Filling patterns
No significant changes in the distribution of the modes are to be noted for 2006 compared to the previous year. The multibunch modes remain dominant, making up 63% of the shifts. Figure 147 shows the distribution of the various filling modes in 2006.
Fig. 147: Distribution of the filling modes in 2006. |
The increasing demand for time structure led to the development of a new multibunch filling pattern: the so-called “7/8 +1 filling mode”. The overall lifetime is in the order of 72 hours at 200 mA. The presence of a gap (1/8 of the circumference) avoids beam-ion instabilities, thus maintaining the vertical emittance at the lowest value, around 25 pm•rad. A single bunch of 2 mA, placed in the middle of the gap, is delivered with a contrast ratio of 10-9 between filled and unfilled bunches. To satisfy Users’ requests such as achieving a sharp contrast between the bunch trains and the nearly empty buckets, the first and the last bunch of the train are filled at 1 mA. Figure 148 presents the time structure of the beam around the ring circumference.
Fig. 148: Current versus time of the new 7/8+1 filling mode. A high current per bunch with 62 empty bunches on both sides (at 10-9 level) allows time-resolved beamlines to select a single bunch with a very high contrast ratio. |