MC5: Beam Dynamics and EM Fields
D07 High Intensity Circular Machines Space Charge, Halos
Paper Title Page
WEPTS011 Intra-Beam Scattering Effect in the SOLEIL Storage Ring Upgrade 3106

• A. Vivoli, A. Bence, P. Brunelle, A. Gamelin, L. Hoummi, A. Loulergue, L.S. Nadolski, R. Nagaoka, M.-A. Tordeux
SOLEIL, Gif-sur-Yvette, France

As the work on the design of the upgrade of SOLEIL storage ring advances, the study of the impact of Intra-Beam Scattering (IBS) on the equilibrium emittance is also progressing, showing a significant contribution of this effect. Different measures can be taken to mitigate the emittance dilution, like operating the machine with full transverse coupling and using harmonic cavities to increase bunch length. The calculation of the IBS effect needs then to take into account the different beam dynamics and its effect on the particle distribution. In this paper the current state of the ongoing study is presented, reporting on the results obtained for the different options considered, and comparing the results of different codes and their implicit assumptions.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS011
About • paper received ※ 14 May 2019       paper accepted ※ 18 May 2019       issue date ※ 21 June 2019
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WEPTS014 Coherent vs Incoherent Effects and Debye Length 3116

• G. Franchetti

In this proceeding it is discussed the effect of coherent vs. incoherent effect and discussing the validity of frozen models of space charge according to the Debye length and beam radius. This in view of discussing the relation of IBS and space charge
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS014
About • paper received ※ 15 April 2019       paper accepted ※ 28 May 2019       issue date ※ 21 June 2019
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WEPTS018 Experimental Observation of Low-Order Collective Oscillation Modes in a Strong-Focusing Lattice 3130

• K. Ito, H. Higaki, H. Okamoto
• T. Kurauchi
Hiroshima University, Faculty of Science, Higashi-Hirosima, Japan

In a conventional linear Paul trap (LPT), four electrode rods are placed symmetrically around the trap axis to generate a radio-frequency quadrupole field for transverse ion confinement. The periodic nature of the external focusing potential can give rise to serious ion losses under a specific condition. The loss mechanism is essentially the same as the coherent betatron resonance well-known in intense beam dynamics[*,**]. In fact, the collective motion of an ion plasma in the LPT is shown equivalent to that of a charged-particle beam traveling through an alternating-gradient focusing lattice. In the present study, we perform the direct measurement of low-order coherent oscillation modes in the LPT by detecting image currents induced on the electrodes’ surfaces. The four-rod structure of the LPT allows us to pick up feeble signals of the dipole and quadrupole oscillations of a plasma bunch. These signals are Fourier analyzed to evaluate the coherent oscillation tune at different initial ion densities. The time evolution of the coherent motion is also discussed in this paper.
* K. Moriya et al., Phys. Rev. Accel. Beams Vol.19, 114201 (2016).
** K. Ito et al., Phys. Rev. Accel. Beams Vol. 20, 064201 (2017).

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS018
About • paper received ※ 26 April 2019       paper accepted ※ 21 May 2019       issue date ※ 21 June 2019
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WEPTS022 Stability Tune Diagram of a High-Intensity Hadron Ring 3141

• H. Okamoto, K. Kojima, Y. Tokashiki

To date, the optimum operating point of a high-intensity hadron ring has been determined on the basis of the conventional incoherent picture. It is generally chosen on the tune diagram such that the so-called "incoherent tune spread" of a stored beam does not overlap with low-order "single-particle resonance" lines. We here propose a new approach to construct the stability tune diagram on the basis of the self-consistent coherent picture. The betatron resonance condition recently conjectured from one-dimensional Vlasov predictions is employed for this purpose, which predicts the existence of twice as many resonance stop bands as expected from the well-known incoherent resonance condition at high beam density *,**. The proposed general rules for the stability-chart construction are very simple and free from any model-dependent unobservables like space-charge-depressed incoherent tunes. As an example, we apply the present rules to the lattice of the rapid cycling synchrotron at J-PARC and explain why the operating bare tunes of this machine have been chosen slightly below 6.5 in both transverse directions.
* K. Ito et al., Phys. Rev. Accel. Beams 20, 064201 (2017).
** H. Okamoto and K. Yokoya, Nucl. Instrum. Meth. A 482, 51 (2002).

