Prototype of liquid Xe
Photon Detector
Current Status:
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 CEX beam test at PiE1 beam line |
Current configuration of the large prototype is the followings. The effective volume of the detector is 40cm x 40cm x 50cm. On the front and back sides, 36 + 36 PMTs are set and on the side walls 42 x 3 + 40 PMTs are placed in such a way that the sensitive volume is viewed from all sides. In total 238 PMTs are used to test the performance of the carlorimeter. The tests have been performed using cosmic rays, alpha sources, high energy photon beam at the TERAS electron strage ring of National Institute of Advanced Industrial Science and Technology (AIST) in Tsukuba Japan, electron beam at Acclab NSRF ICR in Kyoto University. Another test has been conducted at PSI using gamma from pi0 decay produced via charge exchange process. Results of the besm test reported in the review meetings can be found: In these tests we have examined not only the perfomance of the calorimeter for high energy photon (and electrons) but also various elements necessary to build the final detector, such as a Xe liquefaction system, with the large prototype detector. A schematic view of the detector placed in a cooling vessel can be seen in the right figure. |
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prototype refrigerator and new one |
Liquid Xe is filled in the inner vessel which is isolated from outside by vacuum for thermal insulation and supported by G10 plates. Total required amount of liquid Xe is about 120 liters. Xe had been liquefied as was done in the small prototype by using liquid nitrogen in early stage of R&D. In 2004 a new pulse tube refrigerator was constructed and mounted on the large prototype. This new refrigerator has a cooling power about three time than the previous one, enabling us to pre-cool the chamber and to liquefy 120 liter xenon without using liquid nitrogen. Liquid nitogen is prepared only for emergency backup. After liquiefaction liquid is kept in stable state by controlling cold head temperature. By now we have succeeded to keep liquid in stable state for longer than 2 months without any serious interuption of operation. |
Even if we start a measurement immediately after completing liquefaction, the remaining water (or oxygen) in the vessel disturbs the scintillation light transmission in the liquid by absorption. Since the xenon fed in the vessel is purified before liquefaction, it is quite unlikely that an impurity like water is contained in the xenon. Such an impurity is presumed to be contained in the vessel without being evacuated by a vacuum pump, and is exuded in the liquid after the volume is filled with liquid xenon. We introduced a xenon circulation system, as shown in the right figure, in order to remove such an impurity. Xenon is pumped from the bottom of the vessel, purified, and returned to the vessel from the top. Liquid xenon pumped from the bottom evaporates immediately around the exit. The heat of evaporation is used to cool the returned xenon in a heat exchanger. A diaphragm pump is employed for circulating xenon, whose maximum flow rate is 25 liter/min and maximum outlet pressure is 150 kPa. The flow rate is controlled with a valve near to the pump to be about 10 cc/min in the liquid. |
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S. Mihara, Mar 21, 2007
