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detectors [2013/12/13 19:09]
pereira [Ionization Chamber] |
detectors [2013/12/13 19:13]
pereira [Cathode Readout Drift Chambers (CRDC)] |
| Two Cathode Readout Drift Chamber (CRDC) are used to measure the transversal positions and angles in the 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 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 50 torr. The 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 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 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 50 torr. The 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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| {{:wiki:crdc-section-drift.jpg?500|Principle of operation of a CRDC.}} | {{:wiki:crdc-section-drift.jpg?400 |Principle of operation of a CRDC.}} |
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| Both CRDCs are equipped with digital electronics, which consist of seven front-end electronic boards (FEE) designed and developed by the [[http://www.star.bnl.gov/|STAR collaboration]] ([[http://www.bnl.gov/rhic/|RHIC]]), followed by interface boards connected to a programmable FPGA VME module ([[http://wwwp.cord.edu/dept/physics/mona/manuals/XLM72UM.pdf|XLM72]]) like the one used with the [[Detectors#Tracking Parallel Plate Avalanche Counters (TPPAC)|TPPACs]] in the intermediate image station. Each FEE includes 32 channels of preamplifier shaper, followed by a switch capacitor array (SCA) and an ADC. The processing of signals is driven by the FPGA module. Each SCA samples the signals after a valid trigger is received and sends the information into the ADC. The digitized data are then stored into the internal memory of the FPGA and read out in block mode. The sampling frequency and number of samples read out are adjustable; typical values are 20 MHz and 8 to 12 samples. The time needed for each sampling is around 16 µs. Thus, the dead time of the electronics is directly proportional to the number of samples read out. The main advantage of the on-detector digitalization technique used with the CRDCs is the reduction of noise by avoiding the transmission of analog signals (448 from the two CRDCs) outside the vacuum chamber, and the possibility to record multi-hit events like in traditional TPC detectors. | Both CRDCs are equipped with digital electronics, which consist of seven front-end electronic boards (FEE) designed and developed by the [[http://www.star.bnl.gov/|STAR collaboration]] ([[http://www.bnl.gov/rhic/|RHIC]]), followed by interface boards connected to a programmable FPGA VME module ([[http://wwwp.cord.edu/dept/physics/mona/manuals/XLM72UM.pdf|XLM72]]) like the one used with the [[Detectors#Tracking Parallel Plate Avalanche Counters (TPPAC)|TPPACs]] in the intermediate image station. Each FEE includes 32 channels of preamplifier shaper, followed by a switch capacitor array (SCA) and an ADC. The processing of signals is driven by the FPGA module. Each SCA samples the signals after a valid trigger is received and sends the information into the ADC. The digitized data are then stored into the internal memory of the FPGA and read out in block mode. The sampling frequency and number of samples read out are adjustable; typical values are 20 MHz and 8 to 12 samples. The time needed for each sampling is around 16 µs. Thus, the dead time of the electronics is directly proportional to the number of samples read out. The main advantage of the on-detector digitalization technique used with the CRDCs is the reduction of noise by avoiding the transmission of analog signals (448 from the two CRDCs) outside the vacuum chamber, and the possibility to record multi-hit events like in traditional TPC detectors. |
| ===== 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 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 left figure below ). 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 volume of __xxx cm x xxx cm x xxx cm__ and 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 left figure below ). 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. |
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| | The principle of operation of the ionization chamber is illustrated in the right figure below. 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 energy-loss resolution of the ionization chamber can be significantly improved after correcting the position and momentum dependences. Elements up to Z=50 can be separated. |
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| {{: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.}} |
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| {{ :wiki:ion-chamber-drawing.jpg?500|Schematic representation of the principle of operation of the ionization chamber.}} | {{ :wiki:ion-chamber-drawing.jpg?500|Schematic representation of the principle of operation of the ionization chamber.}} |
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| The principle of operation of the ionization chamber is illustrated in the right figure above. 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 energy-loss resolution of the ionization chamber can be significantly improved after correcting the position and momentum dependences. Elements up to Z=50 can be separated. | |
| ===== Hodoscope ===== | ===== Hodoscope ===== |
| A Cs(Na) hodoscope detector located downstream of the [[Detectors#Plastic scintillators|E1 scintillator]] is used to measure the total kinetic energy of implanted nuclei, allowing the identification of different charge states. An additional use recently tested is the measurement of isomer gamma-rays emitted from implanted nuclei. | A Cs(Na) hodoscope detector located downstream of the [[Detectors#Plastic scintillators|E1 scintillator]] is used to measure the total kinetic energy of implanted nuclei, allowing the identification of different charge states. An additional use recently tested is the measurement of isomer gamma-rays emitted from implanted nuclei. |