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS022
About • paper received ※ 09 May 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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WEPTS024 Tune Shifts and Optics Modulations in the High Intensity Operation at J-PARC MR 3148
SUSPFO051   use link to see paper's listing under its alternate paper code

• T.Y. Yasui
The University of Tokyo, Graduate School of Science, Tokyo, Japan
• S. Igarashi, T. Koseki, K. Ohmi, Y. Sato, K. Satou
KEK, Ibaraki, Japan

Funding: This study is supported by the MEXT program "Advanced Leading Graduate Course for Photon Science (ALPS)"
J-PARC Main Ring (MR) is the intensity-frontier proton accelerator. The beam intensity of 2.6×1014 protons per pulse has been achieved for the current user operation. In this high-intensity operation, the tune spread caused by the space-charge is one of the main reasons for beam loss. The modulation of the betatron function and the tune shift were simulated with a PIC algorithm calculation code*. The simulation results showed that the space-charge effects were dominant in small particle action, and the sextupole fields effects were dominant in large particle action. Because sextupole strength is large in MR, sextupole fields induce substantial tune shifts. At the benchmark of the space-charge simulation, the simulation results matched the analytical space-charge calculations performed without sextupoles. It was found that the betatron function was modulated at most 6% by the space-charge effects and at most 8% by the effects of sextupoles in J-PARC MR. These effects to the injection beam optics matching and to the beam aperture will be investigated.
* K. Ohmi et al., "Study of Halo Formation in J-PARC MR", Proceedings of the 22nd Particle Accelerator Conf. (PAC’07), Albuquerque, NM, USA, Jun. 2007, paper THPAN040, pp. 3318-3320.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS024
About • paper received ※ 15 May 2019       paper accepted ※ 21 May 2019       issue date ※ 21 June 2019
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WEPTS041 Coupling and Space Charge Studies at the CERN PSB 3192

• F. Asvesta
NTUA, Athens, Greece
• F. Antoniou, H. Bartosik, G.P. Di Giovanni, Y. Papaphilippou
CERN, Meyrin, Switzerland

In the nominal optics of the CERN PS-Booster (PSB), the fourth order coupling resonance is excited by space charge (Montague resonance) due to the same integer tune values. This resonance can be avoided by changing the tunes to different integers. A new PSB optics is presented and emittance measurements crossing the coupling resonance for the nominal and the new optics are shown.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS041
About • paper received ※ 17 April 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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WEPTS042 Detailed Characterisation of the LEIR Intensity Limitations for a Pb Ion Beam 3196

• Á. Saá Hernández, H. Bartosik, N. Biancacci, S. Hirlaender, D. Moreno Garcia, M. Zampetakis
CERN, Meyrin, Switzerland

The equilibrium emittance of the Pb beam in the CERN Low Energy Ion Ring (LEIR) results from the interplay of electron cooling and heating processes, as intra-beam scattering and space charge. In this paper we present the measurements of the emittance evolution as a function of intensity, working point and resonance excitation, and compare them with the simulations of the heating processes. Optimum settings for normal and skew sextupoles have been found for the compensation of resonances excited by the lattice.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS042
About • paper received ※ 18 April 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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WEPTS047 Space Charge Driven Resonances in the CERN PS 3216

• F. Asvesta
NTUA, Athens, Greece
• H. Bartosik, A. Huschauer, Y. Papaphilippou
CERN, Geneva, Switzerland

In the CERN Proton Synchrotron space charge driven resonances are excited around the operational working point due to the periodicity of the optics functions. In this paper, the resonances are studied using analytical methods, i.e. the evaluation of the resonance driving terms connected to the space charge potential of Gaussian distributions. Furthermore, the resonances are characterized in measurements and simulations for various beams. The beams considered are different in terms of brightness, in order to study the dependence of the resonance strength on the space charge force.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS047
About • paper received ※ 17 April 2019       paper accepted ※ 21 May 2019       issue date ※ 21 June 2019
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WEPTS056 Can a Paul Ion Trap Be Used to Investigate Nonlinear Quasi-Integrable Optics? 3251
SUSPFO117   use link to see paper's listing under its alternate paper code

