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Detection Systems

BBS Focal-Plane Detection Systems

The following systems are available for the detection and identification of charged particles entering the focal plane of the spectrometer.

The top-view projection of the focal plane for mode A, B and C shows the length of the focal plane for these modes. The Z-axis is the direction of the nominal ray and the X-axis is the direction perpendicular to it. The high-momentum side is at positive X-values.

The light-ion detection system

This detector system, made by the Institut de Physique Nucleaire at Orsay in France, consists of two Cathode Strip Chambers (CSC's). Each chamber has U- and V-type cathode strips with an active surface of 97 cm by 25 cm. In between each pair of cathode planes is an anode plane made of 12 um diameter wires with a pitch of 1.6 mm. The pitch of the strips on the cathode planes is 6.4 mm. The gap between the anode plane and the cathode plane is 6 mm.

The avalanche created near the anode wires induces an image charge on the cathode strips. The cathode strips are paired and each pair is read out with dedicated electronics, which amplifies, shapes and digitizes the charge signals from the cathode strips. In addition, the electronics calculates the centroid of the induced charge distribution and in this way the position in the horizontal and vertical planes are obtained.

Furthermore, two scintillator layers are used as a trigger and dE-E measuring system. The first layer has four scintillator paddles with a thickness of 2 mm, the second layer has two scintillator paddles with a thickness of 5 mm. Check for further documentation the references, the drawings of the detectors and the man pages of the IPN.

The heavy-ion detection system

The light-ion detection system, made by the Institut de Physique Nucleaire at Orsay in France can be extended with a Parallel Plate Avalanche Counter (PPAC) and an Ionization Chamber (IC). In this way the whole focal-plane detector system can be used for the detection of heavy ions as well. Both the light-ion and the heavy-ion detection systems have been designed to allow a double-hit read-out, in which two particles that traverse the focal plane simultaneously, can be detected.

The focal-plane polarimeter detection system

The Focal-Plane Polarimeter (FPP) positioned behind the focal plane will be used to determine spin observables (asymmetry in the scattering of polarized particles in a graphite slab). A fast rejection send-level trigger based on a Digital Signal Processor enables the use of the polarimeter at high counting rates (> 100 kHz). The system which is presently under construction by the European Supernova collaboration consists of:

  • Two pairs of Vertical Drift Chambers (VDC's) positioned along the focal plane at an angle of 39 degrees with the beam direction. Each pair consists of an X-chamber and a U-chamber (wires at an angle of 30 degrees with respect to the X-chamber). Drift cells have a volume of about 2 mm by 15 mm by 240 mm. The wire pitch for the anode wires is 4 mm. The VDC pairs are separated by 140 mm and are followed by segmented plastic scintillator paddles. The first X-VDC will be positioned along the focal plane of the BBS (tilt angle 36 degrees). In front of this detector anti-coincidence plastic scintillators or beam blockers will be placed. The lateral resolution (fwhm) is 0.15 mm. Every track will trigger at least 4 wires in each detector; this gives enough redundancy in the data to recover from spurious tracks.
  • The Focal-Plane Polarimeter uses a carbon slab with a thickness of several centimeters. The angle over which the protons scatter in this slab can be measured with an accuracy of a few degrees. Therefore, the direction of the track in front of and after the carbon slab will be determined using four multi-wire proportional chambers with X and Y read out. One of these chambers will be positioned in front of and the others behind the carbon slab.

The dedicated 48 cm focal-plane zero-degree detection system

This system uses the Vertical Drift Chamber constructed by J.M. Schippers for the former KVI QMG/2 spectrograph. From spare parts one additional VDC has been assembled. Both VDC's were put in a vacuum box, specifically designed for experiments where the beam from the cyclotron will be stopped at the focal plane.

Laatst gewijzigd:31 oktober 2016 13:54