Arbitrary correlation generation

Particle beams are not just simple bunches of charged particles. Each beam has an internal structure in phase space, which describes how particle positions and momenta are correlated. These correlations strongly affect how the beam evolves and how it performs in accelerators.

In this research, we develop methods to create customized correlations inside a beam. Instead of only compressing, focusing, or steering a beam in standard ways, we aim to shape its internal phase-space structure for specific applications. This capability can help produce tailored current profiles, microbunch trains, and other advanced beam distributions.

The broader goal is to move toward phase-space design: define the beam structure needed for an application, then develop the accelerator methods to generate it.

To experimentally realize the concept of arbitrary correlation generation, we introduced the transverse wiggler as a practical beamline element for controlled phase-space shaping. The photo shows compact transverse wigglers built from small permanent magnets. These devices are designed to give the beam a controlled, position-dependent sideways kick.

A single transverse wiggler imprints a specific correlation into the beam’s transverse phase space. In simple terms, particles entering at different transverse positions receive different changes in angle. This makes the transverse wiggler a basic building block for shaping the beam distribution in a controlled way.

The method becomes more powerful when multiple transverse wigglers are used in sequence. Between wigglers, the beam evolves through transport sections, so each following wiggler acts on a modified phase-space distribution. In this way, a series of transverse wigglers can build increasingly complex patterns step by step, beyond what a single conventional element can produce.

The figure sequence illustrates this idea. Starting from a simple initial pattern, successive transverse wigglers generate more structured phase-space distortions. As a demonstration, we used this concept to produce a target phase-space pattern representing NIU. This result shows how a beamline can function not only as a transport system, but also as a programmable tool for creating customized beam structures.