Schematic of the experiment.
“Raw” data from the fast DAQ. The baselines have been adjusted to show the events more clearly. The bottom green line is the pulse from the photodiode which triggered the system. Most of the ionization fell on the middle, pink line for this flash at 7.4 ms. Neighboring wires show evidence of an induced pulse (negative going) with some spillover due to diffusion on the 2nd, blue, and 4th, grey lines. The excursions at roughly 0.5 ms and 18 ms are sparks.
Electric field lines near and in the MWPCs. Note that the horizontal dimension (x) is 4 mm, in total, while the vertical dimension (z) is ∼35 mm. The 20 μm anode wires are at z = 0 and x = −2 mm, 0 mm, and +2 mm. The grid wires are shown at x = −1 mm and x = +1 mm above and below the anode plane. For this simulation, the grid wires are parallel to the anode wires whereas in reality they are perpendicular to the anode wires. The grey field lines are interior to the MWPC while the red field lines come into the MWPC from the drift field.
Data after signal processing, described in text.
Shows the lateral diffusion data from one scan. The horizontal axis is the distance measured by the linear encoder. The vertical axis is a quantity proportional to the charge falling on the wire. Each color represents a different line.
(a) shows lateral diffusion data for 40 Torr CS2 while (b) shows data for the 30–10 Torr CS2–CF4 gas mixture. For both graphs, the horizontal axis is L/E for the scan in question while the vertical axis is the observed rms width of the ionization with the spot size and 2 mm wire spacing taken into account as discussed in the text. In both cases, the lower dashed line shows the ideal diffusion at room temperature with zero offset. As can be seen in both fits the observed temperature is very nearly room temperature with a finite offset.
(a) and (b) Both figures show averaged waveforms for line 2 as discussed in the text. (a) shows data taken at a drift field of 239 V/cm while (b) shows data taken at a drift field of 118 V/cm.
(a) shows the reduced mobility as a function of drift field for 40 Torr CS2 normalized to STP while (b) shows the same data for the 30–10 Torr CS2–CF4 gas mixture. Both plots show variations well outside of random statistics indicating the presence of some uncontrolled systematic or systematics. The systematics however affect the data only at the ∼1% level.
The arrival time delay for ions traveling through the MWPC. The grid wires are located at y = −1 mm and +1 mm where there are two poles due to a zero in the electric field above the wires. Delay times are normalized to 0 for the shortest time, those ions falling directly between the grid wires.
(a) shows longitudinal diffusion data for 40 Torr CS2 while (b) shows data for the 30–10 Torr CS2–CF4 gas mixture. For both graphs, the horizontal axis is L/E for the scan in question while the vertical axis is the observed rms longitudinal width of the ionization, the averaging, and path length taken into account. As discussed in the text, the barycenter of the spot in y affects this graph. For these data points, y = 0.5 mm was assumed. In both cases, the lower dashed line shows the diffusion at room temperature with zero offset. As can be seen in both fits, the observed temperature is very slightly above room temperature with no offset.
Reduced mobility measurements normalized to STP.
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