Bad Honnef 2006 CMS - VDC 1 A drift velocity measurement chamber for CMS (VDC) Bad Honnef 2006 CMS - VDC title page Jens Frangenheim ~ 150 mm

Bad Honnef 2006 CMS - VDC 2 Bad Honnef 2006 CMS - VDCstructure Structure ● the CMS detector and its gas system ● necessity for a VelocityDriftChamber (VDC) ● the VDC setup ● the trigger (a chance for testing photodiodes) ● further improvements ● results ● HV curves ● classification of the results ● outlook

Bad Honnef 2006 CMS - VDC 3 The CMS-detector and its gassystem 5 wheels - 1 O 2 analyser parallel to each VDC - 1 VDC / wheel (+ 1 backup chamber) - 50 L/h per muon chamber gasroom CMS-detector Endcap

Bad Honnef 2006 CMS - VDC 4 Necessity ● E-field in muon chamber cell is inhomogeneous ● accuracy of muon chamber is limited by: - precision of drift time measurement - mechanical precision - knowledge of E- and B-field - drift velocity v d should be known better than 10 ‰ (so that error is smaller than other value's errors) use a dedicated, small drift chamber with homogeneous E-field to measure v d necessity

Bad Honnef 2006 CMS - VDC 5 The VelocityDriftChamber chamber layout cathode: U c up to -15 kV, E= 210 V/mm 5 MBq 90 Sr sources anode wire: U a ~ +1.8 kV grounded ( U=0) field shaping tubes insulator (Araldite) gas inlet cathode holders (6) Al plates shielding power connection and filter for cathode trigger system E-field V=1 L size ≈ milk bag (tetra pack © ) collimators (2 mm x 15 mm) development: diploma thesis Georg Altenhöfer drifting electrons electron tracks time difference --> drift velocity v d reference volume

Bad Honnef 2006 CMS - VDC 6 Principle of operation co drift time for 42 mm photomultipliers scintillator source Sr 90 collimator (Al wall) field shaping electrodes anode wire sensitive region slit cathode collimator (Al wall) me chamber layout

Bad Honnef 2006 CMS - VDC 7 features  VDC has very homogeneous E-field x component of electric field / V/mm electron beams = sensitive region (42 mm) Garfield ver < 3 ‰ tubes chamber layout

Bad Honnef 2006 CMS - VDC 8 The trigger system ● 2 kinds of "traditional" trigger systems have been tested - 2 scintillators (2 mm and 10 mm thickness) with 1 photomultiplier (d=50 mm ) per scintillator - 1 scintillator (10 mm) with 2 photomultipliers ● in preparation: one scintillator (4 mm thickness) readout via 4 geiger-mode photodiodes (1 mm 2 ) chamber layout - higher rate (from 33 Hz to 60 Hz) (less absorber, same scintillator) new technology, high potential - no HV needed (only ~60 V) - fast (signal rise time < 2 ns) - high quantum efficiency (over 40 % at 630 nm, cooled and 10 % at 400 nm, at room temperature ) - but high noise rate ( ~2 MHz at 20 ˚ C) 1 Hz random 4-fold coincidences expected scintillator

Bad Honnef 2006 CMS - VDC 9 Further HV improvements improvements edges of chamber have been improved - no problems at the moment (until -16 kV) add safety margin - longer holders (through backside) - add insulator to the backside of the cathode - enlarging the chamber by 10 mm

Bad Honnef 2006 CMS - VDC 10 present results ● accuracy of 0.4 ‰ for 5 min meas. (only statistical error !) ● no after pulses ● trigger rate improved ● optimal anode voltage set ● understanding of former peak height difference (unequal distances to PMs) results rate = 60 Hz σ (peak1) = (16.52±0.11) ns σ (peak2) = (17.36±0.16) ns counts(peak1) = counts(peak2) = 6633 signal to noise = 112 measurement with the prototype VDC m

