Beam Dynamics of RF Devices to Improve the Efficiency of Proposed H- Extraction from TRIUMF

Future developments at TRIUMF would benefit from the direct extraction of H- ions in addition to the present stripping extraction of protons. The radial beam density at the first extractor septum must be reduced to achieve 90% extraction efficiency of a 100 ¿A, 450 MeV beam. Two methods have been considered. Installation of RF booster cavities could triple the energy gain/turn at the septum radius. Alternatively a radial RF field at ¿r= 3/2 could generate a coherent betatron oscillation. The subsequent precession could produce local density minima 20% of the average. The beam dynamics for both methods have been investigated using a simple analytic model and a general orbit code. The booster cavities introduce phase-dependent radial and vertical forces (the former leading to phase compression) that may render the motion of some phases unstable. Large coherent oscillations may be unstable near the resonance. Operating tolerances are specified and successful test results of the second scheme are presented.