Experimental studies of the nonlinear momentum compaction factor at BESSY II

Experimental studies were performed, to measure the nonlinear behavior of the momentum compaction factor /spl alpha/ at the BESSY II electron storage ring. Based on these results the momentum acceptance of the storage ring can be derived. Several sets of measurements at different values of the horizontal chromaticity in the range of /spl Delta/Q/sub x//(/spl Delta/p/p/sub 0/)=/spl xi//sub x/=-5.5...+8.1 were generated. Depending on tune and horizontal chromaticity particles in the range from -4%