Beam Instability Issue and Transverse Feedback System in the MR of J-PARC
208
T. Toyama, A. Kobayashi, T. Nakamura, M. Okada, M. Tobiyama
KEK, Tokai, Ibaraki, Japan
Y. Shobuda
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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Space-Charge Particle Resonances and Mode Parametric Resonances
D. Jeon, J.-H. Jang
IBS, Daejeon, Republic of Korea
Y.L. Cheon, M. Chung
UNIST, Ulsan, Republic of Korea
As the beam intensity increases in modern high-power accelerators, self-field effects of the beam become significant. There are two distinct families of space-charge halo mechanisms in high-intensity accelerators, and yet they need to be differentiated: resonances (particle resonances or incoherent resonances) and instabilities (parametric resonances or coherent resonances). What we call resonances are resonances of beam particles excited through the space-charge nonlinear multipoles. What we call instabilities are instabilities of the beam modes. Instabilities are also called parametric resonances because they are parametric resonances of the Vlasov-Poisson equations. They would better be called mode parametric resonances to distinguish them from particle parametric resonances. Resonances and instabilities may look alike in the phase space, and yet they have distinct differences. Instabilities (or mode parametric resonances) do not have the resonant frequency component. Various orders of resonances and instabilities are presented along with the beam distributions with which the particular mechanism is observed.
Exploring Quasi-Integrable Optics with the IBEX Paul Trap
214
J.A.D. Flowerdew
University of Oxford, Oxford, United Kingdom
D.J. Kelliher, S. Machida, S.L. Sheehy
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom
An ideal accelerator built from linear components will exhibit bounded and stable particle motion. However, in reality, any imperfections in the magnetic field strength or slight misalignments of components can introduce chaotic and unstable particle motion. All accelerators are prone to these non-linearities but the effects are amplified when studying high intensity particle beams with the presence of space charge effects. This work aims to explore the non-linearities which arise in high intensity particle beams using a scaled experiment called IBEX. The IBEX experiment is a linear Paul trap which allows the transverse dynamics of a collection of trapped particles to be studied. It does this by mimicking the propagation through multiple quadrupole lattice periods whilst remaining stationary in the laboratory frame. IBEX is currently undergoing a nonlinear upgrade with the goal of investigating Quasi-Integrable Optics (QIO), a form of Nonlinear Integrable Optics (NIO), in order to improve our understanding and utilisation of high intensity particle beams.
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