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pereira [Technical Aspects of the S800]
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   * [[Electronics]]
   * [[Data Acquisition (DAQ)]]
-  * [[Software]]
+  * [[S800 Software]]
-  * Coupled Detectors/Devices
+  * Coupled Devices
-  * Types of Experiments
+  * [[Types of Experiments]]
 ===== Operation of the S800 =====
+  * [[Preparation for tuning the S800]]
+  * [[Tuning the S800 (XDT: Experiment Device Tuning)]]
+  * [[During experiments]]
-==== Magnets ====
+  * [[Division of operation responsibilities]]
-=== Spectrograph Dipoles ===
-Each S800 dipole [3] weights 70 Tons and has a 15 cm gap. The bending radii and angle are 2.8 m and 75°, respectively. The magnet has five main pieces: two top slabs, the inner and outer side yokes, and the pole tip assembly. The maximum current supplied to the coil is 450 A, translating into a 1.6 T maximum central magnetic field, and a maximum magnetic rigidity of about 4 Tm.  Trim coils are installed on the inner and outer radii of the dipoles to achieve a uniform field near the edges of the magnet. The operating current of the trim coils is 43.75% the value of the magnets. A liquid helium feed circuit brings liquid helium through a heat exchanger at the top of the magnet  and delivers the liquid into the bottom of the coils. The helium overflowing the coils fills the dewar to provide cooling for the incoming liquid. Liquid nitrogen is supplied at the bottom of each side. A 0.25 dissipative resistor with a short decay constant is connected to a coil protection switch. In case of cryogenic failure, the switch reroutes the power supplied to the circuit into the resistor. The dipole steel has a 30° edge angle, so that particles are defocused and focused in the dispersive and non-dispersive directions, respectively. The inner and outer radii of the dipoles include trim coils to guarantee the uniformity of the field near the edge.  NMR probes are installed in the flat field region to measure the absolute field setting during operation.
-=== Spectrograph Quadrupole Doublet ===
-In order to maximize the acceptance of the spectrograph, a doublet of superconducting quadrupoles is installed upstream of the two main dipoles [3]. The doublet focuses  the transmitted particles first in the non-dispersive and then in the dispersive directions. The quadrupoles are the iron-dominated type used in the NSCL beamlines, but with larger dimensions.  The pole tip of each quad has a length of 30 cm, and a radius of 12 cm for the first quad and  21 cm for the second one, i.e. almost twice and three times larger than the beamline quadrupoles, respectively.  The doublet weights 5 Tons, including the sextupole at the end of the second quad. The field gradient  of the first quadrupole is 19.7 T/m at a maximum operation current of 86 A. The field gradient of the second one is  7.5 T/m at a maximum operation current of 90 A.  Both quadrupoles have cryogenic Hall generators mounted on the pole tips to measure the  field gradient during operation.  The quadrupoles don’t have protection circuit since they can quench with no damage to the coils.
-=== Spectrograph Sextupole ===
-The only high-order magnet included in the S800 is a sextupole coil  installed around the bore tube of Q2. The purpose of this element is to correct the broadening of the beam at the focal plane due to the dominant (x|2) aberration. This defines a narrower trajectory of the beam, allowing the use of a beam blocker at the focal plane to block the unreacted beam when its magnetic rigidity is close to the tuned setting.
-====== 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
-  *   *   * 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 of responsibilities: device physicist vs. experimenter (training)
-  * Planning an experiment with the S800
-**THE S800 SPECTROGRAPH**
-INTRODUCTION
-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, a small sextupole and two big 75° assembled in a QQ-S-DD configuration (segment 8) that spans vertically from the target station to the focal plane. Table xxx summarizes the features of the different superconducting magnets.
-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  the momentum of each particle beam must be tracked, significantly limiting the resolution at the focal plane (to about 1 part in 1000 in energy). In the dispersion-matching mode the whole system (analysis line + spectrograph) is achromatic in the focal plane. The analysis line is therefore highly dispersive (about 11 cm/%) at the target position, limiting the momentum acceptance to ±0.5%. This mode provides the highest possible energy resolution (1 part in 5000 for a 1-mm wide beam spot), since it does not require momentum tracking. The figures of merit of the S800 are summarized in Table 2. Details on the ion-optics can be found in section 1.2.
-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.  The transformation of focal-plane coordinates into target coordinates is done using an inverse transfer matrix calculated by the COSY code [xx] from the measured field maps of the magnets [xx]. In order to correct the high-order aberrations of the system, the transfer matrix is calculated up to fifth order. This order is sufficient to achieve a precision comparable to the resolution of the detectors. (This method is extensively described in appendix A.) The identification of the fragments produced in the reaction target is done by combining the measurements of their time-of-flight and the energy loss in an ionization chamber. In addition, the incoming beam can be tracked before the reaction target using two xxx located in the intermediate image plane of the analysis line.
-ION OPTICS
-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  , where ρ_0 is the central bend radius for the dipole, B is the dipole field and q is the ionic charge. The coordinates used in ion-opticcs are the longitudinal distance z along the reference path; and the transversal (perpendicular to z) distances x and y with respect to the  reference trajectory in the dispersive and non-dispersive directions, respectively. The angles  and  are referred with respect to the z axis in the xz-plane and yz-plane, respectively. The momentum coordinate is defined according to the equation + 1 = p / p0 where p is the momentum of the particle. The coordinate l is the distance traveled along the central trajectory in relation to the reference particle, l+1=z/z0…… In ion-optics, the state of a charged particle exposed to the action of an electromagnetic field is characterized by a vector (x y θ ∅ l δ). The coordinates of a charged particle change due to the action of an electromagnetic field. This change can be expressed in terms of a transfer matrix, according to:
-DETECTORS
-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.
- A timing detection system is included in the object station
-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)  × 56 cm (dispersive direction), and it is filled with a gas mixture consisting of 80% CF4 and 20% C4H10 at a typical pressure of 50 torr. A schematic view of a CRDC can be seen in Fig xxx, and their technical specifications are listed in Table xxx. Each detector consists of two windows mounted on frames, two printed circuit boards (PCB) and an anode frame.  Each PCB is made of un-masked G-10, and includes a field shaping foil to ensure a uniform field in the active region of the detector. Two G-10 spacers are laminated to the board on each side. The shaping foils are made of 1.9-mm pitch evaporated aluminum strips perpendicularly oriented to the electric field. The anode frame includes a glued cathode grounding plane, an anode wire running across the field, and a Frisch grid. Cathode pads are located in front of and behind the anode wire. The pads have a pitch of 2.54 mm. The anode frame is sandwiched between the two printed circuit boards with two spacers in between, as shown in Fig. xxx.
-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), provides the y position. The resulting position resolution is 0.5 cm. Depending on the position of the track, the typical drift times of the electrons to the anode wires are 0 to 20 s. The relatively long drift times limit the maximum rate that the detector can process properly to around 5000 counts per second . High rates affect also the aging of the anode wire. These problems can be partly  amended by spreading the beam over a large portion of the active area, as it is done in focus mode.
-Both  CRDCs are equipped with digital electronics, which consist of of seven front-end electronic boards designed and developed by the STAR collaboration (RHIC), followed by interface boards connected to a programmable FPGA VME module (XLM72).  Each FEE includes 32 channels of preamplifier shaper, followed by a switched capacitor array (SCA), which acts as an analogic memory, 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 and 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 us. 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.
-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
-Ionization Chamber
-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.
-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  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.
-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/amplifier with remotely adjustable gains. The output signals feed a Phillips 7164H ADC.
-Tracking Parallel Plate Avalanche Counters
-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  in the tracking detectors, which would otherwise contaminate the data.
-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
-plane
-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
-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, namely the maximum rate that
-can be applied to the tracking detectors.
-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.
-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.
-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, the ion chamber is filled with P10 gas at a maximum pressure of
-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
-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, because of path length differences in such large scintillators. It can be recovered
-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.
-. 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, a thickness of 1 mm is also available.
-• This detector is usually left in the beam during experiments and can withstand rates of up to
-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, using an optics calculation that relates the coordinates
-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
-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, and only serve for
-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
-. Digital
-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
-ns 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/s800/Technical/Electronics/Electronics_frameset.htm
-. 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/p0,  being p and p0 the momentums of the transmitted nucleus and a nucleus following the central trajectory, respectively).
-ANCILLARY DETECTORS
-Besides precise momentum and angular measurements, the S800 can be operated in
-	S800 operation:
-	Division of operation responsibilities
-	Preparation for tuning:
-	Software
-	Electronics
-	Gas handling system
-	HV bias
-	NMRs
-	Turn on magnets/settings
-	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)
-	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

S800 Documentation

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