Low-alpha Operation of the Iota Storage Ring

TL;DR

This paper discusses the development and experimental validation of ultra-low momentum-compaction lattices in the IOTA storage ring, enabling new research capabilities in generating short bunches and coherent radiation.

Contribution

It introduces a new procedure for lowering the momentum compaction in IOTA using linear optics and higher-order magnet compensation, with experimental validation.

Findings

Achieved lowest momentum compaction of 3.4×10^{-4} at IOTA.

Developed a measurement technique for momentum compaction.

Enhanced understanding of IOTA optics for future research.

Abstract

Operation with ultra-low momentum-compaction factor (alpha) is a desirable capability for many storage rings and synchrotron radiation sources. For example, low-alpha lattices are commonly used to produce picosecond bunches for the generation of coherent THz radiation and are the basis of a number of conceptual designs for EUV generation via steady-state microbunching (SSMB). Achieving ultra-low alpha requires not only a high-level of stability in the linear optics but also flexible control of higher-order compaction terms. Operation with lower momentum-compaction lattices has recently been investigated at the IOTA storage ring at Fermilab. A procedure for lowering the ring compaction using the linear optics along with compensations from the higher-order magnets was developed with the aid of a model, and an experimental technique for measuring the momentum compaction was developed. The lowest momentum compaction achieved during the available run-time was $3.4\times10^{-4}$, around 15 times lower than previously operated. These feasibility studies ensure an improved experimental understanding of the IOTA optics and potentially will enable new research programs at the facility.