HelXAS Instrumental design
HelXAS momochromator is a wavelength dispersive system, built from a Johann type Rowland circle scanning device, using spherically bent crystal analyzers (SBCA) with 500 mm bending radius and coupled to a conventional 1.

5 kW silver anode X-ray source. Its design allow XAS experiments over energies ranging from 4 keV to 20 keV, covering most 3d transition metal K-edges, lanthanide and actinide L3-edges and 5d transition metal L edges.

The achieved energy resolution is typically ~1 eV at 10 keV depending on the crystal analyzer and the Bragg angle. The instrument is equipped with an helium chamber designed to limit the X-ray absorption by air along their source-analyzer-detector path, which is particularly important in the low energy range.

The maximum x-ray tube power is 1.5 kW but most often the highest throughput that is used is 800 W (with 20 kV, 40 mA).

Available equipment at HelXAS
X-ray source and
power generator
- Seifert/XRD Eigenmann 1.5 kW, Ag anode x-ray tube up to 60 keV (normally max. 30 kV in use),
- Seifert ISO Debyeflex 3003 power generator
Crystal monochromators

- R=0.5 m: Si(111), Si(220), Si(531), Si(533), Si(553), Si(931) (ESRF Crystal Laboratory)

- R=0.5 m: Ge(111), Ge(422) (XRS-Tech)

- R=1.0 m: Si(111) (ESRF Crystal Laboratory)

Detectors - Silicon drift diode (Amptek X-123SDD 75 mm2 OEM with a flexible 8" cable)
- Silicon drift diode (Amptek X-123SDD 75 mm2 with a rigid 50 mm detector extender)
- Photon counting imaging detector (AdvaCam Timepix with a 500 um thick Si sensor, 256 x 256 pixels of 55 um x 55 um) - for spectral imaging of heterogeneous samples
Sample environments - Sample exchanger wheel with 16 sample slots
- An air-tight sample wheel for 8 samples
Auxiliary equipment Acrylic He chamber with 25 um thick Kapton windows

A fire-proof gas bottle cabinet and gas sensors are also available in the experimental room allowing in situ chemical reaction studies. A multi-sample exchanger is also available in order to automatize batch of samples measurement without user's intervention.