MWPC 1 has been exchanged on 17th-Nov-1999. It has a little different geometry, which can be found in New MWPC 1 properties.
The original chambers have the following properties:
Chamber 1 (inner) 2 (outer) ===================================================================== Dimensions ---------- Active length [mm] 350 540 All length [mm] 580 730 Min. diameter [mm] 90 206 Max. diameter [mm] 152 255 Diameter anode [mm] 120.3 240.2 Diameter inner cathode [mm] 115.2 235.2 Diameter outer cathode [mm] 125.0 245.2 Inner cathode - anode gap [mm] 2.55 2.5 Volume of chamber [cm^3] 660 2035 Total chamber thickness [mg/cm^2] 53.9 74.8 Total chamber thickness [rad.length] 1.4E-3 2.0E-3 Anode wires ----------- Number of anode wires 192 384 Anode wire spacing [mm] 1.96 1.96 Anode wire tension (min-max) [N] 0.44-0.48 0.44-0.51 Resistence of anode wire [Ohm] 110 155 Resistance between anode-anode [Ohm] 560k 560k Capacity between anode-ampl. [pF] 1000 1000 Cathode strips -------------- Number of inner cathode strips 2 x 64 192 Angle of slope inner cathode [deg] 36.960 44.602 Number of outer cathode strips 2 x 64 192 Angle of slope outer cathode [deg] 33.650 42.339 Width of cathode strips [mm] 3.0 2.4 Gap between strips [mm] 0.4 0.3 Resistence of strips (6u Al) [Ohm] ~1.5 ~2.0The chambers were fabricated in Dubna and sucessfully tested with radioactive sources and 32 channels read out at PSI end of 94. The following picture shows the efficencies and current of the chambers from those tests:
The spacial resolution of the cathode strips was measured using the following technique:
When a particle crosses the chamber and produces a signal, the
charge is received by several (typically 5) cathode strips. Following picture
gives an example of such an event:
The position of this hit is determined by fitting a gaussian to this hit pattern. While in the lateral (z) direction of the chamber all positions are possible, in the rotational (phi) direction only those positions near a wire can produce some charge, since the charge avalanche forms only around the anode wires. Therefore, by plotting measured phi-positions of arbitrary hits for a given z=const., one can see the individual wires:
By measuring the width of those peaks, on can determine the resolution of the cathode strips in the z-direction, where no discretisation by the wires occur. The result of this measurement give a 0.2mm resolution (FWHM). The double pulse resolution which is critical for our experiment is not yet fully measured but is in the range of 1 to 2 mm.
The gas consumption was measured in te beamtime 1999 over 1 week. The Excel file can be downloaded. The gas pressure as a function of time is plotted here and can be downloaded as PS-file
H.P. Wirtz, 13-Jul-1999