Gas, Cooling, and Vacuum Systems

The gas system mixes two gases and supplies the blended gas to the gas manifolds, which circulates it in the system. Further, the gas is required to cool the ROESTI boards, which overheat quickly and break. The vacuum system keeps the detector solenoid in vacuum, and monitors it to drive the vacuum pump safely. Figure 3.11 illustrates the system design.

The mass-flow controllers control the flow of both gases from the cylinders to mix them in the blender in the desired ratio. The blended gas flows in the gas manifolds of the straw tracker. The gauges at the entrance and exit monitor the pressure; the relief valve releases the gas for safety if its pressure exceeds a certain threshold.

The green gas line in the figure indicates the cooling system through which the gas emitted from the manifolds is circulated. A heat sink is attached to every board and the compressor enhances the gas flow rate to 50 l/min to exhaust the heat out of the ROESTI boards efficiently. In addition, the

3.5. Gas, Cooling, and Vacuum Systems

Figure 3.10:Prototype LV divider. The input voltage supplied from the bottom right plug is regulated for each output channel on the left panel, whose voltage and current are monitored.

heat exchanger and tiller are used to make the gas even colder. The first pilot system was built to examine the design that uses a diaphragm pump and refrigerator instead of the compressor and the tiller, and the required flow rate was achieved.

The air in the detector solenoid was exhausted by a rotary pump and turbomolecular pump through the purple line in the figure. However, if the vacuum is broken, such as when a straw tube breaks, the pressure rises rapidly and can destroy the turbomolecular pump. Therefore, the vacuum pressure needs to be monitored constantly so that gate valve can be closed instantly and the vacuum system can be disconnected in such a situation.

gauge gate

valve pump

gas cylinders

valves

mass-flow controllers

blender sampler (if required)

gauge gauge

straw-tracker stations (#1~5)

relief valve

exhaust (to duct)

heat exchanger

~ ~ ~

tiller (or refrigerator)

1 2 3 4 5

compressor flow

divider

Figure 3.11: Diagram of the gas, cooling, and vacuum systems for the straw tracker. The two gases are blended and flown into the gas manifolds. The cooling system (green line) compresses and cools down the gas to exhaust the heat out of the ROESTI boards. The air is expelled through the vacuum system (purple line), and it is decoupled from the detector solenoid by the gate valve when the vacuum breaks.

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3.5. Gas, Cooling, and Vacuum Systems

We constructed a prototype of the gas and vacuum systems as shown in Figure 3.12 for the ex-periment to evaluate a prototype of StrECAL, as discussed in Chapter 5. The mass-flow controllers mounted on the right panel control the flow rate of argon, C₂H₆, and CO₂. Either C₂H₆ or CO₂ is shut out by the valve, and the other is mixed with argon via the blender behind the panel. The gas mixture enters the gas manifold through the controllable valve. In this prototype, the return gas is not circulated but released into the air through the bubbler and the pressure gauge. Both mass-flow meters and the bubbler are used to confirm the gas flow visually. The vacuum pressure gauge moni-tors the pressure in the container of the straw tracker prototype. The digitizer and controller devices communicate with the mass-flow controllers and vacuum pressure gauge, configure the flow rate, read the actual flow rates and vacuum pressure, and send the data to the DAQ computer. Further, they can open and close gas-line valves and close the gate valve (not shown in the picture). We can control and monitor the environmental status with these systems.

Mass-flow controllers

Mass-flow meters Valves

Vacuum pressure gauge Gas cylinders

Digitizer and controller devices Controllable

valves

Released gas pressure gauge

Bubbler Blender (behind)

Figure 3.12: Prototype of gas and vacuum systems. The right panel contains all items used for controlling, mixing, and monitoring the gas flows. The digitizer and controller devices digitize the values monitored by the mass-flow controllers and vacuum pressure gauge, send them to the DAQ computer, and control the valves to open and close the gas-flow line.

4

Electromagnetic Calorimeter (ECAL)

An ECAL is installed at the end of the beamline, and it measures the total energy deposition, position, and timing of the incoming particles. The role of the ECAL is divided into the following considering the beam measurement program before the Phase-I experiment.

Trigger: The ECAL is the only trigger detector used in Phase-II. Its trigger electronics monitor the energy depositions in real time, generate trigger candidates, and transmit them to a trigger system that makes the trigger decision.

Determination of time origins Some COMET detectors require the time origin (T₀) of events. For example, any tracking algorithm needs to first reconstruct a drift time or distance in each straw tube. Thus, the exact timing required for the track to pass through the straw tubes—calculated fromT₀considering the track path—is required.

Support of Tracking by the Straw Tracker The ECAL can measure the two-dimensional position on its surface where particles arrive. Further, this role can tend to track fitting. Alternatively, it is a good criterion for track reconstruction to verify its consistency with the track reconstructed from the straw tracker hits.

To accomplish these, the ECAL must exhibit high energy, position, and time resolutions; a detailed investigation into its response against each particle type is also required. Since 2012, the Kyushu Uni-versity group has been developing an ECAL by constructing prototypes and conducting experiments to evaluate their performance. Considering all roles of the ECAL, we designed it to comprise seg-mented inorganic scintillating crystals.

This chapter describes the detail of the requirements for the ECAL and the design created to meet these requirements; further, it includes several experimental results that support the philosophy of the design.

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