Operation Overview

In normal operation the target will be under one of the following situations described below.

1. The target is in ``beam position'', the fast raster set to a nominal 4 mm $\times$ 4 mm area coverage and the experiment is running to collect physics data. In this configuration the monitoring of the target consists of reading a set of temperatures of the pumping cell, target cell and reference cell. The temperature in the pumping cell provides feedback for the temperature controller. A spectral-analyzer is monitoring the laser wavelength and the relative intensity. One viewing camera which looks at the pumping cell will be on. All interlocks of electron beam and laser beam should be on.

2. The beam is turned off and the target is moved to ``Pickup Coil Position'' (polarized $^3$He target in a position between the NMR pickup coils) and a polarization measurement is performed using the NMR (AFP) method. The laser beam will be stopped first. If the polarization is in the transverse mode, a rotation of the polarization to the longitudinal direction is performed (procedure described in Chapter ). Once the measurement is completed the target cell will be moved back to the ``beam position''. If the next running is in transverse mode, a rotation of the polarization to the transverse direction is performed. The laser beam will be turned on. The beam interlock is reset and the fast raster enabled before turning the beam back on target. The physics data taking should resume.

3. The ``Polarized $^3$He Target'' is in ``beam position''. The data taking is stopped and the beam is turned off. An EPR measurement is performed (procedure described in Chapter ). After the measurement is completed and the fast raster enabled, the beam is put back on and data taking resumes.

4. The ``BeO Target'' is moved to ``beam position''. The electron beam current lowered (to $< 5 \mu$A with raster-off) as not to damage the BeO target. The monitoring of the beam position is performed by looking at the TV monitor which displays the view of the target.

5. The 7-foil $^{12}$C ``Optics Target'' is in ``beam position''. Data on the optics target are taken for spectrometer optics study or detector calibration. Since the BeO and the optics target are in beam at the same time, the above two measurements are often performed at the same time.

6. The target ladder ``Empty Target'' frame is moved to ``beam position'' whenever beam tuning is performed, and when checking for possible beam halo background.

7. The ``Reference Cell Target'' is in ``beam position'' with the beam fast raster on and data on the reference cell are taken for calibration.