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-====== Technical Aspects of the S800 ======
+====== 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 Introduction =====
-==== General ====
+===== Technical Aspects of the S800 =====
-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.
+  * [[Introduction]]
+  * [[Stations]]
+  * [[Magnets]]
+  * [[Modes of Operation]]
+  * [[Determination of Angles and Momentum]]
+  * [[Detectors]]
+  * [[Electronics]]
+  * [[Data Acquisition (DAQ)]]
+  * Software
+  * Coupled Detectors/Devices
+  * Types of Experiments
-{{:wiki:s800_layout.png|}}
+===== Operation of the S800 =====
-=== 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.
+==== Magnets ====
-=== Spectrograph ===
+=== Spectrograph Dipoles ===
-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.
+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.
-^ Momentum Resolution (p/Δp)      | 2×10<sup>4</sup> |
+=== Spectrograph Quadrupole Doublet ===
-^ Momentum Acceptance             | 5.8%             |
+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.
-^ 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           |
+=== 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.
-==== 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.

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