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