CLAS apparatus

Apparatus

Target

The target materials used in the EG1b experiments were [math](15)NH_3[/math] and [math](15)ND_3[/math]. The first one was used for the polarized protons and the second for the polarized deuterons. These materials satisfy several conditions which are suitable for scattering experiments. Ammonia targets produce high polarization and are resistant to radiation damage(it will be changed) which can be easily repaired by an annealing process. Also,it has high ratio of free nucleons(3/18).
The target material was prepared in the following way. The ammonia gas was frozen at 77 K and then crushed into little pieces, about 1-3 mm in diameter, because it heps to have them efficiently cooled by the liquid helium during the experiment and prevent from potential damage by the beam heating.

Cherenkov detector

The six superconducting coils placed by angles of 60 degrees in the azimuthal angle [math]\Phi[/math] around the electron beam line produces the 5 T magnetic field.It is important to minimize the amount of material in all of the detectors to minimize hadron and electron absorption and secondary particle production upstream of the time-of-flight scintillators and calorimeters.The detector is divided in the six sectors with each sector independently instrumented to be an effective spectrometer. The Cherenkov detector was designed to maximize the coverage in each of the sectors up to an angle [math]\theta=45[/math] degrees.
In the extreme regions of the angular acceptance of the spectrometer the number of detected photoelectrons is too low. To get acceptable efficiency of the detector in these regions were placed photomultiplier tubes.(?????? stringent requirements, within budgetary constraints ????????????, were placed on the photomultiplier performance).The produced Cherenkov light is in the ultraviolet region, because of that the photoelectron conversion efficiency should be high at short wavelengths.