Bad Honnef 2006 CMS - VDC 11 HV curves for anode (1) HV-curves constant difference higher anode voltage → larger gas avalanche U a = 1.60 kV U a = 1.85 kV U a = 2.60 kV HV too low: too few signals HV optimal: sharp peaks, low sigma HV too high: too much background (only statistical errors shown) measurements: - duration: 10 min - U c = 14 kV counts sigma(peak 1) / ns (20.3±0.6) ns (27.9±0.3) ns (16.7±0.1) ns U a / kV time / 32/25 ns working region U a / kV error for v d independent from U a

Bad Honnef 2006 CMS - VDC 12 HV curves for anode (2) field around anode accelerates HV-curves but time differences between electron beams are constant (around optimal voltage) anode voltage / kV time / ns anode voltage / kV v d / µm/ns not understood: effect outside working region working region t1t1 t2t2 ∆v d = 0.07 µm/ns time / ns

Bad Honnef 2006 CMS - VDC 13 HV curves for cathode HV-curves kV at U c =15 kV: same E-field as max. in muon chambers possible effects of overcurring sigma of peaks decreases with E-field sigma(peak1) / ns v d / µm/ns cathode voltage / kV but... dominated by width of electron beam data from peak width measured from v d other effect in the gas cathode voltage / kV

Bad Honnef 2006 CMS - VDC 14 Classification of the results results VDC: - unclean gas ? --> 99.7 % clean --> 80 ppm H 2 O (manufacturer) - going to repeat measurement with % clean gas measurement by T. Zhao, Y. Chen, S.Han, J.Hersch (1994) --> no information about systematic errors (E-field) --> cathode plates used --> inhomogeneous E-field ? --> influence of dielectrica ? preliminary data from VDC Ar/CO 2 85/15 comparison with other v d -measurement (only 1 serious with E-fields above 100 V/mm)

Bad Honnef 2006 CMS - VDC 15 Estimation of errors results - homogenety of E-field: 3 ‰, but periodic, so estimate < 1.0 ‰ - power supply for cathode: accuracy: 5 V, amplitude max. 10 V, б ≈ 2 V observed < 0.2 ‰ - light propagation fluctuations in scintillator (simulation ) < 70 ps, ∆t= 1000 ns < 0.1 ‰ - TDC bin size 0.8 ns, measurement: = 0.16 ns, ∆t= 1000 ns < 0.2 ‰ - statistical error (5 min measurement) < 0.4 ‰ - multiple scattering -> Geant4 (soon). Error permitted, to stay below 10 ‰ total error < 8.0 ‰ time to detector / ns

Bad Honnef 2006 CMS - VDC 16 Outlook outlook... if there is enough gas ➔ start of batch fabrication (7 chambers) ➔ finalize trigger test ➔ simulation of the VDC with GEANT 4 (multiple scattering) ➔ determination of absolute systematic error (by using more than one chamber) ➔ integrating new electronics (VME coincidences, discriminators, counters) ➔ transport to CERN: summer (06 ?) 2007 ➔ start of CMS gas system: 0x/2007, start of LHC: 09/2007 (?) We will keep on testing...

Bad Honnef 2006 CMS - VDC 17 Peoples and references references - master of the project: Hans Reithler - chief of the institute:Thomas Hebbeker - development, construction and first test of VDC: Georg Altenhöfer - building of VDC:Josef Grooten - planning, drawing of chamber-layout:Barthel Phillipps - electronics: Franz Adamczyk & Günther Hilgers & Henry Szczesny - supporter for improving read-out-software:Michael Sowa - supporter for HV supply programming:Oleg Tsigenov & Michael Bontenackels - final DAQ and DCS software: Gyorgy Bencze & Anita Kapusi & Gyula Zilisi - systematic tests and trigger development: J.F. The VDC on the web: This talk: Diploma thesis of Georg Altenhöfer: Paper about measurements of drift velocities: T. Zhao, Y. Chen, S.Han, J.Hersch; Nuclear Instruments and Methods in Physics Research A349(1994) T. Zhao, Y. Chen, S.Han, J.Hersch; Nuclear Instruments and Methods in Physics Research A349(1994) Geiger mode photodiodes from Photonique SA: for further question: Debrećen