• L. Martin, S.L. Sheehy
JAI, Oxford, United Kingdom
• D.J. Kelliher
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom

Here we describe the design of an experimental setup using the IBEX Paul trap to test nonlinear quasi-integrable optics, an accelerator lattice design to create stable high intensity beams. In 2010 Danilov and Nagaitsev found a realisable nonlinear potential which can create integrable optics in an accelerator when embedded in a linear lattice that provides round beams. This concept will be tested in the IOTA ring at Fermilab. It is important to further test this concept over a wide parameter range, preferably in a simplified experimental setup such as IBEX. The IBEX Paul trap is capable of replicating the transverse dynamics of a high intensity accelerator without dispersion or chromaticity.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS056
About • paper received ※ 30 April 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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WEPTS057 Recent Studies of the Resonances at a Cell Tune of 0.25 Using the Ibex Paul Trap 3255

• L. Martin, S.L. Sheehy
JAI, Oxford, United Kingdom
• D.J. Kelliher
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom

We use the IBEX linear Paul trap to study the resonance at a cell tune of \frac{1}{4} with both equal and unequal transverse tunes, at a range on intensities. We compare this experimental result to simulation using the PIC code Warp. We find that the experimental result differs from the simulation, which may be explained by the ion loss in the IBEX experiment, which more closely replicates a real accelerator. Knowledge of the tune corresponding to greatest beam loss is important for the design of future high intensity machines.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS057
About • paper received ※ 30 April 2019       paper accepted ※ 21 May 2019       issue date ※ 21 June 2019
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WEPTS068 A Novel S-Based Symplectic Algorithm for Tracking With Space Charge 3279

• J.P. Edelen, D.T. Abell, D.L. Bruhwiler, N.M. Cook, C.C. Hall, S.D. Webb

Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics under Award Number DE-SC0011340
Traditional finite-difference particle-in-cell methods for modeling self-consistent space charge introduce non-Hamiltonian effects that make long-term tracking in storage rings unreliable. Foremost of these is so-called grid heating. Particularly for studies where the Hamiltonian invariants are critical for understanding the beam dynamics, such as nonlinear integrable optics, these spurious effects make interpreting simulation results difficult. To remedy this, we present a novel symplectic spectral space charge algorithm that is free of non-Hamiltonian numerical effects and, therefore, suitable for long-term tracking studies. Results presented here include a detailed study of the solver’s performance under a range of conditions. First, we show benchmarking and convergence studies for different particle shapes and different particle distributions. Then we demonstrate the solver’s ability to preserve Hamiltonian structure by studying the formation of space-charge driven resonances using both our algorithm and traditional PIC.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS068
About • paper received ※ 14 May 2019       paper accepted ※ 23 May 2019       issue date ※ 21 June 2019
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WEPTS078 Chaos Indicators for Studying Dynamic Aperture in the IOTA Ring with Protons 3301

• K. Hwang, C.E. Mitchell, R.D. Ryne
LBNL, Berkeley, California, USA

The Integrable Optics Test Accelerator (IOTA) is a novel storage ring under commissioning at Fermi National Accelerator Laboratory designed (in part) to investigate the dynamics of beams in the presence of highly nonlinear transverse focusing fields that generate integrable single-particle motion. In this study, we explore the sensitivity of the lattice dynamic aperture to the presence of nonlinear space charge. For this purpose, two distinct chaos indicators are compared (frequency map analysis and forward-backward integration). Because the integrability of motion requires integer betatron tune advance between passes through the nonlinear magnetic element, a large role is played by space-charge-induced tune spread. As a result, these tools are also applied to a toy model of the IOTA lattice to investigate the sensitivity of dynamic aperture to violations of the integer tune advance condition.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS078
About • paper received ※ 14 May 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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