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BEAM LOADING EFFECTS IN THE CERN PS BOOSTER by F. PedersenAt intensities > 2 × 1012 protons per ring, and at reduced RF voltage, fast growing beam loading instabilities occur in the PSB with complete loss of the beam. The observed thresholds are reported; they are lower than those given by Robinson's criterion. A dynamic linearized model of the beam loading interaction including the feed back loops controlling RF amplitude, phase and cavity tuning is derived. In the general case, beam loading causes cross-coupling be tween all three loops which changes the thresholds. For low beam loading, which was assumed for the basic systems design, the loops are practically independent. The Robinson criterion is a limiting case of this model (no feedback loops). A method for designing better loops taking into account the strong change of loop dynamics under heavy beam loading conditions is described. It has the advantage over other cures, such as lowering of the cavity Q or feeding the cavity with a current equal to the beam current but of opposite phase, that it does not require extra RF power.

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