Beam Dynamics and Electromagnetic Fields




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Particle Diffusion due to Coulomb Scattering
V. Lebedev, S. Nagaitsev, FNAL, Batavia

Conventionally, the multiple and single particle scattering in a storage ring are considered to be independent. Such an approach is simple and often yields sufficiently accurate results. Nevertheless there is a class of problems where such an approach cannot produce correct results and the single and multiple scattering need to be considered together. This can be achieved by solving an integro-differential equation for the particle distribution function, which correctly treats particle coulomb scattering. A derivation of the equation for the cases of single- and two-dimensional betatron motion is presented in the article. Numerical and analytical solutions for important practical cases are also considered.

Type of presentation requested : Poster

Classification : [D03] High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling


1559 - Longitudinal Cooling of A Strongly Magnetized Electron Plasma
J. Lee, J. Cary, Center for Integrated Plasma Studies, Boulder, CO

For a strongly magnetized plasma the small gyroradius compared with the mean interparticle spacing makes the energy exchange between perpendicular and parallel almost vanish, so that the two energies are nearly independently conserved. In this case, the thermodynamic property of crystallization depends almost exclusively on the parallel temperature, as the perpendicular degrees of freedom act like internal degrees of freedom. On the other hand, only the perpendicular degree of freedom is well coupled (through synchrotron radiation) to the outside. Thus, in the presence of a distant, low-temperature wall, the perpendicular temperature decreases, while the parallel temperature remains high, and crystallization is not achieved. We propose to cause crystallization through use of microwaves, which transfer parallel energy to perpendicular. Our calculations show that crystallization can be achieved in reasonable times (a few hours) by this method.

Type of presentation requested : Poster

Speaker :
Professor. John Cary

Classification : [D03] High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling


1579 - Analysis and Simulation of the CSR Induced Modulational Instability
R. Li, TJNAF, Virginia

Recent analytical studies [1-3] and simulation [4] indicated that coherent synchrotron radiation (CSR) could induce microbunching instability for short electron bunches passing through magnetic bending systems, such as in the case of a bunch compression chicane or a storage ring. In this paper, we present our simulation results on the study of the CSR induced microbunching or modulational instability, especially the dependence of the growth rate on the design bunch distribution and on the bunch transverse dynamics. We also describe our simulation algorithm for the investigation of this instability, and carry out analysis to explain the simulation results.

*This work was supported by the U.S. Dept. of Energy under Contract No. DE-AC05-84ER40150

[1] S. Heifets and G. Stupakov, Proceedings of 2001 Particle Accelerator Conference, 2001.

[2] E. L. Saldin, et al., Proceedings of the FEL2001 Conference, 2001.

[3] S. Heifets and G. Stupakov, SLAC-PUB-8988, 2001

[4] M. Borland, Proceeding.s of the 2001 Particle Accelerator Conference, 2001

Type of presentation requested : Poster

Speaker :
Rui Li

Classification : [D03] High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling


843 - Space Charge Dynamics Simulated in 3-D in the Code ORBIT
A.U. Luccio, J. Beebe-Wang, N.L. D'Imperio, BNL, Upton, Long Island, New York

ORBIT is a PIC simulation code for beam dynamics in synchrotrons, developed jointly by Oak Ridge and BNL. Work is in progress at BNL to validate the code against (1) physics, (2) machine experiments, and to (3) apply the code to different types of lattice. This is coordinated with similar work done at ORNL, that uses in some cases different approaches, algorithms and coding, while the basic formulation is the same.In the BNL implementation (ORBIT++), 3D space charge is calculated by slicing the beam in many longitudinal sections, with the calculations done simultaneously in each slice with MPI on a parallel computer. ORBIT uses distance along the ring as the independent variable, so at each space charge 'node' the beam is expanded to 'freeze' each macro particle in its position at a given time. Image forces and currents on walls are calculated by solving the Poisson/Ampere equation with boundaries and then finding the impedances (in the ORNL version the same calculations are done using impedances as input). We have applied ORBIT++ to study a reference simple FODO machine, the Rapid Cycling Medical Synchrotron (RCMS), the AGS Booster and the AGS synchrotron. Results are discussed.

