires were to be placed in the most dangerous configuration and no FFTV protection, power in Fourier spectra is at least 10dB lower that the reference damage level of 10mA, 11kHz, 50% duty cycle square wave  No other first order effects have been suggested  Danger to most of IBL and SCT would need to come from unidentified second order effects  Largest identified effect would be for SCT EC bonds  The most dangerous “foreseen” conditions for IBL and SCT occur if a very high Level-1 rate is used for one or a few bunch-trains  FFTV-B veto would improve SCT safety factor from -10dB to -30dB  FFTV-B veto would improve IBL safety factor from -22dB to -50dB  Impact of FFTV-B veto on ATLAS running not yet evaluated  May already get bunch trains in first week of collisions  Many “unforeseen” trigger configuration could cause almost square-wave like conditions, similar to those  Improper vetoing of Tile laser signals  Incorrect bunch group selection by Trigger Shifter  Operation of the L1Calo with LAr and/or Tile un-configured and incorrect bunch group  Safety factor for vdM scans in all configuration is at least -30 dB  vdM scan scenarios that will give a very quick and accurate luminosity result are incompatible with the proposed FFTV-B vetoes

Backup

Further reading  “Overview of B-field effect on wire bonds”  “IBL operation in magnetic field: Fixed Frequency Trigger” ides/0.pdf  “A Fixed-Frequency-Trigger Veto for the ATLAS SCT”  “Resonant Bond Wire Vibrations in the ATLAS SemiConductor Tracker”, Nucl. Instr. Meth. A538 (2005)  “Wire-bond failures induced by resonant vibrations in the CDF silicon detector”, Nucl.Inst. Meth. A518 (2004)

Amplitude will depend on duty cycle of signal