Speaker
Description
Optimizing lattice and beam tuning in high-current hadron linacs requires reliable characterization of the full three-dimensional phase space. However, longitudinal diagnostics in linacs are inherently sparse, leading to limited observability and ambiguities in phase space. In J-PARC linac, only a few bunch shape monitors are available, and their use is constrained by operational limitations, making them insufficient for routine high-precision longitudinal matching. As an alternative, we develop a measurement scheme based on longitudinal acceptance. By sampling the effective acceptance under multiple conditions—either at different locations or with varied upstream longitudinal focusing—and analyzing the transmitted beam, the longitudinal phase space can be inferred even in the presence of space charge and nonlinear effects. The reconstructed phase space enables more reliable beam tuning and provides insight into transverse–longitudinal coupling, particularly in the context of phase-space “temperature” control. This is directly relevant to the mitigation of intra-beam stripping (IBSt) and distributed beam loss in high-intensity H⁻ linacs, as demonstrated in recent J-PARC operations.
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