SAPHiR (under construction)

Six Anvil Press for High pressure Radiography and TOF diffraction

The instrument provides extreme pressure and temperature environments for time-of-flight neutron diffraction and neutron radiography of polycrystalline and liquid samples.

The instrument shares a thermal neutron beamline (wavelength range 1 – 2.4 Å) with the upstream instrument POWTEX. The centrepiece is a six-ram multianvil press that is placed on a positioning and rotation table for sample adjustment and surrounded by detectors for neutron diffraction and radiography.

The six independently adjustable rams provide a combined pressing force of up to 23.5 MN (2400 tons) that is transferred via a set of smaller second-stage anvils to a cubic sample assembly. An approx. 20 mm³ sample capsule can be subjected to P and T conditions of up to 15 GPa (150 kbar) and > 2000°C. Aided by an anvil positioning and advancing system with a precision in the sub-micron range, samples can be deformed at strain rates varying from approx. 10^-3 to 10^-7 s^-1 for in situ stress and strain measurements.

An elliptical neutron guide with a variable supermirror coating of m = 1.5 – 4 will guide and focus the neutron beam between POWTEX and the press to the sample cross-section of 3 × 3 mm². For radiography, different pinholes can reduce the divergence of the neutron beam to attain L/D ratios larger than 500 at reasonable neutron fluxes so that a resolution better than 100 μm can be achieved.

Typical applications

Radiographic applications

Critical behaviour and miscibility of fluid-silicate melt systems
Melt/fluid distribution in crystalline silicate systems
Falling sphere viscosimetry
Sintering kinetics

TOF neutron diffraction

Crystal structure and stability of water-bearing high-pressure phases
Phase diagrams and transformation kinetics of light materials
Equations of state at extreme conditions
Structure of silicate melts
Cathion ordering
Magnetic ordering
Rheological flow laws of high-pressure materials
Elastic properties of materials at high pressure and temperature

Sample environment

Assembly: Depending on sample volume and pressure requirements 10 – 15 mm diameter cubic sample assemblies are used with dewatered pyrophyllite or magnesium oxide pressure media that are compressed by 5 – 9 mm truncation length Ni-bound tungsten carbide anvils.
Furnace: Internal platinum or rhenium foil or graphite resistance furnaces (up to > 2000°C)
Cooling system: An additional cooling option is available; jackets surrounding the secondary anvils are flushed by liquid nitrogen, which allows temperatures to < 90 K. The cooling system can be combined with the heating furnace.
Samples: Cylindrical Pt or Re sample capsules for solid (polycrystalline) or liquid/molten samples with a typical diameter and height of 2 – 4 mm (approx. 20 mm³ sample volume)
Sample adjustment: ±10 cm in x-y-z direction and ±15° rotation of the press relative to the beam on a positioning table
Angular coverage: 1.5 – 3 mm wide anvil gaps for entering and escaping neutrons at low and high 2Θ angles and at 90°

Technical data

Neutron beam and guide

SR-5: thermal neutrons downstream from POWTEX
TOF neutron wavelength range: 1 – 2.4 Å
Elliptical neutron guide, length 10 m, supermirror coating m = 1.5 – 4
Entering and exit width: approx. 7 mm

Chopper

Puls chopper frequency (POWTEX):	200 s^-1
Press chopper frequency:	50 s^-1
Chopper disc diameter:	750 mm
Pulse width:	10 μs

Collimation and flux (numerical modelling with VITESS)

TOF diffraction (50 s^-1 chopper frequency): ~10⁷ n s^-1cm^-1 on a 3 × 3 mm² sample
Radiography (continuous beam): ~5 × 10⁸ n s^-1cm^-2 (L/D = 250), ~4 × 10⁷ n s^-1cm^-2 (L/D = 500)

TOF Detectors

640 ³He 8 mm tubes at 2Θ ~90° and ~10 – 35°, position resolution 3 mm
Scintillator banks at large 2Θ angles 135 – 170°, position resolution 2 × 2 mm²
Angular range of detector banks (2 Θ): ~10 – 35°, ~85 – 95°, and ~135 – 170°, Q ≈ < 1 – 10 Å^-1