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+ | ====== The NSCL S800 spectrograph ====== | ||
+ | Welcome to the wiki page of the NSCL S800 spectrograph. The page provides technical information about the S800, as well as instructions to operate the S800 prior to and during an experiment. | ||
- | **The S800 spectrograph** | ||
- | ====== Technical Aspects of the S800 ====== | ||
- | ===== Technical | + | ===== Technical |
- | ==== General ==== | + | * [[Introduction]] |
- | The S800 [1] is a superconducting spectrograph used for reaction studies with high-energy radioactive beams produced at the NSCL Coupled-Cyclotron Facility (CCF) and the A1900 Separator | + | |
+ | * [[Magnets]] | ||
+ | * [[Modes | ||
+ | * [[Determination of Angles | ||
+ | * [[Detectors]] | ||
+ | * [[Electronics]] | ||
+ | * [[Data Acquisition | ||
+ | * [[S800 Software]] | ||
+ | * Coupled Devices | ||
+ | * [[Types | ||
- | + | ===== Operation | |
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- | ====== Headline ====== | + | |
- | ====== Headline ====== | + | |
- | + | ||
- | ====== Headline ====== | + | |
- | ====== Level 1 Headline ====== | + | |
- | ===== Level 2 Headline ===== | + | |
- | ==== Level 3 Headline ==== | + | |
- | === Level 4 Headline === | + | |
- | == Level 5 Headline == | + | |
- | + | ||
- | ---- | + | |
- | ∑ | + | |
- | * Unordered List Item | + | |
- | * * Unordered List Item | + | |
- | * * Unordered List Item | + | |
- | * | + | |
- | * Technical Introduction | + | |
- | + | ||
- | * Ion optics | + | |
- | * Detectors | + | |
- | * SCI OBJ | + | |
- | * TPPACs | + | |
- | * CRDCs | + | |
- | * IC | + | |
- | * FPSCI | + | |
- | * Hodoscope | + | |
- | * Electronics | + | |
- | * Diagrams | + | |
- | * Triggers | + | |
- | * Signal optimization | + | |
- | * Software | + | |
- | * Log in to use different applications | + | |
- | * Barney | + | |
- | * Bklq | + | |
- | * Panel Mates | + | |
- | * DAQ | + | |
- | * Experiment types | + | |
- | * Coulex | + | |
- | * CE | + | |
- | * Knockout | + | |
- | * ... | + | |
- | * Supported detectors (Background suppression): | + | |
- | * Gamma | + | |
- | * CAESAR | + | |
- | * SeGA | + | |
- | * GRETINA | + | |
- | * Neutron | + | |
- | * LENDA | + | |
- | * Charge particle | + | |
- | * HiRA | + | |
- | + | ||
- | * Organization | + | |
- | * Planning an experiment with the S800 | + | |
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- | **THE S800 SPECTROGRAPH** | + | |
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- | INTRODUCTION | + | |
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- | The S800 [xx] is a superconducting spectrograph used for reaction studies with high-energy radioactive beams produced at the NSCL Coupled-Cyclotron Facility (CCF) and the A1900 Separator [xx]. It was designed for high-precision measurements of scattering angles (ΔΘ=2) and momentum (p/Δp=2×104), and large momentum and solid-angle acceptances (ΔΩ=20 msr, Δp=6%). The S800 layout is shown in Fig. 1. It consists of two parts: the analysis line and the spectrograph. The analysis line extends from the object position to the target station. It includes four 22.5° dipoles, five quadrupole triplets, and two vertically steering magnets, assembled in two segments with configurations QQQ-H-DD-QQQ (segment 6) and QQQ-DD-H-QQQ-QQQ (segment 7) symmetrically oriented around an intermediate image plane. The spectrograph consist of two quadrupoles, | + | |
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- | The analysis line can be used in two different modes. In the focus mode, the maximum momentum acceptance is achieved (±2%) by making the analysis line achromatic (with maximum dispersion at the intermediate image plane).In this mode the position of the fragment at the spectrograph focal plane is sensitive to the momentum of the beam impinging on the target. Consequently | + | |
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- | In the S800, the angles, positions and energy of the fragments in the reaction target are determined from the angles and positions measured at the focal plane. | + | |
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- | ION OPTICS | + | |
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- | The optical coordinates used in the S800 are described in relation to a central trajectory passing through the center of the S800 magnets, and with the reference momentum given by p_0=qBρ_0 | + | |
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- | DETECTORS | + | |
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- | The standard detection system of the S800 includes a plastic scintillator at the object station; two tracking detector at the detector station in the Intermediate Image plane; a pair of cathode readout drift chambers (CRDC) located about 1 m apart; a multi-segmented ion chamber, and four large plastic scintillators of thicknesses 3 mm, 5 cm, 10 cm and 20 cm, respectively. | + | |
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- | A timing detection system is included in the object station | + | |
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- | Cathode Readout Drift Chambers (CRDC) | + | |
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- | 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). | + | |
