Prime pagine RA2010FUS:Copia di Layout 1 - ENEA - Fusione

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084 progress report 2010 Arb. units Counts/s 10 13 10 11 10 9 0 10 4 10 2 10 0 γ rays (NE213) 33519 33516 33517 33520 33522 33512 33661 a) Time (s) γ rays (GEM) 0 1 Time (s) Figure 361 – Comparison of gamma-ray signals in FTU plasma discharges: a) time traces from a NE213 detector; b) time traces from GEM pad #1 a) 1 33519 33516 33517 33520 33522 33512 33661 b) -33012 -2577 GEM–based neutron detector for 2.5 and 14 MeV The development of a gas electron multiplier (GEM)–based neutron detector for simultaneous 2.5 MeV (DD) and 14 MeV (DT) measurements has continued in the frame of an EFDA task on Diagnostics (WP10–DIA–04–01–xx–02). The detector, consisting of a proton recoil neutron converter and a triple GEM structure based on a Ar/CO 2 /CF 4 – 45/15/40 gas mixture, is divided in two sub–units (U DT and U DD ) respectively measuring 14 MeV neutrons only and 2.5 + 14 MeV neutrons [3.27]; the U DT sub–unit is provided with an aluminum layer (200 μm thick) for the rejection of protons produced by 2.5 MeV neutrons. The detector has been installed just outside the cryostat of the Frascati Tokamak Upgrade (FTU) device on the equatorial plane between ports 11 and 12. Preliminary acquisitions have been performed during plasma discharges in the 2010 experimental campaign. Unfortunately, as hydrogen gas (instead of deuterium) was used in these discharges due operational constraints, it has been possible to study just the response of the detector to gamma rays produced by runaway electrons. Note that this detector is also sensitive to gamma rays when a high high voltage (HV) setting is used. Results for seven discharges are shown in figure 3.61 (HV=1180 V): in all cases the GEM signals correctly reproduce the time behaviour and relative intensity of the gamma signals from the reference gamma-ray scintillator detector. Further tests with the GEM neutron detector have been carried out by using a 241 AmBe neutron source in the frame of an EFDA Joint European Torus (JET) Fusion Technology task (JW9–FTFT–5.31). The source (sketched in figure 3.62 as a cylinder) has been placed diagonally at about 2 cm from the detector. Results are shown in figure 3.62. At high HV both neutrons and gamma–rays are detected by the two sub-units units. At lower HV the detected signal is due to neutrons only and is mainly seen by the U DD sub–unit as the aluminum layer in the U DT cuts the signal due to neutrons with E
technology programme (cont’d.) progress report 2010 085 Counts 10000 100 14 MeV neutrons Q S /Q L 1 0.8 0.6 0.4 0.2 γ 14 MeV n from dt 2.5 MeV n from dd 300 200 100 0 0 0 400 800 1200 1600 2000 1 0 1000 Channels 2000 Figure 3.63 – Example of 14 MeV monoenergetic neutron beam measurement during the CNS detector characterization campaign at PTB Q T /Arb. units Figure 3.64 – CNS capability of n/γ discrimination and simultaneous 2.5 MeV and 14 MeV neutron measurements: 98% of the recorded pulses represent good data (2% of bad reconstructed pulses have now been fixed using the last release of the pre-processing routine) characterization matrix is on–going. Moreover, data collected in the previous JET experimental campaign have been analyzed in order to study the system’s performance during plasma discharges (see fig. 3.64): some minor bugs in the data pre–processing routine have been found and fixed. The final installation and commissioning at JET of the CNS diagnostic is foreseen in 2011–2012. 3.10 Cryogenics Liquid helium service The temperature of liquid helium at normal boiling point is 4.2 K (about –296°C). It is therefore used as a typical refrigerant for cooling of experimental equipments at very low temperatures. Helium, however, is rather expensive, so that recovering the helium evaporated during experiments may be beneficial, provided that the overall helium consumption is large enough. The gas recovered and compressed in a suitable storage system can indeed be liquefied again, subject to prior purification, thus allowing recycling the same amount of helium many times. A number of activities pursued by the Fusion Technical Unit at the Frascati Research Centre of ENEA require considerable amounts of liquid helium every year. The experiments with the FTU need liquid helium to cool down the magnets of the auxiliary heating facility electron cyclotron resonance heating (ECRH), or to freeze solid deuterium pellets to be injected at high speeds into the fusion plasma, as well as to keep plasma diagnostics at low temperature. The Superconductivity laboratory also uses sizeable amounts of liquid helium for experiments with large superconducting magnets, as well as to test critical components at low temperatures. A helium recovery facility and a helium liquefier are therefore operating in the Centre, which allows helium to be recycled many times, thus saving a considerable amount of money. The helium liquefier is a Linde TCF20, featuring a cold box equipped with an internal auto–purifier and two turbine expanders for gas pre–cooling, a screw driven DS220 recycling compressor equipped with an oil removal system, a line drier, a pressure control panel, two self–pressurizing dewars (1.000 l each) for liquid helium storage, two transfer and decant lines, a 7 m 3 pure helium buffer tank and an analytical panel equipped with a purity monitor and a moisture meter. An Allen Bradley Programmable Logic Controller automatically controls the plant, which was supplied by Linde Cryogenics Ltd. (UK) on April 1999. The nominal liquid helium production rates, with or without liquid nitrogen precooling, are of 60 and 30 l/h. In 2010, nearly 14.300 litres of liquid helium have been delivered to the users, which is slightly less than the amount of the previous year (about 19.500 litres). About 20% of the liquid evaporates (to the recovery system) while decanting it from the storage vessel to transport dewars (in order to deliver the product to the users). Moreover, the self–pressurizing storage dewar features an evaporation rate of about 25 liter/day, due to the unavoidable heat losses; of course, the helium vaporized from the liquid storage is recovered too. As a consequence, the overall liquid helium inventory managed in 2010 turns out to be roughly 23.200 litres. Nearly
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PROGRESS REPORT Euratom-ENEA Associ
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progress report 2010 001 2010 Progr
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progress report 2010 003 038 JET Co
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