Measurements of Stability Limits for a Space-Charge-Dominated Ion Beam in a Long a. G. Transport Channel

The Single Beam Transport Experiment at LBL consists of 82 electrostatic quadrupole lenses arranged in a FODO lattice. Five further lenses provide a matched beam from a high-current high-brightness cesium source for injection into the FODO channel. We call the transport conditions stable if both the emittance and current remain unchanged between the beginning and end of the channel, and unstable if either the emittance grows or the current decreases because of collective effects. We have explored the range of single-particle betatron phase advance per period from σ0 = 45° to 150° to determine the stability limits for the space-charge depressed phase advance, σ. No lower limit for σ (down to 7°) has been found at σ0= 60°, whereas limits have clearly been identified and mapped in the region of σ0 above 90°.