No abstract

Some general features of the beam emittance are discussed. The significance of rms values for the emittance calculation and emittance measurements is emphasized and it is shown that the emittance of a beam is not necessarily constant in a drift space.

We present a study on the emittance evolution of electron bunches, externally injected into laser-driven plasma waves using the three-dimensional particle-in-cell (PIC) code OSIRIS. Results show order-ofmagnitude transverse emittance growth during the injection process, if the electron bunch is not matched to its intrinsic betatron motion inside the wakefield. This behavior is supported by analytic theory reproducing the simulation data to a percent level. The length over which the full emittance growth develops is found to be less than or comparable to the typical dimension of a single plasma module in current multistage designs. In addition, the analytic theory enables the quantitative prediction of emittance degradation in two consecutive accelerators coupled by free-drift sections, excluding this as a scheme for effective emittance-growth suppression, and thus suggests the necessity of beam-matching sections between acceleration stages with fundamental implications on the overall design of staged laser-wakefield accelerators.

Laser-plasma accelerators, providing high electric field gradients, are promising candidates to drive next-generation compact light sources and high-energy applications. However, conservation of beam emittance, a prerequisite for future applications, is very challenging, as the accelerated beam has to be matched to the plasma’s strong focusing forces. Here we derive with simulations ideal laser and plasma density profiles to match an electron beam in and out of a plasma stage, thus relaxing required beta functions for injection and minimizing divergence and emittance growth after the plasma

Due to the conservation of the canonical angular momentum, charged particle beams which are generated inside a solenoid field acquire a kinetic angular momentum outside of the solenoid field. The relation of kinetic orbital angular momentum to the field strength and the beam size on the cathode is called the Busch theorem. We formulate the Busch theorem in quantum mechanical form and discuss the generation of quantized vortex beams, i.e., beams carrying a quantized orbital angular momentum. Immersing a cathode in a solenoid field presents an efficient and flexible method for the generation of electron vortex beams, while, e.g., vortex ions can be generated by immersing a charge stripping foil in a solenoid field. Both techniques are utilized at accelerators for the production of nonquantized vortex beams. As a highly relevant use case we discuss in detail the conditions for the generation of quantized vortex beams from an immersed cathode in an electron microscope. General possibilities of this technique for the production of vortex beams of other charged particles are pointed out.