By far the largest fuel supply in Hall B consists of the inventory of plastics. Most of the plastic is in the cable jacketing or dielectric, although a significant fraction is found in the detectors. An overall summary of the plastics and gas inventory is shown in See Also: Total combustible inventory in Hall B. . The scintillator material for essentially all systems is polyvinyltoluene (PVT), with very small admixtures of other chemicals. Included in the scintillator inventory is a small fraction of acrylic, of which the light guides (which join the phototube to the scintillator) are fabricated. A breakdown of the plastics inventory as a function of location in Hall B is shown in See Also: Plastics inventory as a function of location. .
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Note: target gas as quoted is only contained in the hall in liquid form; in gaseous form only a small volume is in the hall (unless the cell ruptures) |
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The scintillator material for essentially all systems in polyvinyltoluene (PVT), with very small admixtures of other chenicals. Included in the scintillator inventory is a small fraction of acrylic, of which the light guides (which join the phototube to the scintillator) are fabricated. A breakdown of the plastics inventory as a function of location in Hall B is shown in Table 4.
In general, utility power cables are routed through metal conduit throughout the hall. A minimal number of individual cables are contained within a given conduit. Flexible power leads are used for many of the crate power supplies; these are typically kept short (< 10 feet). As a whole, utility power cable jacketing provides little fuel.
In the drift chamber systems, a fraction of the electronics is located directly on the chambers. This electronics is powered by 354 relatively long cables (~70 feet) distributed along the chambers and the space frame on Levels 1, 2, and 3. Each cable cont ains two conductors surrounded by a braided metal shield and an outer jacket. All plastic parts are PVC. These are referred to as the `drift chamber low-voltage cables.'
Another category of `power cables' is what is referred to as `high voltage cables.' (These are in no way power cables in the ordinary sense, since the typical power delivered through them ranges from 0.1 to 2 watts.) The high voltage cable associated with the drift chambers is a commercial multiconductor cable with 12 conductors individually insulated by a teflon jacket, surrounded by a braid shield and a PVC jacket. These are also distributed along the length of the drift chambers, and on Levels 1 and 2 of the space frame.
For the phototube-based detectors, the high voltage cable is a coaxial cable, RG-59 style, constructed of polyethylene and PVC. These cables are distributed on all three levels of all four platforms, but the largest number are located between the calorime ters and the carriages on which the calorimeters are mounted (forward carriage Levels 0, 1, and 2, and south carriage Level 1 and 2).
Most of the cable volume in the hall is due to, broadly speaking, `signal' cable.
For the phototube-based detectors there is one type of signal cable, referred to as `delay cable', which accounts for the largest fraction of the plastics in the hall. This delay cable is associated with all of the phototube-based systems: all calorimeter s, all time-of-flight scintillators, all Cerenkov counters, and the timing scintillators of the photon tagger. This delay cable is RG-213 type coaxial cable. There are 2211 individual cable assemblies, averaging 300 feet in length. They are distributed ov er all four carriages, but concentrated in Level 0 of the forward carriage and Level 0 of the south carriage.
Most of the phototube-based systems also use what is referred to as `trigger cable'; this is of the low-loss RG8 type (`air-core'), with a PVC jacket and a semi-hollow polyethylene core. These are distributed over all four carriages, but are concentrated in the areas between the calorimeters and the carriages which support them.
For the drift chambers the cables there are 2208 signal cables which average 70 feet in length, and which are routed from the drift chambers to racks on Levels 1, 2, and 3 of the space frame. This cable has 17 twisted pairs with individual PVC jackets, su rrounded by an overall shield, within an outer PVC jacket.
The time-of-flight scintillators are rectangular bars of BC408 scintillator material with acrylic lightguides at both ends. They are all 5 cm thick and range in length from approximately 30 cm to approximately 450 cm. In total there are nearly 300 of thes e detectors, arranged in a single layer completely enclosing the drift chambers and Cerenkov counters like a `skin'. The only barrier between the `fuel' and the outside world is a thin layer of fire-retardant plastic (carbon impregnated mylar), 0.002" ; of aluminum foil and 0.005" of lead metal on the front face. Although it is not in direct contact with any ignition source (except perhaps the high voltage divider circuit, which is enclosed in a sealed container), there is a very large surface are a exposed, and the basic scintillator material is quite flammable.
There are two categories of calorimeters: the `forward angle' calorimeters and the `large angle' calorimeters. The former are triangular shaped assemblies mounted on the forward carriage in all six sectors, while the latter are rectangular assemblies moun ted on the south carriage in two sectors only. Both types are of the lead-scintillator sandwich design, with steel-and-foam composite plates covering the large surface area sides. In addition to the scintillator plastic, the light guide structures and the phototube housings are also plastic, but are mostly enclosed within the metal of the aluminum light cover. The plastic inside could only be available as fuel to a fire which is large enough to decompose the epoxy binding of the composite front or back pl ates, or melt the 1.5" thick aluminum side walls, or if it got hot enough the plastic could perhaps melt and drip out the lowest point on each module. The plastic is interleaved with lead metal sheets which would additionally slow the heating process . For these reasons, the plastic in the calorimeters is only available as fuel in the event of a large fire in an advanced stage which occurs in close proximity to the modules, such as could perhaps only occur on Level 0 of the forward carriage.
Hydrogen gas is only used in the endstation as a nuclear target. The volume of the cryogenic target hydrogen gas at STP is about 46 cubic feet, including the volume of supply lines. This is still a tiny amount of fuel compared to the cable plant, although a significant explosion potential exists under the proper circumstances.
Sheet metal is used to enclose a number of the electronics rooms to isolate the cooling air flow from the surrounding spaces.