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- | Fig xxx illustrates the principle of operation of a CRDC. The nuclei passing through the detector ionize the gas, dissociating electrons which drift towards an anode wire under the action of a vertical electric field. The collection of charge in the anode induces a positive charge on the cathode pads, which are read out individually. The x position is determined by fitting the charge distribution on the cathode pads with a Gaussian function. The drift time of the electrons to the anode wire, measured with respect to a trigger signal (typically from a scintillator), | + | |
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- | Both CRDCs are equipped with digital electronics, | + | |
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- | Active Area 53 cm × 30 cm | + | |
- | Active depth 1.5 cm | + | |
- | Number of cathode pads per detector 232 | + | |
- | Number of cathode pads per PCB 116 | + | |
- | Cathode pad pitch 2.54 cm | + | |
- | Filling gas 80% CF4 and 20% C4H10 | + | |
- | Operating pressure 140 Torr | + | |
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- | Ionization Chamber | + | |
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- | An ionization chamber downstream of both 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 at a typical pressure of 300 torr, although this value can be increased up to 600 torr for light nuclei. A technical layout of the detector is shown in Fig. Table xxx lists some of the technical specifications. The detector consists of 16 stacked-parallel plate ion chambers with narrow anode-cathode gaps, placed along the detector’s central axis. Each anode is sandwiched by two cathodes foils made of aluminum evaporated mylar. | + | |
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- | The principle of operation of the ionization chamber is illustrated in Fig. xxx. The electrons and positive ions liberated by the ionization of the gas along the particle trajectory drift towards the closest | + | |
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- | 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 16-channel CAEN N568B shaper/ | + | |
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- | Tracking Parallel Plate Avalanche Counters | + | |
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- | Some experiments are particularly sensitive to the incoming positions and angles of the nuclei impinging on the target. Two tracking parallel plate avalanche counters (TPPAC) are installed in the intermediate image plane of the analysis line. The position and angles measured with both TPPACs are transformed into the corresponding coordinates in front of the target, using the transfer matrix of the second half of the analysis line. The analysis-line dipole magnets downstream of the intermediate image plane filter the particles produced | + | |
- | Each TPPAC has an active area of 10 cm × 10 cm and is filled with isobutane at a typical pressure of 5 torr. The detector consists of a cathode foil with a series of aluminum strips oriented in the non-dispersive direction, followed by an anode plate and a second cathode foil with the strips oriented in the dispersive direction (see Fig xxx). A total of 128 pads are connected to the strips of each cathode foil, with a pitch of 1.27 mm. | + | |
- | The particles transmitted through the TTPAC ionize the gas, producing electrons and positive ions. The drift of electrons towards the central anode plane induces an image charge on the aluminum strips. The signals are send | + | |
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- | plane | + | |
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- | As mentioned in Section 1, some experiments | + | |
- | require tracking of the incoming particles before | + | |
- | they interact with the reaction target. Experiments | + | |
- | using radioactive beams where an array of detectors | + | |
- | surround the reaction target are especially | + | |
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- | sensitive to the incoming positions and angles of | + | |
- | the particles. On the other hand, tracking detectors | + | |
- | located in front of the target can significantly | + | |
- | contaminate the data of the experiment. The | + | |
- | workaround used in the S800 takes advantage of | + | |
- | the analysis line in which detectors can be installed | + | |
- | between its two bends, so that most particles reacting | + | |
- | in the tracking detectors are rejected by the | + | |
- | last bend. The coordinates of each individual | + | |
- | particle at the reaction target location are then | + | |
- | calculated using the transfer map of the second | + | |
- | half of the analysis line. This method has already | + | |
- | been applied in some experiments [4] but with | + | |
- | some limitations, | + | |
- | can be applied to the tracking detectors. | + | |
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- | Since the | + | |
- | signals in these detectors occur earlier than the | + | |
- | valid triggers, they need to be later correlated with | + | |
- | the correct events. In the past, fast clear or delay | + | |
- | lines techniques have been used but they are either | + | |
- | rate limited or degrade the signal too much. The | + | |
- | SCA contained in the front-end electronics of the | + | |