Type of presentation requested : Poster

Classification : [D03] High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling


1055 - Coherent Motion of a Bunched Beam and its Resonances
S. Machida, KEK, Ibaraki-ken

It is now clear that resonances of a space-charge detuned coasting beam in a circular accelerator is described by coherent motions, not a single particle incoherent tune [1,2]. For the lowest order resonance, the 2-dimensional envelope equations predict that almost two times higher tune shift (precisely speaking, it is 8/5) can be accommodated than the one estimated by incoherent tune shift formula. It is, however, not obvious that it is also true for a bunched beam. Synchrotron oscillations may destroy the coherence. Line density, which is assumed constant in the 2-dimensional model, varys along the bunch. We study coherent motion of a bunched beam with multi-particle tracking code Simpsons.

[1] R. Baartman, AIP Conf. Proc. 448, (1998) p.56.

[2] S. Machida and M. Ikegami, ibid., p.73.

Type of presentation requested : Poster

Classification : [D03] High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling


184 - Beam Loading and Waveguide Buncher Optimizing for High Current Relativistic Beam.
E. Masunov, MEPhI, Moscow

The problem of the bunching of a high current relativistic electron beam in travelling-wave structure is studied. At a high initial beam power the bunching efficiency is determined by the beam itself in the waveguide structure, rather than by the external rf fields. Optimization method for beam phase-focusing action are suggested. There is a detailed discussion of the final stage of the beam interaction in the rf structure, in which an equilibrium is established between the bunched beam and its own microwave field. It is shown that the parameters of the structure can be chosen to optimize the integrated characteristics of the bunched electron beam.

Type of presentation requested : Poster

Classification : [D03] High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling


42 - Beam Dynamics Study of a Muon Cooling Experiment with 200 MHz Cavities in the Framework of the CERN Cooling Study
M. Migliorati, L. Palumbo, Dipartimento di Energetica, Roma; K. Hanke, A.M. Lombardi, CERN, Geneva; F. Tazzioli, C. Vaccarezza, INFN-LNF, Frascati (Roma)

Muon cooling is one of the building blocks for a Neutrino Factory. It has the potential to increase the muon flux at the detector of an order of magnitude. Different set-ups for the experimental observation of cooling are proposed and discussed by an international collaboration [MICE]. In this paper we present the results of the tracking studies for a cooling experiment based on 200 MHz cavities with superconducting solenoids and liquid hydrogen absorbers. The cooling factor (i.e. the increase of the number of particles in a given acceptance) achieved for a 200 MeV muon beam passing through a system of 4 cavities at 7.6 MV/m is of the order of 10 %. This is believed to be well within the capability of the measurement apparatus and sufficient to gather important information for the final design of a full-scale cooling channel.

Type of presentation requested : Poster

Classification : [D03] High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling


505 - Thin Foil Physical Effects on the Transport of an Intense Relativistic Electron Beam
O. Mouton, D. Guilhem, CEA, Bruyères-le-Châtel

While it crosses a perpendicular thin foil, an electron beam suffers a well known emittance growth due to the Coulomb scattering mechanism which alters the propagation of the beam. It also suffers a foil focusing effect caused by the beam induced foil charges. We have implemented these effects in an envelope simulation code TRAJENV capable of studying the beam propagation along transport lines. The moments are calculated in two different manners: the first one via a numerical integration and in the second one analytical solutions are used. Simulations results are compared to experimental measurements for relativistic electron beams (6 MeV, 3 kA) propagating through solenoidal chanels.

Type of presentation requested : Poster

Classification : [D03] High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling


1363 - Flip-Flop Phenomenon Observation at VEPP-2M
I. Nesterenko, P. Ivanov, A. Valishev, BINP, Novosibirsk

In this paper the experimental studies of flip-flop phenomenon at two different excitation modes for vertical emittances of e+e- colliding beams are presented. This experimental data was obtained at VEPP-2M in summer, 2000. A comparison of the phenomenological model with the experimental data is given. It is shown that a non-resonant generation of the vertical emittances (by means of excitation of the vertical dispertion in bending magnets such as to exclude the dependence of the natural vertical emittance on the linear optics distortion due to a beam-beam interaction) permits to increase significantly the blowup threshold in comparison with the mode when the emittances are determined by coupling of vertical and horizontal betatron oscillations and by vicinity of the betatron tunes to coupling resonance.

Type of presentation requested : Poster

Classification : [D03] High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling


289 - Design of the ACR Electron Cooler at RIKEN
M. Nishiura, T. Katayama, Toshiya Tanabe, RIKEN, Saitama; A. Sidorin, JINR, Dubna, Moscow Region; I. Watanabe, TOSHIBA

The radioisotope beam factory (RIBF) is under construction at RIKEN. In the RIBF, multi-use experimental storage rings (MUSES) consists of an accumulator cooler ring (ACR) and an electron-RI beam collider (e-RI Collider). The ACR is equipped with an electron cooler (EC). The 3 dimensional calculations of magnetic fields and beam trajectories are carried out in order to obtain better configuration in the gun and the toroidal section of the ACR-EC. The cooling time is calculated using these parameters.

