Further measurements of bremsstrahlung from the insertion device beamlines of the Advanced Photon Source.

Bremsstrahlung is produced in the Advanced Photon Source (APS) storage ring when the positron beam interacts with the storage-ring components or with the residual gas molecules in the storage-ring vacuum. The interaction of the positrons with the gas molecules occurs continually during storage ring operation. Bremsstrahlung is important at the insertion device straight sections because the contribution from each interaction adds up to produce a narrow mono-directional beam that travel down the beamlines. At the APS, with long storage ring beam straight paths (15.38 meters), gas bremsstrahlung in the insertion device beamlines can be significant. The preliminary results of the bremsstrahlung measurements in the insertion device beamlines of the APS was presented at SATIF3. This paper presents the results of further measurements at the two insertion device (ID) beamlines with higher statistics in the data collection. The beam current and the vacuum normalized bremsstrahlung power is fairly constant in a beamline for a given storage ring fill pattern, but may vary from beamline to beamline. The average bremsstrahlung power is measured as 118 {+-} 9 GeV/s/nT/mA at beamline 11 ID and as 36 {+-} 2 GeV/s/nT/mA at beamline 6 ID. These results, along with the results from the four previous independent bremsstrahlung measurements, enabled us to conclude upon the various reasons causing this variation.