SwissFEL Alvra Experimental Station

Cartoon of beamline components and features in green, blue and grey

Alvra specializes in measuring the ultrafast dynamics of photochemical and photobiological systems using a variety of X-ray scattering and spectroscopic techniques. Alvra consists of two instruments: Alvra Prime and Alvra Flex. Prime is a helium/low vacuum atmosphere chamber designed to perform a range of techniques, including serial femtosecond crystallography (SFX), X-ray scattering (XDS), and X-ray absorption and emission spectroscopy (XAS and XES) over the full SwissFEL hard X-ray photon energy range of 2-12.4 keV. Flex is a flexible instrument designed to accommodate user experiments with an X-ray spectrometer that can be used for many different types of measurements, including inelastic X-ray scattering (IXS) and high energy resolution off-resonant spectroscopy (HEROS), as well as host user-provided setups. An overview of the Alvra design parameters can be found here and on the SwissFEL facility here. A user laboratory, to support chemistry and biology experiments is also available on-site. The summary of the lab infrastructure and equipment can be found here.

Alvra is currently in full user operation mode, with both the Prime and Flex instruments commissioned at 100 Hz. A summary of the experimental station parameters follows

Metal chamber on a table with cables and tubes

Alvra Prime

The Alvra Prime chamber is used for the majority of experiments at the Alvra Endstation. 

Alvra Prime is a compact chamber which is usually operated under a low-vacuum Helium environment. The main door provides access to the XYZ stage and chamber interior. Several additional through-put ports are available for experimental setups.

The specifics of the chamber and its adjoining components are detailed in the table below.

Photon energy range2 – 12.4 keV (full SwissFEL Aramis photon energy range)
Beam profileMeasured focus 20 µm (FWHM) at 2 and 4.5 keV (defocussed beam also possible)
 Measured focus 2 µm (FWHM) at 12 keV (defocussed beam also possible)
 Unfocused beam: 500 µm to 1 mm (FWHM) energy dependent
 Flexible KB mirrors can also provide an asymmetric focus
BandwidthSASE 0.25% (pink beam)
 Monochromatic: Si(111), Si(311) and InSb(111)
Sample EnvironmentFrom vacuum (5 x 10-4 mbar) up to 800 mbar pressure (He or N2)
Sample delivery systemsLiquid jet for chemistry:
 - Flat jet (100, 200 and 300 µm) with gear or peristaltic pump
 - Round jet (20-100 µm) with HPLC pump
 LCP viscous injector (50-100 µm)
 GDVN injectors tested in chamber
 Solid samples
Detectors and Spectrometers16M Jungfrau forward scattering detector at 10 cm distance (<1 Å resolution at 12.4 keV)
 4M Jungfrau forward scattering detector at 10 cm distance (1.5 Å resolution at 12.4 keV)
 2 x 2 crystal von Hamos dispersive X-ray emission spectrometer (1-12.4 keV)
 Diodes for x-ray absorption measurements

Alvra Flex

Alvra Flex is, as its name suggests, a flexible experimental area where users can build up their required setup.

At a basic level, Alvra Flex is a large table with an XYZ stage sitting downstream of the Alvra Prime chamber. Various motors and stages are installed and can be used for a variety of setups. A 1M JUNGFRAU detector is also permanently mounted and available for use.

The details of Alvra Flex and its adjoining components are detailed in the table below.

A metal XYZ stage with cables and other motors in the background
Photon energy range6 – 12.4 keV
Beam profileFlexible focus from 10 to >100 µm (FWHM)
 Unfocused beam: ~1 x 1 mm2 (FWHM) energy dependent
BandwidthSASE 0.5% (pink beam)
 Monochromatic: Si(111), Si(311) and InSb(111)
Sample EnvironmentAtmospheric conditions (in-air setup)
Sample delivery systemsLiquid jet for chemistry:
 - Flat jet (100, 200 and 300 µm) with gear or peristaltic pump
 - Round jet (20-100 µm) with HPLC pump
 LCP viscous injector (50-100 µm)
 Solid samples
Detectors and Spectrometers3 crystal von Hamos dispersive X-ray emission spectrometer with 1M Jungfrau detector
 Diodes for x-ray absorption measurements
Laser table with mirrors, glass and cables

Optical Pump Laser

The majority of experiments at the Alvra Endstation make use of the optical pump laser. 

The system is developed and maintained by Philip Johnson from the Pump Laser Group.

Primary pump source800 nm, 35 fs FWHM, 10 mJ (Ti:Sapphire)
Secondary pump sources240 nm – 2.5 micron (OPA with additional nonlinear conversion options). At present pulse energies at the sample location for 240-400 nm have been measured in the range of 10-30 µJ. We expect pulse energies of 150-500 µJ between 400 nm and 780 nm; 150-500 µJ between 1 µm and 2.5 µm. Pulse durations are expected to be approximately 50 fs fwhm.
Timing diagnosticsAlvra currently has two spectral encoding time-tools available, one pre and one post-interaction region. This approach has been demonstrated at several other facilities and works well for experiments that use the full SASE pulses at the full X-ray range of the endstation (2-12 keV) and for monochromatic experiments at the higher x-ray energies (>6 keV).
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