Simulation studies of transverse resonance effects in space-charge-dominated beams 1 Work performed under the auspices of the U.S. Department of Energy by LLNL and NRL under contracts W-7405-ENG-48, DE-AI05-92ER54177, and DE-AI05-83ER40112. 1 (original) (raw)
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Simulation studies of transverse resonance effects in space-charge-dominated beams
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1998
Particle-in-cell simulations exploring the effects of transverse envelope resonances on the emittance of space-chargedominated beams have been carried out using a new 2-D transverse "slice" model in the WARP particle-in-cell code. In this paper, we consider resonances between an applied quadrupole field error and harmonics of the asymmetric mismatch mode of beam envelope oscillation. We examine both acceleration and bunching, and show that rapid passage through a major resonance significantly reduces the attendant emittance growth. Published by Elsevier Science B.V.
Observations and simulation of a fourth order resonance with space charge
2003
A benchmarking experiment with a high intensity bunched beam stored for 1.2 s in a nonlinear lattice has been performed at the CERN Proton Synchrotron (PS). Beam emittance and beam intensity have been measured for several working points at different distances from a lattice-induced resonance. We found a regime of emittance growth for machine tunes far from the resonance and a regime of emittance shrink/beam loss for working point close the resonance. We compare the observations with 3D simulations and in the blow-up regime we find good agreement. We interpret these results in terms of space charge induced trapping and de-trapping on the lattice resonance. We show that this mechanism is responsible of halo formation which depends on the distance from the resonance and discuss the interplay of dynamic aperture and halo size as main mechanism to explain beam loss in the experiment.
Compensation For Bunch Emittance In A Magnetization And Space Charge Dominated Beam
In order to obtain sufficient cooling rates for the Relativistic Heavy Ion Collider (RHIC) electron cooling, a bunched beam with high bunch charge, high repetition frequency and high energy is required and it is necessary to use a "magnetized" beam, i.e., an electron beam with non-negligible angular momentum. Applying a longitudinal solenoid field on the cathode can generate such a beam, which rotates around its longitudinal axis in a field-free region. This paper suggests how a magnetized beam can be accelerated and transported from a RF photocathode electron gun to the cooling section without significantly increasing its emittance. The evolution of longitudinal slices of the beam under a combination of space charge and magnetization is investigated, using paraxial envelope equations and numerical simulations. We find that we must modify the traditional method of compensating for emittance as used for normal non-magnetized beam with space charge to account for magnetization. The results of computer simulations of successful compensation are presented. Alternately, we show an electron bunch density distribution for which all slices propagate uniformly and which does not require emittance compensation.
Space charge driven resonance trapping phenomena observed at the CERN proton synchrotron
2003
The combined effect of space charge and nonlinear resonance on beam loss and emittance was measured in a benchmarking experiment over a 1.2 s long flat-bottom at 1.4 GeV kinetic energy in the presence of a single controllable octupole. By lowering the working point towards the resonance, a gradual transition from a loss-free core emittance blow-up to a regime dominated by continuous loss was found. We compare the observation with 3D simulations based on a new analytical space charge model and obtain good agreement in the emittance blow-up regime. Our explanation is in terms of the synchrotron oscillation, which causes a periodic tune modulation due to space charge, and leads to trapping and de-trapping on the resonance islands. For working points very close to the resonance this induces a beam halo with large radius. The underlying dynamics is studied in detail, and it is claimed that the predicted halo in conjunction with a reduced dynamic aperture for the real machine lattice is the source of the loss observed in the experiment.
Experimental study of large-amplitude perturbations in space-charge dominated beams
Physical Review Special Topics - Accelerators and Beams, 2010
Detailed experimental measurements are presented concerning the propagation of space-charge waves of varying amplitudes in an intense, charged-particle beam. A short perturbation to the density profile is applied at the electron gun, and both current and mean energy profiles are measured at two locations downstream. The measurements are compared to predictions of a linear 1D cold-fluid model, and selfconsistent particle-in-cell simulations. For sufficiently small perturbation amplitudes, the experiment, simulation, and 1D theory agree. For larger amplitudes, the simulation begins to diverge from theoretical predictions due to nonlinear effects. Experimental observations for large-amplitude perturbations differ markedly from either theory or simulation. With the aid of simulations with mismatched and misaligned beams, this departure of experiments from predictions is demonstrated to be caused by the loss of beam current due to scraping aided by the larger radius of the perturbation.
Review of beam dynamics and space charge resonances in high intensity linacs
2002
Recent systematic studies of resonant space charge effects and anisotropy have helped to narrow the gap between idealized beam physics models of halos and high-current linac design. We review the beam dynamics basis of nonequipartitioned beams, discuss the consequences of bunch anisotropy, and introduce "3D free energy equivalence" as a new concept to model halo growth in linac bunches. Results are applied to the CERN-SPL, the SNS and the ESS superconducting (sc) linac designs.
