Mitigating chromatic effects on the transverse focusing of intense charged particle beams for heavy ion fusion

A final focusing scheme designed to minimize chromatic effects is discussed. The Neutralized Drift Compression Experiment-II (NDCX-II) will apply a velocity tilt for longitudinal bunch compression, and a final focusing solenoid (FFS) for transverse bunch compression. In the beam frame, neutralized drift compression causes a sufficiently large spread in axial momentum, pz, resulting in chromatic effects on the final focal spot during transverse bunch compression. Placing a weaker solenoid upstream of a stronger final focusing solenoid (FFS) mitigates chromatic effects, and significantly improves transverse focusing for relevant NDCX-II parameters.