production and certification of multi wires proportional chambers for the lhcb muon system at cern...
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PRODUCTION and CERTIFICATION of Multi Wires Proportional Chambers for the LHCb Muon System at CERN
K.Mair for the LHCb Muon Group CERN*Poster anlässlich der 55. Jahrestagung der Österreichischen Physikalischen Gesellschaft, September 2005
* J.-S. Graulich (Université de Genève), A. Kachtchouk (Petersburg Nuclear Physics Institute), K.Mair (CERN), B. Schmidt (CERN), T. Schneider (CERN)
5 Muon Stations
Calorimeters
Tracker RICH-2
Vertex Locator
Magnet
RICH-1
Muon Detectors
Iron Filters
The Large Hadron Collider beauty experimentfor precise measurements of CP violation and rare decays:
The aim of the LHCb experiment is to fully investigate CP violation in the Bd and Bs systems, and to possibly reveal new physics beyond the Standard model.
Multi Wire Proportional Chambers (MWPC) in the LHCb Muon System
MWPC Production at CERN
• A muon trigger is given by a coincidence of all 5 muon stations within 25ns • >99% efficiency/station in 20ns time window• Time resolution <3ns• Up to 500 kHz/cm2
• total of 1368 MWPC in the Muon System
for fast muon triggering and offline muon identification
Design Parameters:• Wire: Gold-plated Tungsten, 30 μm Ø• Wire spacing: 2 mm • Wire length: 250 to 310 mm • Wire mechanical tension: 65 gr • Gas gap: 5 mm • Gas mixture: Ar/CO2/CF4 (40:55:5)• Operation Voltage: HV = 2.650 kV • Field on wires: 262 kV/cm• Field on cathodes 6.2 kV/cm • Gas gain: G ≈ 50 000• Gain uniformity: ≤ 30% • Rate/channel: < 1 MHz
Cross section of a 4-gap MWPC
Anode Wires
Cathode Pads
Segmentation:• Catode Pads on PCB with gold-coated copper foil• Gold plated tungsten anode wires grouped in strips4-gap MWPC-Sandwich:• 2 double-side wired panels in between 3 non-wired cathode panels
Chamber Certification
3. Gas Gain Uniformity Test2. Chamber Conditioning
1. Gas Leak Test
Wire Conditioning:• apply negative HV up to -2300V• tip-like dirt on wires → e--emission• electromagnetic wire cleaning• test: apply positive HV up to +2900V• check currents with radioactive sourceCathode Conditioning: • apply positive HV, turn gamma-ray on• observe Malter currents due to deposits on cathode (~15% of all gaps) • “heal” with gamma–ray exposure (GIF) and CF4 (~ 100 hours exposure time)• no dark current → conditioning finished
Specifications:• < 2 mbar leak / hour at 5 mbar overpressureMeasurement principle:• Test against a gas-tight-proved reference chamber • measure overpressure for 4 hours• measure internal parameters: T, P
Procedure: • panel fixed between 2 bolts along HV and read-out bar to guide wire• 1 bolt ring-like, 1 bolt double spiral• bolt pitch 2mm• panel in wiring automate• first wire aligned by hand, then automatic spooling• wires glued and soldered to panel
2. Panel Wiring
3. Panel Finalization
• wires cutting• components soldering• final inspection (microscope)• HV training
4. Chamber Assembly
Automatic Wiring Machine
• sandwich: 3 non-wired, 2 wired panels• gap size defined by 2.5 mm bars + 2.5 mm spacers between layers• gas tight by O-rings
TCh = TRef = const.dV/V ~ d(PCh-PRef)/PCh
absolute error on Patm cancels out
Wiring Tolerances:• nominal wire distance: 2 mm 95% of all distances within 50 μm all within 100 μm• nominal wire tension: 65 gr all values above 50 gr
1. Panel Production
Cathode Panel:• Printed Circuit Board (PCB)• coated by 35 μm copper 5 μm nickel, 0.2 μm gold
Cathode Panel
TEST: half gap size
HV bar
read out bar
side
bar
side
bar
panel
Non-wired Panels:• Gas inlets• Connectors for pad read out• Kapton foil
Wired Panels:• 2 wire fixation bars (HV, read-out), 2 side-bars• bar thickness defines half-gap size: 2.5 mm• Precise bars gluing
TEST:
wire pitch: measured by 2 cameras with telecentric lenses
wire tension: measurement of wire oscillation, excited by high voltage pulses
Specification:• Nominal Gas Gain: G0 = 50 000• uniformity within one gas gap: 95% of gap area must provide a gas gain within 30% G0
• uniformity between different gas gaps: average gap gas gain variation within 25% G0
Principle:• 241Am source emits 60 keV gamma rays• excitation of copper in panel → 8 keV gamma rays (absorption length less than 1 mm)• photoelectric effect in Ar (gas) → electrons of few keV• collected signal on anode → ADC counts distribution with peak position proportional to gas gain
Not wired panel
Wired panel
Side bar
Wire fixation bar
Spacer
MWPC Sandwich
Test setup
e-
Principle
camera shot of 3 wireswire distance measurement
wire pitch and tension measuring device
Specification:• half-gap size: 2.5 mm• tolerance: 50 μm
[mbar]
Relative Gas Gain distribution over one gas gap
relative gas gain [G0]pad number in y
pad nr in x
wire sample
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