LCLS-II Design & Performance

LCLS-II Design

LCLS-II Design

Figure 1. The future LCLS-II X-ray laser (blue, at left) is shown alongside the existing LCLS (red, at right). LCLS uses the last third of SLAC’s 2-mile-long linear accelerator – a hollow copper structure that operates at room temperature and allows the generation of 120 X-ray pulses per second. For LCLS-II, the first third of the copper accelerator will be replaced with a superconducting one, capable of creating up to 1 million X-ray flashes per second. (SLAC National Accelerator Laboratory)

Working closely with DOE’s Office of Science, SLAC configured LCLS-II to meet requirements laid out by the Basic Energy Sciences Advisory Committee (BESAC). The conceptual design:

  • Adds a new, 4 GeV superconducting linac in an existing SLAC tunnel, avoiding the need for excavation.
  • Increases the repetition rate from 120 pulses per second to 1 million per second. It will be the world’s only X-ray free-electron laser capable of supplying a uniformly-spaced train of pulses with programmable repetition rate.
  • Provides a tunable source of X-rays, by replacing the existing undulator (used to generate X-ray laser pulses) with two new ones. This ability to tune the X-ray energy on demand will enable scientists to scan across a wide spectrum – opening up new experimental techniques and making efficient use of the valuable beam time.
  • Provides access to an intermediate X-ray energy range that is currently inaccessible with LCLS, but which is likely critical for studies of new materials, chemical catalysis and biology.
  • Extends the operating range of the facility from its current limit of ~11 keV X-rays to ~25 keV.
  • Supports the latest seeding technologies to provide fully coherent X-rays (at the spatial diffraction limit and at the temporal transform limit)
  • Maintains the existing copper-based warm linac and upgrades parts of the existing research infrastructure to take advantage of the new configuration.


Figure 2. LCLS-II beamlines. (SLAC National Accelerator Laboratory)

LCLS-II Performance

Calculated photons per pulse

Figure 3. Calculated photons per pulse for high-repetition-rate operation from LCLS-II soft X-ray undulator (SXU) and hard X-ray undulator (HXU) at 4 GeV. Note that photons/pulse is constant with repetition rate up to ~300 kHz, and scales inversely with repetition rate above ~300 kHz. Also shown is the extended energy range from the Cu-linac (120 Hz) with the tunable HXU. (SLAC National Accelerator Laboratory)

Calculated average spectral brightness

Figure 4. Calculated average spectral brightness for high-repetition-rate operation from LCLS-II soft X-ray undulator (SXU) and hard X-ray undulator (HXU) at 4 GeV. Note that LCLS-II average brightness is roughly constant above ~300 kHz (energy/pulse scales inversely with repetition rate above ~300 kHz). (SLAC National Accelerator Laboratory)

Read more in the news feature Major Upgrade Will Boost Power of World’s Brightest X-ray Laser