Linearization of Bunch Compression (2nd order ) Includes 2nd-order chicane compaction (T566) Reduce BC1 energy (250  225 MeV) to reduce V39 by 10%

LCLS-II Longitudinal Tracking with Variable 3.9-GHz Voltage Nominal: V39 = 64.7 MV j39 = -150 deg V39 = 60.0 MV j39 = -160 deg RF Gradients (MV/m): L0 L1 L39 L2 L3 Nom. 16.3 13.6 13.4 15.5 15.7 60 MV: 16.3 14.2 12.4 15.4 15.7 no change

LCLS-II Longitudinal Tracking with Variable 3.9-GHz Voltage Nominal: V39 = 64.7 MV j39 = -150 deg V39 = 57.0 MV j39 = -165 deg spike appears RF Gradients (MV/m): L0 L1 L39 L2 L3 Nom. 16.3 13.6 13.4 15.5 15.7 57 MV: 16.3 14.6 11.8 15.6 15.7