- | CRDCs turns out to be the perfect analog storing | + | |
- | device needed for this kind of application. In this | + | |
- | tracking detector mode of operation, the SCA | + | |
- | continuously samples the signals, acting like an | + | |
- | analog buffer, until a valid trigger is issued. At this | + | |
- | point, the sampling stops and the SCA pointer is | + | |
- | backed by a pre-determined number of samples | + | |
- | (depending on the delay between the tracking | + | |
- | signal and the valid trigger) to the time when the | + | |
- | signal corresponding to the trigger occurred. This | + | |
- | technique allows one to use the tracking detectors | + | |
- | at their maximum rate capability without affecting | + | |
- | the quality of the data. It is already being used on | + | |
- | the A1900 fragment separator parallel plate avalanche | + | |
- | counters (PPACs) with individual strip | + | |
- | readout, and will be on the S800 analysis line as | + | |
- | well as other beam lines at the NSCL. | + | |
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- | The traversing particle ionizes the gas, generating electrons and positive ions. The charge collected by the anode plate induces an image charge on the aluminum strips connected to the pads. | + | |
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- | b) Particle identification | + | |
- | • Downstream of the two CRDC detectors are the ion chamber for energy loss measurement, | + | |
- | followed by a thin plastic scintillator of either 1 mm or 5 mm thickness (default is 1 mm), | + | |
- | itself followed by a 32-fold segmented CsI(Na) hodoscope. | + | |
- | • They provide time as well as energy loss and/or total energy measurements. | + | |
- | • Note that the CRDC detectors cannot function without at least one scintillator to provide a | + | |
- | time reference to measure the drift time of the electrons. | + | |
- | • In standard configuration, | + | |
- | 600 torr and is able to separate elements up to Z=50, after momentum and position | + | |
- | corrections are applied. | + | |
- | • The ion chamber now consists of 16 pairs of alternating anode and cathode aluminum | + | |
- | evaporated mylar foils, . With this geometry electrons and ions are collected on a much | + | |
- | shorter distance than in the previous empty gas volume configuration (about 1.5 cm | + | |
- | compared to 30 cm). Both pile-up and position dependence effects are reduced by using this | + | |
- | configuration. | + | |
- | • The timing resolution for a point-like beam spot in the focal plane is around 100 ps. | + | |
- | S800 Spectrograph | + | |
- | Service Level Description | + | |
- | 30 August 2012 Page 6 of 14 | + | |
- | bazin@nscl.msu.edu | + | |
- | • However, this resolution worsens significantly (up to 1 ns) when the whole focal plane is | + | |
- | illuminated, | + | |
- | by tracking the position of each event on the scintillator from the position and angle | + | |
- | information provided by the CRDC detectors. | + | |
- | • The 32 CsI(Na) hodoscope crystals are 2” thick and cover the whole active area of the focal | + | |
- | plane. They provides a measurement of the total kinetic energy of the particles that stop | + | |
- | within the crystals. The purpose of the hodoscope is to provide charge state identification | + | |
- | orthogonal to the traditional A/Q identification provided by time-of-flight measurement. | + | |
- | Commissioning tests have shown good separation for isotopes up to Z=30 so far. | + | |
- | 2. Tracking in analysis line | + | |
- | The S800 analysis line is equipped with a number of tracking detectors for measuring the | + | |
- | characteristics of the particles prior to their interaction with the target. | + | |
- | a) Object | + | |
- | • The object box of the S800 analysis line contains a thin plastic scintillator (125 μm) for timeof- | + | |
- | flight measurements. For lighter projectiles, | + | |
- | • This detector is usually left in the beam during experiments and can withstand rates of up to | + | |
- | 1 MHz. | + | |
- | b) Intermediate image | + | |
- | • The intermediate image box is equipped with two tracking Parallel Plate Avalanche Counters | + | |
- | (PPAC) with individual strip readout for tracking the trajectories of the incoming particles. | + | |
- | • The individual strip digital readout allows them to function at rates of up to 0.1-1 MHz | + | |
- | independently of the trigger rate, and with no latency. | + | |
- | • They cover a surface area of 10 cm x 10 cm and provide measurements of positions and | + | |
- | angles in both the dispersive and non-dispersive planes. | + | |
- | • Please note that the tracking PPAC efficiency drops significantly below Z=10, and becomes | + | |
- | extremely dependent on the intrinsic disruptive limit of the individual detectors, as well as on | + | |
- | the count rate. | + | |
- | • The tracking of particles with Z below 10 is not supported at the moment. Some attempts to | + | |
- | use small CRDC detectors have been made, but have proven unreliable due to fast aging | + | |
- | problems. | + | |
- | • The characteristics of the incoming particles at the target location can be calculated in much | + | |
- | the same way as for the spectrograph, | + | |
- | at the target to the coordinates at the intermediate image. | + | |
