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D16 - acoustic levitation

A series of short movies showing how neutron experiments are prepared or performed. Some of these movies have an historical interest since they captured important moments in the life of the ILL.

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Acoustic levitation

D16 is a versatile 2-axis diffractometer at small momentum transfer. Several applications range from SANS to diffraction in reflection and transmission geometry on oriented multilayers, such as stacked membranes or intercalated layers, powder and liquid diffraction, and single crystal diffraction.
In some case it is well suited for the experiment to avoid any parasitic signals and any sample contamination given by the sample holder.
Sample levitation techniques are thus especially advisable since they make is possible to measure a sample without any wall, glue or sample holder in the beam.
There are several containerless techniques used in large-scale facilities:

  • Electromagnetic levitation is restricted to conducting materials that can efficiently couple to a RF field.
  • Electrostatic levitation can be used for metallic alloys, semiconductors, silicate glasses and ceramics but the instrument set up is quite complicated.
  • Aerodynamic levitation coupled with laser heating is adapted for sample at very high melting point (up to 3000K). It has a simple set-up but the nozzle is usually partially in the neutron beam.
  • Acoustic levitation: in an effort to open the door to a new class of experiments, D16 recently bought an acoustic levitation device which can levitate solids or liquids materials in aqueous solutions. 

The Single-axis Acoustic Levitator (SAL) enables non-contact positioning and manipulation of solid and liquid samples in the size range 1-3 mm and at temperatures from about 190K to 400K by means an Oxford Cryostream where aqueous liquids and low melting materials can be studied. The SAL uses two vertically-opposed, high output acoustic transducers that operate at a frequency of 22 kHz and can produce sound pressure levels to 160 dB. Small solid or liquid particles are suspended in the nodal points of a standing ultrasonic wave formed by the transducers. Samples are introduced into the "sound field" using a small syringe or a wire gauze spoon and they can be translated by adjusting the phase between the transducers or "squeezed" by modulating the acoustic levels with variable frequencies.
The device was designed and fabricated by Materials Development, Inc. (MDI), an Illinois corporation which is dedicated to providing specialized instruments for scientific research on materials under extreme temperature conditions (
The sample size is of 3-4 mm and weight should be less then 1 gr.
This particular sample environment allow the study thermophysical properties for liquids, the fluid dynamics experiments of free drops and bubbles, and the containerless solidification of undercooled liquid metals and alloys. Moreover it will be adopted for in situ chemical and crystallization processes in soft matter applications.

The SAL was designed for the installation on D16, D22, D4 and D20 instruments but it could be installed in the most of instruments at ILL.
The movie below shows a levitation test of this new sample environment device using water drops and polystyrene balls, prior its installation on the instrument itself.

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