Transverse collective instability in the PSR

An instability in the Proton Storage Ring (PSR) is observed as fast loss of beam during accumulation and storage when the injected beam current exceeds a threshold value. Instabilities are observed during both coasting-beam and bunched-beam operation. Large coherent transverse oscillations occur prior to and during the beam loss. The growth times are rapid, typically in the range 10-100 mu s. The instability threshold is observed to depend strongly upon RF voltage, beam size, injected momentum spread, and nonlinear fields. Weaker dependences upon betratron tune, vacuum pressure, and stripping-foil bias voltage have also been observed. A possible e-p oscillation component of the unbunched beam instability is suggested. Growth times suggest a significant Re(Z/sub perpendicular to /) of approximately 0.2-0.5 M Omega /m; the source of this is not yet precisely identified. >