Loss Monitors

When the Touschek scattering rate suddenly rises because of resonant depolarization, an increase of scattered electron pairs should be detected outside the vacuum chamber. At the SLS storage ring a pair of scintillators was already installed downstream of the in-vacuum undulator U24. The closed gap of this undulator reduces the aperture to 8 mm in the straight section which leads to an increase of the signal intensity of the loss monitors. When the scintillators registered an event in coincidence we assume this a Touschek scattering event. During stable beam conditions this loss signal is constant. As soon as the beam is excited at the resonant depolarizing frequency the signal jumps to higher values. This is a very useful method to distinguish jitter of the lifetime and current readings (see figures 6 and 7) from ``real'' peaks. An example is given in figure 8 where the loss monitor jump clearly identifies the sudden increase of Touschek loss rates.

Figure 8: Excitation of the beam at the resonant depolarizing frequency leading to a jump in the rate of Touschek scattered particles as seen by scintillation monitors.