Measurement of Resonant Space Charge Effects in the J-parc Linac

Traditionally, high intensity linac designs follow the “equipartitioning condition”, a strict control of the transverse and longitudinal tune ratios throughout the linac that ensures space-charge driven emittance exchange between the longitudinal and transverse planes is minimised. However, equipartitioning imposes strict rules on the linac design, thus limiting the design options and increasing the overall construction cost. More recently, practical tools have been developed that offer guidelines in designing non-equipartitioned linacs, by charting the stable regions in a tune ratio diagram (Hofmann’s Charts). While these stability diagrams have been backed by extensive multiparticle simulations and some experimental evidence, questions still remain regarding the practical consequences of crossing the resonances. In this paper preliminary results are presented from an experimental study conducted in the J-PARC linac, where for the first time we measured both the transverse and longitudinal emittance for different linac working points. A detailed analysis will be presented as well as a discussion on the wider implications of this experiment.