Physics of Plasmas, 2010
The Paul Trap Simulator Experiment ͑PTSX͒ is a compact laboratory experiment that places the physicist in the frame-of-reference of a long, charged-particle bunch coasting through a kilometers-long magnetic alternating-gradient ͑AG͒ transport system. The transverse dynamics of particles in both systems are described by the same set of equations, including nonlinear space-charge effects. The time-dependent voltages applied to the PTSX quadrupole electrodes in the laboratory frame are equivalent to the spatially periodic magnetic fields applied in the AG system. The transverse emittance of the charge bunch, which is a measure of the area in the transverse phase space that the beam distribution occupies, is an important metric of beam quality. Maintaining low emittance is an important goal when defining AG system tolerances and when designing AG systems to perform beam manipulations such as transverse beam compression. Results are reviewed from experiments in which white noise and colored noise of various amplitudes and durations have been applied to the PTSX electrodes. This noise is observed to drive continuous emittance growth and increase in root-mean-square beam radius over hundreds of lattice periods. Additional results are reviewed from experiments that determine the conditions necessary to adiabatically reduce the charge bunch's transverse size and simultaneously maintain high beam quality. During adiabatic transitions, there is no change in the transverse emittance. The transverse compression can be achieved either by a gradual change in the PTSX voltage waveform amplitude or frequency. Results are presented from experiments in which low emittance is achieved by using focusing-off-defocusing-off waveforms.
Simulations of Beam Emittance Growth from the Collective Relaxation of Space-Charge Nonuniformities
2004
Beams injected into a linear focusing channel typically have some degree of space-charge nonuniformity. For unbunched beams with high space-charge intensity propagating in linear focusing channels, Debye screening of the selffield interaction between particles tends to make the transverse density profile flat. An injected particle distribution with a large systematic charge nonuniformity will generally be far from an equilibrium of the focusing channel and the initial condition will launch a broad spectrum of collective modes. These modes can phase-mix and experience nonlinear interactions which result in an effective relaxation to a more thermal-equilibrium-like distribution characterized by a uniform density profile. This relaxation transfers self-field energy from the initial space-charge nonuniformity to the local particle temperature, thereby increasing beam phase space area (emittance growth). Here we employ twodimensional electrostatic particle-in-cell (PIC) simulations to investigate the effects of initial transverse space-charge nonuniformities on the statistical emittance growth of beams with high space-charge intensity propagating in a continuous focusing channel. Results are compared to theoretical bounds of emittance growth developed in previous studies. Consistent with earlier theory, it is found that a high degree of initial distribution nonuniformity can be tolerated with only modest emittance growth and that beam control can be maintained. The simulations also provide information not addressed by the theory on the rate of relaxation and characteristic levels of fluctuations in the relaxed states. This research suggests that a surprising degree of initial space-charge nonuniformity can be tolerated in practical intense beam experiments. r
A modified space charge routine for high intensity bunched beams
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1996
In 1991 a space charge calculation for bunched beam with a three-dimensional ellipsoid was proposed, replacing the usual SCHEFF routines. It removes the cylindrical symmetry required in SCHEFF and avoids the point to point interaction computation, whose number of simulation points is limited. This routine has now been improved with the introduction of two or three ellipsoids giving a good representation of the complex non-symmetrical form of the bunch (unlike the 3-d ellipsoidal assumption). The ellipsoidal density distributions are computed with a new method, avoiding the difficulty encountered near the centre (the axis in 2-d problems) by the previous method. It also provides a check of the ellipsoidal symmetry for each part of the distribution. Finally, the Fourier analysis reported in 1991 has been replaced by a very convenient Hermite expansion, which gives a simple but accurate representation of practical distributions. Comparisons with other space charge routines have been made, particularly with the ones applying other techniques such as SCHEFF. Introduced in the versatile beam dynamics code DYNAC, it should provide a good tool for the study of the various parameters responsible for the halo formation in high intensity linacs. Improvements of the method are under development by the authors. These improvements, which might lead to a new step in space charge computations, are however beyond the scope of this article. 016%9002/96/$15.00 Copyright 0 1996 Elsevier Science l3.V. All rights reserved PII SO168-9002(96)00427-5 P. Lapostolle et al. I Nucl.
One-dimenssional electromagnetic simulation of multiple electron beams propagating in space plasmas
Journal of Geophysical Research, 2010
It is by now well known that electron beams play an important role in generating radio emissions such as type II and type III radio bursts, commonly observed by spacecraft in the interplanetary medium. Electron beams streaming back from Earth's bow shock into the solar wind have been proposed as a possible source for the electron plasma waves observed by spacecraft in the electron foreshock. Recent observations suggest that during the natural evolution of the foreshock plasma, multiple electron beams could be injected over a period of time, losing their individual identity to coalesce into a single beam. In this work, we use an electromagnetic particle-in-cell (PIC) code "KEMPO 1D, adapted" to simulate two electron beams that are injected into a plasma at different times. The first beam disturbs the background plasma and generates Langmuir waves by electron beam-plasma interaction. Subsequently, another beam is inserted into the system and interacts with the first one and with the driven Langmuir waves to produce electromagnetic radiation. The results of our simulation show that the first beam can produce electrostatic harmonics of the plasma frequency, while the second beam intensifies the emission at the harmonics that is produced by the first one. The behavior of the second beam is strongly determined by the preexisting Langmuir wave electric fields. The simulations also show, as a result of the interaction between both beams, a clear nonlinear frequency shift of the harmonic modes as well as an increase of electromagnetic and kinetic energies of the wave-particle system.