A schematic of the deflection
magnet is shown in Fig. 1. It is a C type magnet that
provides up to 0.3 Tesla-meter field integral for deflecting ep elastic
electrons in the horizontal plane. It has a compact design,
allowing it to be placed very close to the scattering chamber
with little weight ( about 5 tons).
The deflection magnet is positioned at 45 degree with respect to the
electron beam line Fig. 2. The distance between target
center and magnet's central vertical plane is 110 cm. The fringe
magnetic field on the beam line reaches 200 Gauss but was reduced by
means of iron clamps and pipe to the level of 0.3 Gauss.
 Fig 1: Schematic side view of the deflection magnet. |
 |
Fig 2: Plan view of the Deflection magnet.
The magnet gap varies from 10.5
cm at small angles to 33.5 cm at large angles, which is well matched to
the acceptance of the RCS detector over the kinematic range of
interest. The length of the gap is such that the magnet operates at a
fixed location as the RCS detector is moved to different angles (see
Fig. 2). The length of the gap also imposed limitation on scattering
angle of electrons, as it is shown in Fig. 2, that angle can vary
from 20 to 76 degree. The field integral is about a factor of 3 less
for large scattering angles, but it is still sufficient for deflecting
electrons, whose energy is low at large scattering angle. The current
is about 600 A and the voltage drop on coils is about 70 Volts. Since
the field integral of the magnet can be calibrated using elastic
electron scattering, a detailed field mapping was not necessary.