Mitigating transition in the Fermilab Booster using a triple phase jump

The PIP-II project currently under construction will boost neutrino production for DUNE, Fermilab's flagship long baseline neutrino oscillation experiment, by doubling the beam power delivered by the accelerator complex. To accomplish this, the total charge injected from the linac into the existing Booster RCS ring will increase from 4.5 to 6.5E12 while the machine ramp rate will be raised from 15 to 20 Hz. The Booster accelerates beam from 800 to 8000 MeV and crosses transition at γ = 5.45 In current, pre PIP-II operations, no formal gamma-t jump system is used and the longitudinal emittance blowup is limited with an active quadrupole mode feedback system. Due to the slip-stacking process used in the dowstream Recycler Ring to accumulate and increase bunch intensity, to prevent excessive particle loss the longitudinal emittance at extraction limited is set to 0.1 eV-s (95%). Given that collective fields scale with intensity, it is anticipated that additional measures will need to be put in place to meet this requirement. We look at the so-called triple phase-jump technique a possible candidates for transition mitigation and present some simulation results. Despite known limitations, attractive aspects of the triple jump are that the phase manipulations are incorporated within the digital LLRF system; no additional magnets or pulsed power supplies are needed and the technique is compatible with active quadrupole mode feedback.