Energy

Hall A has two way of measuring beam energy ARC and EP methods. The ARC measurement, based on beam deflection in a known magnetic filed in the beamline. EP method, based on elastic electron-proton scattering.

The EP measurement utilized the stand-alone system located along the beamline 17 m of upstream the target. The beam energy is determined by measuring the scattered electron angle and the recoil proton angle in the H(e,e'p) elastic reaction.

The ARC method consists of two measurements. One is measurement of magnetic field integral of the bending elements (eight dipoles in the arc). That measurement is done based on a reference magnet (9-th dipole) measurement. The other measurement is for bend angle value, based on superharp. The superharp is moved across the beam path, and record the beam position before and after bending. Schematic diagram of the ARC section of beamline is presented on Figure:

E02013 experiment is not using anyone of the standard Hall beam energy measurements. GEN experiment utilized so called Tiefenback Energy - energy information based not on direct measurement, but on the calculation based on the ARC method.

Another way to got beam energy is based on knowledge of beam polarization direction. With known polarization direction one can calculate beam energy by following equation: