High-field strong-focusing undulator designs for X-ray Linac Coherent Light Source (LCLS) applications

Linac-driven X-ray Free Electron Lasers (e.g., Linac Coherent Light Sources (LCLSs)), operating on the principle of single-pass saturation in the Self-Amplified Spontaneous Emission (SASE) regime typically require multi-GeV beam energies and undulator lengths in excess of tens of meters to attain sufficient gain in the 1Å-0.1Å range. In this parameter regime, the undulator structure must provide: (1) field amplitudes B₀ in excess of 1T within periods of 4 cm or less, (2) peak on-axis focusing gradients on the order of 30 T/m, and (3) field quality in the 0.1%-0.3% range. In this paper we report on designs under consideration for a 4.5-1.5 Å LCLS based on superconducting (SC), hybrid/PM, and pulsed-Cu technologies