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detectors [2016/12/29 09:28]
pereira [Cathode Readout Drift Chambers (CRDC)] |
detectors [2018/02/15 12:44]
pereira [Cathode Readout Drift Chambers (CRDC)] |
| ===== Plastic scintillators ===== | ===== Plastic scintillators ===== |
| In order to determine the Time-Of-Flight for the particle identification, the S800 includes a plastic scintillator at the [[Stations#Object_station|object station]] (S800_OBJ) and at the [[Stations#focal_plane_station|focal-plane station]] (E1). The detector material typically used is | In order to determine the Time-Of-Flight for the particle identification, the S800 includes a plastic scintillator at the [[Stations#Object_station|object station]] (S800_OBJ) and at the [[Stations#focal_plane_station|focal-plane station]] (E1). The detector material typically used is |
| [[http://www.detectors.saint-gobain.com/uploadedFiles/SGdetectors/Documents/Product_Data_Sheets/BC400-404-408-412-416-Data-Sheet.pdf|BC-400]] or [[http://www.detectors.saint-gobain.com/uploadedFiles/SGdetectors/Documents/Product_Data_Sheets/BC400-404-408-412-416-Data-Sheet.pdf|BC-404]] made from polyvinyltoluene (>97% ) and organic fluors (<3%) with a density 1.032 g/cm<sup>3</sup> and a refractive index 1.58. The thickness of the detectors is chosen on the basis of the charge of the nuclei to be measured. The available thicknesses are __127 μm and 1 mm__ for OBJ_SCI and __1 mm and 5 mm__ for E1. The OBJ_SCI has an active area of __xxx__ and is connected to a photomultiplier __xxx__. The E1 scintillator is connected to photomultipliers [[EMI 98807B]] in both ends (up and down). The time signal from the E1 scintillator is calculated as the average time signal from each photomultipliers. | [[http://www.detectors.saint-gobain.com/uploadedFiles/SGdetectors/Documents/Product_Data_Sheets/BC400-404-408-412-416-Data-Sheet.pdf|BC-400]] or [[http://www.detectors.saint-gobain.com/uploadedFiles/SGdetectors/Documents/Product_Data_Sheets/BC400-404-408-412-416-Data-Sheet.pdf|BC-404]] made from polyvinyltoluene (>97% ) and organic fluors (<3%) with a density 1.032 g/cm<sup>3</sup> and a refractive index 1.58. The thickness of the detectors is chosen on the basis of the charge of the nuclei to be measured. The available thicknesses are __127 μm and 1 mm__ for OBJ_SCI and __1 mm and 5 mm__ for E1. (Guidelines explaining the installation of E1 scintillator can be found [[Installation FP SCI|here]]). The OBJ_SCI has an active area of __xxx__ and is connected to a photomultiplier __xxx__. The E1 scintillator is connected to photomultipliers [[EMI 98807B]] in both ends (up and down). The time signal from the E1 scintillator is calculated as the average time signal from each photomultipliers. |
| Different Time-of-flights can be constructed by combining the timing signals from these two detectors with the timing signals from the [[https://groups.nscl.msu.edu/a1900/|A1900]] focal plane, and the RF cyclotron. The E1 detector is also used to define a valid trigger from the S800. The timing resolution for a point-like beam spot in the focal plane is around 100 ps. However, this resolution worsens significantly (up to 1 ns) when the whole focal plane is illuminated, because of path length differences of the traversing nuclei. It can be recovered by tracking the position of each event on the scintillator from the position and angle information provided by the [[Detectors#Cathode Readout Drift Chambers (CRDC)|CRDC]] detectors. The plastic scintillators can withstand maximum rates up to 1 x 10<sup>6</sup> particles per second. | Different Time-of-flights can be constructed by combining the timing signals from these two detectors with the timing signals from the [[https://groups.nscl.msu.edu/a1900/|A1900]] focal plane, and the RF cyclotron. The E1 detector is also used to define a valid trigger from the S800. The timing resolution for a point-like beam spot in the focal plane is around 100 ps. However, this resolution worsens significantly (up to 1 ns) when the whole focal plane is illuminated, because of path length differences of the traversing nuclei. It can be recovered by tracking the position of each event on the scintillator from the position and angle information provided by the [[Detectors#Cathode Readout Drift Chambers (CRDC)|CRDC]] detectors. The plastic scintillators can withstand maximum rates up to 1 x 10<sup>6</sup> particles per second. |
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| ===== Cathode Readout Drift Chambers (CRDC) ===== | ===== Cathode Readout Drift Chambers (CRDC) ===== |
| Two Cathode Readout Drift Chamber (CRDC) are used to measure the transversal positions and angles in the [[Stations#Focal Plane station|focal plane]]. The first detector (CRDC1) is located at the nominal optical focal plane, and it is separated 1 m from the second downstream detector (CRDC2). Each detector has an active depth of 1.5 cm, an active area of 26 cm (non-dispersive direction) x 56 cm (dispersive direction), and [[Gas handling system|it is filled]] with a gas mixture consisting of 80% CF<sub>4</sub> and 20% C<sub>4</sub>H<sub>10</sub> at a typical pressure of 40 torr. The [[HV bias#CRDCs|operating high power]] depends on the charge of the measured nuclei. A schematic view of a CRDC can be seen in the figure below. | Two Cathode Readout Drift Chamber (CRDC) are used to measure the transversal positions and angles in the [[Stations#Focal Plane station|focal plane]]. The first detector (CRDC1) is located at the nominal optical focal plane, and it is separated 1 m from the second downstream detector (CRDC2). Each detector has an active depth of 1.5 cm, an active area of 26 cm (non-dispersive direction) x 56 cm (dispersive direction), and [[Gas handling system|it is filled]] with a gas mixture consisting of 80% CF<sub>4</sub> and 20% C<sub>4</sub>H<sub>10</sub> at a typical pressure of 40 torr. The detector frame has a volume of 68 cm (dispersive) x 38 cm (non-dispersive) x 10.3 cm (depth). The [[HV bias#CRDCs|operating high power]] depends on the charge of the measured nuclei. A schematic view of a CRDC can be seen in the figure below. |
