ATLAS-ALFA as a beam instrument Sune Jakobsen (BE-BI-PM and PH-ADO) on behave of the ATLAS-ALFA community LS1 LBOC meeting

LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 2/18 The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion The ALFA detector

Absolute Luminosity For ATLAS - ALFA Beam pipe ATLAS sub-detector. LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 3/18 Detectors inside Roman Pots. Approach the beam vertically to few mm. A total of 8 detector, 4 per beam. The detectors are based on scintillating fibers read out by MAPMTs. The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

ALFA detector - Main trigger Main detector (Tracker) Main trigger tiles Overlap trigger tiles Overlap detector (Alignment) Main trigger scintillator tile PMT for main trigger tile LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 4/18 The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

Trigger system upgrade in LS1 LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 5/18 This makes is possible online to monitor the rates for all bunch crossings over time for each detector (or even for logic between detectors). New Front End electronics: Reduces the dead time from ~600 ns to 88.5 ns New Back End electronics: Main purpose is to reduce latency to keep ALFA trigger signals inside the ATLAS latency. The new Back End electronics also add advanced monitoring: Individual scalers per detector per bunch crossing. The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

ALFA as beam instrument LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 6/18 Only use rates from trigger tiles. That makes each of the 8 ALFA detectors into a pair of scintillators with PMT readout capable to be positioned very close to the beam: Efficiency: Higher than 99 % for MIPs Noise: No measureable noise after coincidence internally in the detector. Rate measurement per bunch crossing for each of the 8 detectors. The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 7/18 ALFA experience of measure ring beam properties in Run1 The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

Observations on de-bunching on raw ALFA trigger signals in 2011 Beam 1 Beam 2 Conclusion: Beam 2 have much more triggers not associated with any bunch. RP1 RP2 RP3 RP4 RP5 RP6 RP7 RP8 Triggers from filled bunch Time position 1 without any filled bunch Time position 2 without any filled bunch Observation of trigger signals made directly on an oscilloscope while the Roman Pots where in position for data taking with β* = 90 m optics. LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 8/18 The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

Observations on de-bunching in 2012 Online plot of ALFA trigger rates for empty bunches (no bunches at +/- 5 BC) during data taking with Roman Pots in position. (Fill 2836 with 112 bunches and 90 m optics). Conclusion: Beam 1 is de-bunching significantly faster than Beam 2. Change of ATLAS bunch group settings Special ATLAS trigger items made to be able to monitor the rate of e.g. empty bunches. Reminder for Run2: Each bunch has an individual scalar, such that development over time can be observed. LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 9/18 The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

Halo observations for low intensity 90 m run 2012 Raw rates from each ALFA detector Scraping of TOTEM horizontals Roman Pots clearly seen. Halo level of beam 2 falls immediately to the level of beam 1 when the collimators are extracted to loss maps positions. Beam 2 has orders of magnitude more background than beam 1. Online rates also used in additional fills for finding clean halo condition for data taking with Roman Pots at 3 σ nominal. 6 σ nominal 8 σ nominal 9.5 σ nominal Move all ALFA Roman Pots to 6 σ nominal Scraping of TOTEM horizontal Roman Pots Move all ALFA Roman Pots to 8 σ nominal Rates for detectors on beam 2 Rates for detectors on beam 1 Collimators moved to loss map positions Move all ALFA Roman Pots to 9.5 σ nominal Loss maps LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 10/18 The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

Method of background cleaning in β* = 1000 m optics 2012 Beam pipe Beam loss monitor Primary collimator ALFA Roman Pot Goal: Data taking with Roman Pots at 3.0 σ nominal without being dominated by background. Scrap down the beam with the TCPs (Primary collimator) in IR7 to 2.0 σ nominal. Repopulation of the gab and background returning. Retract TCPs to 2.5 σ nominal and continue data taking with reduced background. Halo Position Roman Pots at 3.0 σ nominal. Very large background from TCP spray observed. Move TCPs out to 2.5 σ nominal. Data taking with greatly reduced background. Repeat scraping with TCPs to 2.0 σ nominal. Enormous background while scraping. Sune Jakobsen LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 11/18 The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

