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Fermilab is constructing the Integrable Optics Test Accelerator (IOTA) as thecenterpiece of the Accelerator R&D Program towards high-intensity circularmachines. One of the factors limiting the beam intensity in present circularaccelerators is collective instabilities, which can be suppressed by a spreadof betatron frequencies (tunes) through the Landau damping mechanism or by anexternal damper, if the instability is slow enough. The spread is usuallycreated by octupole magnets, which introduce the tune dependence on theamplitude and, in some cases, by a chromatic spread (tune dependence onparticle's momentum). The introduction of octupoles usually has both thebeneficial (improved Landau damping) and harmful properties, such as a resonantbehavior and a reduction of the dynamic aperture. One of the research goals atthe IOTA ring is to achieve a large betatron tune spread, while retaining alarge dynamic aperture, using conventional octupole magnets in a special butrealistic accelerator configuration. In this paper, we present results ofcomputer simulations of an electron beam in the IOTA by particle tracking andthe Frequency Map Analysis. The results show that the ring's octupole magnetscan be configured to provide a betatron tune shift of 0.08 (for particles atlarge amplitudes) with the dynamical aperture of over 20 beam sigma for a150-MeV electron beam. The influence of the synchrotron motion, lattice errors,and magnet imperfections is insignificant for the parameters and levels oftolerances set by the design of the ring. The described octupole insert couldbe beneficial for enhancing Landau damping in high intensity machines.

Single-Particle Dynamics in a Nonlinear Accelerator Lattice: Attaining a Large Tune Spread with Octupoles in IOTA