1. Comments on 2mm MWPC pitch
W. Riegler, December 2002
Impact on specifications, guard wire and some other parameters

2. ra: anode wire radius
Va: anode wire voltage
: ion mobility
q: charge per hit
R: rate/cm2
rc=(s/2) Exp(h/s) equivalent cathode radius
Ea=Va/(ra ln(rc/ra)) anode wire surface field
Ec= Va/(s ln(rc/ra)) cathode surface field
t0= ra2 ln(rc/ra)/(2Va) signal tail
V=Rsh2q ln(rc/ra)/(4Va0) voltage drop due to space charge effect
Details: LHCb-muon

3. Parameters and Specifications for h=2.5mm,ra=15m, s=2(1.5)mm
Ea (Gain105): kV/cm
Va: 2750V (3150) V
Ec: 6.18 (8.24) kV/cm 0.75
rc: (44.86) mm
ln(rc/ra): (8.00)
t0: 1.50 (1.50) ns
V Voltage drop due to space charge: factor 1.33 larger, negligible
Specs:
When does the wire surface field differ by 1% i.e. the gas gain differ by 20% ?
Gap: 88(75) m
single wire X: 130(90) m
single wire Y: 310(250) m
wire plane Y: 330(300) m
No Guard Wire: (325), 269(277), 263(266), 262(263), 262.3(262) kV/cm
200m Guard Wire: 70.4(76.5), 251(249), 260(260), 262(262), … kV/cm

4. Conclusions
With respect to specifications, rate capability, signal tail and guard wire issues the 2mm pitch doesn’t have any drawbacks compared to the 1.5mm pitch.