BBI Effects in lattice 4160_113005 vs 4260_092605_v1
6 December 2005
Comparison of positron bunch current dependence of maximum horizontal beta and Welch-Temnykh B parameter for the September 2005 operating lattice at 4260 MeV and new 4160 design for the coming running period. The latter design procedure incorporates compensation for the parasitic crossings with 2 mA/bunch, as described here.
These calculations were performed in the 8x5 configuration employed in September, 2005 at 4260 MeV. The effect of the beam-beam interaction at the IP has been excluded.
The first two plots (old 4260:left, new 4160:right) show the increase with positron bunch current of the maximum value of the electron horizontal beta function in the ring, which is MUCH smaller in the new 4160 lattice. The value reached at the empirical operating limit of 2 mA in the 4260 lattice is not reached until a bunch current of 4 mA in the new lattice. It is also interesting to note that bunch 1 suffers more in the new lattice,while bunch 3 is better off. The new lattice design was optimized for bunch 3 rather than bunch 1.
The second pair of plots show the increase with positron bunch current in the Welch-Temnykh parameter normalized to bunch current.The limiting hyperbola of B = 1.2 is included, showing the value of bunch current where the lifetime is expected to go bad. Here the improvement in the new lattice is still appreciable, but not as dramatic as for the horizontal beta function. Here bunch 1 is the worst case in both designs. The limiting value for t1.b1 is 2.4 mA in the old lattice and 2.8 mA in the new lattice.
Log files: 4260 and 4160.
Creation date: 12/06/05.