This page summarizes the proposed final design of the mounting structure of the T0 counters to be installed behind ring 1 on the N side and behind ring 2 on the P side (the complete set of design drawings can be found by clicking here). In each position, 10 T0 counters will be installed. If one does not take into consideration the fact that the frame has to have a finite thickness around the PMTs, the ideal locations of the PMTs would be
N side: center of PMTs at 9.3 cm from beam axis (z = -123.0 cm)
P side: center of PMTs at 8.7 cm from beam axis (z = 247.5 cm)
If one takes into consideration that, given the overall weight of the assembly, we need 5/16" of material on the inside of the frame, and at least 3/16" of material between the counters, we conclude that the closest we can put the radiators to the beam axis is about 10 cm (see the front and side views shown in the following figure). Given the fact that this distance is larger than the ideal distances on both the P and the N side, the support frames shown here can be used on both the P and the N side. In addition, the interface between that connects the support frame of the PMTs to the stands was design in such a way that its interface is identical to the interface of the supports installed currently between ring 3 and the Cherenkov array, and as such, the support frames of the current design also can be installed at the remote locations, without any modification to the existing supports.
The drawing which shows the T0 frame and the support structure (see figure shown above) gives an idea how the T0 arrays will be installed. The U-shaped bottom part of the support is not realistic at the moment, since its dimensions will be defined only after we have determined the exact region that must be cleared by this part of the support (determined mainly by the rail structure on the N side and the cable tray on the P side; see Base Issues).
The support provides motion in the horizontal plane, using the same concept as was used for the current supports. The adjustments in the vertical direction will be provided by an elevating table, which will be purchased commercially (see http://velmex.com/pdf/g-cat-pdf/g2002.pdf). The choice of table was determined by the weight of the overall array which is currently estimated to be just about 30 pounds.
The assembly of the array is similar to the assembly of the current array, except that the frames are not split in the middle, but are split such that there are 6 T0 counters mounted in the lower section and 4 T0 counters mounted in the top section (see the figure below for a view of the mounting frames from the IP; the black fame is the frame closest to the IP). Since the T0 counters are mounted in a slightly tilted position, the holes for the T0 counters are angled. Each frame can thus be mounted in only one position. To ensure that when the top part is connected to the bottom part of the frame it is installed in the correct position, the pin and screw holes are oriented such that there is only one possible orientation of the top part of the frame with respect to the bottom part of the frame.
Due to the increase in distance of the radiators from the beam direction, the overall efficiency of the system is slightly reduced:
N side: <N> = 0.70 => P(N=0) = 50%
P side: <N> = 0.51 => P(N=0) = 60%
The probability to see one hit on each side is now 20% compared to 26% in the ideal design, and the probability to see at least on counter fire is now 70% compared to 76%.
In order to determine the amount of material required for the mounts, we have used the following two drawings, which show the required parts, laid out on top of a 2' x 4' sheet of Ultem. Since this material is expensive, we can save close to $ 1000 if we make all parts out of two sheets.
The goal of our conference on Tuesday morning will be to:
The final drawings will be submitted to BNL for final approval by the end of the week of 7/29.