PPPL, Princeton, New Jersey
Funding: Research supported by the U. S. Department of Energy.
This paper presents a survey of the present theoretical understanding based on advanced analytical and numerical studies of collective interactions and instabilities for intense one-component ion beams, and for intense ion beams propagating through background plasma. The topics include: discussion of the condition for quiescent beam propagation over long distances; the electrostatic Harris instability and the transverse electromagnetic Weibel instability in highly anisotropic, one-component ion beams; and the dipole-mode, electron-ion two-stream instability (electron cloud instability) driven by an unwanted component of background electrons. For an intense ion beam propagating through a charge-neutralizing background plasma, the topics include: the electrostatic electron-ion two-stream instability; the multispecies electromagnetic Weibel instability; and the effects of a velocity tilt on reducing two-stream instability growth rates. Operating regimes are identified where the possible deleterious effects of collective processes on beam quality are minimized.
PPPL, Princeton, New Jersey
Funding: Research supported by the U.S. Department of Energy.
This paper reports on recent advances in the development of a numerical scheme for describing the quiescent loading of a quasi-equilibrium beam distribution matched to a periodic focusing lattice*. The scheme allows for matched-beam distribution formation by means of the adiabatic turn-on of the oscillating focusing field, and it is examined here for the cases of alternating-gradient quadrupole and periodic solenoidal lattices. Furthermore, various distributions are considered for the initial beam equilibrium. The self-similar evolution of the matched-beam density profile is observed for arbitrary choice of initial distribution function and lattice type. The numerical simulations are performed using the WARP particle-in-cell code.
* M.Dorf et al., Phys. Rev. ST Accel. Beams, submitted for publication(2009).
PPPL, Princeton, New Jersey
Funding: Research supported by the U. S. Department of Energy.
The transverse dynamics of an intense charged particle beam propagating through a periodic quadrupole focusing lattice is described by the nonlinear Vlasov-Maxwell system of equations where the propagating distance plays the role of time. To find matched-beam quasi-equilibrium distribution functions one need to determine a dynamical invariant for the beam particle moving in the combined external and self-fields. The standard approach for sufficiently small phase advance is to use the smooth focusing approximation, where particle dynamics is determined iteratively using the small parameter (vacuum phase advance)/(360 degrees) < 1 accurate to cubic order. In this paper, we present a perturbative Hamiltonian transformation method which is used to transform away the fast particle oscillations and obtain the average Hamiltonian accurate to 5th order in the expansion parameter. This average Hamiltonian, expressed in the original phase-space variables, is an approximate invariant of the original system, and can be used to determine self-consistent beam equilibria that are matched to the focusing channel.
PPPL, Princeton, New Jersey
Funding: Research supported by the U.S. Department of Energy.
The Paul Trap Simulator Experiment (PTSX) is a compact laboratory Paul trap that simulates a long, thin charged-particle bunch coasting through a kilometers-long magnetic alternating-gradient (AG) transport system by putting the physicist in the frame-of-reference of the beam. Results are presented from experiments in which the axial distribution function is modified by lowering the axial confinement barrier to allow particles in the tail of the axial distribution function to escape. Measurements of the axial energy distribution and the transverse density profile are taken to determine the effects of the modified distribution function on the charge bunch. It is observed that the reduced axial-trapping potential leads to an increase of the transverse effective temperature.
PPPL, Princeton, New Jersey
LLNL, Livermore, California
LBNL, Berkeley, California
Voss Scientific, Albuquerque, New Mexico
Funding: Research supported by the US Department of Energy.
Neutralized drift compression offers an effective means for particle beam focusing and current amplification. In neutralized drift compression, a linear radial and longitudinal velocity drift is applied to a beam pulse, so that the beam pulse compresses as it drifts in the focusing section. The beam intensity can increase more than a factor of 100 in both the radial and longitudinal directions, totaling to more than a 10,000 times increase in the beam density during this process. The optimal configuration of focusing elements to mitigate the time-dependent focal plane is discussed in this paper. The self-electric and self-magnetic fields can prevent tight ballistic focusing and have to be neutralized by supplying neutralizing electrons. This paper presents a survey of the present numerical modeling techniques and theoretical understanding of plasma neutralization of intense particle beams. Investigations of intense beam pulse interaction with a background plasma have identified the operating regimes for stable and neutralized propagation of intense charged particle beams.
