Quasimonoenergetic electrons from unphased injection into channel guided laser wakefield accelerators

Abstract

A high-quality electron beam can be extracted from a channel guided laser wakefield accelerator without confining the injected particles to a small region of phase. By careful choice of the injection energy, a regime can be found where uniformly phased particles are quickly bunched by the accelerator itself and subsequently accelerated to high energy. The process is particularly effective in a plasma channel because of a favorable phase shift that occurs in the focusing fields. Furthermore, particle-in-cell simulations show that the self-fields of the injected bunches actually tend to reduce the energy spread on the final beam. The final beam characteristics can be calculated using a computationally inexpensive Hamiltonian formulation when beam-loading effects are minimal.

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.…”

Radiation sources based on laser–plasma interactions

“…New strategies for pre-bunching to compress the injected bunches to 10 fs or less are required. As will be discussed later, one approach adopted has been not to worry about the problem and live with a long bunch while allowing the focusing and defocusing parts of the plasma wakefield accelerator to naturally select a segment or segments of the injected electron bunches (Gordon et al 2005). This has the disadvantage of increasing the absolute energy spread, but is still useful for accelerators achieving 1 GeV and higher energies because the relative energy spread shrinks with increase in energy.…”

“…Because the trapped charge fraction depends on the phase velocity of the injection electrons, so do beam loading effects (Reitsma et al 2005). There is an optimal beam charge which will cause the wake variation to be ironed out and, therefore, lead to significantly smaller energy spreads (Gordon et al 2005;Reitsma et al 2005).…”

“…It is clear that reducing the bunch length using conventional RF and magnetic bunchers represents a substantial technological challenge, as we saw above. Promising but lossy bunch compression occurs when an electron bunch overlaps the whole of the accelerating and decelerating parts of the wakefield potential (Gordon et al 2005). The repulsive parts of the accelerating fields filter out electrons, which would otherwise produce a long low energy tail.…”

“…Two distinct regimes are distinguished by the position relative to the wake at which electrons are injected. We will see below that for electron bunches with a duration t l Rl p injected directly into the wake, the bunch is compressed by a large factor at the expense of charge loss and a relatively large absolute energy spread (Gordon et al 2005). An alternative method, where low-energy electron bunches are injected ahead of the wake, and compressed by a combination of longitudinal and transverse repulsion forces at the head of the wake is discussed in Khachatryan et al (2004) and references therein.…”