Apparatus

High power diode lasers (about 100W) provide an intense monochromatic light beam for optical pumping. The lasers are housed in a large shielding house, known as the ``laser hut'', which is located about 5m away from the target on one side of the beam line. An overview of a typical arrangement of the target components in the Hall is shown in Figure .

Figure: Overview of the target setup. Shown are the laser hut, the beam pipes covering the laser beam line extending to the target area, and the Helmholtz coils with the RF assembly and support sub-assembly.

The polarized target comprises several components beyond its target cell (see Fig. ) related to its operation, they are in section:

1. A double sets of Helmholtz coils which provide the target spins with a holding magnetic field of few tens of Gauss as well as define the orientation of the polarization in any required direction.

2. A pair of RF coils which allow for the measurement of the target polarization using the Adiabatic Fast Passage (AFP) technique and the Electron Paramagnetic Resonance (EPR) technique.

3. A multi-purpose RF enclosure which holds the RF coils but more importantly is crucial for the containment of the target cell in case of explosion. It also provides a containment volume for the $^4$He gas to cool the target windows with cooling jets, minimizing the radiation length crossed by the electron beam.

4. An oven with all its related components for providing the necessary temperature to the pumping cell in order to bring the rubidium in its vapor phase and control its number density.

5. A target ladder subassembly which supports a target cell, a reference cell, (which can be filled with $^3$He, Nitrogen or $^4$He gas with pressure up to 10 atmospheres to study dilution, density or background), a 7-foil $^{12}$C optics target, a BeO beam viewer and an oven. It also includes a full mechanism for positioning the targets and bears the target cell viewing mirrors and the optical beam line mirrors.

6. A laser shielding house known as ``laser hut'' where two laser beam lines are formed by seven 30-Watt diode lasers. These laser beam lines are used for optical pumping of the rubidium alkali atoms in the direction either along the electron beam (longitudinal, 4 lasers) or perpendicular to the electron beam line (transverse, 3 lasers). The nominally longitudinal laser beam can also be directed at a different (specific) direction.