Longitudinal phase-space manipulation of ellipsoidal electron bunches in realistic fields

Abstract

Since the recent publication of a practical recipe to create ''pancake'' electron bunches which evolve into uniformly filled ellipsoids, a number of papers have addressed both an alternative method to create such ellipsoids as well as their behavior in realistic fields. So far, the focus has been on the possibilities to preserve the initial ''thermal'' transverse emittance. This paper addresses the linear longitudinal phase space of ellipsoidal bunches. It is shown that ellipsoidal bunches allow ballistic compression at subrelativistic energies, without the detrimental effects of nonlinear space-charge forces. This in turn eliminates the need for the large correlated energy spread normally required for longitudinal compression of relativistic particle beams, while simultaneously avoiding all problems related to magnetic compression. Furthermore, the linear space-charge forces of ellipsoidal bunches can be used to reduce the remaining energy spread even further, by carefully choosing the beam transverse size, in a process that is essentially the time-reversed process of the creation of an ellipsoid at the cathode. The feasibility of compression of ellipsoidal bunches is illustrated with a relatively simple setup, consisting of a half-cell S-band photogun and a two-cell booster compressor. Detailed GPT simulations in realistic fields predict that 100 pC ellipsoidal bunches can be ballistically compressed to 100 fs, at a transverse emittance of 0:7 m, with a final energy of 3.7 MeV and an energy spread of only 50 keV.

Low-Energy-Spread Ion Bunches from a Trapped Atomic Gas

“…In the crossover regime these two effects cancel, leading to a further reduction of the relative energy spread. Related effects have been predicted in simulations of high-density electron bunch dynamics [17,18]. GPT calculations also show this behavior for large values of R (see Fig.…”

Single-electron pulses for ultrafast diffraction

“…The interplay of laser parameters and surface morphology defines the initial phase space of photoemission. Second, the provided data and relations shall be useful for energy-filtered diffraction and microscopy (43,44), femtosecond needle sources (45,46), propagation of elliptical packets (47), and for electron pulse compression with time-dependent fields (2,14,15,17). The outlined measurement approach is a practical way to investigate and optimize the energetic, temporal, and spatial characteristics of femtosecond electron packets for these and other applications.…”

Radial bunch compression: Path-length compensation in an rf photoinjector with a curved cathode

“…Compression occurs either ballistically at a longitudinal position at some point after the buncher or inside the buncher itself, in both cases resulting in short bunches with low emittance. Although the method works particularly well for ellipsoidal bunches [7] and can be incorporated in one single device [8], it always requires additional independently phased rf power.…”