Bad Honnef 2006 CMS - VDC 18 Backup slides backup slides

Bad Honnef 2006 CMS - VDC 19 The CMS gas system CMS detector

Bad Honnef 2006 CMS - VDC 20 Electronic chamber-layout scintillator (BC-416) light guide (plexiglass) photomultipliers (EMI, d=50 mm) preamplifier + shaper (from UA1-experiment) anode wire discriminator coincidence 18-channel NIM to ECL-Twisted Pair converter (Desy F56) timing unit (for gated mode) 3. Physikalisches Institut RWTH Aachen (Günther Hilgers) me VME-Bus (CAEN VME-MXl2) Win-PC with National interface ( LabView 8.0 DAQ- Software) CAEN SY-127 HV for anode HV for cathode CAEN A432 (4 ch., + 6 kV, 200 A ) CAEN A426 (2 ch., -20 kV, 200 A) CAEN-bus controller (CAEN C139) CAMAC-Bus Linux-PC with Camac ISA-controller (C++-software based on "surface" by Christian Autermann) TDC (CAEN V767, 0.8 ns resolution) power-supply for photomultipliers (CAEN N126, 1 ch., +6 kV, 3 mA) temp. sensor O 2 -content pressure temperature HV to cathode+field shaping tubes (incl. filter and voltage divider) drifting electrons

Bad Honnef 2006 CMS - VDC 21 data analysis results ➢ LabView gets data from TDC: time from anode pulses after trigger signal ➢ other data (pressure, temperature) also recorded ➢ analysis software (C++, root) reads data files and puts TDC data into histograms ➢ finding global maximum (small averaging regions) ➢ searching for a second peak on the left/right of global max. ➢ for each peak: searching down to the left/right until a value < average x factor is reached ➢ fit gaussian to fit region (iteratively) ➢ bad data can be detected, if no clear peaks are found time 32/25 ns counts

Bad Honnef 2006 CMS - VDC 22 Anode curves 5 (=83 Hz) counts / 1000/min U a / kV HV-curves

Bad Honnef 2006 CMS - VDC 23 photodiodes trigger structure photodiodes scintillator peltier elements coincidence photodiodes mounting box holders for cooling backside made of plastic (isolating to the chamber) preamplifier + filtering inside the box Very compact !

Bad Honnef 2006 CMS - VDC 24 pressure pressure sensor produced in Aachen

Bad Honnef 2006 CMS - VDC 25 O 2 content O2O2 O 2 content is measured at the exit of the chamber for additional detection of contamination

Bad Honnef 2006 CMS - VDC 26 inside the chamber field shaping tubes are laser welded

Bad Honnef 2006 CMS - VDC 27 Peoples and references references - master of the project:Dipl. -Phys. Dr. rer. nat. Hans Reithler - chief of the institute: Dipl. -Phys. Univ.-Prof. Dr. rer. nat. Thomas Hebbeker - development, construction and first test of VDC: Dipl. -Phys. Georg Altenhöfer - building of VDC:mechanical master craftsman Josef Grooten - planning, drawing of chamber-layout:chief of mechanic Dipl. -Ing. Barthel Phillipps - electronics: Dipl. -Ing. electrical engineering Franz Adamczyk & attending technician Günther Hilgers &Dipl. -Ing. electrical engineering Henry Szczesny - supporter for improving read-out-software:Dipl. -Phys. Michael Sowa - supporter for HV supply programming:Dipl. -Phys. Oleg Tsigenov & Dipl. -Phys. Michael Bontenackels - final DAQ and DCS software: Dipl. -Phys. Dr. Gyorgy Bencze &Dipl. -Phys. Anita Kapusi & Dipl. -Phys. Dr. Gyula Zilisi - systematic test and trigger development:J.F. The VDC on the web: This talk: Diploma thesis of Georg Altenhöfer: Paper about measurements of drift velocities: T. Zhao, Y. Chen, S.Han, J.Hersch; Nuclear Instruments and Methods in Physics Research A349(1994) Geiger mode photodiodes from Photonique SA: for further question: aachen.de aachen.de Debrećen