A. Lasheen, H. Damerau, K. Iliakis
CERN, Meyrin, Switzerland
In the context of the LHC Injector Upgrade (LIU) project, the main longitudinal limitations in the CERN PS are coupled bunch instabilities and uncontrolled emittance blow-up leading to losses at injection into the downstream accelerator, the SPS. To complement beam measurements, particle tracking simulations are an important tool to study these limitations. However, to avoid excessive runtime, simulations are usually targeting only a fraction of the cycle assuming that bunches are initially matched to the RF bucket. This ignores all initial perturbations that could seed an instability. Simulations were therefore performed along the full PS cycle by using the BLonD tracking code optimized with advanced parallelization schemes. They include beam manipulations with several RF harmonics (batch compression, merging, splittings), controlled emittance blow-up, a model of the beam coupling impedance covering a wide frequency range, as well as beam and cavity feedbacks. A large number of macroparticles is required as well as arrays to store beam induced voltage spanning several revolutions to account for long range wakefields.
R. Ainsworth, A.V. Burov, N. Eddy, A. Semenov
Fermilab, Batavia, Illinois, USA
Recent advances in the theoretical understanding of beam stability in the presence of strong space charge, has suggested a new class of instabilities known as convective instabilities. A novel approach to excite and study these instabilities will be to install a ‘waker’ system, a dedicated wake-building feedback system. The System was installed in the Fermilab Recycler and commissioned during 2021. The first results are presented.
T. Toyama, A. Kobayashi, T. Nakamura, M. Okada, M. Tobiyama
KEK, Tokai, Ibaraki, Japan
JAEA/J-PARC, Tokai-mura, Japan
In the J-PARC MR, according to the beam power upgrade over 100 kW, beam losses due to transverse collective beam instabilities had started to appear. We had introduced "bunch-by-bunch feedback" system in 2010. Continuing beam power upgrade over 250 kW again caused the transverse instabilities. We introduced "intra-bunch feedback" system in 2014. This has been suppressing those instabilities very effectively. But further beam power upgrade over 500 kW (2.6·10+14 ppp, 8 bunches) needs upgrade of "intra-bunch feedback" system. The current understanding of the transverse instabilities in the MR and the effect of the feedback system are presented from the view points of simplified simulation without the space charge effect and measurements. We are upgrading the system in two steps. The first step is "time-interleaved sampling and kicking" with two feedback systems. The second step is getting the sampling rate twice as much as the current rate, ~110 MHz. Details are explained using simulation.
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