Linear Vlasov solver for microbunching gain estimation with inclusion of CSR, LSC and linac geometric impedances

TL;DR

This paper extends a linear Vlasov solver to include various impedance effects such as CSR, LSC, and geometric impedances, enabling more accurate microbunching gain estimation in accelerator beamlines.

Contribution

The authors develop an enhanced Vlasov solver that incorporates additional impedance models and beam acceleration, improving microbunching instability analysis accuracy.

Findings

Gain functions and spectra for a transport arc beamline are presented.

Comparison with particle tracking simulations validates the extended solver.

Insights into collective effects and limitations of the current model are discussed.

Abstract

As is known, microbunching instability (MBI) has been one of the most challenging issues in designs of magnetic chicanes for short-wavelength free-electron lasers or linear colliders, as well as those of transport lines for recirculating or energy recovery linac machines. To more accurately quantify MBI in a single-pass system and for more complete analyses, we further extend and continue to increase the capabilities of our previously developed linear Vlasov solver [1] to incorporate more relevant impedance models into the code, including transient and steady-state free-space and/or shielding coherent synchrotron radiation (CSR) impedances, the longitudinal space charge (LSC) impedances, and the linac geometric impedances with extension of the existing formulation to include beam acceleration [2]. Then, we directly solve the linearized Vlasov equation numerically for microbunching gain amplification factor. In this study we apply this code to a beamline lattice of transport arc [3] following an upstream linac section. The resultant gain functions and spectra are presented here, and some results are compared with particle tracking simulation by ELEGANT [4]. We also discuss some underlying physics with inclusion of these collective effects and the limitation of the existing formulation. It is anticipated that this more thorough analysis can further improve the understanding of MBI mechanisms and shed light on how to suppress or compensate MBI effects in lattice designs.