Measurements and Corrections to the Beam Properties in the TRIUMF Cyclotron

The recent commissioning of two centring probes and four pairs of internal slits has for the first time made possible systematic measurements and improvements to the central orbits, and internal selection of beam emittance and phase acceptance. The beam signals are digitized and computer-processed to allow rapid analysis and correction of the centring by means of steering electrodes and harmonic trimming coils. Radial-longitudinal coupling effects agree with theory and are used to optimize the injection conditions for the wide phase acceptance. With the internal slits it has been possible to improve the incoherent radial betatron oscillation amplitude and to observe isolated turns to 220 MeV and turn structure out to 500 MeV. Fluctuations in the dee voltage (~ ±0.1%) and the magnetic field (± 2 x 10r-6) give rise to fluctuations in the energy and intensity of highly selected beams. Improved stability has been achieved by regulation of both RF voltage and frequency with beam-derived signals.