Optimization of the ballistic guide design for the SNS FNPB 8.9 Å neutron line

The optimization of the ballistic guide design for the SNS Fundamental Neutron Physics Beamline 8.9 Å line is described. With a careful tuning of the shape of the curve for the tapered section and the width of the straight section, this optimization resulted in more than a 75% increase in the neutron flux exiting the 33 m long guide over a straight m=3.5m=3.5 guide with the same length.