background studies with hera beam
DESCRIPTION
Background studies with HERA beam . Torsten Limberg. Overview of studies with beam. Synchrotron radiation background studies: Beam Based Alignment Dedicated e+ runs with special filling patterns Positron particle background studies: Collimator studies upstream of experiments - PowerPoint PPT PresentationTRANSCRIPT
Background studies with Background studies with HERA beam HERA beam
Torsten LimbergTorsten Limberg
Overview of studies with beamOverview of studies with beamSynchrotron radiation background studies:Synchrotron radiation background studies:
Beam Based AlignmentBeam Based AlignmentDedicated e+ runs with special filling patternsDedicated e+ runs with special filling patterns
Positron particle background studies:Positron particle background studies:Collimator studies upstream of experiments Collimator studies upstream of experiments Beam tail studies with scrapers and increase of positron tail density Beam tail studies with scrapers and increase of positron tail density with HERMES targetwith HERMES targetBeam position/angle scans at IPBeam position/angle scans at IP
Proton background studies:Proton background studies:Background rates vs. local IR pressure bumpsBackground rates vs. local IR pressure bumpsRamp detector solenoid to check for trapped ionsRamp detector solenoid to check for trapped ionsUse e+ beam as vacuum measurement inside detectors Use e+ beam as vacuum measurement inside detectors
Beam Based AlignmentBeam Based Alignment
Question: Question: Are magnets so far Are magnets so far off their design position that off their design position that steering through the steering through the Interaction Regions without Interaction Regions without radiating into the experiment radiating into the experiment is impossible?is impossible?
BBA MethodBBA Method
Principle:Principle:
in itia l o rb it
d ire c tion IP d ire c tio n a rc
M isa lig n ed q u ad is v a rie d in s tre ng th
R esu lting o rb it d iffe re n ce is ta k en o u t w ith tw o co rre c tio n co ilsQ u ad ru p o le o ffse t is ca lcu la te d fro m the n ec essary co rre c to r c h an g e s.
BBA ResultsBBA ResultsControlled Bridge movement successfully measured
Found magnets sufficiently close to Design positions (here at ZEUS)
e+ only Runs e+ only Runs
Separates synchrotron radiation background (linear in Separates synchrotron radiation background (linear in positron current) from positron particle background positron current) from positron particle background (quadratic in good approximation)(quadratic in good approximation)
Detector drift chamber currents vs. time differentiates Detector drift chamber currents vs. time differentiates between directly hitting synchrotron photons and between directly hitting synchrotron photons and backscattered radiation (needs special fill patterns)backscattered radiation (needs special fill patterns)
Determine proton contribution to background ratesDetermine proton contribution to background rates
H1 Drift Chamber Current vs. IH1 Drift Chamber Current vs. Ie+e+
ZEUS Drift Chamber Hits vs. TimeZEUS Drift Chamber Hits vs. Time(for the passing of a ‘single’ bunch)(for the passing of a ‘single’ bunch)
Positron Particle Collimator StudiesPositron Particle Collimator Studies
Positron particle collimators at 15 and 40 Positron particle collimators at 15 and 40 meters do not improve e+ particle meters do not improve e+ particle backgroundbackgroundSimulations show that they will not be Simulations show that they will not be effective against e+ particles scattering in effective against e+ particles scattering in an 80 meter range upstream of the an 80 meter range upstream of the detector detector
Beam Tail Studies with ScrapersBeam Tail Studies with Scrapers
Beam Loss Monitors
Scraper Jaws
Scraper MeasurementScraper Measurement
Result of Scraper StudiesResult of Scraper Studies
Measured horizontal and vertical tails of Measured horizontal and vertical tails of positron density distribution with scrapers:positron density distribution with scrapers:– Similar to 2000 runningSimilar to 2000 running
Increased pressure in HERMES gas target Increased pressure in HERMES gas target to reduce positron life time. Repeated to reduce positron life time. Repeated scraper measurement and found tail scraper measurement and found tail population increased by a factor of ten:population increased by a factor of ten:– No significant deterioration of background No significant deterioration of background
conditions (at 4 mA) conditions (at 4 mA)
Beam Position and Angle Scans at Ip’sBeam Position and Angle Scans at Ip’s
Results of Beam Position ScansResults of Beam Position Scans
… nothing unexpected
Studies of Proton BackgroundStudies of Proton Background
Measure increase in background rates for Measure increase in background rates for local pressure increase at different local pressure increase at different positions in the IRpositions in the IR(Pressure bumps by controlled out-gassing of Hydrogen while heating TSP (Pressure bumps by controlled out-gassing of Hydrogen while heating TSP pumps)pumps)
Exclude ion trapping in solenoid fieldsExclude ion trapping in solenoid fieldsMeasure detector vacuum with e+ Measure detector vacuum with e+ bremsstrahlung ratesbremsstrahlung rates
Controlled out-gassing by heating TSP PumpsControlled out-gassing by heating TSP Pumps
Comparison of e+ bremsstrahlung rates from non-colliding bunches (measured with the ‘Luminosity Monitor’) yields a pressure increase between factor 5 and 10 between the years 2000 and 2002
Measuring the Detector Vacuum with the e+ Beam
The Solenoid ExperimentThe Solenoid ExperimentTest for ions trapped by the solenoid fieldsTest for ions trapped by the solenoid fields Friday, late shiftFriday, late shiftrun down H1 Solenoid at the end of a luminosity run with keeping run down H1 Solenoid at the end of a luminosity run with keeping collisions and with chambers oncollisions and with chambers on
H1 SolenoidRadMon CJC2
eBeam Current
SummarySummaryBeam Based Alignment Beam Based Alignment excluded grossly misaligned magnets as the source of the excluded grossly misaligned magnets as the source of the problemproblem
Dedicated e+ runs yielded:Dedicated e+ runs yielded:– direct synchrotron radiation photons hits can be reduced to small values (between direct synchrotron radiation photons hits can be reduced to small values (between
noise level and 10% of e+ background) with orbit optimizationnoise level and 10% of e+ background) with orbit optimization– Backscattered synchrotron radiation from absorbers is the main photon sourceBackscattered synchrotron radiation from absorbers is the main photon source– Ratio between positron background (synchrotron radiation and particles) and proton Ratio between positron background (synchrotron radiation and particles) and proton
backgroundbackground– Proton background from beam-gas collisions is at least as severe as the positron Proton background from beam-gas collisions is at least as severe as the positron
backgroundbackground
Backscattered photon rate can reduced by absorber plating andBackscattered photon rate can reduced by absorber plating andshielding => leaves proton background as the major problemshielding => leaves proton background as the major problem
Proton background studies:Proton background studies:– Excluded high density ion trapping (Solenoid experiment)Excluded high density ion trapping (Solenoid experiment)– Provide data for of vacuum profile and detector sensitivityProvide data for of vacuum profile and detector sensitivity
Controlled out-gassing at TSP pumpsControlled out-gassing at TSP pumpsMeasuring average detector vacuum with e+ bremsstrahlung ratesMeasuring average detector vacuum with e+ bremsstrahlung rates
lead to self-consistent model for vacuum pressure profile and detector response.lead to self-consistent model for vacuum pressure profile and detector response.