The Bremsstrahlung radiator is the last element in the Hall A beam line before the scattering chamber, and is about 72.6 cm from the center of the physics targets. Its design is based on the Hall C radiator system built by David Meekins, and documented in the Hall C operations manual.
The central component of the system is a U-shaped, oxygen-free copper target ladder, with six positions for differing thicknesses of oxygen-free Cu foils. The ladder is designed so that it never intersects the beam. The 3.175-cm wide gap in the ladder is spanned only by the target foils, which are 6.35 cm wide, 3.175 cm high, and 3.332 cm apart (center to center). A stepper motor moves the target ladder with foils up and down, into and out of the beam. Hard stops prevent motion of the ladder beyond the limit switches. Water cooling of the radiator ladder cools the foils, preventing damage from overheating by the beam.
The interaction of the beam with the foils produces background radiation in the Hall. At 3 GeV, ion chamber trip levels do not need to be adjusted, and increases in detector background rates are minimal; further tests are planned for 0.8 GeV. No local shielding is installed, as calculations indicate that this will not significantly affect dose at the site boundary. Any installation and/or subsequent modifications must be coordinated with RadCon.