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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.
+  * Technical Aspects of the S800
+     * Introduction
+     * Magnets
+     * Stations
+     * Modes of Operation
+     * How are angle and momentum measured?
+  * Detectors
+  * Electronics
+  * Software
+  * Data Acquisition
+  * Experiment detectors
+  * Coupled Detectors and Devices
-**The S800 spectrograph**
+====== Technical Aspects of the S800 ======
+===== Technical Introduction =====
+==== General ====
+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 [2]. It was designed for high-precision measurements of scattering angles (ΔΘ=2 msr) and momentum (p/Δp=2×10<sup>4</sup>), and large momentum and solid-angle acceptances (ΔΩ=20 msr, Δp/p=6%). The S800 layout is shown in Fig. 1. It consists of two parts: the analysis line and the spectrograph.
+[[wiki:pirolilla]]
+{{:wiki:s800_layout.png|}}
+=== Analysis Line ===
+The analysis line extends from the object position to the target station, with a total length of 22 m. 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 maximum rigidity is 5 Tm, although it depends on the tune of the quadrupoles. The acceptances of the analysis line depends on the optical mode.
+[[s800]]
+pirola pirola
+=== Spectrograph ===
+The spectrograph consist of two quadrupoles, a sextupole and two big dipoles assembled in a QQ-S-DD configuration (segment 8) that spans vertically from the target station to the focal plane, with a total length of 18 m. The figures of merit of the spectrograph are summarized in Table 1. Achieving the nominal angle and momentum resolution require the control of different conditions such as object size (less than 0.5 mm), target thickness, uncertainty of the incident angle on the target, intensity, and whether or not the incoming beam needs to be tracked.
+^ Momentum Resolution (p/Δp)      | 2×10<sup>4</sup> |
+^ Momentum Acceptance             | 5.8%             |
+^ Angle Resolution                | 2 msr            |
+^ Solid Angle Acceptance          | 7º×10º or 20 msr |
+^ Momentum Dispersion (x/δ)       | 9.5 cm/%         |
+^ Angle Dispersion (y/b)          | 0.9 mm/mrad      |
+^ Magnification(x/x)              | 0.74             |
+^ Focal Plane Size (x × y)        | 55 cm ×15 cm     |
+^ Maximum Rigidity                | 4 Tm             |
+^ Detector Position Resolution (x)| 0.3 mm           |
+^ Detector Position Resolution (y)| 0.3 mm           |
+==== S800 Stations ====
+The S800 includes several detector stations:  object, intermediate plane, target, and focal plane. The object box (see (picture) Fig. xxx) contains a plastic scintillator for time-of-flight measurements. This detector is usually left in the beam during experiments and can withstand rates up to 1 MHz. A large surface (5 cm × 5 cm) PIN 0.3 mm silicon detector is also installed in the this box and serves to measure the energy loss of the beam particles. This detector is intended to check the composition of the incoming radioactive beam and is not meant to stay in the beam during data accumulation. The rate is limited to 1 kHz.
+The intermediate image box (see (picture) Fig. xxx) is equipped with two Tracking Parallel Plate Avalanche Counters (TPPACs) .
+The standard configuration of the S800 used to employ a scattering chamber (see (picture) Fig. xxx) that contains a ladder for holding the targets. This ladder is mounted on a drive that allowed for continuous rotation as well as vertical translation for the fine adjustment of the target position and thickness. This scattering chamber also contains two fixed-position drives movable by 1" increments located in front of the target, as well as a table that can be inserted from the chamber top covering the whole area of the chamber. The inside dimensions of this chamber are 1 m along the beam axis by 1 m transversally. It can be configured for a fixed set of spectrograph angles using a set of welded front flanges for 0°, 5°, 8°, 10°, and 18°.
+A much larger scattering chamber (see (picture) Fig. xxx) is available to accommodate for bigger detector systems such as HiRA. This chamber retains a target mechanism similar to the one described above (vertical translation + rotation), but with the additional possibility of shifting the target position along the beam axis. This feature is necessary for experiments that require more space "downstream" of the target to detect particles at forward angles. Note, that moving the target "upstream" of the nominal position reduces the solid angle of the spectrograph and requires a retune of the last two quadrupole triplets of the analysis line.
+As mentioned before, the scattering chamber is equipped with drives that can accommodate any kind of tracking detector (with a small adaption). Standard PPAC detectors (limited to 1 kHz count rate) can be installed at those locations. However, one should keep in mind that reaction products stemming from interaction of the beam with the detectors pose a possible contamination of the beam and require "background runs" to be subtracted out when running an experiment with a thin target. Therefore, these detectors should only be inserted to check the tracking deduced from the intermediate image and it should be avoided to leave these detectors in the beam during data accumulation.
+Some detection systems do not require a scattering chamber. In this case, the chamber will be removed and the target is slid into a pipe surrounded by the detector array. SeGA, CAESAR, GRETINA, PLUNGER, LENDA have standard frames and setups to be used with the S800. Other detector arrays would require the design and fabrication of new hardware. In this configuration a target change presently requires venting the target section and dismounting part of the hardware to access the inside of the beam pipe. This operation typically takes about 30-45 minutes.
+ The S800 focal plane box (see (picture) Fig. xxx) is equipped with various detectors including two position sensitive Cathode Readout Drift Chambers (CRDCs) for tracking the trajectories of the particles, a ion chamber for the measurement of energy loss, a timing scintillator  E1, and an Hodoscope for total kinetic energy measurements.
+{{:wiki:s800_layout.png|}}
+==== Magnets ====
+=== 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
-  * Brief technical details
-      * Unordered List ItemPrecise angular and momentum measurements
-  * High acceptance to cover large emittances of RNB
-  * Layout / magnets
-  * Figures of merit
-  * Modes of operation
-  * How are angle and momentum measured?
   * Ion optics
   * Detectors
-  * SCI OBJ
+      * SCI OBJ
-  * TPPACs
+      * TPPACs
-  * CRDCs
+      * CRDCs
-  * IC
+      * IC
-  * FPSCI
+      * FPSCI
-  * Hodoscope
+      * Hodoscope
   * Electronics
-  * Diagrams
+      * Diagrams
-  * Triggers
+      * Triggers
-  * Signal optimization
+      * Signal optimization
   * Software
-  * Log in to use different applications
+      * Log in to use different applications
-  * Barney
+      * Barney
-  * Bklq
+      * Bklq
-  * Panel Mates
+      * Panel Mates
   * DAQ
-  *
   * Experiment types
-  * Coulex
+      * Coulex
-  * CE
+      * CE
-  * Knockout
+      * Knockout
-  * ...
+      * ...
   * Supported detectors (Background suppression):
-  * Gamma
+      * Gamma
-  * CAESAR
+      * CAESAR
-  * SeGA
+      * SeGA
-  * GRETINA
+      * GRETINA
-  * Neutron
+      * Neutron
-  * LENDA
+      * LENDA
-  * Charge particle
+      * Charge particle
-  * HiRA
+      * HiRA
-  *
-Organization of responsibilities: device physicist vs. experimenter (training)
+  * Organization of responsibilities: device physicist vs. experimenter (training)
-Planning an experiment with the S800
+  * Planning an experiment with the S800
@@ Line 58: / Line 163: @@
-THE S800 SPECTROGRAPH
+**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.
@@ Line 76: / Line 191: @@
 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.
@@ Line 113: / Line 229: @@
 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.
@@ Line 126: / Line 243: @@
 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.

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