The Polarized End Station

The E143 experiment measures the spin structure function for the proton and the deuteron.

The E154 experiment measures the spin structure function for the neutron.

End Station A Operation

The electron beam energy at the source is 60 keV. The beam is injected at this energy into the 3-km SLAC linac, where it is bunched and accelerated to energies as high as 29 GeV. (The ESA beam line is currently being upgraded to transport beams with energies up to 50 GeV for experiments E154 and E155.)

The electron spin is longitudinal at the source and remains longitudinal upon injection into the linac. At the end of the linac the beam is deflected with horizontal bend magnets by an angle of 428 mrad into the ESA beam line. This deflection causes the spin to precess with respect to the momentum vector. The polarized beam electrons are scattered by the polarized target and are detected in two spectrometers as shown in the above figure. The polarized electron beam and polarized nuclear target can be set up to have their relative spins longitudinally aligned either parallel or anti-parallel. From the measured cross-section asymmetry for these two cases, the nucleon spin structure functions can be determined.

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