Beam Acceleration and Transition Crossing in the Fermilab Booster

To suppress eddy currents, the Fermilab rapid cycling Booster synchrotron has no beam pipe; rather, its combined function dipoles are evacuated, exposing the beam directly to the magnet laminations. This arrangement significantly increases the resistive wall impedance of the dipoles and, in combination with the space charge impedance, substantially complicates longitudinal dynamics at transition. Voltage and accelerating phase profiles in the vicinity of transition are typically empirically optimized to minimize beam loss and emittance growth. In this contribution, we present results of experimental studies of beam acceleration near transition. Using comparisons between observed beam parameters and simulations, we obtain accurate calibrations for the rf program and extract quantitative information about parameters of relevance to the Booster laminated magnets longitudinal impedance model. The results are used to analyse transition crossing in the context of a future 50% increase in beam intensity planned for PIP-II, an upgrade of the Fermilab accelerating complex.