Basically CSE equipment with the Fresnel lens consist in an axis orientated to the Polar Sun, that is, parallel to the earth rotation axis. This axis is computer controlled to have a single daily rotation (Fig. 1).

The altitude of the sun is hand controlled because the equipment is simpler. Every morning we change this altitude and then the focal spot is on position.

Then, after we focalize the sun in the morning in the focal point the focal spot will be maintained at the same place the whole day because the axis makes 1 rev. per day following exactly the sun track. By computer control we can change the turning speed and register the temperature time heating and cooling curves of the sample.

Because of the angle of the axis and the weight of the Fresnel lens frame and other elements, the axis has a tie with a screw to adjust exactly the angle and to avoid oscillations when the wind is large or the weigh is heavy.

2.3. Fresnel lens

The Fresnel lens is ca. 0.8 sq. m and exist in the market at moderate price, ca. 200 €. Is made in polymeric material, 3 mm thick, and, consequently is very light in weight. The lens is covered while no working. A cover with a hole in the center let us to put the focal spot in the right place. To work the cover is put out and the heating of the sample start.

Polar oriented axis computer controlled

Fig. 2. General view of equipment

The Fresnel lens is made by Edmund Optics, Ltd. Main characteristics are summarized in Table I. Fig. 2. show a general view of the equipment.

Typical design of the Fresnel lens consist in the substitution of the curve of the conventional lens with a series the concentric groove. This lens is molded in the surface of a thin, light weight plastic sheet with the appropriate curvature. The conical grooves act as individual refracting surfaces like tiny prisms when viewed in cross section bending parallels rays in a very close approximation to a common focal length.

One added advantage of the thinner plastic lens to the light weight is that because it is very thin there is very low absorbance of solar beams, i. e., it is a very high transmission. Fresnel lenses are a compromise between efficiency and image quality that depends of the groove density. High groove density increases image quality but low grooves density
produces higher efficiency that is our main interest. In infinite conjugated systems, as is in our case, the grooved side of the lens should face the longer conjugated.

2.4. Reaction chamber

Our installation has a double wall watere refrigerated reaction chamber that allow us to work in atmospheres of different composition. An inlet and outlet allows to introduce the gas of the required composition. To avoid the introduction of air we work with a slight over pressure of some cm of water.

The cylindrical chamber has a quartz window in one of the circular sides to allow the concentrated beams reach the sample inside the chamber. In the opposite side there is a system to introduce and withdraw the sample and for the thermocouples exit.

2.5. Samples

The samples we used to obtain SHS intermetallic coatings on steel consist in a small steel cylinder 6 mm thick, 14 mm diameter with an internal hole 12 mm in diameter.