Longitudinal density modulation and energy conversion in intense beams

Abstract

Density modulation of charged particle beams may occur as a consequence of deliberate action, or may occur inadvertently because of imperfections in the particle source or acceleration method. In the case of intense beams, where space charge and external focusing govern the beam dynamics, density modulation may under some circumstances be converted to velocity modulation, with a corresponding conversion of potential energy to kinetic energy. Whether this will occur depends on the properties of the beam and the initial modulation. This paper describes the evolution of discrete and continuous density modulations on intense beams, and discusses three recent experiments related to the dynamics of density-modulated electron beams. PACS

Controlling nonlinear longitudinal space charge oscillations for high peak current bunch train generation

“…All of these methods suffer from increasing the charge in the beam. The modulation blurs and tends to disappear when longitudinal space charge (LSC) forces begin to play a significant role in the beam evolution [10][11][12]. Considering the beam as a non-neutral relativistic plasma, the time scale for the evolution of the beam distribution under space charge forces is set by the relativistic plasma…”

Generation of relativistic electron bunches with arbitrary current distribution via transverse-to-longitudinal phase space exchange

“…The techniques based on shaping of the photocathode drive laser distribution are prone to the space-charge effects which are prominent at low energies and tend to smear the impressed shaping. Although it has been pointed out that the density modulation is indeed converted into an energy modulation and can be later recovered by a proper longitudinal phase space manipulation, the final bunching factor is significantly lower [22]. Similarly, the techniques based on nonlinear transformations generally have a limited tunability.…”

Nonlinear Longitudinal Space Charge Oscillations in Relativistic Electron Beams

“…Boscolo et al [9] have looked into using RF velocity bunching as a way to compensate for the longitudinal space charge effects and recover the initial distribution. In all these cases, the problem arises on how to preserve such modulation for large enough beam currents when longitudinal space-charge effects might contribute to smearing-out any structure in the temporal beam profile [10] thus limiting the attainable peak currents in bunch train mode.…”