Initial FELs
Three nominal initial FEL beamline types and performance features.
Three initial FEL beamlines are planned. One of the FELs will be capable of producing “two-color” X-ray pulses, using a short-pulse laser seed and undulator tapering; another will provide better energy resolution with longer pulses and high temporal coherence using high-gain harmonic generation (HGHG). The third FEL will be a self-seeded SASE device capable of operating at the full repetition rate of the linac, thereby providing very high average power X-ray beams.
Nominal performance parameter ranges for three notional initial FEL configurations.
FEL beamline type |
Seeded, narrow bandwidth |
Two-color seeded |
Self-seeded* |
Feature |
Short coherent pulses |
Two-color X-ray pump-probe with adjustable delay and ~femtosecond pulses |
High average flux and brightness |
Pulse length (fs, FWHM) |
~10 to 100 |
≤1 to 5 |
~30 to 300 |
Photon energy range (fundamental, keV) |
0.1 to 0.6 |
0.27 to 1.0 |
0.27 to 1.2 |
Maximum repetition rate (kHz) |
100 initially, potentially |
100 initially, potentially |
1,000 |
Photons/pulse |
~1011 (150 fs, 0.6 keV) |
~109 (~1 fs, 1 keV) |
~1011 (150 fs, 1.2 keV) |
Peak power (GW) |
~0.5 (0.6 keV) |
~0.02 (1 keV, ~fs) |
~0.5 (1.2 keV) |
Average power (W) |
~10 (150 fs, 0.6 keV) |
~0.002 (1 keV, ~fs) |
~100 (150 fs, 1.2 keV) |
Energy bandwidth (meV, FWHM) |
≥50 (150 fs) |
≤1,500 (≥fs) |
≥50 (150 fs) |
Polarization |
Variable, linear/circular |
Variable, linear/circular |
Variable, linear/circular |
*A fourth FEL, operating in a limited tuning range of ~2.0 – 2.5 keV (covering the S and P K-edges), has been considered, and could provide very-high-average power (initially SASE, ultimately seeded) for bio-imaging at sub-nm resolution.
Schematic layouts of the three nominal initial FEL concepts
