Optimization of the Ballistic Guide Design for the SNS FNPB 8.9 A   Neutron Line
  The optimization of the ballistic guide design for the SNS Fundamental Neutron Physics Beamline 8.9 A 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 75% increase in the neutron flux exiting the 33 m long guide over a straight m=3.5 guide with the same length. 
Takeyasu M. Ito, Christopher B. Crawford, Geoffrey L. Greene