First peek on β* = 1000 m data The rate of the “anti-golden” events was used online to evaluate the background compared to physics events: Online rates Offline estimate of signal vs. background rates Online rates is a strong measure of halo even very close to the beam. Elastic “golden” trigger “Anti-golden” trigger IPAC2013: TUPFI037 Maybe worth to invest time in measuring the repopulation speed of the gap from existing data? LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 12/18 The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 13/18 Run conditions in Run2 The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

Run conditions for Run2 Any use case would naturally have to be approved be ATLAS/ALFA to ensure it does not compromises the main goals for the detectors system. Very low beam intensity (MD type): Conditions similar to “beam based alignment” of the Roman Pots. Up to 2 bunches + probes at full beam energy (more at lower beam energy). Roman Pot movement possible outside STABLE BEAMs with override key (made for bba). Roman Pots can (with MPP permission) move to any distance up to the primary collimators (like in bba). Up to about 700 bunches (beyond the ALFA detector suffers from too high rates/radiation). Medium beam intensity (Intensity ramp type): Only movement in stable beams and position minimum about 15 σ nominal. High beam intensity (Luminosity production type): Online feedback: Open connection to ATLAS and using ATLAS online monitoring (like in ALFA data taking). Not recommendable for all fills (radiation damage and single-events-upsets). Offline data: If desired the rates can be stored at end of fill (like luminosity data). ALFA experts can help with rates plot etc. Only movement in stable beams and position minimum about 15 σ nominal. Impedance heating of Roman Pots might also put limitations. LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 14/18 The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 15/18 Initial ideas for use cases The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

Initial ideas for use cases in Run2 De-bunching: Relative de-bunching over time like in Spread of de-bunched particles over BCs Time evolution of de-bunching after e.g. a collimator scraping. Relative population in the About Gap. Measure the rates of particles in the halo directly with ALFA detectors. Halo population. See additional ideas on next slide for “MD for active halo control”. New ideas coming up after a wider audiences is aware of the capabilities of the ATLAS sub-detector ALFA. Relative population of (empty) bunches during vdM scans. Any use case would naturally have to be approved be ATLAS/ALFA to ensure it does not compromises the main goals for the detectors system. LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 16/18 The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

Proposal: ATLAS-ALFA during MD for active halo control To measure the relative population of the halo during the MD is essential. If the ALFA detectors were positioned e.g. like shown there would be a direct online measurement of the tertiary and quartiary halo population. Very low total intensity (so Roman Pots can move in without stable beam). No colliding bunches, so no collision debris, only halo. Collimator group highly involved, so experts available during MD. Information of rates in non-filled BC after each steep could also be provided. Conditions very good for use of Roman Pots: There is a MD being prepared for “Active halo control”. See R. Bruce LMC talk: LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 17/18 The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion

Conclusion Using only the trigger tiles of the ALFA detectors can provide online feedback on rates per bunch crossing. ALFA have already in Run1 measured de-bunching and halo population and due to upgrades in LS1 this can now be done even better (less dead time and measurement per bunch crossing). Especially for very low intensity ALFA could be a strong addition to the existing beam instrumentation. Help for operations in limited periods like MDs could be provided by ATLAS/ALFA. Any use case would naturally have to be approved be ATLAS/ALFA to ensure it does not compromises the main goals for the detectors system. Various cases for use for measuring de-bunching and halo pointed out. Discussion started if it is interesting to use ALFA for “MD on active halo control”. LS1 LBOC meeting ATLAS-ALFA as a beam instrumentSune Jakobsen 18/18 The ALFA detector Run1 experience Run2 run conditions Use cases Conclusion