OTR and SLI

OTR is a device which detects the emitted radiation from a thin ($10 \mu{\rm m}$) Carbon foil as beam passing through. It can measure both the center position and the size of the beam. Although its accuracy is less than superharp, it can be used continuously as a monitor.

An OTR system is installed at the C12 position, middle point of the Hall C arc. Thus, its continuously meausred beam size provides the intrinsic energy spread with respect the central value. Thus, it measures another important beam energy quality. Since this spread cannot be corrected as that of central drift that can be corrected by the fast feedback system, if the size measured at C12 exceeds the desired energy spread, MCC should be contacted.

Although OTR uses thin foil, it was seen that it did produce halo in the beam. Thus, a new device will be installed at the same location (C12) soon, replacing the existing OTR. The new device is SLI. This device does not have any material in beam but can measure the size of the beam as OTR does. By using it at the location of C12 to measure continuously the beam size, the intrinsic energy spread can be checked and monitered constantly.