Type of presentation requested : Poster

Classification : [D03] High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling


639 - Electron Cooling Experiment at HIMAC synchrotron
K. Noda, T. Honma, M. Muramatsu, NIRS, Chiba City; T. Furukawa, Chiba University, Chiba; S. Shibuya, SHI, Tokyo

One of the objectives of HIMAC is to develop new technologies in heavy-ion therapy and related basic and applied research. For the purpose, it is very important to improve beam property and enhance capability of handling it. The electron-cooling method can provide high-intensity or high-quality beams by cool stacking and by its strong phase-space compression. The aim of our study is to apply those techniques of accelerator physics to medical and other fields. These techniques will lead to the following: (1) an increase in the intensities of positron-emitter beams for the ion range measurements and of heavier ions, such as Fe and Ni, (2) micro-beam probe for the cellular radiation-response, and (3) short-bunched beams for time-resolving measurements. At HIMAC synchrotron, thus, electron-cooling experiments have been carried out. In the transverse cooling-experiments, a cooling time and an equilibrium emittance at horizontal direction were measured and an intrabeam scattering was also measured. Beam intensity was increased by one order through the cool-stacking method. Beam bunch was compressed from around 400 ns to 40 ns by the electron cooling. The experimental results will be presented.

Type of presentation requested : Poster

Classification : [D03] High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling


432 - Parametric Resonances in Intense Hadron Beams
H. Okamoto, Hiroshima University, Higashi-Hiroshima; S. Machida, K. Yokoya, KEK, Ibaraki-ken

This paper presents several interesting results of resonant beam instability induced by the periodic nature of external focusing force. Firstly, an eigenvalue equation that determines the frequencies of collective oscillation modes in a one-dimensional beam is given by solving the Vlasov-Poisson equations. Approximate formulae for the resonance stopbands and growth rates are derived from the eigenvalue equation. It is shown that the beam becomes unstable not only when a coherent tune is close to an integer but also when it is near a half integer. Secondly, a general Hamiltonian formalism is constructed for the study of two-dimensional space-charge-dominated beams in circular accelerators. The theory suggests the possibility of a novel resonant instability driven by momentum dispersion and space charge. The particle-in-cell simulation technique is employed to confirm the existence of a "dispersive resonance" stopband.

Type of presentation requested : Poster

Classification : [D03] High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling


433 - A New Experimental Approach to Space-charge Effects
H. Okamoto, K. Ito, A. Ogata, R. Takai, Y. Wada, Hiroshima University, Higashi-Hiroshima

In recent papers[1], we proposed a novel experimental approach to investigate various collective effects in space-charge-dominated beams. It was demonstrated that either a radio-frequency quadrupole trap or a solenoidal trap could reproduce nonlinear collective processes equivalent to those in a beam transport channel. In the present paper, we outline the essence of the idea, showing typical trap configurations for beam-physics applications. We also briefly discuss possible trap experiments that greatly deepen our current understandings of collective beam instabilities including coherent resonances and halo formation.

[1]. H. Okamoto, Hiroshima University Preprint HUBP-01/98 (1998); H. Okamoto and H. Tanaka, Nucl. Instr. Meth. A437 (1999) 178.

Type of presentation requested : Poster

Classification : [D03] High Intensity - Incoherent Instabilities, Space Charge, Halos, Cooling


434 - On the Maintenance Condition of a Crystalline Beam
H. Okamoto, K. Okabe, Y. Yuri, Hiroshima University, Higashi-Hiroshima

It is widely believed that the so-called "maintenance condition" must be satisfied to achieve beam crystallization in a cooler storage ring. The condition requires the ring lattice to have a betatron phase advance below about 127 degrees per single superperiod[1]. In the present work, we show that this condition is not sufficient in general situations. Systematic multi-particle simulations and analytic studies suggest that the phase advance per lattice period should be lower than 90 degrees in order to totally avoid half-integer resonance crossing during the cooling process.

[1]. J. Wei, X.-P. Li, and A. M. Sessler, Phys. Rev. Lett. 73 (1994) 3089; J. Wei, H. Okamoto, and A. M. Sessler, Phys. Rev. Lett. 80 (1998) 2606.
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