There are two FPP chambers behind the rear analyzer, which are called chamber 3 and chamber 4. Each contains six planes of straws, and is protected and supported by 13 mil thick carbon fiber panels. To provide further support and protection for chamber four, an additional 1.5 inch thick plastic honeycomb is attached to the outside lower carbon fiber face. Most of the volume of the straw and carbon fiber package is gas, so the weight is minimal, despite the large sizes. Almost all of the chamber weight is in the support structures.
Each of the two rear chambers has six planes of straws, as summarized in the following table.
| Plane | Chamber 3 Name / Coordinate Measured | # of Straws | Chamber 4 Name / Coordinate Measured | # of Straws |
|---|---|---|---|---|
| 1 | U1 | 239 | U1 | 276 |
| 2 | U2 | 239 | U2 | 276 |
| 3 | V1 | 239 | U3 | 276 |
| 4 | V2 | 238 | V1 | 276 |
| 5 | X1 | 246 | V2 | 276 |
| 6 | X2 | 245 | V3 | 276 |
The coordinate system is defined relative to the beam Z axis, which is inclined
45o up from horizontal.
+X points downward at a 45o angle, while +Y is horizontal and to
beam left, to make a right-handed coordinate system.
The UV axes are rotated 45o from the XY axes, with +U between
+X and +Y, and +V between +Y and -X.
The planes are listed in order by increasing Z coordinate.
Chamber Dimensions
The straw area of chamber 3 measures about 107 inches by 49 inches, leading to a volume of about 7.6 cubic feet or 217 liters. The gas volume is about 6.0 cubic feet = 170 liters, with the remaining volume being largely air between the straws. The chamber is positioned on a 1.5 inch thick ~15 inch wide plastic honeycomb, aluminum face composite, that also provides a mounting surface for gas, high voltage distribution, and readout boards. The composite is attached to 5 inch by 3 inch aluminum I beams that provide most of the structural support. The outer dimensions of the I beam frame are 79.1 inches by 139.4 inches. The supporting rails for the chamber are 56.6 inches wide, and the inner side of the roller bearings that slide on the rails are separated by 146.9 inches.
Chamber 4 is constructed similarly to chamber 3, but is about 1 foot larger in each dimension. The straw area is 56.25 by 116.88 inches, leading to a gas volume of 7.5 cubic feet or 213 liters. The outer edges of the honeycomb panels are about 82.5 by 144 inches. The outer dimensions of the I beam frame, planned as 88.9 by 151.5 inches, were 89.2 by 149.8", leading to a 2.25" wide shelf on the inside edge of a hole 83.7" by 144.3". The inner hole for the active area is 53.25" wide by 114.12" long. The support rails are moved further apart by about 16 inches.
In each chamber, the main support I beam is 5 inches high, and the flanges are 2.75" wide. The 5-inch wide, 0.25-inch thick shelf is bolted to the bottom flange of the I beam. The honeycomb panels are both continuously glued to the shelf, and also bolted on; there are clearance holes in the honeycomb and holes tapped for 1/4-20 screws in the shelf. The honeycomb itself is 1.5 inches thick plus facing plus 1/16 inch 6061-T6 aluminum panels on each side; thus a 2" shaft 1/4-20 screw goes about flush to the bottom of the shelf.
Revised May 6, 1996 Norma Lucero