Stability Regimes in a Rotating Quadrupole Focusing Accelerator (original) (raw)

Transverse beam stability with an “electron lens”

Physical Review E, 1999

Stability analysis is presented for an antiproton beam interacting with an electron beam of an "electron lens" proposed as a beam-beam tune shift compensator. Coherent antiproton-electron interaction causes coupling of the antiproton synchrobetatron modes which may lead to a transverse mode coupling instability (TMCI). Analytical studies and numerical simulations of this effect are presented.

Electromagnetic instability supported by a rippled, magnetically focused relativistic electron beam

Journal of Plasma Physics, 1984

The coupling of volume, long-wavelength TM electromagnetic and longitudinal space charge (electrostatic) waves by the rippling of magnetically focused electron beams is examined analytically. The dispersion relation is obtained and then solved for these types of wave. Instability, with growth rates proportional to the relative ripple amplitude of the beam, is found and discussed.

Wave-particle interactions on relativistic electron beams. Final report

1983

A summary of research performed under subject contract is given. The work is in the main concerned with the theory, both linear and non-linear, for the gain of a free electron laser (FEL) in a strong axial magnetic field. Both wiggler and wiggler-free configuration are considered. An experimental study is described of the transition from helical to non-helical orbits in a wiggler with a guide field. THe exact magnetic field of a filimentary bifilar current-carrying helix is given. The degradation in gain of a FEL without axial guide field due to velocity spread is given. Twelve published papers are appended.

Electron surfing acceleration by mildly relativistic beams: wave magnetic field effects

New Journal of Physics, 2008

Electron surfing acceleration (ESA) is based on the trapping of electrons by a wave and the transport of the trapped electrons across a perpendicular magnetic field. ESA can accelerate electrons to relativistic speeds and it may thus produce hot electrons in plasmas supporting fast ion beams, like close to astrophysical shocks. One-dimensional (1D) particle-in-cell (PIC) simulations have demonstrated that trapped electron structures (phase space holes) are stabilized by relativistic phase speeds of the waves, by which ESA can accelerate electrons to ultrarelativistic speeds. The 2(1/2)D electromagnetic and relativistic PIC simulations performed in the present paper model proton beam driven instabilities in the presence of a magnetic field perpendicular to the simulation plane. This configuration represents the partially electromagnetic mixed modes and the filamentation modes, in addition to the Buneman waves. The waves are found to become predominantly electromagnetic and nonplanar for beam speeds that would result in stable trapped electron structures. The relativistic boost of ESA reported previously is cancelled by this effect. For proton beam speeds of 0.6 and 0.8c, the electrons reach only million electron volt energies. The system with the slower beam is followed sufficiently long in time to reveal the development of a secondary filamentation instability. The instability forms a channel in the simulation domain that is void of any magnetic field. Proton beams may thereby cross perpendicular magnetic fields for distances beyond their gyroradius.

Instabilities for a relativistic electron beam interacting with a laser-irradiated plasma

Physical Review E, 2012

The effects of a radiation field (RF) on the unstable modes developed in relativistic electron beam-plasma interaction are investigated assuming that ω0 > ωp, where ω0 is the frequency of the RF and ωp is the plasma frequency. These unstable modes are parametrically coupled to each other due to the RF and are a mix between two-stream and parametric instabilities. The dispersion equations are derived by the linearization of the kinetic equations for a beam-plasma system as well as the Maxwell equations. In order to highlight the effect of the radiation field we present a comparison of our analytical and numerical results obtained for nonzero RF with those for vanishing RF. Assuming that the drift velocity u b of the beam is parallel to the wave vector k of the excitations two particular transversal and parallel configurations of the polarization vector E0 of the RF with respect to k are considered in detail. It is shown that in both geometries resonant and nonresonant couplings between different modes are possible. The largest growth rates are expected at the transversal configuration when E0 is perpendicular to k. In this case it is demonstrated that in general the spectrum of the unstable modes in ω-k plane is split into two distinct domains with long and short wavelengths, where the unstable modes are mainly sensitive to the beam or the RF parameters, respectively. In parallel configuration, E0 k, and at short wavelengths the growth rates of the unstable modes are sensitive to both beam and RF parameters remaining insensitive to the RF at long wavelengths.

Stability regimes in a helical quadrupole focusing accelerator−theory and simulation

Physics of Fluids B: Plasma Physics, 1991

The inclusion of helical quadrupole (stellarator) and axial guide fields in high current spiral line or recirculating accelerator configurations provides a high tolerance to energy mismatch and confines the beam against space charge forces. Such a configuration is studied via three-dimensional particle simulation. It is found that the electron beam centroid motion can interact with the external fields and with the TE11 waveguide mode to obtain (i) highly unstable particle orbits, (ii) the electromagnetic three-wave instability, or (iii) a fully stable beam. Theoretical stability conditions are presented in the limit of zero beam current and are found to be good predictors of simulation results. Minor departures from the stability conditions at high current are discussed in terms of the full linear dispersion relation. Saturation of the instability without beam loss is observed in some cases. This is the result of detuning in the relativistic cyclotron wave number as the beam energy ...

Effects of azimuthal and radial spreads of canonical momentum on electron-beam focusing characteristics in the presence of space-charge forces

Journal of Applied Physics, 1995

A theoretical and numerical investigation of the effects of azimuthal and radial spreads of canonical momentum on an electron beam focused by a magnetic lens in the presence of space-charge forces is presented. The particles are inserted with an initial Gaussian distribution in the transverse space and in the momentum coordinates or with a uniform initial current distribution. The particle trajectory equation is derived for parameters of an arbitrary applied fields configuration with cylindrical symmetry, and a nonvanishing initial canonical momentum. In the absence of an initial momentum spread particles launched above a critical radial distance from the axis exhibit a phase-space tearing effect in the electron distribution. The inclusion of initial canonical momentum spread in the model allows for skewed trajectories with strong centrifugal force which prevents the appearance and overshadows the effect of strong space-charge forces near the axis, which are responsible for the phase-space tearing effect. 0 199.5 American Institute of Physics.

Experimental confirmation of transverse focusing and adiabatic damping in a standing wave linear accelerator

Physical Review E, 1997

The measurement of the transverse phase-space map, or transport matrix, of a relativistic electron in a high-gradient, radio-frequency linear accelerator ͑rf linac͒ at the UCLA photoinjector is reported. This matrix, which indicates the effects of acceleration ͑adiabatic damping͒, first-order transient focusing, and ponderomotive second-order focusing, is measured as a function of both rf field amplitude and phase in the linac. The elements of the matrix, determined by observation of centroid motion at a set of downstream diagnostics due to deflections induced by a set of upstream steering magnets, compare well with previously developed analytical theory ͓J. Rosenzweig and L. Serafini, Phys. Rev. E 49, 1599 ͑1994͔͒. The determinant of the matrix is obtained, yielding a direct confirmation of trace space adiabatic damping. Implications of these results on beam optics at moderate energy in high-gradient linear accelerators such as rf photoinjectors are discussed.