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| {{:wiki:crdc-drawing.jpg?600|Schematic view of the two S800 CRDCs.}} | {{:wiki:crdc-drawing.jpg?600|Schematic view of the two S800 CRDCs.}} |
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| ===== Ionization chamber ===== | ===== Ionization chamber ===== |
| An ionization chamber downstream of both [[Detectors#Cathode Readout Drift Chambers (CRDC)|CRDCs]] is used to identify the Z number of the transmitted nuclei from their energy loss. The detector has an active volume of __xxx cm x xxx cm x xxx cm__ and [[Gas handling system||is filled]] with P10 gas (90% argon, 10% methane) at a typical pressure of 300 torr, although this value can be increased up to 600 torr for light nuclei. The detector consists of 16 stacked-parallel plate ion chambers with narrow anode-cathode gaps, placed along the detector’s central axis, perpendicular to the beam direction (see figure). The plates are constructed from 70 mg/cm<sup>2</sup> polypropylene with 0.05 µm of aluminum evaporated on each side. The entrance and exit windows of the chamber are made of 14 mg/cm<sup>2</sup> Mylar with an overlay of Kevlar filaments and epoxy. | An ionization chamber downstream of both [[Detectors#Cathode Readout Drift Chambers (CRDC)|CRDCs]] is used to identify the Z number of the transmitted nuclei from their energy loss. The detector has an active area of __xxx cm x xxx cm__ and a depth of approximately 406 mm (16 inches). It [[Gas handling system||is filled]] with P10 gas (90% argon, 10% methane) at a typical pressure of 300 torr, although this value can be increased up to 600 torr for light nuclei. The detector consists of 16 stacked-parallel plate ion chambers with narrow anode-cathode gaps, placed along the detector’s central axis, perpendicular to the beam direction (see figure). The plates are constructed from 70 mg/cm<sup>2</sup> polypropylene with 0.05 µm of aluminum evaporated on each side. The entrance and exit windows of the chamber are made of 14 mg/cm<sup>2</sup> Mylar with an overlay of Kevlar filaments and epoxy. |
| {{:wiki:ion-chamber-picture.jpg?500 |Picture of the S800 ionization chamber with its alternating cathode and anode plates.}} | {{:wiki:ion-chamber-picture.jpg?500 |Picture of the S800 ionization chamber with its alternating cathode and anode plates.}} |
| The electrons and positive ions liberated by the ionization of the gas along the particle trajectory drift towards the closest anode-cathode pair. The drifting electrons and ions absorb the energy stored in the detector capacity and produce a voltage change of the anodes across the resistor. The main advantages of the anode-cathode configuration is that the electrons and ions are collected on a very short distance (about 1.5 cm), thus reducing pile-up and position dependence of the signals. Moreover, dividing the detector into 16 sections reduces the detector capacitance and consequently its noise. The operating voltage depends on the charge of the measured nuclei (e.g. __xxx for xxx and xxx for xxx__). Each anode is attached to a small preamplifier inside the ion chamber. This significantly reduces the electronic noise, although it involves the venting of the whole chamber whenever a malfunctioning preamplifier needs to be replaced. The electronic signals from the preamplifier are sent into a [[https://groups.nscl.msu.edu/nscl_library/manuals/caen/MOD.N568B.pdf|CAEN N568B]] 16-channel shaper/amplifier with remotely adjustable gains. The output signals feed a [[https://groups.nscl.msu.edu/nscl_library/manuals/phillips/7164H.pdf|Phillips 7164H]] ADC. | The electrons and positive ions liberated by the ionization of the gas along the particle trajectory drift towards the closest anode-cathode pair. The drifting electrons and ions absorb the energy stored in the detector capacity and produce a voltage change of the anodes across the resistor. The main advantages of the anode-cathode configuration is that the electrons and ions are collected on a very short distance (about 1.5 cm), thus reducing pile-up and position dependence of the signals. Moreover, dividing the detector into 16 sections reduces the detector capacitance and consequently its noise. The operating voltage depends on the charge of the measured nuclei (e.g. __xxx for xxx and xxx for xxx__). Each anode is attached to a small preamplifier inside the ion chamber. This significantly reduces the electronic noise, although it involves the venting of the whole chamber whenever a malfunctioning preamplifier needs to be replaced. The electronic signals from the preamplifier are sent into a [[https://groups.nscl.msu.edu/nscl_library/manuals/caen/MOD.N568B.pdf|CAEN N568B]] 16-channel shaper/amplifier with remotely adjustable gains. The output signals feed a [[https://groups.nscl.msu.edu/nscl_library/manuals/phillips/7164H.pdf|Phillips 7164H]] ADC. |