- | • The principal advantage of this method is to use the final bend of the analysis line to | + | |
- | eliminate the contamination due to reactions in the tracking detectors. | + | |
- | • The transfer map between the target and the intermediate image depends on the optics mode | + | |
- | used in the S800. | + | |
- | S800 Spectrograph | + | |
- | Service Level Description | + | |
- | 30 August 2012 Page 7 of 14 | + | |
- | bazin@nscl.msu.edu | + | |
- | • Note also that a pair of “classic” PPACs can easily be installed at the intermediate image, for | + | |
- | tracking secondary beams of low intensity (up to 50 kHz). These have the advantage of a | + | |
- | simpler and faster readout, but are equally limited to Z>10. | + | |
- | c) Target | + | |
- | • As mentioned before in section III, the scattering chamber is equipped with drives that can | + | |
- | accommodate any kind of tracking detector (with a small adaptation). | + | |
- | • Standard PPAC detectors (maximum rate 1 kHz) can be installed at those locations. | + | |
- | However, one has to keep in mind that reaction products from these detectors contaminate | + | |
- | those produced from the target, and require background runs to subtract their contribution | + | |
- | when running with thin targets. | + | |
- | • They should therefore not be left in the beam during data accumulation, | + | |
- | checking the tracking deduced from the intermediate image. | + | |
- | • Detector systems beyond the standard configuration outlined in this document and their | + | |
- | readout are entirely within the responsibility of the experimenters. None of the detectors | + | |
- | installed the scattering chamber are part of the standard configuration. | + | |
- | F. Electronics | + | |
- | 1. Digital | + | |
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- | focal plane CRDCs and intermediate image tracking PPACs are equipped with digital | + | |
- | electronics. | + | |
- | • They consist of a number of front-end electronics boards as designed for the STAR TPC | + | |
- | detector at RHIC, followed by interface boards feeding and receiving data to and from a | + | |
- | programmable FPGA VME module called XLM72 built by JTEC instruments. | + | |
- | • Each chain of these 3 components forms an independent data acquisition system of its own, | + | |
- | driven by state machines programmed into the FGPA. | + | |
- | • The signals occurring on the detectors are sampled by the electronics and locally stored into | + | |
- | the internal memory of the XLM72 modules. | + | |
- | • The sampling frequencies are adjustable, and have typical values of 50ns for the CRDCs and | + | |
- | 100ns for the PPACs. | + | |
- | • The number of samples read out is also adjustable, with typical values between 8 to 12. | + | |
- | • The dead time of the digital electronics readout and the amount of data to transfer through the | + | |
- | VME crate are directly proportional to the number of samples. | + | |
- | • This dead time is around 16μs per sample, therefore the readout code reading sequence starts | + | |
- | with other modules first (such as Camac), and finishes with the XLM72 modules. | + | |
- | • The amount of data also depends on how many channels have fired. As there is no data | + | |
- | reduction performed in the FPGA so far, the relatively large amount of data is read from the | + | |
- | XLM72 in block mode. | + | |
- | • A more detailed description of the digital electronics system will be available at | + | |
- | groups.nscl.msu.edu/ | + | |
- | 2. Trigger | + | |
- | The first-order optics of the spectrograph is point-to-point in the vertical dispersive direction x, i.e. (x|θ)=0, and parallel-to-point in the horizontal non-dispersive direction y, i.e. (y|ϕ)=0 (being θ and ϕ the scattering angles in the dispersive and non-dispersive directions). Since the dispersive terms (y|ϕ) and (x|δ) dominate the transport equations, the x and y positions of a nucleus at the focal plane determine the scattering angle and momentum δ (where δ is defined by equation δ+1=p/ | + | |
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- | ANCILLARY DETECTORS | + | |
- | Besides precise momentum and angular measurements, | + | |
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- | S800 operation: | + | |
- | Division of operation responsibilities | + | |
- | Preparation for tuning: | + | |
- | Software | + | |
- | Electronics | + | |
- | Gas handling system | + | |
- | HV bias | + | |
- | NMRs | + | |
- | Turn on magnets/ | + | |
- | Pilot (XDT) | + | |
- | Unreacted beam | + | |
- | Reacted beam | + | |
- | Device tuning process | + | |
- | S800 scaling (after viewer replaced by target) | + | |
- | Detector diagnostics | + | |
- | Timing | + | |
- | Setting optimization | + | |
- | Focus mode (transmission) | + | |
- | Dispersion-matching mode (resolution) | + | |
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- | During experiment | + | |
- | Scaling | + | |
- | PID | + | |
- | Mask calibration | + | |
- | Use of blocking slits | + | |
- | Handling detectors: | + | |
- | Shimming OBJ | + | |
- | Replacing OBJ | + | |
- | Appendixes | + | |
- | DAQ buffer structure | + | |
- | Trajectory reconstruction from map fields | + | |
- | Documenting | + | |
- | Analysis software | + | |